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Installing Shoulder Harnesses

Installing Shoulder Harnesses

Adding shoulder harnesses in at least the front seats should be a must for any aircraft that does not have them. A&P/IA Kristin Winter reports on the recent installation of a three-point system on an aircraft that previously had only lap belts.

Before the early 1970s, Piper did not provide shoulder harnesses for its aircraft. In fairness, that was only slightly after the auto manufacturers did the same thing. 

Lack of shoulder harnesses have resulted in life-altering brain injuries from accidents in which the front seat occupants could have walked away virtually unharmed. Fortunately, a number of companies have STCs for the retrofitting of shoulder harnesses in Piper aircraft. 

Several retrofit options

The largest manufacturer of restraint systems is AmSafe. It supplies much of the OEM market, be it a GA manufacturer or a commercial aircraft manufacturer like Boeing. 

The only product AmSafe currently offers as a GA retrofit is its seatbelt airbags. (Winter has a set of seatbelt airbags she plans to install in her Twin Comanche, and will report on that project in a future issue of Piper Flyer. —Ed.)

The largest holder of shoulder harness STCs for Piper aircraft is Alpha Aviation in Minnesota. Alpha Aviation has STCs covering early PA-23, PA-24, PA-28, PA-30, PA-32 and PA-39 aircraft. 

B.A.S. in Washington has an STC for the PA-28/32/34. The kit offered by B.A.S. is a four-point shoulder harness/lap belt system. 

Aero Fabricators, a company affiliated with Wag-Aero, has several STCs as well. Wisconsin-based Wag-Aero offers kits for J-3, PA-11, PA-18 and PA-20/22 aircraft, as well as PA-28s. 

Univair in Aurora, Colo. markets AmSafe shoulder harness restraint systems for J-3s, PA-11s, PA-12s and PA-18s.

A brief look at the kits

Most of the STC kits have two sets of components. One is the belts and fittings. 

Some shoulder harnesses have inertia reels, and some include a fixed belt. The latter type generally costs less, but can be a bit less convenient for the pilot when he or she has to loosen the belt in order to reach something in the cockpit. 

The other set of components in a kit is whatever is required to provide the necessary structure in order to mount the shoulder harness with enough strength to provide the necessary protection to the user. 

This typically involves some reinforcements that need to be attached to the fuselage, usually involving riveting. For that reason, this is not a project for an owner alone unless he or she possesses an A&P license and the tools necessary for the job. 

In addition, a shoulder harness installation constitutes a major alteration, and requires that an A&P/IA inspect and sign an FAA Form 337.

Required tools and supplies

The tooling necessary to complete this project will vary a bit depending on what structure is required. Some airplanes may already have the structure installed because shoulder harnesses were an optional item for that particular model year; others may need quite a bit of reinforcing pieces installed in order to provide the necessary support. 

Regardless of the kit, the tools necessary for installing solid rivets—and possibly blind rivets as well—will be a necessity. 

Any practicing A&P is likely to have the necessary tooling, but for an owner that is interested in participating and wants his or her own tools, the major item is a 2X rivet gun. U.S. Industrial Tool, Sioux Tools and Chicago Pneumatic are just a few of several rivet gun manufacturers. 

The most important part of the rivet gun is a good “teasing” trigger that lets the operator control the force and frequency of the blows. The gun also needs a rivet set, which is the part that actually touches the rivet, and a spring retainer to hold it to the rivet gun. 

In addition, a selection of Cleco temporary fasteners and pliers will also be necessary. 

It goes without saying that the ability to drill holes will be key. A #30 drill bit is used for a 1/8-inch rivet and #40 is for a 3/32-inch rivet. There are some excellent YouTube videos done by EAA on the basics of sheet metal work. (See Resources for additional information. —Ed.)

This is a project that any owner with mechanical aptitude can tackle with supervision by an A&P. Doing so will be a great learning experience for those interested in understanding more about what is involved in aircraft maintenance.

A Comanche 250 project

Recently I participated in, inspected and signed the Form 337 on the installation for a 1959 PA-24-250 Comanche which had never had shoulder harnesses installed. The new owner was keen to have the safety advantage of shoulder harnesses. 

