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Lightning Detection: Technology & Tactics

Lightning Detection: Technology & Tactics

Onboard weather avoidance equipment, and techniques for using it.

Anyone who has listened to an AM radio in thunderstorm country knows that lightning creates a lot of static on the radio. Likewise, readers of aviation stories have probably come across the mention of how an ADF will, at times, point to a lightning strike.

Out of this commonly observed phenomenon, airborne lightning detection equipment was born over 40 years ago. Christened the “Stormscope” by its inventor, Paul Ryan, the unit married radio frequency (RF) detection with a cathode ray tube (CRT) screen in order to plot lightning strikes.

One of the beauties of the Stormscope was that it didn’t require the large antenna needed by an onboard radar system. At that time, radar was largely limited to twins which had the room in the nose for the antenna; a few radar installations used a large pod under the wing.

The Stormscope used an ADF-sized antenna, so it was feasible to mount the equipment in most single engine aircraft and any twins that would not easily be outfitted with a radome in the nose. Thunderstorm detection came to the masses.

The term “Stormscope” has been appropriated to refer to all lighting detection equipment, but it is only technically correct when applied to the original line of products.

There are currently three providers of airborne lightning detection equipment (ALDE).

Insight Avionics manufactures a unit called the Strike Finder that analyzes individual strike signal properties to determine the bearing, range and severity. This data is plotted on an LED display as single orange dots. A stabilization module (not a rotating gyroscope) is available as a factory installed option; no field configuration or calibration of the module is required.


Avidyne makes the TWX670 Color Tactical Lightning Detection System which displays on its MFD, as well as some third-party displays. Color-contoured mapping of the electrical activity from the TWX670 sensor is often used as a complement with satellite-based datalink weather.

I’ll deal mostly with the Stormscope in this article, but the operating principles are the same—they all use radio detection to find lightning activity.

Evolution of the Stormscope

Over the years, the patents and trademark for Stormscope passed from Ryan International, to 3M, to B.F. Goodrich, and Stormscope is today owned and produced by L-3 Technologies’ avionics division.

The Stormscope can be thought of as having three generations, though this is a bit of a simplification. The Stormscope WX-7 was the first generation. In 1981, the second generation consisting of the WX-8, WX-9, WX-10/10A and WX-11 came out.


The WX-8 was a simplified unit that displayed a 135-degree forward-looking arc divided up into radial segments with three pseudo range rings that lit up green, orange or red depending on the intensity of the strikes detected.

The red segment was the innermost range/ring and the green was the outermost. WX-8s are still commonly found in General Aviation aircraft, though the unit has been out of production for many years—as have all of the second-generation units.

Another common second generation unit was the WX-10/10A. The units are almost identical, with the WX-10A having an improved processor. WX-10 series units display a 360 view with four range settings: 25 nm, 50 nm, 100 nm and 200 nm. There is also an option to select forward 180 degrees, which can provide better resolution as the unit’s memory only has to store those ahead, and not behind, the aircraft.

The WX-11 was essentially the same as the WX-10, but with the added feature of being gyrostabilized so that display would sync with the aircraft’s heading changes.

The third generation was dubbed by 3M the Series II Stormscope, and the WX-500 and WX-1000 are the two products on the market today. A Stormscope WX-500 will display information on many of the common MFD units, while the WX-1000 has its own display. These third-generation units have improved algorithms to provide more sensitivity and increased accuracy.


How it works

Any of the airborne lightning detection systems use well established radio detection principles and equipment to figure out what direction a lightning strike is coming from. In this, the units are quite accurate.

Ground units can use triangulation to obtain distance to the strike; airborne units do not have that luxury. Instead, the airborne units guess at the distance by comparing the strength of the RF signal made by the lightning strike to an average. The dot is then placed on the display on the measured radial and at the calculated distance relative to the distance ring depending on the range selected by the pilot.

If all lightning strikes were of the average strength, the distance displayed would likely be quite accurate. However, Mother Nature is never that cooperative. Hence a roughly circular cell will paint as an ellipse or sometimes in a stingray-shaped blob with the tail pointing at the aircraft in the center of the screen; this phenomenon is referred to as radial spread.

Usage and risk assessment

With the characteristics of a lightning detection system in mind, some techniques are helpful to interpret what the unit is telling you. The two primary pieces of information that a pilot needs to know when flying in the vicinity of thunderstorms are location and strength.

Determining strength is where the Stormscope is the most helpful. Onboard radar is better for location, but doesn’t tell you as much about the strength.

As lightning strikes more closely correlate with turbulence, and turbulence is more closely associated with inflight breakups, a few tips on determining the strength of a cell are in order.

It seems common sense that the more closely the strikes are displayed on the screen, the stronger the cell. That is true; however, there are other considerations. One of the most important is how fast the strikes are occurring.

One technique that I use is to hit the CLR button from time to time on my WX-10A so that I can watch a particular cell repopulate. A strong cell may add a dot on the display every few seconds so that it pretty much redisplays the cell is a minute or so.


Another technique is to change the range setting. If one is detecting a cell on the outer ring of the 100 nm range setting, I will change to 200 nm and see if more is shown. If so, it may indicate that what I am seeing at first is just a few strong hits and that on the longer range, I can see the outline of a larger cell. Any cell that paints well on the 200 nm range is one to be taken seriously.

Changing to the 50 nm range may show you whether a few of the strikes are strong enough to show on that setting. Tightness of the dots and the rapidity which they will repopulate tell you much about strength of the cell.

It is also good to keep in mind the overall atmospheric conditions when assessing the risk. If the storms are growing, as they typically are through the day with the peak solar energy in early to midafternoon, then the cells are likely getting stronger and extra caution is warranted.

At night, they are typically dissipating and what you see is what you get. I have gone through cells that painted only a strike or two, but painted ominously on the weather radar. Since it was after midnight, I was confident that the air mass cell was just collapsing and dropping water—and it was. (Always be alert to the potential for rapidly changing conditions, and don’t violate your personal margin of safety. —Ed.)

My strategy for using my WX-10A is to leave it set at the 100 nm range. Anything showing up in this range is worthy of the pilot’s attention. As a cell starts to populate on the outer edge, I can watch it move closer.

Once it is clear that I am not looking at a few random discharges that occasionally come and go, I will consider changing course. I have had good success with changing the heading so that no cell is in the 50 nm range within 30 degrees of the nose. That should give 25 nm of clearance from the storm.

To me 25 nm is adequate for the typical air mass thunderstorms, but ones associated with a strong frontal system may need a wider berth. Here is where knowing the overall weather conditions and having recent information on the tops of the cells can assist with the big picture decision-making.

As one changes course, it is important to hit the CLR button (unless the unit has a gyrostabilizer) so that you keep a clear idea of where the storm is relative to the aircraft.

An ALDE makes a nice accompaniment to onboard Nexrad by providing some real-time input, and to better allow the pilot to assess the strength of a thunderstorm and circumnavigate the worst of the cells.

With a little experience, onboard strike detection equipment can be the difference between taking a flight knowing some deviations may be necessary, and keeping the aircraft in the hangar for fear of blundering into a life-altering situation.

Kristin Winter has been an airport rat for almost four decades. She holds an ATP-SE/ME rating and is a CFIAIM, AGI, IGI. In addition, Winter is an A&P/IA. She has over 8,000 hours, and owns and operates a 1969 C model Twinkie affectionately known as Maggie. Send questions or comments to .


