Twin Engine (14)
In the years immediately after World War II, General Aviation was growing—but not very predictably. Manufacturers were constantly going from feast to famine, and several old, venerable airplane companies had gone broke when they found they couldn't survive the market fluctuations.
There was one emerging market, however, in which a few of the more far-seeing planemakers were interested—Business Aviation—bigger, faster, more sophisticated (and profitable) equipment that was flown for commerce instead of for enjoyment.
In 1967, Piper Aircraft began marketing a six- to eight-seat cabin-class twin known as the PA-31 Navajo. Several variants were produced, including a T1000 series aimed at the commuter airline marketplace.
Production of the Navajo ended in 1984 with 3,942 built. Piper had—and still has—the Seneca and Seminole light twins in the lineup, but its cabin-class aircraft offerings thereafter have been limited to single engine models.
The Chieftain version of the Navajo proved popular with regional airlines, tour and sightseeing operations, plus some corporations—but most independent businessmen and small companies purchased a smaller version of the Navajo, or a variant called the Navajo C/R which had safety enhancing counter-rotating props that eliminated the critical engine problem present with most cabin-class twins.
Colemill Panther conversion
After Piper's departure from the piston engine cabin-class twin market, a Nashville, Tenn. company by the name of Colemill Enterprises began marketing an upgraded version of the Navajo.
The Colemill conversion came with 350 hp engines, four-blade Q-Tip propellers, winglets, and redesigned nosebowl cowlings. The Panther conversion established Colemill Enterprises as the source for an improved and very capable Navajo until several unfortunate events, including a flood, combined to drive the company out of business.
With Colemill's exit, access to the Panther conversion STC vanished as well and other than a new coat of paint and spiffy interior, there was little to do with a Navajo other than fix and fly it.
Lock & Key Navajo
At the start of the millennium, Mike Jones was flying turboprops for a small regional airline. After spending a long time in corporate aviation, Jones had heard the siren song of the airlines, got his ATP rating—and soon found himself hand-flying the formidable Jetstream airliner for hours and hours each day. (Back then, shoestring operations like the one that employed Jones figured that they had to have two pilots sitting up front anyway, so why spend the stockholders' money for autopilots?)
Relatively quickly, Jones rose through the ranks to the point where he could bid and hold a two-and-a-half day line between trips, and that situation gave him time to do what many airline pilots do: start a sideline business.
Jones started selling General Aviation airplanes on the side, and once that business was established, he decided that he could take a Colemill Panther conversion aircraft to the next level.
He created what became known as the "Lock & Key Navajo," a total renovation of the Piper Navajo from nosecone to tailcone—and including the Panther modification. It's an airplane that's aimed squarely at the successful businessman who wants the best cabin-class piston twin available.
Jones bought a used Navajo, sunk $350,000 into refurbishing it (including the Panther conversion), and sold it for $675,000 back in 2003. At that time, there was not another Navajo listed with an asking price of more than $350,000. Jones' airplane became the prototype for those that followed.
Providence then took control and forced Jones into a new path. His employer went broke and Jones found himself running a small business as his only source of income.
From Jones' vantage point, he had been given an opportunity. When Colemill Enterprises went out of business soon after the 2010 Tennessee flood, Jones came up with the money to buy the rights to its STCs.
Today, Mike Jones Aircraft Sales, Inc. has become a one-stop shop for renovated Navajos. CEO, CFO, Plant Manager, Advertising Manager, Demo Pilot, Test Pilot, Sales Manager, Supervisor of 15-plus technicians, and Chief Cook & Bottle Washer, Jones has his hands full—but maintains he can best supervise each and every conversion and ensure that the finished product meets his standards only if he oversees everything.
Considering the quality of each Lock & Key Navajo, it would be hard to argue the point.
What's in a name?
To sell a used airplane, dealers and brokers know they need to give it the illusion of youth. Fresh paint; a new interior; avionics that are still factory-supported; no accident history; mid-time or better engines; no fluid leaks; and no corrosion—these items are key to getting the highest price for a used airplane. If an airplane has these attributes and has relatively low time on the airframe, its condition can truthfully be called "above average" in advertisements.
Vref and Bluebook publish price guidance for "below average," "average" and "above average" examples of the various makes and models, but they have a special category for Lock & Key Navajos.
In recognition of the extra steps taken during renovation and the high quality work done by Jones' company, his aircraft have a separate listing that's higher than "above average." Consequently, they bring a premium price—plus, these aircraft appraise, finance and insure in a much different category than regular Navajos.
Jones starts with a good pedigree aircraft with complete logbooks, an accident-free history and an airframe with less than 7,500 hours total time. Over the next six months, zero-time SMOH engines are installed (factory overhauled or brand-new engines are options). Zero-time SPOH four-blade Q-Tip props are coupled to the engines, and around $90,000 is spent for much-above-average paint and interior work. A new avionics package is also included.
Lock & Key Navajo does everything in-house with the exception of painting the airframe. They refurbish all interior parts, including new instrument panels and new overhead switch panels with etched identification labels. Even the throttle Go Around labels are etched into the handles.
To illustrate the attention to detail, the engine firewalls are removed and the surfaces are polished to a high gloss. They are then re-riveted and placed back in the nacelle.
New seals and windlace are installed on all doors. The wing lockers are carpeted to match the interior and resealed as well. All bright work throughout the airplane (interior and exterior) is polished to a high gloss and clear coated to protect it from the elements.
All hoses and belts are replaced; all wear-prone items like the airstair door are renovated and strengthened where necessary. Known problem areas, like the gear doors, are restored to factory-new specifications and the landing gear itself is restored to factory-specification cycle times. Everything is meticulously reviewed during the Lock & Key Navajo restoration process.