The Alpha Aviation kit for the Comanche 250 was very complete and of excellent quality. (See photo 01, page 22.) The kit included all required parts and hardware including restraints for two front seats, an 8130-3 Airworthiness Certificate, an installation manual and a copy of the STC and signed STC authorization. 

First steps

The first step is to gently remove the headliner from the area to provide access to the structure above the rear window. (See photo 02 on page 24, top.) Removing the headliner can be a challenging project and needs to be undertaken carefully to avoid damaging the headliner.

The structural portion of the kit consisted of a stringer and two doubler plates. The two doubler plates are riveted together with a carefully-laid-out pattern, and to this doubler plate assembly is mounted the attachment point for the inertia reel for the shoulder strap. Then a longitudinal stringer and the assembled doubler plate must be fitted and riveted to the airframe above the rear window. 


Measuring and positioning 

Careful measurement is key to making sure that the stringer and doubler are properly positioned. This is done by riveting the bottom of the assembled doubler to the existing stringer that runs above the window, as shown in photo 03 (page 24, bottom). Note that blind fasteners were used here. 

The installation of the assembled doubler sets the position for the new stringer, which runs from the door frame back to the frame at the back bulkhead. 

The photo below shows the assembled doubler and the stringer fitted to the aircraft and held in with spring sheet clamps, referred to colloquially as Clecos. Clecos have been used since before World War II and are indispensable for aircraft sheet metal work. The most common type require a special set of pliers to install and remove them. 


Clecos are color-coded based on the size of the hole they are designed to fill, and are used to pull tight the two sheets of metal. As mentioned earlier, there are several good videos available from EAA that cover Clecos and other basic sheet metal techniques and tools. 

The temporary fastening process

As is good practice, the initial holes were drilled to a smaller size, in this case 3/32 inch, which later were enlarged to 1/8 inch as called for in the instructions. This technique works to clean up any shifting that takes place so that each hole is reasonably precise. 

Once the structure is fitted and all the holes are drilled, the parts are removed in order to clean off the burrs and excess material from around the rivet holes. The parts are then reassembled and held in place with the Clecos.

Anchoring with rivets, and final steps

Solid rivets are generally preferred and more economical, but are not always practical, and the kit from Alpha Aviation provides both solid rivets and blind CherryMax rivets. 

CherryMax rivets are souped-up pop rivets made to an aerospace standard and are designed with a locking collar to fasten the stem into the rivet as the stem forms much of the strength of the fastener. 

CherryMax rivets are used when you can’t get a bucking bar to the back of a solid rivet. They can be seen in photo 04 (below) as they are used to attach the lower side of the assembled doubler to the aircraft’s existing stringer. CherryMax rivets have a number of special pullers that can be used to install them; some are hand-operated and some are pneumatic. 

Once all the rivets are installed, a strong support base has been created to anchor the inertia reel and shoulder harness, as shown in photo 05 (below). 

Reinstallation of the headliner, carefully cutting a hole for the bolt, and subsequently bolting on the inertia reel completes the installation—save for the log entry and completing the Form 337. 


Labor may vary; added safety will not

The labor necessary to install the shoulder harness kit varies with the amount of structure that must be added. It can take anywhere from a handful of hours to a couple of days’ worth of labor, but shoulder harnesses are most needed in the kind of accident that can happen to even the best pilots. 

No restraint will help if you hit a mountain at cruise speed—but landing mishaps, loss of runway control, or even a controlled glide into favorable terrain after an engine failure are more common. These scenarios are where a shoulder harness might make all the difference. 

Know your FAR/AIM and check with your mechanic before starting any work.

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, of which about 1,000 are in the Twin Comanche and another 1,000 in the Navajo series. She owns and operates a 1969 C model Twinkie affectionately known as Maggie. She uses Maggie in furtherance of her aviation legal and consulting practice; she also assists would-be Comanche, Twin Comanche, and other Piper owners with training and pre-purchase consulting. Send questions or comments to .