Weather avoidance equipment

– PFA supporters

Strike Finder Insight Instrument Corp.


L-3 Technologies, Inc.
Other lightning detection products
TWX670 Tactical Weather Detection System
Avidyne Corp.
ADS-B vs. SiriusXM

ADS-B vs. SiriusXM

Michael Leighton compares two popular portable units that can receive in-flight weather and more. 

Perhaps the most significant safety improvement in aviation in the last 20 years is the availability of cost effective, quality, real-time weather and traffic in flight. Once found only on high-end corporate aircraft, real-time weather is now available to any pilot with an iPad using a portable receiver. The most popular portable options are the Stratus 2S ADS-B receiver from Appareo and the SXAR1 receiver from SiriusXM Aviation.

I did a side-by-side comparison of both systems with each receiver dedicated to one of two iPads. My test flights were conducted in a single-engine piston and a single-engine turboprop. 


Both receivers are small and lightweight. Both utilize rechargeable lithium-ion batteries with a life span that exceeds the average fuel leg in most General Aviation aircraft. The Stratus 2S has an eight-hour battery life, while the SXAR1’s battery life is up to six hours. In-flight recharging is easily accomplished with a USB cable, if necessary. 

The light weight of both devices makes a suction cup window mount or a piece of Velcro on the glareshield two practical solutions for mounting the receiver. Both units are simple to operate, featuring exactly one button to turn the unit on or off. 

Both units use indicator LEDs to identify which functions are operating and the status of the battery power. In flight, both receivers display weather in real time on an iPad. 

I use ForeFlight in my cockpit, and both receivers are compatible with ForeFlight. Though some tech-savvy users claim to have made these receivers work with other apps, only ForeFlight is officially supported.


Though both units provide weather information, they do so in very different ways. 

Stratus 2S and ADS-B

The Stratus 2S utilizes the government-developed Automated Dependent Surveillance Broadcast, commonly referred to as ADS-B. 

ADS-B weather is ground-based and subject to line-of-sight limitations; that’s why it’s typically not available when the aircraft is on the ground. Additionally, there are “holes” where ADS-B reception is intermittent. Since ADS-B is the cornerstone of the Next Generation (NextGen) air traffic control, the FAA says that when the system is fully operational in 2020, any in-flight reception issues should be resolved. 

Geographic coverage for ADS-B extends about 20 miles beyond the United States’ borders. On our trips to the Bahamas, we receive ADS-B coverage to about 30 miles offshore at 10,000 feet—our altitude and the lack of terrain obstructions allow the signal to reach farther. 

The weather products available with ADS-B are adequate for the average General Aviation mission. When in flight, composite NEXRAD is available. Base reflectivity and cloud coverage are available on the ground using an internet connection, but not in the air. 

Airborne ADS-B also provides METARs, TAFs, SIGMETs, AIRMETs, TFRs, visibilities, ceilings and flight conditions for graphic display and in text format; notams and Special Use Airspace alerts are also available.

ADS-B with the Stratus 2 includes features you cannot get from SiriusXM Aviation weather. Traffic and a backup PFD are phenomenal features provided by Stratus. I love the backup PFD. I teach my students how to shoot an approach with it in the event of a total equipment failure. 

If your aircraft does not have a traffic avoidance system, ADS-B traffic is useful, but until 2020—when all aircraft are supposed to be equipped with ADS-B—it does not depict all traffic. 

The best part of ADS-B is that the service is free, while SiriusXM uses a paid subscription. However, the receiver to get free ADS-B data can cost more up front: a Stratus 2S lists at $899, not counting any antennas. In contrast, an SXAR1 is priced at $699, and may qualify for a $200 rebate, but subscription fees will be extra.

SXAR1 with SiriusXM Aviation weather

The Sirius product, SXAR1, gets its data not from the ADS-B source, but from SiriusXM satellites. It also has a GPS/WAAS embedded receiver. 

The SiriusXM aviation weather subscription includes the same weather products provided by ADS-B, as well as icing icing, winds aloft, lightning, in-flight base reflectivity radar, radar echo tops, cloud tops, turbulence and surface analysis. The range of coverage includes most of Canada, parts of the Caribbean, and extends much farther offshore. 

A subscription for the SiriusXM Pilot For ForeFlight package is around $40 per month. More comprehensive weather information is available with Pilot Preferred ($59.99/month) and Pilot Pro ($99.99/month) packages. For all SiriusXM aviation weather packages, the ability to listen to your favorite music and news channels in flight, if you so choose, can be added to your weather subscription at a discounted rate. 

One unexpected issue arose with the SXAR1 receiver during my testing. The electrically-heated windows in turboprop airplanes interfere with data reception. Moving the unit to an unheated side window improved my reception. Depending on which side of the plane the receiver was placed also affected the unit’s ability to receive data from the satellite. (We contacted SiriusXM and about this and received this reply: “Heated windscreens on some aircraft may block or interfere with the SXAR1 Receiver data reception. If you experience a weak signal condition, place the SXAR1 close to either side window or you may choose to purchase an optional External Antenna at shop.siriusxm.com or at sportys.com. The antenna can then be placed in the cockpit for best signal and the SXAR1 receiver can be placed out of the way.” —Ed.)

Another difference to address is the display resolution. The resolution is the same for the SiriusXM Aviation via SXAR1 and for ADS-B through the Stratus 2 when viewing weather within 200 nm of the aircraft. Beyond 200 nm, the resolution of the SXAR1 really shines; beyond that range ADS-B reduces the radar resolution, making the radar appear more coarse and pixelated. SiriusXM is consistent with its resolution at longer range. 

Final thoughts

Do you have to choose one over the other? When flying with both units, you do not need to choose only one to use because SXAR1 connects because SXAR1 connects to your iPad with Bluetooth, while Stratus utilizes Wi-Fi. This means you can have both at the same time—on the same iPad. Playing with the displays of Stratus on the backup PFD and the SXAR1 shows the advantages of each; the advanced weather features and better range of the Sirius product and traffic on the Stratus. 

Is SiriusXM worth $39.99 a month? It is to me. From my observations, I can say that I love SiriusXM Aviation weather. Since I regularly fly in real weather, the echo tops, icing and selectable winds aloft features make a difference for me. I love that the weather data is usually loaded and displayed before I take off. I do a fair bit of flying in the Bahamas and XM’s radar coverage, particularly when trying to cross the Gulf Stream, is very useful. 

I have had SiriusXM weather in my plane for 12 years, but it is displayed on a Garmin 530. The limitations of the older Garmin devices preclude receiving all the benefits of the service. The portable SXAR1 unit coupled with an iPad allows a pilot to receive every benefit of the SiriusXM service. The value of in-flight real-time weather cannot be emphasized enough. 

For the owner-pilot who must comply with the ADS-B mandate by Jan. 1, 2020, it is typically far less expensive to install an ADS-B Out-only transponder and buy a portable ADS-B In receiver than to purchase a combined ADS-B Out+In device. A portable receiver allows these operators to enjoy the benefits of ADS-B In—without the installed-in-the-aircraft cost. 

In addition, the portability of the Stratus 2S and the SXAR1 are perfect for a pilot like me who flies several different aircraft. 