Jones then operates the airplane for 15 to 20 hours after the technicians release it. He takes it on cross-country flights to replicate the environment it will be in when turned over to the owner, and checks every system and every component's operation himself. Everything—down to the smallest light bulb—has to work to factory specifications or better, or Jones will not deliver the airplane to the buyer.
The airplane comes with a fresh annual and warranties; plus, Jones promises in writing that his shop will do the first annual after the owner takes delivery and it will cost no more than $5,000.
Is there no downside?
Well, yes, there is. Mike Jones himself admits that the cost of a Lock & Key Navajo is out of reach for many people. At $795,000 for the standard Lock & Key Navajo package, a potential customer will likely end up paying about what a new Seneca would cost once some of the popular options are added. Jones says he has sold as many as three Lock & Key Navajos in one year, but typically sells one a year.
Jones believes in the uniqueness and quality of his product, but don't just take his word for it. Owners of Lock & Key Navajos give the product glowing reviews, calling their aircraft "a fantastic traveling machine" and saying, "We could not have made a better purchase even if we bought a brand-new airplane," and "The plane is superb!"
If you're in the market for a cabin-class twin, you should check out the Lock & Key Navajo. Mike Jones and his customers have dubbed it "The Best Navajo Money Can Buy."
Lock & Key Navajo Renovation Program
May 2014- Last month, I discussed the history and maintenance of the PA-23 Apache. But as a longtime owner, I have some insights about flying and owning an Apache, too. This month I’ll focus on specific flying tips and the practical aspects of ownership of Piper’s original twin.
April 2014- The PA-23 Apache was Piper’s first twin engine aircraft. In 1952 Piper began construction and testing of a prototype, but the original design—with 125 hp engines, a twin tail arrangement and fabric covering—was unsuccessful.
The aircraft was tweaked and the new design included 150 hp Lycoming engines, retractable landing gear, constant speed full feathering Hartzell propellers, all metal construction and a more conventional single tail.
Now called the Apache, the 150 hp prototype flew in 1953. The design received its FAA type certificate on Jan. 29, 1954. There were 2,047 Apaches and 4,930 Aztec models produced from 1954 to 1982, including a few U.S. Navy models.
November 2005- In October of 1958, Piper proposed a twin-engine version of the successful Comanche single. This was not the PA-30 Twin Comanche, planning of which had begun two years earlier but development and production of which would be several years hence (thus the skip in numeric order).
Piper initially planned for the model to be developed in California by Bill Lear, and would furnish a PA-24 Comanche airframe and two 200 hp IO-360 engines. Whether this actually ever happened is not recorded, but in 1962 the PA-30 project was given to San Antonio designer Ed Swearingen.
November 2005- Our charter company operated a 1970 model PA-31-310 Navajo for several years. We purchased it out in California, took the insurance-required flight training and flew it home to Florida, making a stop in Vegas for the night, and another at the Grand Canyon, just to sightsee.
After the 15-hour ride home we thought we knew her pretty well. Six months later we had put about 75 hours on the old girl and had grown to know her even better.
July 2005- One time-tested way to create a light twin is to take a single, remove the engine, and replace it with two engines on the wings. Sometimes the engines are smaller than those on the single—as in Piper’s Twin Comanche. Sometimes the engines are as powerful as that on the single—as in the Beech Baron.
Piper took the first approach with the PA-34 Seneca: it’s basically a Saratoga airframe with the 300 hp single engine replaced by two 200 (later 220) hp wing engines. The result is one of the longest-running twins in General Aviation.
The original Seneca was introduced in 1972, and you can still buy a brand-new Seneca V from Piper today. The original PA-34-200 Seneca had some problems, notably a low single-engine service ceiling.
Piper had success with its twin-engine Seneca, but complaints of poor handling had plagued the early models and Piper had been on a quest for more power and better handling for the Seneca nearly from the outset.
To gain more power for the 4,200-pound (gross weight) Seneca, Piper engineers looked at the possibility of adding a supercharger. They tried out the 220 hp Franklin 6A-350-C1 as well as turbocharged engines from Lycoming and Continental. In tests the 200 hp turbocharged Continental L/TSIO-360-E performed well and was eventually chosen for the powerplant.
In-flight handling was improved by adding aerodynamically balanced ailerons, an anti-servo tab for increased rudder effectiveness and a redesigned stabilator, while ground handling received enhancements in the form of a reworked nosegear steering linkage. To keep things simple engineers chose a fixed wastegate.
If at first you don’t succeed, don’t “tri” again. But Piper’s trimotor testing wasn’t all for naught.
What do you do when you’ve completed initial testing of a new version of your wildly popular single-engine aircraft? If you’re Piper Aircraft in the 1960s, you slap a couple more engines on it and try it out as a trimotor.
That’s just what happened in 1964. Piper had completed initial tests on its PA-32-260 Cherokee Six and used that airframe to attach two more engines to the wings (in this case using the 115 hp Lycoming O-235) while retaining the 250 hp Lycoming O-540 of the “Six” for the center engine.
A flood at the Piper’s Lock Haven facility destroyed the tooling for the Comanche, and Piper Aircraft developed the Seneca as a replacement aircraft for its popular Twin Comanche. Employing “parts bin” engineering and following the marketing strategy of the time, the Seneca is probably most accurately described as a twin-engine Cherokee Six.
The original Seneca, however, was not regarded as a success. Handling problems and poor performance plagued the initial design.
In 1975, Piper introduced the Seneca II. With this aircraft Piper addressed the handling issues found in the original design, but the biggest improvement came from the incorporation of the Continental TSIO-360 engine.
This engine featured a fixed wastegate turbocharger and made the same 200 hp at sea level as the engines on its predecessor, but made 220 hp at 12,000 feet, and maintained 75 percent power all the way to 18,000 feet. The change to a turbocharged engine gave the Seneca II the performance advantage it needed to compete against Cessna and Beech.
