Flight Test: Dave Unwin Reviews The TBM-700
Scything through the summer sky at 5 miles a minute, I was profoundly impressed at not only how civilised the TBM is, but perhaps even more importantly, how easy it is to fly.
“Although with its wood-and-leather interior, Club-Class seating and air conditioning pack, the -700 may not appear to be a pioneering aeroplane, in fact it is! It was the first aircraft in this class (high-performance single-engine turboprop) to achieve certification, and since 1990 has retained its position as one of the worlds most desirable personal aircraft with a price tag of around £1.8 million.
When Socata’s Philipe Segovia asked me if I was interested in flying the machine I accepted his offer and for one very good reason. On paper at least, the TBM-700 looks as if it should be within the capabilities of the majority of General Aviation pilots, and I wanted to find out if it was.
Indeed, one of the biggest selling points of the -700 is that it is certificated for single-pilot operation and is very much aimed at the owner-pilot. I already knew that in order for it to meet FAR Part 23 that it had to stall at or below 61 knots (the new C2 variant actually stalls at 65, see box), and multiplying that value by 1.3 soon reveals that a good speed to use on short final is about 85 knots. As this is only 15 knots quicker than the speed I’d use for a fully loaded Cessna 182, it seemed that the -700 should be within the capabilities of any reasonable GA pilot with some familiarity of complex aircraft.
I met Socata’s Philip Chamberlain at Florida’s Lakeland Airport during this years Sun N Fun, and after a quick briefing we made our way out to the elegant turboprop waiting patiently on the busy parking ramp. While Philip and I removed the various control locks, covers and engine blanks, I took the opportunity to acquaint myself with the aircraft.
As Philip and I continued the pre-flight, it became increasingly apparent to me that this aircraft has been built to a specification, and not a price. For example, not only is there a mirror built into the ELT bay (so that you can inspect the ELT) but there is another in the nosewheel well to check the fuel filter. Obviously, it’s pretty dark in there, so the Socata engineers have thoughtfully included a light.
While grovelling around on my hands and knees, I thought I’d take a quick look at the main undercarriage legs, and was astonished by the size of the hydraulic actuators they look as if they’ve been borrowed from an Airbus.
Three things next caught my eye the ailerons seemed rather small, the single-slotted Fowler flaps seemed absolutely enormous and the wing was fitted with spoilers. Philip confirmed my suspicion that all three were related. Basically, in order to keep the stalling speed below 61 knots (imperative if the -700 was to be certificated in the USA), Socatas engineers found it necessary to install relatively long-span flaps. Indeed, the flaps are so large that they actually cover more than 70% of the trailing edge! As an inevitable side effect of this, the ailerons ended up being slightly on the short side, with a consequent degradation of control around the lateral axis. The elegant solution to this conundrum was to supplement the ailerons with spoilers coupled to the ailerons (correctly termed spoilerons). I soon discovered that this idea works very well indeed.
Pre-flight inspection completed, Philip and I made our way up to the spacious cockpit, strapped ourselves in and prepared to wind the big engine into life. Interestingly, our aircraft was not fitted with the optional pilots door, although the TBM in the static park was. It struck me that the pilots door would prove to be a very useful option, both for freight operators and for private owners. For example, cargo operators will be able to fill the cabin to capacity without having to leave space for the aisle. It is a fact that most small freighters bulk out (run out of space) before they gross out (run out of weight-carrying capacity), hence the cargo pod fitted to the Cessna Caravans operated by FedEx. Furthermore, most private owners prefer to check for themselves that the door has been shut and locked correctly, so although it adds a few pounds (to both the price and the empty weight), I imagine that this is an option that quite a few purchasers will exercise.
And while were on the subject of options, when you look at the impressively comprehensive instrument panel its hard to imagine what optional extras could be needed. The -700s panel contains a multitude of digital delights, including a Bendix/King EFIS and autopilot, weather radar, Stormscope, traffic and terrain warning systems, weather data uplink, dual Garmin GNS530 Nav/Comms, dual transponders, even the Bose headsets are standard. In fact, pretty well everything that you’d ever need, or even want, in this class of aircraft.
Interestingly, not only is this very complete instrument suite fitted at the factory (and thus included in the standard empty weight) but it is also included in the standard price. The only other surprise, at least in my opinion, was the inclusion of a suction gauge for the vacuum pump. I don’t really like suction-powered gyros (vacuum pumps are not the most reliable of ancillaries), and as the TBM has both a main starter/generator and a standby belt-driven alternator, I was amazed that Socata had not opted for an all-electric panel.
Having adjusted the very comfortable seat and strapped myself in, I began to acquaint myself with the layout of the controls. The only noticeable departure from normal conventions was that the yoke also carries a rocker switch for the electric rudder trim. I’d never flown an aircraft with a yoke-mounted rudder trim before, and guessed that a combination of the powerful engine and large four-bladed prop probably meant that regular rudder trimming was required.