The SXAR1 receiver delivers the most complete and comprehensive in-flight weather data available on a portable device. The safety features in the Stratus 2—especially after the ADS-B Out mandate takes effect—are phenomenal. I plan to carry both. 

Michael Leighton is a 11,000-hour, three-time Master Flight Instructor and an A&P mechanic. He operates a Part 141 flight school in South Carolina and South Florida. You can find him on the web at flymkleighton.net. Send questions or comments to editor.




SiriusXM SXAR1
Stratus 2S


SiriusXM Aviation 
In with the New:  An Avidyne IFD540 Plug-and-Play Conversion Part 2

In with the New: An Avidyne IFD540 Plug-and-Play Conversion Part 2

July 2015 -

In my last article, the hardware installation on my new IFD540 was successful—with a few adjustments. I’d expected to be able to remove the 530W and slide in the 540, configure a few screens and be done. It didn’t quite go that way.

The new IFD540 features that required wiring included an additional com receiver; a wire for the yet-to-be-installed Mode S ADS-B Out transponder; and a separate wire to the audio panel to ensure that terrain alerting can’t be disabled. (For details, see “In with the New Part 1” in the June 2015 issue of Piper Flyer. —Ed.)

With this fresh in my mind, I further researched the requirements for the AMX240 audio panel and the AXP340 transponder I’m planning to install and found out that they are not 100 percent plug-and-play, either. I was able to get the necessary wiring for these devices accomplished during the installation of the IFD540 which will save two panel teardowns later. (Future articles will cover Sherer’s other projects. —Ed.)


As I mentioned in part one, my avionics tech, Erich, photographed the GNS 530W configuration screens using his cell phone. It took him five minutes of configuration time and another five minutes of testing to get the new IFD540 working correctly with my GMX 200, GDL 69, GMA 340, Century NSD-360 HSI and Century 2000 autopilot.

The next step was updating map information. For the last decade I’ve subscribed to Jeppesen’s 530W maps and downloaded them using the Jeppesen Services Update Manager (JSUM) program. JSUM software is free with a Jeppesen subscription and very easy to use.

I called Jeppesen’s customer service and within 10 minutes they switched my subscription to the new device. I started up JSUM, downloaded and saved the new file on the flash memory (thumb) drive that came with the IFD540.

To transfer map data to the IFD540, you simply insert the flash drive into the front panel, select a menu on the AUX screen, and the new file copies in just a minute or two. You can then remove the flash drive and take it home for the next time.

A good surprise

While reading the IFD540 manual—which, by the way is very detailed and easy to read and understand—I came across something very good. But first a short story:

Several years ago I landed one night at my then-home base, Racine, Wis. It was about 0 degrees F. I taxied to my hangar and discovered the lock had frozen over. I couldn’t get into my hangar to the safety of my heated automobile.

I pulled out my cell phone to call my wife, but there was very little battery charge left. I chose to call 911 and just got the call out before my phone failed. (I had a charging plug with me, but there is no cigarette lighter socket in the aircraft panel.)

Fortunately, the Racine Police Department called my wife and she came out in the middle of the night to get me. But it was a very cold wait.

The feature I discovered on the IFD540 shows the thoughtfulness and attention to detail of Avidyne’s engineers. The flash drive used for uploading maps and downloading stored checklists for backup has yet another function.

Here’s the passage from the manual:
“The USB port on the front of the IFD bezel is a USB v1.1 compatible USB port and can be used as a ‘high power’ charger as well.

“Most devices are ‘low power’ devices and they will fully charge from the IFD bezel USB port.
“Some devices are ‘high power’ devices and need up to 2.1 amps of power—these devices can also be charged from the IFD USB port. The iPad is a good example of a ‘high power’ device and the IFD supports charging.”

The first flight

So here we are, as Charles Lindbergh said upon landing at Le Bourget Airport in Paris in 1927. Let’s take this baby for a spin!

Since it was January, I asked if I could get in the airplane before the maintenance crew tugged it out of the hangar. Yes was the word, and I climbed into the plane while the crew opened the hangar doors.

I had already done the preflight, put on my seatbelt, locked the door, put on my headset and turned on the battery master. Now the plane was out of the hangar and I did my methodical 60-item checklist and cranked the engines.

Oil pressure came up in about 10 seconds and I let the engines idle while I powered up the Janitrol furnace and radio master on my Seneca.

Firing up

The IFD540’s white LEDs and the Avidyne logo soon became visible on the LCD screen. (These screens have to be warm for the liquid crystal formulation to work, so the display takes a couple of minutes when powering up in cold weather.)

In short order the unit came online and the GPS found itself in Wisconsin and the display showed Burlington (KBUU) when I pressed the map button.

My Garmin GMX 200 MFD powered up and showed KBUU on its display, too—the Avidyne GPS had communicated with the Garmin MFD successfully and correctly. Since I have a hybrid panel with Avidyne, Garmin, Century and Narco equipment, this check was important.

The GDL 69 datalink XM weather receiver started to display NEXRAD weather radar on the IFD540 and GMX 200 MFD. Another promise from Avidyne had been kept: complete compatibility with these two devices.

Initial tests

I did a Direct-To KMRJ, Iowa County Airport in Mineral Point, Wis., about 75 miles away. I took off, entered 6,500 feet in my altitude preselect and engaged the autopilot in GPSS mode.

The airplane turned to a heading of about 290, climbed to 6,500 and entered altitude-hold mode on the autopilot, a Century 2000 configured with the altitude-preselect and GPSS boxes.

During this phase of the flight I tested a multi-leg flight plan and pushed the MON1 button on my new audio panel to listen to the standby frequency on the IFD540. Unfortunately, this function didn’t work, and I jotted this down for my radio guy Erich to debug later.

Every other function that I could think of—and test—was working.

The last big test

The only other untested item at this point in my first flight was an instrument approach. I was now 75 miles west of my home airport and it was time to come home. I entered a two-leg flight plan in the unit—which is amazingly easy—and then pressed the PROC (procedure) button. I selected an RNAV-29 GPS approach and pressed enter.

When I was positioned about 15 miles out of KBUU, I activated the approach and left the autopilot coupled in GPSS mode. That’s when the magic began to happen—and it was amazing to watch.

I was 15 miles west of the airport and would need to move to a position about 10 miles east of the airport, do a course reversal, descend and land. After activating the approach and selecting FAF (final approach fix) on the unit, the airplane flew to the waypoint, did a course reversal and asked if I wanted to hold at the FAF.

If I had wanted to hold, I would’ve pressed the HOLD button on the lower left side of the IFD540. Since I didn’t press the hold button, the unit displayed a message saying that the unit would not hold and proceed to the approach.

Having completed the course reversal and approaching the FAF, I switched the autopilot from GPSS-Heading mode to Approach mode. This tells the autopilot to increase sensitivity and enable glideslope control.

Since I was doing a left pattern approach without vertical guidance, the function wasn’t enabled for this approach. Nevertheless, I had two more approach waypoints with step-downs and the final landing.

Preparation paid off

On my first flight I successfully did a GPS approach with course reversal, two step-downs and a landing. Easy as pie!

I landed with two hours on the hour meter, taxied back to the maintenance shop and powered down. My only squawk was that MON1 that didn’t work. Erich, my radio guy, will work on that shortly.