The model further evolved as Piper introduced the Seneca III, IV and V. The Seneca V is still in production today, and still uses a variant of the Continental TSIO-360, though now it incorporates a sophisticated absolute pressure controller to manage turbo boost (as opposed to the fixed wastegate on the Seneca II).
The Seneca features aluminum construction and utilizes an electrohydraulic power pack to operate the landing gear.
The stock Seneca II is a really good airplane. Like its Cherokee siblings, the Seneca II is somewhat nose-heavy, and with two on board in the front seats, a full-flap landing results in a very flat landing attitude. It is very stable in both pitch and roll, and it is an excellent instrument platform.
The nose baggage compartment is quite large, but limited to only 100 pounds. However, loading the plane inside the requisite CG range is not a challenge, as the CG range is nearly 12 inches at maximum gross weight. The Seneca II and later models feature a nearly 1,700-pound useful load.
The Seneca II is actually a little faster than the normally aspirated Aztec at altitudes where the turbo doesn’t present an advantage. My Seneca turned in 172 knots at 10,000 feet on 26 gallons gph (13 gallons per side) at a power setting of 30.5 inches of manifold pressure and 2,300 rpm. That translates into 70.5 percent power. Of course, go high, and you would go faster—about three knots per thousand feet faster—all the way up to about 18,000 feet.
The turbochargers do create some engine temperature management issues, and do require a deft hand to manipulate the throttles as your right hand is essentially the absolute pressure controller. It is possible to over-boost the engine, despite the automotive-type, pop off over-boost valve.
The original engines were prone to case cracking, but have been replaced by what is referred to as “heavy case” variants of the Continental TSIO-360 engine.
Details and Mods
Where the Seneca shines in my opinion is in ease of entry and exit for the passengers. The Seneca retains the huge left-side cargo door from the Cherokee Six, making access to the aft seats and cargo area—most of which are club-style (though early Seneca IIs featured all forward facing seats)—a breeze. There is no wing to climb over, no great height to heave your cargo through.
The aft seats are held in with ¼-turn fasteners, making removal a snap and creating a nearly six-foot-long cargo bay. I actually hauled a refrigerator down to a friend’s home in the Bahamas using my Seneca. Getting the refrigerator in and out of the aircraft was no problem.
Air conditioning was a factory option on the Seneca II, and was something you could not get on an Aztec.
But like the Aztec, there are all kinds of STCs available for the Seneca, from one-piece windshields and axial flow cowls, to gap seals, recognition light wingtips and three-blade propellers. Parts are not a problem, and it is no challenge to find a mechanic who knows how to work on one.
The popularity of the design is proven by the fact that it is still in production some 37 years after its introduction.
Seneca II Buyer’s Guide
by John Loughmiller
The Seneca II is probably the biggest bang for the buck there is in light twins right now. Not only are parts available from Piper, it has several design features that help keep the complexity (and therefore, maintenance costs) to a manageable level.
THE SENECA II HAS AN ECONOMICAL DESIGN.
For instance, there are no up-locks to worry about for the landing gear—the retraction system is an electrically operated hydraulic pump that holds the gear in the retract position with pressure alone. This means you don’t have to crank the gear down; just release the pressure and the gear will fall down due to gravity.
The flaps are actuated by a simple Johnson Bar lever, as opposed to an electrical system with position sensors. The turbos’ fixed wastegates require pilot management rather than using an automatic controller; while some may find this feature a hassle, it’s definitely cheaper to maintain.
THE SENECA II HAS A 100-HOUR REQUIRED INSPECTION.
Seneca IIs have a recurrent AD for the nosegear. Every 100 hours, the actuator attachment mounting as well as the actual gear casting must be inspected—which takes about eight hours when done correctly. There is a second part to the AD that requires a stack up assembly to be replaced every 500 hours at a parts cost of around $150 and another five hours or so of labor.
A second recurrent AD involves the Janitrol heater which must have a leak down test done every 24 months. The usual cost is $300 to $500 for the inspection, more if anything is found to be wrong.
There’s also a 100-hour inspection of the heater required by another AD for the fuel shutoff switch.
All the other ADs should have been done some time ago and are not recurrent if done—and logged—properly.
THE SENECA II HAS RANGE AND ROOM.
Operationally, flight plan for 23.5 gph fuel burn at 65 percent power and 160 KIAS (at 10,000 feet). Although the airplane has a service ceiling of 25,000 feet, most operations take place below 12,500 feet.
With standard fuel tanks, you’ll be just shy of four hours to tanks dry, and five hours to tanks dry if the long-range tanks are installed.
My Seneca II has long-range tanks and the unbreakable rule I use is to always be on the ground at the four-hour point (when starting with full tanks), so there’s never a chance of running out of fuel due to overly-optimistic flight planning.
There is a Zero Fuel Restriction, so payload calculations require both a standard weight and balance plot, plus a check to make sure you haven’t violated the placarded limit that shows the weight above which the rest of the load has to be fuel.
Speaking of weight and balance, you’ll often see Senecas with a case of oil riding around in the rear baggage compartment. This is because you can go right through the forward balance limit if you have a heavy pilot or two average-weight people up front and no one seated in the cabin. Without some weight in the rear baggage compartment, you can run out of elevator in the flare and land nosegear-first. This is one reason for the nosegear AD.
THE SENECA II HAS GOOD STOCK AVIONICS.
Most Seneca IIs with no avionics upgrades will have a Century IIIC two-axis autopilot with altitude hold and either King or Collins Nav/Coms. If you can find one with a brace of Garmins, so much the better—but the standard IIIC autopilot is still a good one, although parts are getting tough to find. Because it’s not a rate-based system, it will handle turbulence quite well and can easily handle turns at the marker without overshoot.
The engines on the Seneca II are counter-rotating Continental TSIO-360 and LTSIO-360 models. For 1978 Seneca IIs, you will almost certainly have “EB” series engines installed which have an 1,800-hour TBO (but check anyway, since “E” suffix models have a significantly shorter TBO).