Shoulder harness STCs
–PFA supporters
Alpha Aviation Inc.


B.A.S. Inc.


Univair Aircraft Corp.


The Wag-Aero Group


GA seatbelt airbags
AmSafe, Inc.


Fastening tools and supplies
Chicago Pneumatic


Cherry Aerospace


Sioux Tools


U.S. Industrial Tool & Supply Co.


Educational videos
EAA’s Sheet Metal Channel
Accumulating Knowledge: De-Ice Boots

Accumulating Knowledge: De-Ice Boots

A brief history of pneumatic boots, their operation and proper care.

AS Jimmy Doolittle was demonstrating the technique of blind flying in 1929, work was being done by B.F. Goodrich and the National Advisory Committee for Aeronautics (NACA) to address airframe icing. 

William C. Geer, Ph.D., a retired chemist from the B.F. Goodrich Company, became interested in the problem of airframe icing when it caused a number of crashes of airmail planes. With IMC flight in its infancy at the time, airframe icing was seen as a barrier to progress.

In the early 1930s, work by Geer and B.F. Goodrich focused on rubber coatings to inhibit the development of ice. How to get rid of the ice that did accumulate, despite the rubber boot and the concoction that was smeared on them to prevent the buildup, led to the idea of having inflatable tubes to knock off the ice. The de-ice boot was born.


Structure, activation and various types

The boots themselves are generally constructed with five or more spanwise tubes. These are created by layers of rubber laid up in such a way as to create the channels which expand when system pressure is applied to them. The inflation pressure is typically around 18 psi.

Once the concept of inflating tubes in the boots was proven to be effective, complete de-ice systems were soon developed. In addition to the boots themselves, a timer, valves and a pressure source were necessary. 

The researchers also discovered that in normal, non-icing flight, the aerodynamic pressure differentials around the wing could allow the boots to expand somewhat without activation of the system. The solution was to apply a small amount of suction to the boots during the times when the boots were not being operated by the pilot.

Modern systems use a pressure pump driven by the engine(s) which in normal operation discharges through a venturi, which supplies the suction to the boots to keep them tight to the airfoils when the boots are not in use. 

When activated, electrically controlled valves switch the pressure from the venturi to inflate some or all of the boots. The timer will keep the boots inflated for several seconds before switching back to the suction mode.

Many common installations will inflate all the boots simultaneously. One example is the Piper Aztec. 

With the certification requirements for approval for Flight Into Known Icing (FIKI)—which applies only with aircraft certified after 1973 or if the manufacturers chose to obtain FIKI certification—additional boots were added inboard of the engines, and boots were added to cover all tail surfaces. 

With these expanded systems, it is common for the timing system to inflate the wing boots and the tail boots separately. An example is the later Piper Navajo series after FIKI certification. This is likely due to the requirement that the de-ice system still function after the failure of one of the pneumatic pumps.

De-icing systems are available for aftermarket installation. As each aircraft will utilize differently sized boots, and testing is required to make sure that any installation does not hinder the flight characteristics of the aircraft, most aftermarket installations are by STC. B/E Aerospace and Goodrich hold many of these STCs, but not all.

Proper operation 

There is a certain amount of controversy over the proper operation of pneumatic de-ice boots. The common wisdom—which has come down from the early days of icing flight—is to wait until one-quarter to one-half of an inch of ice has accumulated before popping the boots. The concept has been enshrined in numerous aircraft Approved Flight Manuals and POHs. 

The NTSB has been at war against this mindset for a couple of decades. Based on its research, the NTSB, and to some degree the FAA, have been advocating turning the pneumatic wing de-icing system on at the first sign of icing.

Older-style boots (those dating before the 1960s), may have been prone to a condition called “ice bridging.” This is where ice would build to the point that it formed a bridge over the top of the boots. (Ernie Gann reported on this phenomenon on a DC-2 in his semi-autobiographical book “Fate is the Hunter.”) 

However, the NTSB is adamant that modern boots, (i.e., any that have been installed in the last 50 years or so) will not form an ice bridge. 