To prepare for this first flight with the IFD540, I installed the free PC-based simulator and had spent about 10 hours using it over the last month.

This IFD540 simulator allowed me to practice how to configure, load flight plans and play with everything that I could play with on a screen. This preparation was invaluable. When I got in the plane and used the new radio, I had no confusion or think time required. Needless to say, I’m very pleased.

AviKeyboard hand 540 300IFD540 FMS QWERTYIFD540 MAP PinchZoom

Touch screen and buttons

Avidyne’s IFD540 works with buttons or a touch screen (or both), and there is a configuration option that allows the user to turn off the touch screen.

I initially turned the touch screen off as I really prefer pushing buttons. However, upon reading the manual I noticed that there are a couple of functions that only work via the touch screen.

I re-enabled the touch screen capability, but I didn’t use it at all on my first flight. It remains to be seen if I’ll move to using the touch screen over the next few months.

The buttons and knobs on the IFD540 closely match my previous Garmin 530W so I found that I didn’t have to reprogram my brain to use the new radio. In fact, I would say after my first flight that I’m about 90 percent acclimated to the new radio.

One part of a bigger picture

Previously, the panel of my Seneca contained a Garmin GNS 530W GPS/NAV/COM which was linked to a Garmin GMA 340 audio panel, a Garmin GMX 200 MFD, a Garmin GDL 69 remote datalink receiver, a Century NSD360 HSI and a Century 2000 autopilot.

When my project is complete, I will have replaced the Garmin GNS 530W, GMA 340 and my older, trusty Narco AT-165 Mode C transponder and installed an Avidyne IFD540 navcom, AMX240 audio panel, AXP340 Mode S ADS-B Out transponder and either an Avidyne or Garmin ADS-B In receiver.

It’s my intention to continue to receive weather from my datalink receiver (GDL 69/SiriusXM) and only use traffic from the new ADS-B In receiver.

I’ve been using Garmin equipment since 1992 and have enjoyed using the equipment very much. I’ve owned a GPS 155, a GNC 300 and my trusty 530 and I suspect the new GTN equipment is a continuation of the amazing technology that Garmin has brought to our industry.

I chose Avidyne this time around because I felt that its design considerations were more appropriate for my situation. It’s mostly plug-and-play compatible and the same size as my previous Garmin equipment, and this has reduced my conversion cost by thousands—literally. In my opinion, the Avidyne equipment is nothing short of awesome.

Scott Sherer is a multi-engine and instrument rated private pilot. He’s logged 2,600 hours and is the owner of a 1977 PA-34-200T based at Burlington Municipal (KBUU) in Burlington, Wis. Sherer anxiously awaits the day when N344TB finally gets new paint. Send questions or comments to .


Avidyne Corp.

Pilots are able to customize CGR equipment by completing a Marking  and Configuration Requirements (MACR)  document with their order.

Trading Six Instruments for Two: Cluster Gauge Replacement

July 2015 -

You can monitor engine and electrical system parameters, fuel flows and quantities and OAT in two 3 1/8 inch instruments using CGR-30P and the CGR-30C from Electronics International.


I recently moved into the 21st century and upgraded my instrumentation by installing my first glass panel—a tidy engine monitor package from Electronics International (EI) consisting of two round instruments; the CGR-30P and the CGR-30C.

Each of these two instruments fit in a standard 3 1/8 inch instrument hole and together make up the CGR-30P Premium package. The Premium package is designed to provide full systems data and can be configured to suit the application and pilot’s needs. (EI also offers a Basic package that consists of a single CGR-30P instrument. The Basic package is pre-built and configured to display CHT, engine RPM (tachometer), fuel levels and volts. —Ed.)

IMG 1526 

These engine instruments are approved for installation in a wide range of single and twin engine aircraft by STC. Twin engine aircraft require two CGR-30P instruments. In most cases, a single CGR-30C has the capacity to display other needed data.

CGR, as you may have guessed, stands for Cluster Gauge Replacement. I’m now monitoring my engine and electrical system parameters, my fuel flows and quantities and OAT in two 3 1/8 inch instruments. The CGR-30P (“P” for Primary) is on top of the two-gauge stack; the CGR-30C (“C” for Cluster) directly below. I replaced six discrete instruments with two, and my panel is much cleaner.

CGR instruments have active TFT (thin-film transistor) displays with 262,144 colors and are sunlight readable.

The CGR system is almost infinitely programmable. For instance, the RPM channels can display data from engines with as few as two and as many as 12 cylinders. A few wiring changes allow the CGR combo to accommodate LASAR and Light Speed Engineering Plasma II and Plasma III electronic ignition systems.

In order to upgrade to the EI CGR system I removed an old analog manifold pressure gauge; a nice Horizon P-1000 electronic tachometer (a good instrument); a JPI EDM 700 with fuel flow (another good instrument); and three Aerospace Logic instruments: a fuel pressure/ammeter-voltmeter; a left and right fuel quantity gauge; and an oil pressure/oil temperature gauge.

I’ve been flying with the EI CGR-30P and -30C gauges for a month now, and although I’m still going back to the manual to learn all the capabilities of these instruments, I am very happy with my new glass panel displays.

I like the brightness and clarity of the displays; I like that the engine data that I consider critical is on the front page of the -30P and all the other engine data is concentrated in one spot and is very easy to access.

I like the fuel/trip planning and tracking feature; I like the comprehensive programmable alert and warning system; and I like… well, the list goes on. There are a lot of features packed into these two instruments.


Easy leaning

The leaning algorithms in the CGR instruments make it exceedingly simple to perform lean-of-peak (LOP) and rich-of-peak (ROP) mixture setting chores.

When leaning, I’ve found the EI display and data feed very easy to decipher.

In cruise I lean until what EI calls a “telltale marker”—I call it a white line—appears above the first cylinder to peak. The number-two cylinder on my Lycoming O-360 always peaks first. The white line and a numerical readout appear across the EGT portion of the EGT/CHT bar graph at that peak temp.

Since I’ve selected ROP leaning (carbureted engine) with the select knob, all that’s left for me to do is leave the mixture where it is (peak EGT) for maximum economy (at 75 percent power or lower in Lycoming engines, and at 65 percent power or less for Continental engines); or richen the mixture slightly until the digital readout indicates 80 to 100 degrees for a best power fuel/air mixture.

How do I know what percent power I set? Prior to installation of the CGRs I had to do it the old-fashioned way by referring to the power chart in my owner’s manual. Now it’s simple—after programming a page with data gathered from the owner’s manual and one short flight, a percent power number is displayed.

The first step: filling in the MACR

The first step in ordering an EI CGR-30P is to determine how you want to configure the pages of the instruments; then you can fill out the Marking and Configuration Requirements (MACR) document.

Pilots also have the option of selecting five non-primary functions to customize the CGR installation for their airplane. These functions include OAT, horsepower, volts, carburetor air temperature, fuel flow, hydraulic pressure, g meter, cabin altitude, induction air temperature, turbine inlet temperature (TIT), compressor discharge temperature—there’s even a carbon monoxide detector option.

Primary instruments

The first (main engine) screen of the -30P always displays RPM and CHT/EGT data for up to six cylinders. There’s also room on that page for three additional data points in the form of strip gauges.

