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Produced in response to a booming market that saw an increase in demand for commuter airplanes, the Piper PA31 was Piper Aircraft’s answer to this demand.
The Piper PA31 Navajo was generally considered a successful aircraft in the general aviation market despite having a short production life of just 17 years. During that time, it had as many as 11 different variants made.
The Piper PA31 Navajo is a twin-engined aircraft built on the orders of William Thomas Piper (the founder of Piper Aircraft). It is aimed at the small-scale cargo market, small feeder airlines, and the corporate class.
With its production commencing in 1962, this was a brand new aircraft design from the company, unlike any model they had previously produced. Focus shifted from their trademark, smaller single-engine aircraft to this cabin-class, corporate aircraft design to compete with models like the Cessna 401 and 411.
This article aims to look into the production life, design, and operation of the Piper PA31 to give a comprehensive view of this renowned aircraft that has seen it be relevant to date.
History of the Piper PA31
The Piper Aircraft brand has had its fair share of basking in the limelight of the aviation world. Having tasted success with the production of some of the most successful aircraft in the general aviation market, such as the likes of the Piper J3 Cub, whose popularity placed the company name on the maps.
The company’s appetite to venture into other production niches in aviation was heightened. At the time, there was a gap in the corporate and commuter aircraft space. To fill this space in the market, Piper Aircraft responded with the production of the Piper PA31.
Production of this aircraft was set in motion under the project name "Inca" and was later changed to "Navajo" after a Native American tribe based in the southwestern part of the United States. They are federally recognized as the largest tribe in the U.S., occupying the states of Arizona, Utah, and New Mexico.
The first successful flight of the Piper PA31 was on September 30, 1964, just two years after commencing production. Unfortunately, this aircraft never got clearance from the Federal Aviation Authority until two years later, on February 24, 1966. Time constraints had already taken their toll, and distribution never began till the following year, in March 1967.
Though considered a successful model of the Piper brand, the Piper PA31 has had its fair share of hiccups, which partly contributed to the termination of its manufacture in 1984 after demand in the general aviation industry dropped dramatically.
Despite all these tribulations, Piper Aircraft gained valuable experience in the commercial aircraft space, which later led to the production of more sophisticated airframe designs like that of the Piper Cheyenne.
Today, this aircraft is still a popular choice in the general aviation industry. Its sale is still very active in the pre-owned market, loved because of its excellent performance, ease of flying, and comfortable cabin space.
Piper PA31 Design and Specifications
The Piper PA31 Navajo is designed with six to eight seats, low-wing monoplane, twin-piston engine aircraft with a conventional tail.
The air-cooled, horizontally-opposed, six-cylinder Lycoming O-540 piston engine family was the powerplant of choice for this aircraft and was used in almost all of its different variants.
The prototype was powered by dual Lycoming turbocharged TIO-540-A engines, giving the aircraft a total of 310 hp (231 kW).
The Tiger Shark engine cowling design was made to cater to an extended shaft that gave the propeller blades enough clearance to operate in a region of generally undisturbed air, contributing to its improved propulsive efficiency.
The propellers on the prototype had only two blades, but this was changed in the later versions, which had three blades with variable pitch and full feathering capabilities.
The initial design featured only two windows on both sides of the cabin, aft of the cockpit. Later, this was redesigned into three rectangular windows on both sides, with a smaller triangular one on the starboard side. This design is the one that the manufacturer went with until the termination of the product line.
The Piper PA31 was the first aircraft in its class to come with an inbuilt air conditioning system straight from the factory.
Its height of 13 feet gives it ample room for someone to almost stand in the cabin, and the extended fuselage offers enough space for the passengers and crew to feel comfortable.
A year later, in 1968, the second variant of the Navajo was introduced, the Piper PA-31-300. This model was not equipped with a turbocharger. The aircraft featured a pair of Lycoming IO-540-M1A5 engines that provided the aircraft with a total of 300 hp (224 kW).
But with just one year into production, the variant line was discontinued, having the fewest units put into production, with only 14 aircraft released into the market.
The earlier turbocharged version was later unofficially named PA-31-310.
The Piper PA-31 Navajo B came later. It had two Lycoming TIO-540-E engines that gave it 310 horsepower (231 kilowatts) and a three-blade propeller system as an option in some of its units.
The three-blade propellers were later made standard in the Piper PA-31 Navajo C, which was fitted with Lycoming TIO-540-A2C engines but with the same power output as the Navajo B. Some of the later versions of this model were also made with full de-icing equipment, which was later approved by the FAA for use in known ice conditions.