THE SENECA II REQUIRES A PILOT WHO IS A GOOD PLANNER.
Adhere to the two-minute cooldown guidance for the turbos after landing before shutting the engines down if you want the turbos to make TBO. Also, reduce power two inches of manifold pressure at a time, and wait at least a full minute before you make the next two-inch power reduction in the descent. Cracked cylinders from shock cooling can be the result of disregarding this advice.
Patterns are generally flown at 102 KIAS downwind, 92 KIAS base, and across the fence at 80-82 KIAS with full flaps unless the wind suggests otherwise. Gear speeds and flap extension speeds are reasonable but require planning ahead—just as the gradual power reduction requires planning ahead.
Seneca IIs are a bargain right now due to the economy. Search for an airplane with less than 4,000 hours on the airframe, less than 750 hours on the engines, and props that have been overhauled relatively recently. Have a reputable A&P do a pre-purchase inspection for you, and plan on spending around $5,000 to $8,000 for things that were not caught in the inspection.
Finally, you’ll need minimums of 250 hours total time, 100 hours multi-engine time and 25 hours in Senecas to get a reasonable rate on insurance.
Seneca II PA-34T-200
Powerplant: Continental L/TSIO-360-E/200
Wingspan: 38.92 ft
Empty weight: 2,770-2,848 lb
Gross weight: 4,570 lb
Useful load: 1,722-1,800
Max takeoff weight: 4,570 lbs
Fuel capacity: 93 gal usable
Fuel capacity, w/ opt tanks: 123 gal usable
Oil capacity, ea engine: 8 qt
Baggage capacity: 200 lb
Takeoff distance ground roll: 900 ft
Takeoff distance over 50-ft obstacle: 1,240 ft
Rate of climb, sea level: 1,340 fpm
Single-engine ROC, sea level: 225 fpm
Max level speed: 198 kt
Normal cruise, 75%: 191 kt
Economy cruise 55%: 164 kt
Service ceiling: 25,000 ft
Single-engine service ceiling: 13,400 ft
Landing distance over 50-ft obstacle: 1,760-2,090
Landing distance, ground roll: 1,050-1,380
Limiting & Recommended Airspeeds
VMC (min control with critical engine inoperative: 66 KIAS
VX (best angle of climb): 76 KIAS
VY (best rate of climb): 89 KIAS
VNE (never exceed): 195 KIAS
VS1 (stall, clean): 63 KIAS
VSO (stall, in landing configuration): 61 KIAS
I remember the year 1967 as one of conflict and contradiction. At once both troubled and optimistic. Every night the news broadcast images of the Vietnam War, where young men were fighting and dying. John McCain was a naval aviator and in October 1967 he was shot down over Hanoi and remained a prisoner of war for five and a half years.
There were scenes as well of the young men and women back home who were protesting the war. One demonstration at San Francisco’s Kezar Stadium drew 40,000 protestors. There was the Six-Day War in the Middle East, and there were racial riots in Detroit and Newark. It seemed to my young mind at times that the world was going crazy.
Then again, a kid could always turn to the distraction of “The Monkees” or “Star Trek” on TV. Super Bowl I at the Los Angeles Coliseum pitting the Green Bay Packers against the Kansas City Chiefs had started the year off well for sports fans (Green Bay won). Unemployment stood at just 3.8 percent, and GDP was growing at an average of 5.1 percent a year.
At Piper Aircraft, 1967 marked the beginning of deliveries of its new Navajo. The PA-31 Navajo was a six- to eight-place airframe designed to compete with the Beech model 65 Queen Air and the Cessna 411.
The Navajo debuted with a base price of $89,500 and a choice of cabin configurations: six-place standard; six-place executive, with the cockpit cordoned off from the cabin; and eight-place commuter. It was equipped with a turbocharged Lycoming TIO-540-A1A and a Hartzell propeller and could cruise at 217 knots at 75 percent power.
It had been built with the business client in mind and came with a refreshment unit, foldaway tables and a toilet. It could carry 350 pounds of luggage in nose and rear cabin compartments. It gained early acceptance from a number of regional airlines including All Nippon Airways of Japan.
The 1970 Navajo B boasted a 310 hp Lycoming TIO-540-A2B (or A2C) engine and PiperAire air conditioning. Options included a pilot access door, a wide utility door and nacelle wing lockers. The price for the B model had climbed to $115,570. That year also saw the release of the PA-31P Pressurized Navajo, priced at $197,000.
Development of the C model and a C/R model with counter-rotating props began in 1972. The C model was equipped with 310 hp Lycoming TIO-54-A2C and the C/R came with 325 hp Lycoming L/TIO-540-F2BD engines. The C/R model also had engine nacelle luggage compartments that extended beyond the trailing edge of the wings. Interiors were updated (can you say “crushed velour”?) and hushed thanks to Quietized soundproofing. Deliveries began
in December 1974.
In 1978 the C and C/R models got increased gear and flap extension speeds, a new Altimatic X autopilot and Flight Director system along with spiffed-up interior and exterior options. The 1981 models had optional nacelle fuel tanks that could hold 54 gallons of useable fuel and extend the range by up to 375 nm.
The Navajo received many improvements and minor changes over the years before the last production model rolled off the line in 1983.
Shortly after the launch of the Navajo, Piper designers and engineers began work on a bigger, more powerful version. Originally named the Navajo II, it was designed with three basic missions in mind: corporate use for six to eight people; commuter or charter aircraft for nine passengers and a pilot; and cargo hauler for shipments up to 2,000 pounds.
To accommodate the requirements for the baggage area (it was to hold six golf bags, 12 overnight bags and eight suit bags), the Navajo fuselage was stretched by 24 inches forward of the spar. Additional windows were added, the floor was strengthened and the gross weight was increased to 7,000 pounds.