The gauges that Piper configured in a small cluster in my Comanche are termed primary gauges. These primary gauges are specified by FAA regulation for each airplane. The applicable regulation for my Comanche—and for most piston-powered Pipers—is Civil Air Regulation (CAR) Part 3. Most piston-powered Cessna aircraft are also certified under CAR 3.

The primary gauges in my Piper Comanche are fuel pressure, oil pressure, oil temperature, left and right fuel levels, and amps. Since my Comanche has a constant speed propeller, the regulations also mandated a manifold pressure gauge.

There isn’t room to display all of the primary gauges on the -30P main engine screen. I chose to display fuel flow, fuel pressure and oil pressure along with the EGT/CHT bar graphs and the tachometer and manifold pressure displays the main engine page. (Since I could display the other primary gauges on the -30C, I chose those functions for the main page display of the -30P that I thought were most important.)

The other primary data that’s required as well as other operationally important data is in full view just below the -30P on the -30C. This list includes left and right fuel quantity (referenced to fuel level senders in the tanks), oil temperature, outside air temperature (OAT), carburetor inlet temperature, vacuum, volts and amps.

As I filled out the MACR, I wrote in the instrument face markings (red arc, green arc, yellow arc, redline) for each instrument by reference to the owner’s manual or POH. (This is typically something the installing shop will do. —Ed.)

The second screen is used to display functions that don’t need to be displayed continuously such as tach time, engine time, flight time, local and Zulu time.

The third screen in the -30P is the fuel quantities screen. This screen displays estimated fuel levels for different tanks—up to four tanks can be displayed—or total fuel quantity. Provisions for adding fuel and K-factor adjustments for the fuel flow display are on this page.

The fourth screen is the fuel data screen where trip- or leg-specific information based on fuel flow and GPS information is displayed. This data includes range, distance to destination, fuel reserve, time to empty, fuel used during flight and even fuel economy (in mpg). The information on this page is dependent on an RS232 data feed from the airplane GPS.

Since the fuel data screen is tied to the GPS and the fuel flow data, a change in any part of the fuel/time equation (such as a change in destination airport), power settings or mixture strength instantly updates important flight planning data such as, “Do I have enough fuel with my personal fuel minimums to get to my destination at this power setting?”

The big install

EIBox Steve

As I worked my way through the installation checklist I ran into a few hiccups but was always able to get support from Michael Roberts, Dave Arata, Daniel Bennett and Tyler Speed at EI.

The installation was straightforward. All the wires from all the data probes, the fuel flow transducer, the manifold and oil pressure transducers, the electrical system shunt and the resistive fuel level module (RFLM) are fed into three plugs that connect to and feed the engine data converter (EDC).

I mounted the EDC, the vacuum and manifold pressure (MAP) modules and RFLM on a shelf on the cabin side of the firewall. A single serial data wire moves the data stream from the EDC to the -30P and -30C.

The EI CHT probes are different from JPI probes in that they aren’t spring loaded to insure contact against the bottom of the hole. According to Arata, EI can supply the spring loaded probes if the customer desires.

This difference in probes is the reason the CHT numbers differed between the JPI system I removed and the EI system I installed—by approximately 30 degrees F. (The EI CHT readouts are cooler.) The hottest cruise power CHT I’ve seen during the last month is number four, at 343 degrees F.

Since my CHTs were never very hot—I’ve never seen 420 degrees F, the bottom of the yellow warning arc—with either system, this difference is not a big deal on my airplane. To me, the most important function from sampling EGT and CHT is detecting gross engine problems quickly. These problems always show up first on EGT systems. It’s critical to respond quickly to rapid temperature deviations from the norm.

The CGR system has two systems that do this automatically. The first system consists of setting normal operating ranges on both EGTs and CHTs. For instance, if your normal full rich low power EGT readout is 1,100 degrees F, set the range low limit at 1,000 degrees F. If your peak EGT is 1,500 degrees F, set the range upper limit for 1,150 degrees F. A variance outside either limit will cause the EGT bar in the graph to turn white and blink. Whenever a CHT falls outside the upper or lower range limit, that cylinder bar will turn red and blink.

There are four modes of operation used to display CHT/EGT information. Select mode is used to select the EGT and CHT for one cylinder. The temperatures are then displayed numerically at the bottom of the display.

Other modes include the Diff mode that displays the difference between the hottest and coldest CHT and EGT. These numerical values are shown at the bottom of the display as EGT-D and CHT-D.

Then there’s the Scan mode where EGTs and CHTs are continually scanned; the rate of scanning is configurable.

Finally there’s the Hottest mode where the hottest EGT and CHT are shown numerically.

The second way to spot deviations is to use the normalize mode. After setting cruise power, the normalize function can be selected by pushing and holding the Select knob for four seconds or by pushing the rotary knob to activate a cursor above the EGT/CHT bar graph display, then rotating the knob to select “normalize,” and pushing the knob in to select that function. Either method causes the bars of the CHT and the bars of the EGT of the current flight to be compared to bars recorded during a reference flight in the past. Differences are easy to spot.

Like other EI engine monitors, the CGR system incorporates microprocessors that analyze engine data as it is collected. When a deviation from normal operating levels is sensed, the device immediately triggers warnings so pilots can evaluate and take action if necessary.

The master nag

EI CGR Warning system

Each EI CGR system also has a sophisticated warning system that keeps an eye on aircraft systems—engine, fuel flow, electrical, fuel quantity, etc.—and alerts the pilot if these parameters stray.

Since I decided not to rearrange my panel to install the -30P and -30C within eight inches of my vision centerline (as recommended by Advisory Circular [AC] 23-1311), I installed the EI master caution and master warning lights in a row with the “Alt Inop” warning light slightly to the left of my airspeed instrument.

Caution and warning flags also appear on the faces of the instruments. A voice alert and warning signal that’s wired to the avionics audio panel (with panel-mounted on-off-acknowledge switch) is an option.

Each of the strip gauge displays will blink in tandem with the remote caution and warning lights if any function varies from the green arc. Pilots need only push the “E” (escape) button on the face of the instrument to acknowledge the alarm and stop the blinking.

Pilots can toggle between the EI CGR-30P between a variety of EGT/CHT data displays including ROP leaning; LOP eaning, EGT digital operating mode and CHT digital operating modes. The LOP leaning display show the first cylinder to peak, where all cylinders are in relation to the first to peak and the number of degrees the first to peak is lean of its peak.

Fuel transducers

To obtain the most accurate fuel level data, CGR buyers are urged to install EI’s P-300M magnetic fuel level sensors (only one moving part) since these sensors provide a linear voltage output and are extremely accurate; the original resistive-style float sensors can’t provide the same degree of accuracy.

In order to calibrate the arm length and arm travel of a P-330M, the original level sensor must be sent back to EI.

My resistive level sensors had been rebuilt and calibrated recently, and since I was installing a fuel flow transducer to monitor my fuel flows, I elected to connect my existing resistance-type senders to the EDC through the RFLM.

There are also provisions to use capacitive fuel level senders. An interface module such as the RFLM is not required for either magnetic or capacitive level sensors.

The after-installation calibration procedure was very easy (four levels) and the levels displayed on the -30P are consistent with my dipstick readings.