Starting the TBMs turboprop engine was very straightforward, and it being the early morning, the ambient air temperature was still quite low. Consequently the engine lit off promptly with a nice cool start, and although we both kept a close eye on the inter-turbine temperature (ITT) gauge, it never looked like getting close to its upper limit. Power is provided by the ubiquitous Pratt & Whitney PT6 free-turbine (in the case of the TBM it is a 1,583shp PT6A-64). Interestingly, although this engine is capable of producing in excess of 1,580shp at sea level on an ISA (International Standard Atmosphere) day, Socata has flat-rated the engine to 700shp.
This confers two significant advantages. The first is that the engine gets to lead a very under-stressed existence (unlike your editor) as it is only ever running at 50% of its total capacity (much like your editor!) The second advantage is that the engine can continue to produce its full-rated power right up to around 25,000ft, unlike many other engines, which suffer a considerable drop-off in power at altitude.
While we concluded the post-start checks, I glanced at the fuel contents gauge and was interested to see that it was calibrated in gallons. Intrigued, I studied the Shadin ETM 700 engine trend monitoring unit to the right of the undercarriage lever and was surprised to note that it too was calibrated to show fuel flow in gallons per hour. I found this rather curious, as in most turbine-powered aircraft, fuel quantity and flow have always been displayed by weight, not volume. However, on reflection, I suspect that as many potential TBM purchasers would be transitioning up from a complex piston-powered aircraft (which do indicate fuel quantity and flow by volume) that using gallons is probably a logical choice.
While were on the subject of engine trend monitoring, I must say that I thought the Shadin ETM-700 was a most impressive piece of kit. It automatically records a huge amount of data, including every start and shutdown, peak ITT and other engine temperatures and pressures, prop rpm and fuel flow. This information can then be downloaded and analysed to ensure that the engine is running satisfactorily and within limits. Knowledge gained using this system has seen Pratt & Whitney change the TBO from a mandatory 3,000 hours to on condition, which must make operating a TBM-700 even more attractive if you’re paying for the maintenance!
As we taxied out I ensured that the power lever was on the idle stop. However, the sheer power of the beast meant that it consistently wanted to taxi faster than I was prepared to allow it. To avoid constantly riding the brakes, Philip suggested pulling the power lever back into the Beta range (this flattens the prop pitch, which produces less thrust) which I found worked well. As we rolled along I spotted out of the corner of my eye that the fuel tank selector was suddenly rotating itself from Left to Right. Apparently, the fuel tank selector automatically switches between tanks (one in each wing) at regular intervals to prevent a lateral imbalance. I heartily approve of this system, as it means that one more unexciting but very necessary task has been removed from the pilots workload. And, as a pilot, anything that reduces my workload, gets my vote! Cleverly, if you’ve foolishly depleted your fuel to the point that both tanks are showing Low Fuel warnings on the annunciator panel, the fuel selector automatically switches from tank to tank every 75 seconds in order to extract every last drop of Jet A-1.
[ad]Out at the run-up point we concluded the pre-take off checks rapidly, and this also gave me the opportunity to familiarise myself with the cockpit layout. I was very impressed at how neatly and logically the cockpit was laid out, with (for example) the switches for the various de-ice systems all co-located in a clearly defined box. I also liked the comprehensive annunciator panel located in the avionics stack, as well as the orange Master Caution and red Master Warning lights sensibly sited just above the ASI. Overall, I thought that, for such a complex aircraft, the panel was very clear and uncluttered. As on nearly all turbine-powered aircraft, the switches for most of the electrical systems such as the lights, starter and generator are in a neat overhead panel.
With the trims and flaps set, and all other checks completed, I carefully lined the big turboprop up with the centreline before standing on the brakes and slowly increasing power to 40% on the torque gauge. I then released the brakes and pushed the power up to 95%. Usually, you’d use 100% for take-off, but as with only half fuel and just two POB, we were almost 1,500lb below the maximum take off weight of 7,394lb. Consequently, Philip said it wouldn’t be necessary to use full power.
Nevertheless, acceleration was excellent and the rotation speed (Vr) of 85 knots was reached very quickly. Gear up, flaps up, and as soon as we were clear of the busy Lakeland circuit, Phillip instructed me to trim for 140 knots and commence climbing up to our cruise altitude of 26,000ft. This was done with a climb rate of about 1,500ft/min and in a series of steps, as Miami Centre was unable to give us a clearance straight up to 26,000ft. Consequently we had to briefly level off several times while Philip requested and received a clearance for a higher altitude and while doing this, I discovered why Socata has placed the rudder trim on the yoke.
That big prop does indeed produce considerable amounts of torque, precession and P-factor, and I very quickly noticed that whenever I adjusted either airspeed or power, I also needed to adjust the rudder trim in order to keep both the slip ball centred and the pedal forces neutral.