The new model—now named the Chieftain—was launched in 1973 with a price of $141,900 for a base model and $167,045 for an IFR-equipped aircraft.
The Chieftain was well received with small commuter and regional airlines, and Piper wanted to further its reach into that market. On Sept. 1, 1981, Piper set up an airline division and its focus would be sales of the new T-1000 series which were set to deliver in 1982.
Based on the Chieftain airframe, the new “airliner” was designed as an 11-place airplane (two crew, nine passenger) and would feature 350 hp Lycoming L/TIO-540-J2B engines. Weight and safety concerns dictated fixed, non-reclining lightweight passenger seats, a pneumatic emergency gear extension system and strengthened landing gear.
Certified as the T-1020, 22 planes were built and saw service with small airlines before production ended in 1985 signaling the end of the PA-31 line.
In 1985, John McCain was a U.S. representative, anti-apartheid demonstrations were staged in front of the United Nations building and race riots were taking place in England. The Cold War which had experienced a period of détente was heating up again, and the news was filled with reports of airline hijackings.
Like most other aircraft manufacturers in the mid-1980s, Piper was reeling from the effects of onerous product liability lawsuits and insurance costs. Unemployment was 7.2 percent. But then, as in 1967, a person could find distractions on TV in the form of “The Cosby Show”—and “Star Trek” (on reruns).
The Navajo/Chieftain line would go on to spawn the Cheyenne and Pocono, but that’s a story for another time.
PIPER NAVAJO VARIANTS
Initial production version, also known unofficially as the PA-31-310.
Variant of the Navajo with normally aspirated engines; 14 built.
PA-31 Navajo B
Marketing name for 1971 improved variant with 310 hp (231 kW) Lycoming TIO-540-E turbocharged piston engines, new air conditioning and optional pilot access door and optional wide utility door.
PA-31 Navajo C
Marketing name for 1974 improved variant with 310 hp (231 kW) Lycoming TIO-540-A2C engines and other minor improvements.
PA-31P Pressurized Navajo
Pressurized version of the PA-31 Navajo, powered by two 425 hp (317 kW) Lycoming TIGO-541-E1A piston engines.
Referred to as the Navajo “C/R” for counter-rotating. Variant of Navajo with counter-rotating propellers introduced with the PA-31-350 Chieftain. 325 hp (242 kW) Lycoming TIO-540 / LTIO-540 engines.
Stretched version of the Navajo with more powerful 350 hp (261 kW) engines that rotate in opposite directions (a Lycoming TIO-540 and a Lycoming LTIO-540) to eliminate critical engine issues.
Piston engine variant of the PA-31T1 Cheyenne I; 50 aircraft built.
Also known as the T1020/T-1020; variant of the PA-31-350 Chieftain optimized for commuter airline use, with less baggage and fuel capacity and increased seating capacity (nine passengers). First flight Sept. 25, 1981; 21 built.
Also known as the T1040/T-1040; turboprop powered airliner with fuselage of the PA-31-350T1020, and wings, tail and Pratt & Whitney Canada PT6A-11 engines of PA-31T Cheyenne. First flight July 17, 1981; 24 built.
Experimental version of PA-31-350; two built.
Unbuilt airliner variant with fuselage lengthened by 11 feet, 6 inches (3.51 m) compared to the PA-31-350.
Version of Chieftain built under license by Embraer in Brazil.
Turboprop conversion of EMB 820C, fitted with two Pratt & Whitney Canada PT6A-27 engines flat-rated to 550 shp. The Carajá’s MTOW of 8,003 pounds was 1,000 pounds more than that of the Chieftain.
Re-engined Navajo with 350 hp (261 kW) Lycoming TIO-540-J2B engines, four-blade “Q-Tip” propellers and optional winglets. Conversion designed by Colemill Enterprises of Nashville, Tenn.
October 2004 -
When I bought 1176X four years ago, I really did not plan to restore or modify the aircraft in any way, but as I got into the project, I discovered that there are more than 50 Supplemental Type Certificated products or modification for the PA-34-200T.
These STCs can be for things as simple as a better sun visor to as complicated as a vortex generator set that actually changes the way the aircraft flies. After careful consideration, I selected the STCs that I felt yielded the best "bang for the buck."
Maintenance issues compelled me to purchase the Bogart Oil Filter Access Door STC. This modification allows you to perform an oil change, including the filter, without dropping the lower cowl.
Copper starter cables were purchased because the factory-installed aluminum cables drew so much current that the aircraft was difficult to start under any conditions. The copper cables were so effective you could almost taxi the airplane on the starter motor alone.
The one-piece windshield and Rosen sun visors came with the aircraft, though I would have opted for both of them. The same for the JPI engine analyzer. I don't see how you can properly operate a turbocharged piston engine without one.
The Nayak auxiliary nacelle tanks were also installed on the aircraft when I purchased it. This mod brings total fuel capacity to 128 gallons.
In October of 1958, Piper proposed a twin-engine version of the successful Comanche single. This was not the PA-30 Twin Comanche, the planning of which had begun two years earlier but development and production of which would be several years hence (thus the skip in numeric order).
Piper initially planned for the model to be developed in California by Bill Lear, and would furnish a PA-24 Comanche airframe and two 200 hp IO-360 engines. Whether this actually ever happened is not recorded, but in 1962 the PA-30 project was given to San Antonio designer Ed Swearingen.
In the case of the PA-31, W.T. Piper dictated that, among other things, he wanted an airplane on which the tailcone did not begin its taper until it was aft of the cabin.
Not much is known about what went on until 1964, when Piper engineers at Lock Haven began development of a new cabin-class twin. It was initially named Inca and then changed to Navajo. The six-to-eight-place aircraft was powered by two Lycoming TIO-540-A engines of 310 hp each, and flew on Sept, 30, 1964.