Against this, northern pilots do occasionally claim to have seen ice bridging occur in newer aircraft. 

After half a dozen years flying in the ice of the Great Lakes and in Southeast Alaska, I can say that I have never seen ice bridging—but that does not mean I am completely sold on the NTSB’s recommendation to activate the boots at the first sign of ice on the wings.

The other consideration is whether the boots leave less residual ice if they are operated continuously, or if they are cycled after a small buildup. 

I believe that this issue is a bit more nuanced than the NTSB is willing to recognize. When to operate the boots encompasses numerous factors, in my experience. 

It is a fact that the ice sheds better at higher speeds as the force of the airflow on the ice increases exponentially with airspeed. It is also beyond argument that some airfoils are much more sensitive to an accretion of ice than are others. Outside air temperature, the type of ice, and the condition of the boots all affect the ability of the boots to shed the ice. 

The NTSB guidelines seem to assume that all wing de-ice systems can be turned on and that they will then cycle at intervals. This is not the case on most aircraft where you have to individually activate each cycle. When flying single-pilot IFR, I rarely have time to sit and punch the wing de-ice button every few seconds. 

I tend to wait until I have a noticeable accumulation of ice before popping the boots. I don’t wait for one-quarter of an inch, and certainly not a full one-half inch; I generally try to activate them during a high speed descent, and again if I get into air that is at freezing or above. I also try to make a final activation after breaking out of the ice, or on final approach if I haven’t gotten out of the ice. (This is the author’s personal procedure in her own aircraft, and is for readers’ information only. Piper Flyer urges all pilots to read NTSB and FAA recommendations. —Ed.) 

Care for pneumatic boots

A set of de-ice boots is very expensive, so they should be cleaned and protection should be applied. 

There are three manufacturers of boot cleaning and sealant products. Goodrich Corp. makes ShineMaster for cleaning and AgeMaster for protecting boots. Jet Stream Aviation Products makes Pbs Boot Prep and Pbs Boot Sealant. Real Clean Aviation Products makes a similar de-ice boot care system called Real Shine. 

In my experience there is one product that needs to be on your shelf, and that is B.F.G’s Icex II. Even after cleaning and sealing, the application of a slippery coating before charging off in the ice is a very good thing. It makes a huge difference in the ability to shed ice. Icex II is expensive, but you won’t have regrets about the cost when the ice is being shed off the wings cleanly. Besides, a quart can last a couple of years for most pilots.

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, of which about 1,000 are in the Twin Comanche and another 1,000 in the Navajo series. She owns and operates a 1969 C model Twinkie affectionately known as Maggie. She uses Maggie in furtherance of her aviation legal and consulting practice; she also assists would-be Comanche, Twin Comanche, and other Piper owners with training and pre-purchase consulting. Send questions or comments to .


De-icing equipment
– PFA supporters

B/E Aerospace, Inc.
Goodrich Deicer Service Center

De-ice boot care
– PFA supporter

ShineMaster, AgeMaster, Icex II

Goodrich Corp.
(UTC Aerospace Systems)

Other de-ice boot treatments and protectants

Jet Stream Aviation Products, Inc.
Real Clean Aircraft Detailing Products

Further reading

AMT Airframe Handbook

Volume 2, Chapter 15:
Ice and Rain Protection. 

U.S. Department of Transportation Federal Aviation Administration Flight Standards Service, 2012.

Available at PiperFlyer.org/forum under “Magazine Extras”

Moving Up to a Twin? Read this First

Moving Up to a Twin? Read this First


Photography by James Lawrence

A practical and honest examination of the pros and cons of flying and owning a twin-engine Piper.

Few single-engine pilots have not looked longingly at a sexy twin from time to time. To pilots who are used to only one fan in front, the twin seems cool and exotic. As someone with thousands of hours flying a twin, I will let everyone on a little secret: They are cool!

Of course, cool does not equal practical. And while some are fortunate enough not to worry about practicalities, most people considering upgrading their ride are the practical type. I will sort through the myths, pitfalls and rationales for upgrading to a twin-engine aircraft.