Upon reaching our cruise altitude I engaged the excellent autopilot, set power and rpm for max cruise and then sat back to record the all-important numbers for true airspeed and fuel flow. The -700 quickly accelerated to a TAS of 300 knots (Mach 0.5!), for a fuel flow of just under 46 Imp gal/h. As the aircraft can carry up to 234 imp gals of useable fuel, this confers a range of about 1,300nm and an endurance of over four hours with a 45-minute IFR fuel reserve. Of course, this is the max cruise speed, which is achieved with a prop setting of 2,000rpm. Pull the prop back a few hundred rpm and while the TAS drops to around 260 knots the fuel flow reduces to less than 31 imp gals. Range (with IFR reserves) now grows to almost 1,700nm, while endurance (no reserves) is a bladder-bursting seven hours!
This really is a serious travelling machine, specifically designed for people who have some serious travelling to do. The Shadin ETM 700 also comes in handy in the cruise, as it along with its engine monitoring attributes also functions as an air data computer and can display altitude, OAT, TAS, wind speed and direction at the turn of a switch. It can also display the optimum power setting, based on altitude and temperature.
Phillip then cancelled our IFR clearance and directed me to descend rapidly down to 8,000ft for some general handling, so I disengaged the autopilot, drew the power off and lowered the nose. Socata has blessed the -700 with a very strong airframe, and its Vne of 266 knots IAS is usefully high. This means that should an emergency descent be required (if, for example, the pressurization has failed) rates of descent as high as 9,000ft/min are achievable! Philip explained that this facility is also very useful when flying into large, busy international airports, where controllers will sometimes hold you at altitude before issuing what is known in the states as a slam-dunk approach.
And while were talking about the pressurisation system, it functioned so smoothly that I was oblivious to its presence! If you’re interested, cabin pressurisation is about 6.2psi, which equates to a cabin altitude of approximately 9,000ft when the aircraft is at its certified operating ceiling of 31,000ft.
Once level at 8,000ft, Philip asked Miami Center for a block of airspace in which we could manoeuvre, before inviting me to assess the -700s general handling and stability. As we had a relatively forward CG, the longitudinal stability was, as you’d expect, distinctly positive, while directional stability was also positive and lateral stability neutral.
Control around all three axes was good, with the roll rate being particularly sprightly for such a large aircraft clear testimony to the efficaciousness of the combination of ailerons and spoilerons. An investigation of the 700s slow-speed handling proved illuminating, as despite its ability to cruise fast n high, the slow side of the speed envelope is comparable with that of many larger piston singles. With full flap and a touch of power, the needle of the ASI was actually flickering below the 60-knots mark! A fully loaded Beechcraft Bonanza stalls at 59 knots, and while we were a long way from being at MAUW, I still found it incredible that such a large, fast, machine could fly so slowly.
Having explored the TBMs slow-speed handling with a variety of different flap and undercarriage combinations, it was time to try a few circuits. Due to the incredible volume of traffic at Lakeland we decided to go to Avon Park, a small, relatively quiet airfield about 50nm away to the southeast. As soon as I spotted Avon immediately felt that I was both high and fast. How was I going to simultaneously descend and slow down in time to enter the circuit at the correct altitude and speed?
I shared my concerns with Philip, and asked him if perhaps I shouldn’t dissipate some of our excess speed and height with a 360 turn. Dave he replied, you keep forgetting that this is a TBM. Just pull the power right back, lower the nose, increase speed and you’ll make it, easy. I’d forgotten that with the prop lever at 2,000rpm and the power lever at idle, that the prop blades would automatically go to fine pitch in order to maintain turbine rpm. The prop disc then creates a giant air brake, and this, combined with the high Vne, makes the -700 an incredibly amenable aircraft. Indeed, although I started from a position where I felt too close, too high and too fast, I actually ended up having to add a smidgen of power as we entered the downwind leg. A very impressive demonstration of the TBMs flexibility.
A power setting of 55% torque and a speed of 100 knots seemed about right on the downwind leg, and as we passed abeam the numbers, I selected the first stage of flap and lowered the undercarriage before commencing the turn onto base. As we turned final, the long nose somewhat blocked my view of the runway, but the application of landing flap smoothly pitched the nose down, which greatly improved power reduction on short final saw us crossing the fence bang on the Vref of 80 knots. Having already experienced the incredible braking power of the prop disc at flight idle, I took care to avoid closing the power lever completely until the mainwheels touched. Although the prop is fully reversible, Philip recommended only pulling the prop lever back into the Beta range, which still produced significant deceleration. On the next landing, Philip pulled the prop right back into reverse and then you really stop.
In conclusion, I would say that the TBM-700 is a truly remarkable aircraft. Not only is it an extraordinarily capable machine, but you don’t even have to be a professional pilot to make full use of its extraordinary capabilities. Indeed, any competent pilot with an Instrument Rating and a few hundred hours on a TB21 or similar, should be able to convert onto the TBM relatively easily. And bearing in mind that this aircraft can carry six people while cruising at Mach 0.5, is certified to 31,000ft yet comes over the fence at 85 knots this truly is a triumph of very clever design. The TBM-700 essentially created the high-performance single-engine turboprop class, a class that it continues to dominate more than 15 years after it first flew. Having flown one, it’s not hard to see why.