 Basic tech facts

Over Lap Connectors OLC 1

EI uses overlap connectors (OLC-1) throughout the installation wherever two (20 gauge or smaller) wires must be connected. The OLC-1 connector consists of a reddish colored nonconductive barrel. Wires are connected by tightening a tiny Allen head set screw after inserting each wire into opposite ends of the barrel.

EI developed the OLC-1 to resolve dissimilar metal corrosion problems and issues related to mis-crimped and/or poorly crimped wiring. At first I was flummoxed because it seemed like I needed a third hand to hold two wires in position and the barrel of the OLC-1 while carefully manipulating a tiny Allen wrench to install the set screw, but before too long I had it down.

The total electrical load for the CGR-30P, -30C, EDC, RFLM, all the pressure (and vacuum) sensors and the fuel flow sensor is less than two (12 VDC system) amps. This low electrical load insures that the pilot will be able to continue to monitor engine, fuel and electrical system health without the need to shut these systems down to preserve battery power in the event of a charging system failure.

Configuration screens

EI checklist screen

The EI CGR-30 system permits many configuration options. Fuel flow K-factor, EGT and CHT bar graph range settings, USB and data recording rates and fuel alarms—I set my fuel alarms to signal when my total fuel gets down to 10 gallons—and units (gallons, liters, etc.) information can also be configured.

Much of these configuration chores are done by the installing shop and except for the instrument face markings (red arc, green arc, yellow arc, redline) referred to earlier, these values may be changed as necessary in the field.

In addition, there’s a page on the CGR-30C for checklists. Checklists can also be configured for the airplane and pilot’s personal preferences. All monitored data can be downloaded and displayed on a spreadsheet or graphed. (Contact Electronics International for more information on this activity. —Ed.)

Daniel Bennett at EI’s sales and support department told me that installation times on Piper singles are reported to be between 12 and 18 hours. That seems about right for a savvy technician and well-equipped shop.

The hardest part for me was waiting for the box from EI to arrive after sending in the MACR. Now that the installation is finished and working well, I’m impressed.

I’m considering making a few more 21st century changes in my Comanche, but right now I’m just happy going to the hangar so I can continue to learn more about the features of my new glass panel engine monitor.

Steve Ells has been an A&P/IA for 43 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and the proud owner of a 1960 Piper Comanche. He lives in Templeton, Calif. with his wife Audrey. Send questions and comments to .


Electronics International, Inc.



It’s 2015. Do you know where your iPad is?

It’s 2015. Do you know where your iPad is?

If you’re not using an iPad in the cockpit, you could be missing out on one of the greatest and most cost-effective innovations for aviation in decades.

June 2015-

No question, the iPad has changed the way we fly. About a year ago, I stopped carrying paper charts completely, and I carry two iPads instead. I even cancelled my Jepps approach plate subscription—which I’ve had since 1980—because it’s all in the iPad now.
A few years back at the Gathering in Waupaca, I spoke to association members about Electronic Flight Bag (EFB) technology and specifically about using an iPad in the cockpit.
Three years later, there are many more uses and apps designed just for aviation and many of them are very good. Here is a brief description of just a few of the apps that are available to a pilot in 2015.

Flight planning
For flight planning and in-flight display, I have been flying with ForeFlight. ForeFlight has partnered with Appareo Systems, the company that manufactures the Stratus ADS-B receiver. The Stratus device receives ADS-B transmissions in-flight and displays weather and traffic on the chart of your choice on your iPad.
In a recent upgrade, the company has added an AHRS feature that looks just like a PFD. While not legal for use in IFR conditions, it is an amazing safety feature. It has also added Canadian charts and World Aeronautical Charts (WAC) to the available library. I regularly use both.
Other nice features include georeferencing your position on the approach plate (and especially the taxi diagram); notams that are decoded and route-specific; an internal weight and balance program; and the ability to place the approach plate directly onto the chart so you can see both at the same time.
TFRs, ceilings and visibilities, winds aloft, fuel prices along the route and cloud coverage are just some of the other available features you can view.
I use ForeFlight to file and brief all my flight plans. Another feature I use a lot is the record feature. ForeFlight lets you press a button and “record” your flight path. I use this when teaching instrument approaches. It plays back on Google Earth-like maps, and is a great teaching tool.

WingX Pro
WingX Pro 7 by Hilton Software is an equally powerful app. It too displays ADS-B weather and traffic on the iPad. In my opinion, the coolest feature in this app is the ability to load arrival and departure procedures and approaches into the flight plan and have all of the waypoints displayed on your chart.
A few years back, Hilton Software added a synthetic vision feature to WingX Pro. I haven’t seen it, but a buddy of mine who flies with WingX Pro 7 has been raving about it, so I’m going to have to try that.
WingX Pro works with more than a dozen different receivers. The program also features a flight simulation mode which lets you play with the software’s features and see what it looks like.

Garmin Pilot
Garmin Pilot is Garmin’s entry into the iPad EFB arena. Much like ForeFlight, it only plays on one ADS-B receiver; in this case, it’s the Garmin GDL 39.
I have a student that uses Garmin Pilot and when we fly her plane, I get to sample the app. My student uses SiriusXM weather (a subscription) and it plays on Garmin Pilot—something other apps don’t permit.
Garmin Pilot also features European flight charts, a feature that is currently not available on ForeFlight or WingX Pro. (JeppDirect offers electronic chart service for Europe in various configurations at various price levels. —Ed.)

FltPlan was the first company to offer free in-flight apps on both iPad and Android tablets. FltPlan Go for iPad works with five ADS-B receivers, and subscribers to XM weather can enable the display to receive weather data.
This great site does tons of things, including weight and balance; it has a logbook program, plus an E6B calculator and even an AFD feature.
While FltPlan.com does have a mobile app, creating your flight plan through your account on the FltPlan.com website provides additional features.

iFlightPlanner, FlyQ
In-flight planning and chart apps like iFlightPlanner and FlyQ are available to iPad pilots too, but I just haven’t had the time to thoroughly investigate and fly with these apps yet. I plan on interviewing the developers at Oshkosh later this year and writing about my experiences with these products after I fly with them.

Weather and filing apps
weatherTAP, Zoom Weather
WeatherTAP is a subscription weather application, and in my opinion it provides the best weather. It’s not that the information is different; weather is, well… weather. But the format is great and it’s easy to use.
One of my favorite features is the animated enhanced infrared water vapor satellite page—you can see exactly how the atmosphere is moving, and view half the country on one page. I haven’t found those features available anywhere else. (Other resources do offer infrared water vapor depictions, but not in exactly the same fashion. —Ed.)
The Aviation Weather section of the app features a predictive satellite and radar page that computer forecasts precipitation, and I’ve found it to be extremely accurate.
TAP Publishing also offers a free app for iPad/iPhone called Zoom Weather which displays radar, current and forecast conditions with an hourly and daily presentation. Like weatherTAP, Zoom Weather is simple and easy to use.

Also on my iPad are DTC DUAT and CSC DUATS—the same providers we pilots have been using for years. I have them as backup.
Both programs offer aviation weather and the ability to file a flight plan. The ForeFlight app I discussed earlier in this article can use your CSC DUATS account to file flight plans, so if you don’t have a DUATS account already, I suggest you go sign up. It’s free.

Logbook apps
If you are thinking about keeping your logbook on your iPad, there are a wide range of logbook options available, and some are free.