At a gross weight of 6,500 pounds, the PA-31-310 had a top speed of 228 knots and a 75 percent cruise of 217 knots. Piper also made the Navajo available with normally-aspirated 300 hp Lycoming IO-540-M1A5 engines. Although this model, dubbed the PA-31-300, was rated at a lower 6,200-pound gross weight, it proved disproportionately slower, with a top speed of 196 knots and cruise of 184 knots at comparable power settings.
Deliveries of both models began in March 1967, and 90 were sold at an average price of $114,000. A new Navajo flight test building was erected to accommodate the traffic, and a new plant to manufacture subassemblies was built 60 miles northwest of Lock Haven at Quehanna. The 310 hp Navajo proved so popular that the 300 hp version was dropped after only 14 were completed.
In 1970 Piper developed the Navajo B. It had new air conditioning and avionics systems and options of a pilot access door, wide utility door and nacelle baggage compartments.
In 1972, the disastrous flooding of the Susquehanna River devastated the company’s facilities at Lock Haven. Inventory and tooling were ruined and the single-engine Comanche line was shut down for good.
Fortunately, Piper had earlier built a facility in Vero Beach, Fla. to manufacture the Cherokee line, and in the wake of the flood, everything was moved to Florida. Navajo production was accomplished there and at nearby Lakeland.
In 1974 the improved Navajo C debuted, along with the Navajo C/R with counter-rotating 325 hp Lycoming L/TIO-540-F2BD powerplants. The higher-power C/R provided a few knots of speed at cruise at the cost of three gallons of fuel per hour. Average delivery prices rose to $187,500 and $227,600, respectively.
More than 1,300 Navajo 300/310s had been delivered when production ceased in 1984, by which time their asking price had grown to in excess of half a million dollars.
The Navajo II
The PA-31-350 started development in 1968 as a commuter aircraft to counter Cessna’s 402 and the Beech 99. It was basically a Navajo with two-foot fuselage extension that could accommodate two more seats, 350 hp Lycoming L/TIO-540-J2BD engines, and an increase in gross weight to 7,000 pounds. Unfortunately, the second prototype and first production airplane were lost in the 1972 flood.
Piper named it the Navajo Chieftain upon its 1973 introduction, and its average price was $142,000. Production was transferred to Lakeland, where #31-7405401 (N74999) was the first airplane off the line in June. In 1980, “Navajo” was dropped from its name, and production ended in October 1984, when the price had risen to $587,000.
The PA-31P and T
Piper had begun exploring the concept of a pressurized cabin as far back as 1962. In 1966 they began work on the PA-31P. It was a six-seat version of the Navajo with 425 hp TIGO-541-E1A6 engines and 7,800-pound gross weight. It could top 240 knots and cruise at 233 knots. Priced at an average of $275,000 when it was introduced as a 1970 model, just over 100 were sold before production ceased in 1977.
In 1980, Piper developed a new pressurized cabin-class twin, the PA-31P-350 Navajo Mojave. This aircraft, with its Cheyenne I fuselage, 350 hp counter-rotating Lycoming L/TIO-540-V2AD engines, the Chieftain’s tail unit and the wings from the PA-31-353, was short-lived. Deliveries of the Mojave—“Navajo” was dropped from the name—began in July 1983 and ended in June of 1984. But the Mojave had given the company valuable experience in pressurization, which led to the Cheyenne series and eventually to the single-engine Malibu and Mirage.
To prove the concept of turboprop engines on a Navajo airframe, Piper pulled #31-1 and sent it to Swearingen Aircraft in October 1966, where 500 shp Pratt & Whitney PT6A-20 turbine engines and Hartzell three-blade props were installed. It first flew in April 1967 (and last flew in 1969, after which it was donated to the local fire department).
Piper installed two 620 shp PT6A-28 turbines on the Pressurized Navajo airframe and added wingtip fuel tanks in 1969, also modifying the flight control system to accommodate the increased power. The model was named the PA-31T Cheyenne and was certified in May 1972, but production at Lock Haven was delayed because of the flood. The first production airplane rolled out in May 1973 and deliveries began the next spring.
In 1978, the lowest-priced turboprop on the market was introduced—the PA-31T1 Cheyenne I (at which time the original Cheyenne was renamed the Cheyenne II), base-priced at about $500,000. It reverted to 500 shp PT6s and deliveries began in mid-1978.
The next year, the PA-31T2 was developed, a Cheyenne II with 24-inch fuselage stretch. Other variations followed, but softening General Aviation markets and rising costs forced manufacturers to make drastic cuts—and, in some cases, discontinue models in the mid-1980s.
All told, however, Piper Aircraft produced nearly 3,400 PA-31 twins and several hundred turbine models based on the basic PA-31 design.
Piper Aircraft: The development and history of Piper designs. Roger W. Peperell. Air Britain, 1996.
Most aircraft profiles start out with a long dissertation on the history of the aircraft’s type and its lineage—blah, blah, blah—okay, so here’s what you need to know to set the stage for this story.
The PA-23 Apache/Aztec was the first twin-engine aircraft built by the Piper Aircraft Company, and between 1952 and 1981 they turned out nearly 7,000 of them. Of all of the surviving airworthy Aztecs, the one owned by father and son partners Jerry and David Naylor is, without a doubt, the coolest, most technically advanced of them all.
Pretty heady praise indeed—but believe me, it’s well deserved. The partners have invested a stack of money and an incredible amount of time in bringing their 1978 Aztec F up to 2008 functionality, reliability and safety.
I was too polite to ask just how much they’ve invested, but as David Naylor explained it, when they told Bob Ferguson, manager of Autopilots Central, Inc. in Tulsa, Okla., about their ambitious plans for the Aztec’s Chelton and Garmin avionics upgrade, Ferguson’s response was pretty telling. "Well, if you ever want to sell it, you better sell the avionics and tell them it comes with two free engines," Ferguson said.
