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Flight test: Piper PA-31 Navajo Chieftain

PUBLISHED: 15:20 25 April 2019

Piper PA-31 Navajo Chieftain

Piper PA-31 Navajo Chieftain

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A bargain-basement eleven-seat piston twin with great load capacity and reasonable running costs | Words Bob Davy - Photos Keith Wilson

Price-wise there has never been a better time to buy a used piston twin than right now. Quite often they can be had for less than the cost of their engines and props, which is why a lot of them are being broken up for spares.

It's due to a combination of ageing light twin fleets, rising fuel prices and a looming recession−all playing their part in pushing prices down.

At the time of writing and without much effort I found a 1976 Piper Seneca for sale in the UK at US$45,000−yes, with high engine and prop hours, but the price is still remarkably low. And a friend in the trade knows of a Piper Twin Comanche for $35,000.

Or how about a nine-passenger, 250mph baby airliner for $100,000? Seriously, shop around and you can get a PA-31 Chieftain for this. These aircraft are still being used to carry passengers in commercial service, and quite right too: the PA-31 is the finest piston twin that Piper ever built.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

The test aircraft is just such a 'bargain basement' PA-31 although you would never know to look at it. Built in 1979 it has plenty of hours left on its engines and props, reasonable paint and a plush interior with ten leather seats to match.

These are proper adult leather seats with arm rests, more comfortable and with better leg room than you would get in a business A320 or B737 cabin. It might be a niche market but there are people who have regular need of an aircraft with more than four to six seats plus luggage, to ferry them between business meetings, altiports, and shoots of all kinds.

If you fill most of the seats (and you can with a PA-31, and still fill it up with fuel) the cost per seat drops below the equivalent airliner business seat around Europe: £50 per seat per 200nm doesn't sound bad, does it! And I'd rather take off from my local airfield than from Luton or Heathrow any day. Door-to-door, it's usually quicker as well as more convenient.

Unlike many piston twins, if a Piper Chieftain engine fails you have a fighting chance of flying away from the scene. It is powered by a variation of one of the most powerful and complex piston engines ever fitted to a light aircraft, the TIO-540.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

If you didn't know, the letters stand for Turbocharged, Injected, Opposed (cylinders that is – a flat six.) The '540' is cubic inches−nearly nine litres! Only the GTSIO-540 is more complex (the G standing for Geared prop, the S for Supercharged) and inevitably the next step was turboprop power.

Garrett and P & W turbine engines eventually took over from these biggest of piston engines, at first commercially and later to a lesser extent with private owners. In fact the Chieftain begat the turbine-powered Cheyenne, an aircraft which deserves a Pilot feature all of its own.

Beech's big twin, the Queen Air was powered by IGSO-540s (go on, work it out) and was developed into the PT6-powered King Air. Cessna's big piston Titan was developed into the Garrett-powered Conquest.

Almost 4,000 PA-31 Navajos and Chieftains were constructed between 1967 (for the smaller Navajo, 1973 for the Chieftain) and 1984, when production ended – that's more than all the piston competition added together.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

Was the Chieftain the best of the bunch? Possibly not, but let's look deeper into it.

A touch of luxury

If you are new to this class of aircraft I have to tell you that the sense of theatre begins long before engine start, as you walk up to the big Piper Chieftain across the tarmac and climb aboard. A very airliner-like split clamshell cabin door is opened, the lower half fitted with integral stairs.

You will of course have just deposited your monogrammed luggage into the huge baggage compartment behind the nearest engine−big enough to take a body (or a full-sized step ladder on the test day). Originally they housed the streamlined exhaust systems, designed to blow over the trailing edge of the wing.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

This didn't produce any more lift−just soot−so the cowlings were extended all the way to the trailing edge and turned into humongous lockers instead. There is also plenty of space for luggage in fore and aft lockers producing a total of over sixty cubic feet!

Operators tend to load the luggage starting at the back because the wing lockers are close to the C of G so only contribute weight to the equation.

Once aboard you still have quite a walk to get to the business end, perhaps noticing that the cabin cross section is constant i.e. it doesn't taper from the rear−an original demand by William T Piper himself−and perhaps taking care not to trip over the spar running across the floor between seat rows one and two (I didn't, so I did.)