January 1966 saw Piper Aircraft leap a step further with the manufacture of its first-ever pressurized aircraft to be introduced on the market, the Piper PA-31P. This was a major milestone for the manufacturer as it gained more experience in uncharted waters. The aircraft later got certification from the FAA in 1969.
This variant was the most sophisticated aircraft that the manufacturer had produced at the time. It came with two Lycoming TIGO-541-E1A turbocharged engines, which gave it a total of 425 hp (317 kW) of power.
Despite this monumental leap, the Piper PA-31P faced high operating cost issues brought about by its choice of engines.
The time between overhauls for the TIGO-541-E engines was rather too short, set at just 800 hours, and even today, after several tweaks, the time has just increased to 1200 hours. Considering this is a twin-engine aircraft, it means the cost of overhauling the engine doubles.
Since this variant is still in use today, owners have the option of switching the powerplant to Pratt & Whitney turboshaft PT-6 engines, similar to those used in the Cheyenne II, that have a total shaft horsepower of 620 hp each and are way more cost-effective in terms of maintenance.
Next in the production line and the variant that saw the most success was the Piper Navajo PA-31-350 Chieftain. Production of this variant began in September 1972, but its rollout into the market was delayed till 1973 after the production factory based in Lock Haven, Pennsylvania, was flooded by heavy rains from Hurricane Agnes.
Despite this, the Chieftain had a total of 1,825 units produced. This variant came equipped with a TIO-540 engine mounted on the left wing and an opposite-rotating LTIO-540 engine mounted on the other wing, each providing the aircraft with 350 hp (261 kW) of thrust.
These engines had an initial time between overhauls of 1200 hours but were later tweaked to 1800 hours thanks to improved maintenance techniques. Even further, under special conditions, this time can be stretched to up to 2000 hours!
The counter-rotating propellers of this variant gave it the advantage of preventing critical engine problems associated with the handling of a twin-engined aircraft in case one engine fails.
The fuselage of the Chieftain was also lengthened by 2 feet (0.61 m), which made the cabin big enough to fit up to 10 seats.
The Piper Navajo C/R was the next production in this series, with the ‘C/R’ basically meaning counter-rotating. In reality, this variant is just the same as the Chieftain, the only difference being it had lower-powered L/TIO-540-F2BD engines fitted in the Chieftain. The C/R engines are rated at 325 hp (242 kW).
Piper Aircraft later introduced an airliner division dubbed the T1000 with production at the Lakeland, Florida plant in May 1981.
This series had two aircraft manufactured under its belt, the T1020 and the T1040.
The T1020 was just a Chieftain redesigned to properly fit this new audience, earning it the name "the stripped Chieftain" among some circles. It featured reduced fuel carrying capacity and baggage capacity but with an increased seating of up to 11 passengers.
The second production in this series, the T1040, is officially known as the Piper PA-31T3, a hybrid model of the T1020, featuring the same fuselage construction but having the nose section and tail of a Cheyenne I. Similar wings, but with a reduced fuel carrying capacity and equipped with baggage carriers same as the ones in the Chieftain. The power plant for the T1040 was also similar to that of the Cheyenne I, featuring a pair of Pratt and Whitney PT6A-11 engines.
The last variant to enter production in the Piper PA31 family was the Piper Mojave, a hybrid variant, but instead of turboprop engines, it was equipped with slightly different models of the L/TIO-540 piston engines featured in the Chieftain. The only difference is that these engines had intercoolers and pressurized mags.
Piper PA31 Specifications
What Is the Cost of Owning a Piper PA31?
The Piper PA31 is a useful aircraft. Its spacious interior, good lifting capability, and performance make it a good choice for corporate clients and charter companies.
But how much does one cost?
The difference in variants and conditions of operation makes this question lack a straightforward answer.
We can also count on the fact that there are always other related costs that come with ownership of an aircraft, such as insurance, hanger charges, maintenance, and repair costs that will fluctuate despite having a definite purchase price.
In general, all aircraft costs can be split into fixed costs and variable costs. Looking at these two independently can give a clearer picture of how much the Piper PA31 costs.
Fixed costs remain constant throughout the ownership of the aircraft, and as long as you own one, these charges will always be there, whether the aircraft is flown or not. They include costs such as insurance costs, inspection charges, hanger fees (if you don’t own one), etc.
Variable costs, on the other hand, just as the name suggests, will fluctuate depending on the usage. These include costs such as repairs and maintenance, fuel, personal upgrades or alterations, etc.