These days, a pilot curious about purchasing a twin usually starts on the internet, often asking questions on one or more of the popular forums. Usually someone will chime in with the blanket statement that twins are twice or three times as expensive to operate as a single. 

Someone else is bound to chime in that insurance is impossible for someone without significant twin time. Another will quote Richard Collins’ contention that twins have a fatality rate per accident that is four times greater than that of a single-engine aircraft. 

Collins is correct on the statistic, but it’s misused as an anti-twin argument. Collins’ statistic appears to compare all single-engine crashes with all twin-engine crashes. This is misleading in two respects. The first is that twins have a higher stalling speed on average than twins. Thus they crash at a faster speed. A set of statistics that does not differentiate a Piper Cub from a Cessna 421 is, in my opinion, flawed.

The statistic is also flawed in that it does not account for the number of engine failures in a twin that do not result in a crash and end in a safe landing at an airport. Those incidents are not tracked and are usually not reported. 

Having said that, a twin-engine aircraft is costly and might be overkill for some pilots’ needs. If one’s main use for an airplane is to look at scenery and for the odd hundred-dollar hamburger, then the cool factor is all you are really getting for your airplane-owning dollars—and you’re definitely paying extra for it. 

Certain missions do argue for a twin-engine airplane, however. Pilots that make frequent flights over water or remote areas—especially at night—are probably safer in a twin if they keep their skills current. For frequent operations in low IFR conditions, twins offer redundancy and capability that most singles do not offer. 

Business-related travel, or the need to get back home for business purposes, are the kinds of flights where a capable airplane is more critical. Local flying or traveling with no particular deadlines to be anywhere, such as retirees often enjoy, diminishes the need for weather capability and redundancy.

Twins can usually carry a bigger load than can the average single, unless the single is turbine-powered. But turbine singles are a whole other level of cost and complexity; beyond the scope of this discussion.


The advantages of redundancy

Much of the potential safety advantages of a twin-engine aircraft come down to redundancy of propulsion and systems. This is of benefit to anyone using an aircraft for travel when timeliness of completing a flight is important. 

Electrical system – Electrical system redundancy is of greatest importance when flying in IMC conditions. This is particularly true when low IFR eliminates the option to hold a compass heading and descend through the clouds to VFR underneath. 

Anyone who has shot an ILS to minimums when the nearest VMC is a couple of states away knows how desperate the situation would be without electric power for key navigation equipment. Even in decent weather at night, electrical power is more than a convenience. Many are the stories of pilots flying home with a flashlight held in their mouth. 

More and more, modern high performance singles are offering backup alternators that will provide a second source of power. These backup systems vary in capability. If the alternator fails on a single, even if you have a backup alternator you will only be able to run some critical equipment. Twins have the built-in redundancy of dual alternators and can usually run most or all of the equipment on the output of just one alternator.

Engine redundancy – While modern high performance singles offer much-improved systems redundancy, albeit often at a much higher cost than an older twin, even the most tricked-out Cirrus SR22 offers no propulsion redundancy. 

Most all twins will fly on one engine, giving the pilot many more options when it comes to selecting a location and manner of landing after the failure of one engine. 

While an aircraft parachute such as those installed in a modern high performance single can save lives, in open water or extremely rugged terrain, the parachute mostly just alters the angle and speed of impact after losing an engine.

For pilots based on an island or who need to regularly cross large bodies of water, the second engine can literally be a lifesaver. One common example in this country are the pilots who need to cross Lake Michigan on a regular basis. 

In addition, night flying over much of the United States does not offer appealing options for a dead-stick landing. Many flight instructors sardonically explain the hazards of night dead-stick landings by advising their students, in mock seriousness, that as they are gliding down in the dark that they should turn on the landing light when getting close to the ground. Then they tell the student that if they don’t like what they see, they should turn off the landing light. 

Out in much of the west and most of Alaska, even daylight is not much help when it comes to trying to find a place to make a survivable crash landing. Over dark, inhospitable terrain, a second engine is a great comfort and should provide a higher level of safety.