Shimmy into the left seat, then raise the neat little folding armrests and settle into the extremely comfortable, padded leather captain's seat. Although I rarely smoke these days, I must admit to having had a sudden urge to put on an airline pilot's jacket and light up a Rothmans, just as the period ads suggested you might when driving an old Jaguar.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

As you would imagine, the cockpit instrumentation is plentiful and complicated, the only concession to anything in the 21st century being a centrally-mounted GPS navcom. Everything else is from the '70s and '80s – I love it.

There are clever and complex systems in this aircraft. For example, the hydraulic test of the gear is done by putting in a couple of circuit breakers on the left cockpit wall, then selecting the chunky gear selector down from neutral.

This sequences the down cycle−activating a hydraulic pump−then returns the lever to neutral with a click, thus confirming correct operation; very cool. Essential for a proper twin or airliner with so much switchery is the extra panel above the windscreens, this one housing important stuff like ice protection, interior and exterior lights, and seat belt and 'no smoking' signs (yes really.)

It also has the fuel tank gauges but they are marked in fractions of fullness rather than the numeric quantity of the tanks−the only unprofessional items on the whole aircraft in my view. Up there too are the fuel pump, mags and starter switches which look like they came out of a BAe 146/Avro RJ, and the same big rocker switches.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

Getting started

Starting is quite straightforward. I push the throttle and mixture levers fully forward then hit the fuel pump for five seconds, close the throttle and mixture levers, switch on the mags and then toggle the starter switch (just one switch for both engines).

A few blades pass, then the first engine fires smoothly and I quickly bring the mixture lever up, watching for an oil pressure rise. Repeat for number two. The engines warm up at 1,200rpm. In the meantime I bring the services on line, the avionics with a switch left of the centre console, and other radios on the stack. The throttle quadrant is missing its gated baseplate on our day of test so it looks like the throttles, prop and mixture levers are mounted in a big square bucket, but it doesn't cause a problem.

Engine management is chiefly by using those humungously large dials across the top of the centre instrument panel rather than from the printing on a baseplate. Mixture control is done using the EGT gauges and at night it's better done visually!

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

An old Chieftain pilot told me that he would lean the mixture so that the exhaust stubs turned cherry red at night and then mark the position with a china pencil for day operation: when pilot becomes blacksmith.

I've got the aircraft owner in the back and his pilot friend, Tim in the right seat (a retired Cathay 747 captain no less) keeping an eye on me. The wings can take 710 litres in four tanks (the fuel selector is a chunky affair at the rear of the centre console.)

Yep, it's an eye-watering £1,300 to fill 'er up−but we've only got about 250 litres on board today. So when I release the parking brake with the T handle under the yoke, and push and release the rudder pedals, we immediately start rolling forward.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

Even though we're light, nosewheel steering is quite heavy if you're used to light aircraft, but not if you fly anything bigger. Turning radius is a little underwhelming, using the pedals alone. To tighten a turn simply open up the engine on the outside of the turn. For really tight manoeuvring the nosewheel can castor through eighty degrees.

Being a long aircraft, the Chieftain is pitch trim-sensitive and it's crucial to set it correctly for takeoff, based on how you have it loaded. Today, with only one passenger and no bags, we are nose heavy and so set the trimmer at the back end of its takeoff range. Another crucial control is the cowl flap for each engine.

It has to be set open for takeoff and virtually closed for cruise. We take off clean because we're light and the runway is huge but for short and/or heavy takeoffs we would set one stage of flap. You wouldn't call a PA-31 a STOL machine but it only needs about 800m TODR at max weight.

We do the power checks, which are completely straightforward, then taxi onto Blackbushe's long tarmac runway. Feet firmly on the pedals and then progressively firewall the throttles because there are waste gates fitted−i.e. you can't over-speed/over-boost the engines and turbos.

So, a check of Ts and Ps, release the brakes and we're off! It's a twin so there's little or no rudder required, and because we're light we accelerate fast, quickly reaching our rotate speed of 85kt. The column goes from heavy to very light due to the airflow over the stabiliser and I actually have to check forward again as the nose leaves the runway lest we over-rotate−I was warned about it by Tim beforehand.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

It's important to keep the nose down to accelerate past the single engine safety speed of 87kt−below that we wouldn't have enough rudder authority to hold one engine at full power if the other failed. I reach down and raise the gear−the wheels come up with three loud thumps and then the lever returns to neutral.