The perfect fit.
Sorry, I’m getting a bit ahead of myself here. Before we get into what the Naylors did, let’s visit a bit with David Naylor and find out why they did it.
"I grew up flying with my father, Jerry. He’s had his pilot’s license since 1945 and is still actively flying today," Naylor said. "In fact, at 81 years young, my dad is buying his 14th airplane—a new 2008 Flight Design CTLS LSA."
The younger Naylor has had his license since 1978 and has since gone on to add his multi-engine and instrument ratings. To date, he’s amassed some 1,800 hours of total time as pilot in command. The Naylors use their Aztec F for both business and pleasure flying. That combination is the catalyst for their extensive upgrade project.
"This is our third Aztec. We bought it in 1990 and have enjoyed flying it for the past 17-plus years. It’s an awesome airplane for us," Naylor said. "When my dad transitioned to his first twin, he did it in a Twin Comanche. It’s a neat little plane, but you had to be on top of it all the time. It could get ahead of you pretty fast. Dad wanted something more forgiving and, along with that, he decided he really needed a six-place airplane to haul the family and an occasional load of seeds."
"It was an FAA examiner who actually pointed him toward the Aztec," Naylor continued. "He said that bar none, the Piper Aztec was the safest, most forgiving twin in the sky. That’s what dad was looking for—safe, forgiving and fun." (With a dirty stall speed of just 55 knots, the Aztecs were arguably the most docile six-place piston twins ever built.)
Obviously Mr. Naylor found what he was looking for in the Aztec; anyone who buys three of anything must be satisfied. "Dad and I both just absolutely love it," Naylor said. "For what it may give up in streamlined looks and top-end speed, it more than makes up for it in usefulness."
That usefulness has served the family business well on more than a few occasions. "We’re [Naylor Seed Company] in the field seed business and we’ve actually hauled seed to and from many locations," he continued. "We’ve taken all the seats out and loaded it up with bagged foundation seed from Indiana and hauled them back here to Scotch Grove [Iowa]. That’s not uncommon."
But as much as they loved their trusty Aztec F, its systems were starting to become less than reliable. The Naylors did their share of window shopping, but always came to the same conclusion. "There’s just nothing new out there than can match our Aztec for comfort and load carrying capability—not without spending a couple million anyway," Naylor said. "More importantly, at my dad’s age, the last thing he wants is a different airplane. He can fly the Aztec almost with his eyes closed." (A practice Piper Flyer does not recommend.)
So they decided to give their beloved Aztec F a panel upgrade. You know the usual, new radios, an audio panel. Pretty standard stuff. So they thought, anyway….
The best laid plans…
"We were having all kinds of avionics issues with the original stuff," Naylor said. "Between the old radios and autopilot, every time I flew it one or two things would not work. It was all intermittent. I didn’t even want to fly it anymore."
Trips to Autopilot Central had become commonplace. And it was during one of these trips that the Naylors decided to get a quote to upgrade their avionics. That’s when things took a dramatic turn. "We were getting ready to replace the stack with a complete Garmin panel—340 audio panel; 530, 430, 330 transponder—we were looking to replace all the old stuff," Naylor said. "While they were working on the estimate, I picked up an AOPA flier that showed the Commander Sweepstakes plane with the Chelton glass in it."
"I looked at the picture and asked, ‘Why we couldn’t do that to our Aztec?’ And that’s what started it," Naylor said.
"So, with the help and advice of Shannon Curran, Pres. of Flight Management Group, Inc. of Utah, we put out bids and elected to go with Tim McCandless Avionics in Waterloo, Iowa. Turned out it was their first experience with installing the Chelton system.
Since the Electronic Flight Information Systems (EFIS) they planned to install would be the signature piece of the entire system, the Naylors chose the top-of-the-line 3D Synthetic Vision system with Chelton’s Highway-In-The-Sky (HITS) capability.
The 3D Synthetic Vision is the only FAA-certified version of Chelton’s FlightLogic system. It shows a forward-looking 3-D image that conforms accurately to the terrain ahead giving the pilot optimal situation awareness. According to Chelton, the display conforms so closely to the actual terrain view that it’s been called "VFR-IFR Equivalence."
The Naylors also included Chelton’s HITS, which makes it simple to program and fly even a complex flight plan. "The system is just amazing," Naylor said. "This is a whole new way to fly instrument approaches. It’s so much more intuitive than the ‘old’ way. You basically just keep the airplane symbol in the box and you’re flying the precise course or approach."
Back to the future
"David’s dad has flown Aztecs for a lot of years and they decided if they can’t buy a new one, they’d make this one as good as they could," explained Tony Will, Avionics Manager at Tim McCandless Avionics. "We pretty much accomplished that. This 30-plus-year-old airplane is as close as you can come to anything coming out of the factory today.
Other than the basic outline of the panel, there isn’t much left from what rolled out of Piper’s plant in 1978. "We pretty much gutted the panel. I don’t think we’ve ever gone that deep into an airplane before," he added. "You do a basic autopilot or GPS installation all the time—this was so much more involved than that."
Will said that after they met with the Naylors and looked over their Aztec, the next step was to put together a detailed game plan. "This was our first Chelton installation, so we had one of our main technicians go through the Chelton school. That was really important. Without that, it would never have worked. That’s something that Chelton requires and I understand why they do," Will said. "It’s a complicated installation and you need to know what you are doing to get everything correct."
Let the fun begin…
"We actually installed the Chelton displays, a Chelton autopilot and the Garmin radios initially," Will said. "The Chelton autopilot did not work out. They had too many problems with the pitch servos. Chelton discontinued the product and refunded the money. We couldn’t put the old Century autopilot back in—that’s one of the reasons they did the upgrade in the first place."