Logten Pro
Logten Pro interfaces directly with ForeFlight: you can press a button and export your flight from ForeFlight directly into your logbook. Logten Pro costs $50 a year to use, but it’s the most detailed and flexible flight log app I have found. The app uses cloud storage; the logs aren’t resident on your device.

Other pilot tools
Weight and balance
Warbred Studios makes a great little app called FlightScale. You input in the information about your airplane directly from your AFM or POH and this app creates a weight and balance report that is color coded and graphed; you can email, save and print this data. In my experience, FlightScale is simple, fast and awesome.

… yes, there is an app for that. Several, in fact. ASA and Sporty’s are two of the more popular ones. With searchable data features that let you find what you want quickly, I think every pilot should have an FAR/AIM reference on their iPad. (For those pilots who use Android devices, ASA’s app is available at GooglePlay, too. —Ed.)

Electronic E6B
Some of the EFB/flight planning apps have built-in E6B calculators, but you may prefer a separate app. If so, there are several stand-alone E6B apps out there, including those that work on Android platforms.

Flight training
Sporty’s offers pilots a lot of training material specifically for use with an iPad. You might expect that they now offer written test prep courses for private pilot, sport pilot, instrument and commercial via iPad, but Sporty’s also has courses on how to use everything from in-flight weather radar to the Garmin GTN 750.
For the aspiring CFI, lesson plans are available, too. Teaching tools, like airspace review and communications training apps, as well as subject-specific training programs like weather flying and a biannual flight review are also available through Sporty’s website.

Radionav Sim, E6B simulators
Since I teach a lot, I also have a radio navigation simulator app called Radionav Sim that lets me demonstrate radio magnetic indicator (RMI), course deviation indicator (CDI) and horizontal situation indicator (HSI) presentations.
I also use an E6B simulator (yes, the old style “whiz-wheel” kind) that we still need to teach private pilot candidates. There are several out there, so choosing one is a matter of personal preference.
Sporty’s E6B is the iPad-based E6B calculator that I use for teaching. The app is menu driven with a built-in
calculator function.

Stay informed
These days, publications dedicated just to sharing information about aviation software, apps and accessories for iPad pilots are a reality.
One good one is Sporty’s ipadpilotnews.com website, which has various tips, FAQs, product news, articles and videos available. Future news and information can be emailed to you by signing up for the monthly newsletter.
There are so many iPad apps out there for pilots and more are coming all the time. Stay tuned!
As always, if you have questions, do not hesitate to contact me. I always respond to association members’ questions.

Michael Leighton is an 8,800-hour, three-time Master Flight Instructor, as well as an A&P mechanic. He operates an aircraft maintenance facility and flight training company in Spartanburg, S.C. You can find him on the web at flymkleighton.net. Send questions or comments to .

Note: This article provided a brief look at several apps currently available to pilots. PFA members can expect to see more in-depth articles about various apps in upcoming issues of Piper Flyer. —Ed.


Apps from
PFA-supporting companies

Garmin Pilot
buy.garmin.com, search “Garmin Pilot”

Sporty’s training apps

Flight planning



WingX Pro

Weather and filing




Logten Pro

Weight and balance

Flight training
Radionav Sim

iPad app news and information
iPad Pilot News

The Soul of a New GPS: Avidyne’s IFD540

The Soul of a New GPS: Avidyne’s IFD540

In 1982, journalist Tracy Kidder won a Pulitzer Prize for “The Soul of a New Machine,” a book that described the development of a next-generation computer by Data General Corp. and its competitor Digital Equipment Corporation (DEC). For engineers in the story, the time-to-market pressure was constant. As Wikipedia notes, “The ‘soul’ of the new machine comes from the dedicated engineers who bring it to life with their endless hours of attention and toil. The soul is theirs, stored in silicon and microcode.”

February 2015-

Thirty-three years later, a similar narrative is playing out just 30 miles from the site of that original drama. Avidyne Corp. of Lincoln, Mass., has introduced the IFD540, a plug-and-play GPS Nav/Com. Pilots are already embracing this exciting new choice in the avionics market. Avidyne’s next product, the IFD440, should be available this spring.

Meet Richard Sears
Richard Sears was an early developer of data centers that served thousands of customers, including Oprah Winfrey’s e-commerce division. In 2008, Sears and his partners sold American Internet Services for tens of millions of dollars.
Sears had made more than enough money to retire at age 46, but didn’t. He’d fallen in love with aviation while serving as a military police officer with the United States Marines. He learned to fly with the Armed Services Aero Club in Okinawa, Japan. After returning to San Diego in 1988, he joined some partners to buy a Cessna 152 and 172XP.
That led to the purchase of faster planes, then a high performance aircraft, and then to Piper’s M-Class. The turbine powered Meridian that Sears purchased was ideal for shuttling clients of his internet company to different locations in
California and Arizona.
Handheld Peace of Mind: the DeLorme inReach

Handheld Peace of Mind: the DeLorme inReach

December 2014-

A ferry pilot uses this global satellite communicator
for practical purposes—and also for fun.

Ferrying an aircraft is one of the most taxing activities a pilot can undertake. From checking weather to packing the right equipment, your whole focus revolves around one question: How can I complete this flight as safely as possible?
My number-one piece of safety equipment is my DeLorme inReach, which I've lovingly nicknamed "DeeDee."


Leading Edge: Personal Locator Beacons

findmyfriends hero 300

September 2014- Five-and-a-half years ago, Search and Rescue Satellite (SARSAT) monitoring of the 121.5 MHz and 243 MHz emergency frequencies ceased. Citing statistics that indicated many more false alarms than actual emergencies, the international consortium that administers the global network of search and rescue programs called for mandatory conversion to a new system operating on 406 MHz beginning Feb. 1, 2009.


Leading Edge: Engine Monitoring- Predicting the Future with Electronics

Fig 2 G4 Twin-1

June 2014- Traditionally, a pilot has had one EGT gauge and one CHT gauge that he or she would use to keep track of the performance of an engine. The aircraft's manufacturer determined the probable location of the hottest running cylinder, placed a single probe there and then screwed an EGT probe into the exhaust pipe a few inches downstream from where the exhaust pipe joined the exhaust manifold. The theory was this: if you lean the engine by reference to what is normally the hottest cylinder and the exhaust temperature, you won't fry any of the cylinders or over-lean the engine.

Figure 1

Noise Reduction Headsets

March 2014- Short of sitting in the front row of a Metallica concert for a few hours, there are few things that compare with the hearing damage a piston engine-powered airplane can cause.

In fact, until recently, you could spot a longtime pilot at a social gathering by homing in on the person who said “Huh?” a lot in spite of the fact he or she was under age 60. Throw in a sun-damaged face plus a Breitling Navitimer wristwatch (real or fake), and there would be no doubt you were in the company of a fellow pilot.

Nowadays, a fancy watch may be your only clue. With the advent of good sunscreen and noise-reducing headsets—particularly those that also offer an Active Noise Reduction (ANR) feature—there are few pilots that waltz around the skies without sunblock and hearing protection.

The buzzwords

Every technical subject has its own set of buzzwords and the subject of noise reduction is no different. The Big Daddy of buzzwords is “decibels,” or as those in the know say, “dB.”