Weather capability – Twins have traditionally been a better choice for reasonably all-weather operations. For decades, if you wanted the equipment for weather penetration, a twin was your only option. De-icing equipment was only available on twins. The same was true for weather radar. 

Improvements in technology have made high-end, high performance single-engine aircraft much more weather-capable. TKS anti-icing systems, pneumatic de-icing boots, lightning detectors and the ability to obtain Nexrad have all helped improve the all-weather ability of some high performance singles—but at substantial cost, as these aircraft are usually fairly new. 

Still, twins are best suited for onboard radar, also the old-fashioned pneumatic de-icing system does not rely on a limited store of fluid, which can be difficult to obtain when away from base unless one is only flying into the major reliever airports that are geared to accommodate the business flyer.

Larger loads – Horsepower is what picks up big loads. With few exceptions (and without getting into the turbine market), singles are limited to slightly over 300 hp. 

Piston twins can double the horsepower which can translate into more speed, more useful load, or a combination of both. Even if you can fill the tanks on your single and punch out into weather with three passengers, your passengers are not likely to be too comfortable doing so.


A twin pilot’s responsibilities


In addition to the added financial commitment that a twin requires, obtaining the safety benefits requires a greater dedication on the part of the pilot/owner. 

Training – Many singles can be flown by the proverbial seat-of-the-pants. Twins, with their higher wing loading and the ever-present possibility of being put into an asymmetrical thrust situation, must be flown by the numbers. 

Twins require more thought on every flight, as the pilot has choices to make if an engine fails. For this reason, an instrument rating and regular recurrent training are nearly mandatory. This is particularly true for the novice twin driver. This is an area where insurance companies have some say. 

Insurance – Contrary to some of the wisdom dispensed on the internet, the newbie twin driver can get insurance. It will come with strings attached and a hefty price tag for at least the first year. A VFR-only private pilot will have the fewest options and pay the most for insurance. 

Many insurers believe that an instrument rating should be the minimum level of licensing for a new twin engine pilot/owner—and I believe that, too. 

A requirement of 25 hours of dual instruction is a common requirement, which if the rating is to be gotten in the just-acquired twin, is probably a minimum anyway. After the first year, the insurance premiums will come down drastically. That high first year premium just needs to be considered as a startup cost.

Insurance companies used to give lower rates for twins as the common assumption was that twins are safer. But the reality is that they require greater proficiency and if there is a runway excursion, landing gear problem, etc., there are two engines to tear down and two props to have repaired or replaced. 

Piloting differences – While everyone focuses on the engine-failure-after-takeoff scenario, it is likely that other aspects of twin engine operation cause more grief. Depending on what a new twin driver has been flying in the past, the twin may offer significantly higher approach and landing speeds. 

The higher wing loading and the additional drag caused by an extra windmilling prop has caught more than one pilot unaware on landing and resulted in some shop time. Needless to say, the jump from a single-engine Comanche to a Twin Comanche is much smaller than the jump from a Cherokee 140 to an Aztec.

Costs – Corresponding to the increase in complexity that a new twin owner will experience, there is a concomitant increase in expense. 

The rules of thumb spouted on the internet or around the coffeepot at the local pea patch are of less value than runway behind you or sky above you. The increase in cost going from a Cherokee 140 to an Aztec will be in whole-number multiples. The increase in cost from a Comanche 260 to a Twin Comanche is maybe a third more at most. 

Real-world fuel expenses are not hard to obtain. Unplanned maintenance expenses—in other words, fixing what breaks—are much more of a guess. Annual inspection, engine reserves, a larger hangar if needed, higher insurance, additional training and recurrency costs can all be figured fairly closely.

If the additional costs and commitments are not deal-breakers, and if one’s typical mission will benefit from the redundancy and capability that twins can offer, then upgrading to a twin can be an eminently reasonable decision.

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, of which about 1,000 are in the Twin Comanche and another 1,000 in the Navajo series. She owns and operates a 1969 C model Twinkie affectionately known as Maggie. She is a recognized authority on Piper Comanche aircraft. Currently she is serving as Director of Operations for a commuter airline in Southeastern Alaska. Send questions or comments to

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