By chance, David Naylor had met with Greg Plantz, S-TEC’s Vice President of Sales and Marketing, during EAA AirVenture Oshkosh 2005. "The guys at the avionics shop, as well as some other pilots recommended the S-TEC Fifty Five X autopilot," Naylor said. "They talked up its performance and reliability, plus it had Altitude Pre-Select. I really wanted that feature."
The only problem was there was no available STC to install the S-TEC Fifty Five X in Naylor’s Aztec F. While that would have deterred many an owner—the FAA’s STC process is notoriously laborious and time- and money-consuming—team Naylor, along with Curran’s guidance, wasn’t going to let that get in their way. Fortunately, S-TEC was interested in obtaining just such an STC for their popular Fifty Five X autopilot.
"The Naylors, along with all other Aztec owners, love their airplanes but until now, have been unable to enjoy the reliability and functionality that they will get with a modern autopilot," Plantz explained. "By replacing their legacy autopilot with a new System Fifty Five X, they can enjoy the advanced capabilities and peace of mind that comes with having a high-performance autopilot in their aircraft."
Plantz said that along with the overall improvement in reliability that comes with a brand-new autopilot, the S-TEC System Fifty Five X also gives Aztec owners a host of features and capabilities that were unavailable in previous autopilot options including GPSS (GPS Steering), Altitude Pre-Select, Vertical Speed Control, Control Wheel Steering and more.
"GPSS is one of the features that has helped make S-TEC’s System Fifty Five X the most popular aftermarket autopilot in General Aviation," Plantz said. "By taking commands directly from the aircraft’s GPS navigation system, the GPSS function permits the autopilot to not only precisely fly en-route GPS courses, it also does an excellent job of precision flying GPS approaches, missed approaches and any other phase of flight where the System Fifty Five X is ‘flying’ the airplane."
While David Naylor appreciates all the features his new Fifty Five X brings to his Aztec, he admits to having two favorites. "The two things I love most about the S-TEC autopilot are the Altitude Pre-Select and the simple fact that it works," Naylor said. "Our old autopilot was worn out. We battled with it a lot just trying to keep it alive. I have total confidence that the Fifty Five X is going to work."
"The autopilot’s Altitude Pre-Select capability eliminates another thing a pilot has to do. In the past, ATC would tell me to climb to 9,500 feet and the next thing I know I’m at 10,000—I forgot to level off. I get busy with the GPS or charts or whatever," Naylor added. "With the Altitude Pre-Select function, I set the altitude and it climbs to it. It does it for me—I just love it. And it gives me a couple hundred-foot warning and automatically reduces the rate of climb as it approaches the selected altitude. When it levels off it just says ‘altitude.’ It’s awesome."
"It’s the same with the descent—I dial in an altitude and the rate-of-descent and as I approach that altitude, it automatically reduces the descent rate
and levels off," Naylor explained. "I enjoy a nice smooth transition. It’s a great peace of mind and security feature."
While using their beloved Aztec to get the FAA STC on the autopilot was time consuming, it wasn’t as much of an issue as was first thought. "We did the initial installation here and then it went down to S-TEC in Mineral Wells [Texas] and they did the STC part of it," Will said. "Overall it took about six weeks, but a lot of that was due to weather."
"David and his father were very gracious in allowing a lot of time for both the installation of the Chelton displays and the new autopilot," he added. "I’d say their investment was well worth it."
Everything old is new again.
Installing the two Chelton Synthetic Vision Displays, the new Garmin stack and S-TEC System Fifty Five X autopilot would seem like plenty for an avionics shop to accomplish, "But," Will said, "there was more to the project."
"We decided to take out the old radar. It had some issues and the repair costs were so far exceeding the value of the unit. We did take the opportunity to go ahead and do the wiring for an XM weather receiver for David," Will explained. "It’s ready to go. For now though, he has the Garmin 496 and he really likes the weather display on that. But if he wants to switch to XM down the road it’s already wired. It was easier to go ahead and do it while the interior and panel was taken out than to go back in later on."
"About the only ‘original’ things left in the panel are the engine instruments," he added. "And we left the Stormscope in. Other than that, it’s pretty much all new stuff."
Was it worth it all?
The one question I—and all of you—would ask is, "Was it all worth it?" The money? The time without the airplane? All of it?
"Absolutely!" Naylor said. "It took longer than expected, but we couldn’t be happier. Along with an amazing airplane, we have built some great friendships throughout the project."
"The Chelton displays are amazing. I am extremely impressed with them. They are an awesome update for safety and situational awareness," he added. "The airplane is safer and a real pleasure to fly."
Tony Will shares that sentiment. "I tell you what, we went and flew it the other day again and it’s great! It’s a really neat system—the Chelton displays and the S-TEC autopilot—we did a couple ILS approaches and stuff. I tell you if you’re doing the WAAS approach and the ILS, you are actually flying the ILS, but you are superimposing the Chelton WAAS approach. That thing flew in the boxes all the way down. Wow!
"I have a lot more to learn about the Chelton system and I’m looking forward to it," Naylor said.
"We are currently awaiting software updates so that our Autopilot/Flight Director will capture the Vertical guidance (VGP) for the GPS and WAAS approaches. Currently the only vertical guidance we have to the autopilot is the ILS/GS and VSI modes. We want to have the autopilot to be able to select between source one and two, just like the corporate jets. We have been told the upgrade is on the way—hopefully soon."
"And with that said, the airplane is a real pleasure to fly. I feel more confident and more aware than I ever have in an airplane before. Would I do it again? I sure would!
Dale Smith has been in love with airplanes and flying forever. A prolific aviation journalist, along with Piper Flyer, Dale writes for Plane & Pilot, Pilot Journal, Aviation Maintenance Magazine, Avionics News, Professional Pilot, Aviation Business Journal, Flight Training and other aviation magazines. When he’s not writing fun stuff about airplanes, Dale is also a principal partner in Flying Boat Creative Services, an advertising agency specializing in aviation.