According to Wikipedia, the decibel (dB) is a logarithmic unit used to express the ratio between two values of a physical quantity and is usually measured in units of power or intensity. (The term “logarithmic” means a scale of measurement displaying the value of something using intervals that correspond to orders of magnitude, rather than a linear scale.)

So what does that mean in terms non-engineers can understand?

For the subject at hand—the ear-splitting noise inside a light airplane—the value dB is measuring how loud something is compared to the level of normal background noise without all the commotion made by motors and of wind rushing past the cockpit.

The usual way to understand all of this is with a graph. Take a look at Figure 1. The first thing to look at is the “X” axis which runs horizontally.

Check out the numbers on the X axis, which are audio frequencies. See how they aren’t spread equally (linearly) across the graph, but rather appear in groups? The first group is from one cycle per second (buzzword: “Hertz”) to 100 cycles per second. Notice also that the frequencies themselves within the group are not linear either.

Next there is a second group, from 100 to 1,000 Hertz. And again the individual frequencies are not spaced linearly. Continuing along the X axis, you have another group from 1,000 Hertz to 10,000 Hertz. These frequencies groups—and the frequencies within the groups—are displayed logarithmically.

Looking at the “Y” (vertical) axis, you can see the intensity scale, measured in dBSPL (“SPL” is another buzzword representing “sound pressure level”). From the graph, you’d think that 2 dB is twice as much as 1 dB but that’s not correct as far as how the ear perceives sound. In order to double the apparent intensity of a sound wave to the ear, you have to increase the signal by 3 dB. By the same token, if you lower the intensity by 3 dB, you halve the apparent loudness.

This is an important thing to keep in mind when you’re reading noise reduction specifications.

Fig 2

Figure 2

 Noise in piston engine airplanes

Take a look at Figure 2, a plot of typical light airplane cockpit noise levels.

Looking at this graph, the most obvious feature is how much of the noise in the cockpit is clustered between 20 Hertz and just less then 500 Hertz. This is noise coming primarily from the engine(s) and it’s 40 dB louder than the noise coming from the prop(s) and the slipstream.

Since each 3 dB increase equals twice-as-loud, the low frequency noise in a piston engine powered light airplane is 33 times louder than the higher-frequency noise levels—a tremendous difference.

Although the brain has built-in frequency filters which can attenuate certain frequencies to a degree (so you can pick information out of noise), the net effect of extremely loud noise is to overload the sense of hearing plus cause fatigue. It’s a bad situation that eventually damages hearing permanently and degrades the ability to hear speech properly immediately.


There are really only two countermeasures for excessive noise: either lessen the noise or block it from reaching the brain. Since we can’t do much about engine noise, that leaves blocking it from reaching the brain as our only option. So let’s take a look at a good passive noise reduction (PNR) headset.

Fig 3

Figure 3

  The blue line on Figure 3 shows the attenuation you can expect from a high quality PNR-only headset. The good ones reduce the noise from 19 dB to 24 dB and, as you can see from the graph, they reduce the noise linearly across the audio spectrum (meaning all frequencies are reduced the same amount).

But with most of the noise contained in the low frequencies, wouldn’t it be better to reduce that noise level more than the upper frequencies? That’s what the Active Noise Reduction (ANR) design engineers thought, too, so look at what happens when you add ANR to PNR.

Fig 4

Figure 4

Figure 4 shows the effect when you turn on the ANR feature (green line) of a good PNR+ANR headset. Doing so adds anywhere from 12 dB to nearly 20 dB more attenuation in the frequency range between 20 Hertz and 500 Hertz—right where the engine noise lives. This is in addition to the 19 dB to 24 dB of passive noise attenuation you already have.

ANR works by introducing an exact duplicate of the cockpit 30-to-500-Hz spectrum into the headset after flipping the phase of the signals 180 degrees. This cancels the sound in that band as far as your brain is concerned. By doing this and adding PNR reduction, these PNR+ANR headsets attenuate low frequency noise to the level where bone conduction takes over and additional headset attenuation is impossible.

ANR-only approaches

But what of those expensive ANR-only headsets that do not clamp the head tightly? They have an excellent reputation and do not claim much in the way of PNR properties at all. How is that possible?

Non-PNR headsets with ANR capabilities only are worn on the ear as opposed to over the ear. As a result, they are much more comfortable, but also generally much more expensive than PNR-only or even PNR+ANR headsets.

They greatly attenuate the low frequency band and also electronically process portions of the audio spectrum dedicated to human speech. If you can afford them, they will attenuate low frequency noise as much as a conventional PNR+ANR headset and also help you better understand ATC and intercom conversations. To those with significant hearing loss, they are a godsend.

The exact methodology they use (which frequencies they reduce, which ones they enhance, and how much processing they do) is a closely held secret. They certainly work well, but are they worth the money they cost? The graphs below are aimed at this question: do regular, less expensive, PNR-only headsets help us hear ATC enough, or do we need the PNR+ANR or the ANR-only headset?

Let’s take a look at what it takes to hear and understand the spoken word and see if biting the bullet and paying for a more expensive headset make sense.

Fig 5

Figure 5

In Figure 5, we can see the sound level percentages of the three primary frequency bands present in human speech. Although the tone and timbre of the human voice is different for males and females, these frequencies are the three bands used for 83 percent of human speech. Notice that there is around 55 percent energy present between about 125 Hertz and 500 Hertz; 35 percent between 500 and 1,000 Hertz; and only 4 percent from 1,000 to 4,000 Hertz.

But there’s more to it than just sound energy levels.

What’s even more important is where the most speech intelligibility is located within those three bands—in other words, which frequencies cause you the most problems communicating if you cannot hear them well?

Fig 6

Figure 6

Look at Figure 6. The frequencies you need to hear are not the ones with the most energy!

As far as understanding what you hear, half of speech intelligibility occurs between 1,000 and 4,000 Hertz which contains only 4 percent of the sound energy as shown in Figure 5. If you lose your high frequency hearing ability, you must rely on the mid-range frequencies where only about 35 percent of the intelligibility lives and the lower frequencies where only 4 percent of the intelligibility is found. This is something very few laymen know, but it’s critical to understanding how you hear.

Fig 7

 Figure 7

In Figure 7, we can see the whole picture. What’s happening with noise-reducing headsets is the brain is relieved of having to filter out the low frequencies. That’s good, but the brain still can’t do the job of enhancing the frequencies where human speech intelligence is contained. It needs external help with the frequencies above 500 Hertz—particularly those from 1,000 Hertz to 4,000 Hertz.

If you use PNR-only noise reducing headsets, you’re not nearly as sound fatigued at the end of a long flight and you do understand the spoken word a little bit better as a result of some noise reduction in the 20 to 500 Hertz area. The improvement is much greater with PNR+ANR. The PNR+ANR headset attenuates ambient noise to an extent and also attenuates the low frequency noise where the 40 dB overload is occurring, so people will certainly understand speech better.

But since the over-the-ear ANR-only headset reduces fatigue (both sound fatigue and physical fatigue), negates low frequency noise as well as a PNR+ANR headset, and enhances the frequencies associated with human speech, that’s the clear winner overall.

John Loughmiller is a 4,600-hour commercial pilot and CFII MEI-A. He lives in Kentucky with Donna, his wife of 39 years, and often commits random acts of aviation. Send questions or comments to . 

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