Buying Price of a Piper PA31
With the production of this aircraft decommissioned, getting a brand new one is next to impossible. Unless you have enough influence to place an order with the manufacturer to have one more specially made for you.
Or maybe you were just fortunate enough to find someone who bought one but never really came around to using it (which is highly unlikely).
You can easily get a pre-owned model in mint condition. Prices of the PA31 in the pre-owned market range from as low as $180,000 to $525,000 as indicated on Controller although modern avionics and other alterations can drive up the price.
As you can see, the cost of buying this aircraft can be pretty low, but this is countered by the cost of maintaining it, which is on the higher side. Aided by the fact that this is a twin-engined aircraft, everything is inspected twice, and every modification done on one engine must be mirrored on the other engine.
The Cost of Operating and Maintaining a Piper PA31
As stated earlier, the cost of aircraft cannot be straightforward. Maintenance and operation costs largely contribute to this variation. We can also consider the region as a factor since prices for commodities such as fuel and mechanical services will depend on where you are. But this would be too much data to handle and process for this segment.
On average, the cost of operating and maintaining a Piper PA31 can be set at approximately $152,000 based on an average flight time of 200 hours per year.
To get a clearer picture of this figure, let’s look deeper into this by splitting the costs into fixed and variable costs.
Since these costs generally remain constant during the ownership period of the aircraft, they are easy to determine.
Given that you will need to rent a hangar if you do not own one. The cost of renting a hangar space will depend on the type of hangar but will average about $25,000 per year.
Insurance for the aircraft also needs to be accounted for and, depending on the type of cover, this cost will average around $6,000 per year.
Annual inspection fees will also have to be catered for. These cover basic airframe, engine, and propeller inspections plus labor charges and the cost of any parts used during corrective maintenance. The inspection fee for the PA31 can be set at around $10,000 per year.
Summarizing the fixed costs.
These costs are harder to determine as they mostly depend on aircraft use, age, and mechanical efficiency, to name just a few. Some of these costs are not even necessary at some points, such as cleaning or after-market pilot subscriptions used during flying (the aircraft can still operate perfectly well without these).
One of the most popular and most definite variable costs is fuel. You cannot fly without fuel, but the amount you’ll need will depend on the distance to be traveled, the engine power setting during flight, and the altitude being operated at.
With this aircraft consuming fuel at an average burn rate of 38.4 gallons per hour and assuming the average price of AvGas is at $7.25 per gallon, the approximate budget for fuel can be set at $55,680 per year based on an annual flight time of 200 hours.
The cost of an oil change can average around $1,100 per year, assuming the cost of oil sits at $6 per liter.
The Piper PA31 requires an engine overhaul after an average operation time of 1,200 hours. This short TBO greatly contributes to the high maintenance cost, averaging about $30,000 per year.
Other costs such as unscheduled maintenance, unexpected repairs, the cost of replacement spare parts, aircraft cleaning, after-market pilot subscriptions, etc. can be bundled into one cumulative average budget of about $24,220 per year.
Summarizing the variable costs.
Just to reiterate, these costs are not standard for all Piper PA31’s, they are just to give a visual idea of owning and operating the aircraft.
Piper PA31 Maintenance and Associated Problems
Even though the PA31 has a good reputation in the twin-engine market, there have been problems with some of its models.
One of the most commonly reported problems is associated with the engine cylinders experiencing cracks. But this was noted to be mostly caused by noncompliance during operation, such as not observing proper engine warmup procedures and rapid throttle movement, which contribute to engine deterioration.
These defects prompted Lycoming to issue a letter in 1982 aimed at increasing the service lifespan of its engines. This letter covered operational techniques, many of them targeting temperature management, such as avoiding detonation and avoiding takeoffs using partial-throttle to guarantee proper fuel cooling.
The PA31 also uses retractable landing gear, which complicates its landing system and makes it susceptible to malfunctioning parts, thus the need to keep a closer eye.
The FAA also issued several ADs regarding this aircraft and, due to its age, added it to the Aging Airplane Safety Rule.
Some of the design-specific ADs set were targeting flight controls, flight control surfaces, fuselage structures, landing gears, and even operations and handbook changes.
One of the more stringent AD was aimed at limiting the use of flaps to avoid strain and asymmetrical flap deployment, negatively affecting this aircraft’s takeoff and landing performance.
That being said, aftermarket improvements in flap transmissions and other systems do offer some solutions to this issue.