I pull the throttles back to a nominal climb power of 35 inches and the props back to 2,350rpm. We are climbing now at 120kt and 1,200fpm. We could trade the climb rate for more airspeed if we were in a hurry or drop back to a Vx of 105kt for better close-in terrain clearance.

Up and away

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

The Chieftain might not be able to fly at jet speeds but the cabin has a feeling of luxury missing from today's short haul airliners and many of the long haul ones, so often trending towards the low cost end of air travel.

Neither noisy nor quiet, the cabin is nevertheless comfortable, light and spacious with big windows to look out of. There would be no better way of doing a tour through Africa for instance and I was pleased to find out that the Chieftain is still the weapon of choice for many operators out there.

From the crew seats the view is really special and I'm surprised how easy this big little aircraft is to fly and operate. The controls are light and powerful albeit with the expected roll inertia you get when hanging engines from wings instead of the nose.

Pitch trim is not particularly sensitive to speed and you can leave it alone unless the passengers start walking about down the back. It really is a joy to fly, even when manoeuvring next to the camera ship with all the speed, height and configuration changes.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

One exception though is the lag between throttle movement and manifold pressure indication. It acts like one of those human performance tests you get when applying to be a military pilot. Everything else though is super straightforward.

We level out at 3,500ft still at 35in and 2,300rpm and are getting an honest 170kt IAS, flying up to the camera ship. Fuel consumption at this speed is around forty US gallons per hour. You can go quicker with more power/height, commercial pilots I talked to tending to put 176kt on their flight plans for a typical trip. Alternatively you can economise with 27in/2,280rpm/155kt and just 33USG per hour−potentially only 3.3 gal per occupant per hour.

We didn't do any single-engine work because it's just not fair on the owner. Especially with a turbocharged aircraft, because no matter how hard you try there is always a bit of shock cooling then insufficient heating involved in shutting down and restarting an engine: it's why flying school twins rarely reach their TBO.

For the record, the book figure for single engine out at MTOW is a climb of 230fpm−remember that's with one engine at full throttle and max rpm, the other engine feathered, cowl flaps respectively open and shut, gear up and flaps retracted. Doesn't sound much, but it's better than many piston twins, only turbine twins generically doing consistently better.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

Thoughts turn to home and with Tim's guidance I set up a constant descent with the power at 25in and 2,350rpm, letting the speed build up to 200kt as we start back to Blackbushe and eventually return to circuit height. Levelling off, we allow the speed to bleed slowly back to circuit speeds.

This is the proper way to plan a descent with all the big '540 engines, especially the GTSIOs: their pilots say you should climb, cruise and crash at the same power setting. At 160kt we can start introducing flaps, followed by the gear at 150. On base leg we're at 120 and final at 100.

Only at the flare should you need to touch the throttles. Well, that's the theory anyway. I turn in tight, doing a silly curved approach like I was flying a Spitfire and have to reduce power earlier than Tim planned.

The touchdown itself is slightly quirky in itself in that I manage to get the mainwheels to kiss the runway but it's almost instantaneously followed by the nosewheel−I was just about to land when I landed. Relatively new to type himself, Tim graciously said he hasn't managed to land it any differently than that yet.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

What an aircraft! The Chieftain has joined my all-time top ten. It's a proper mini-airliner, flies as well as it looks, and many other positive clichés besides. It's numerically the most successful of its type, but is it the best of the breed?

The pilots I asked who had operated it commercially were divided. To sum it up, the consensus was that this big Piper was the Land Rover Discovery of its day whereas the Cessna Titan and Beech Queen Air were the Range Rovers. So horses for courses.

If you are serious about wanting to buy one I could enter a whole new field of clichés (about buying being the joining fee etc) but the best single bit of advice would be: if you buy one abroad check that all the ADs have been complied with before you import it. And don't forget its slightly smaller brother, which might better meet your needs.

Piper PA-31 Navajo ChieftainPiper PA-31 Navajo Chieftain

Since I flew the Chieftain Tim has asked whether we should put our gang together for a trip to Europe this summer. The answer is a resounding yes!

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