• (John Absolon)
    (John Absolon)

John Absolon takes a brand new TBM850 turboprop, the fastest single engine turboprop in the world, for a run over Ballarat.

When Daher SOCATA, formerly EADS SOCATA, joined with Mooney to design a high performance single engine business aircraft, they envisioned an aircraft capable of carrying six occupants in comfort powered by a turboprop. The designation ‘TBM’ is formed by the initials of ‘TB’ for Tarbes, the French town where the aircraft is built, and ‘M’ for Mooney. The first TBM received French certification in 1990. Shortly after, Mooney withdrew from the project.

The 850hp PT6A-66D powered TBM850 was first introduced in 2007. The TBM850 uses 700hp for take-off but uses the extra horsepower to increase the climb performance and cruise speed with the flat-rated horsepower to achieve 320KTAS, which is around 15 per cent faster than the older TBM700.

If you want a powerful single engine turboprop business aircraft with stylish lines, proven track record and long range, then the TBM850 is for you. This is an aircraft that defines sophistication; an aircraft that displays great operating economics when compared to today’s new crop of light jets. It may be a little more expensive than the cheapest entry level jet, but with the larger cabin and six seats, it makes a lot of sense.

The TBM850 is a speed machine and, as with the Pilatus PC-12, it is quite a large single engine aircraft. But this doesn’t mean it’s hard to handle; to the contrary it’s a delight to fly, both through its superb Garmin avionics or if you just want to hand fly it.

The TBM850 is luxuriously fitted with four leather-upholstered seats in a club arrangement in the main cabin behind the two cockpit seats. A pull up and fold down table is attached to the right side wall. A further section of this table then folds out to provide table access to the rear seat occupant. All seats have individual air outlets and readings lights.

The TBM850 features a sleek, long fuselage behind the single turboprop power plant atop a long high aspect ratio aerodynamically efficient wing. The TBM850 can trace its pedigree back to the aerodynamics of those famous, efficiently designed Mooneys of years gone by - designs which featured many innovative aerodynamic features, like flush riveting for drag reduction to name one. The long nose is more of a function of the PT6 installation being lighter than an equivalent piston engine and therefore needing to be sited further forward to accommodate the centre of gravity. This extra space is used well with a forward locker capable of holding 50kgs.

With such a high aspect ratio wing, the TBM850 is fitted with spoilers to assist the rather small span ailerons in achieving acceptable roll rates. The roll control spoilers, which are used to augment the ailerons, are located inboard and forward of the ailerons. A small wing fence is also located in line with the inboard edge of the spoilers, which also helps to maintain laminar flow over the outboard sections of the wing and to improve roll control at slow speeds. Combine these with the yaw damper in the Garmin flight control system and rudder use is made easier.

The TBM850 is fitted with large span slotted flaps that not only angle down when extended but also extend aft, thereby effectively increasing the wing area for take-off and landing and reducing take-off and landing speeds. The TBM850 approaches at a reasonable 80-85 knots, which isn’t bad for such a fast aircraft. Combining the slowish approach speeds and similar take-off speeds, the TBM850, with its wide track landing gear, is stable in almost all situations on the ground.

Walking around the TBM850 gives an impression of its size and design features. The aircraft sits relatively low to the ground, and with its wing having such high aspect ratio, it looks longer than it actually is.

The wing and rudder flight controls are cable operated, with the elevator push rod activated. All surfaces have electrically activated trim controls. To aid in high altitude high speed cruise, a pair of ventral strakes are fitted to the underside of the rear fuselage. These, in combination with the Garmin flight control system’s yaw damper, provide safe and comfortable high speed cruise stability up to the TBM850’s record 320KTAS and maximum ceiling of FL310.

There are only minimal protrusions on the underside of the wing – mainly the fairings over the flap tracks and the two heated pitot heads. Apart from the de-icing boots and electrical heated stall warning sensor, the leading edge on the left wing is interrupted by the radome for the weather radar. Situated well outboard of the fuselage to avoid any possible interference with returns from the propeller, the radar antenna is in a streamlined radome pod protruding from the leading edge only a little thicker in diameter than the wing itself.

Each wing contains an integral fuel tank of 550 litres. The tanks are filled through a key lockable fuel cap on the wing top surface just inboard of each wingtip. The fuel system is automatically managed by the aircraft by cycling the fuel tank selection between tanks every few minutes to maintain balance, thereby reducing pilot workload and improving balance and aerodynamic performance. However, the fuel system can be managed manually if necessary at times when a non-normal operation is required.

The main landing gear, which retracts inwards, is of a vertical strut arrangement instead of a trailing link arrangement, which takes a bit of getting used to for that great touchdown. It is electrically selected and hydraulically operated, and an emergency hand pump can be used in an emergency to lower the gear.

Being of French design for mainly the North American market, the TBM would’ve been designed mainly for sealed surfaces. The tyre size is also a little small for what I would consider would be advantageous for other than sealed surface work or smoother unsealed surfaces. The 200mm ground clearance of the 2.3 metre diameter four bladed reversing Hartzell propeller is also a bit limiting in this regard as well.

Up front and inside
The nose of the TBM850 is characterised by the familiar PT6 intake design and exhaust ducts and intakes for the cabin air conditioning system. Compared to the TBM700, these exhaust ducts are slightly longer and angled a little further away from the fuselage to reduce those unsightly marks on the fuselage and to avoid the possible ingestion of exhaust gases into the engine and air conditioning system during ground operations.

The TBM’s PT6 intake system is also fitted with an Inertial Separator that can be inserted after selecting the system ON electrically. This helps to protect the PT6 from the ingestion of ice or foreign debris on the ground. The system does slightly reduce the power available under these conditions, but it’s a small price to pay to achieve reliable and long lasting operation and avoid possible engine damage from FOD. When the separator is selected OFF after take-off the torque will rise slightly. Normal operation is to have it ON for all take-offs and landings or flight through icing conditions.

The air intake’s leading edge along with the propeller are both anti-ice equipped. With regards to airframe anti-ice protection, the wing, horizontal tailplane and fin are protected with pneumatically operated boot systems that cycle tubes on and off to prevent the accumulation of ice. A wing inspection light is provided in the fuselage sides so that the pilot can visually check at night for the possible formation of airframe ice and the windscreen is electrically heated.

Entry into the TBM850 cabin is made easy via the quite wide rear electrically operated entry door and fold down stairs. The single piece door is hinged at the top, and when closed the stairs fold neatly into a recess on the inside of the door lining and don’t protrude into the cabin. As you enter the cabin you first become aware of the low headroom. When I say low, the 1.22m maximum ceiling height is typical of a six-seat aircraft of this size and certainly more than some modern six place piston twins. Compared to maybe a King Air it is a little smaller, but still a little larger than some entry level jets.

To the rear of the cabin is a netted baggage compartment capable of carrying up to 100kgs. In front of the rear forward facing, almost bench seat arrangement are two similar seats facing rearward in a club arrangement with a walkway between to gain access to the cockpit.

Folding upwards and down from a stowage on the side wall is a folding table with drink container inserts. The table can then be further folded rearwards to provide a convenient working area for the rear seat occupants.

The whole cabin is pressurised and air conditioned. In the TBM850, pressurisation air is taken from the P2.5 section of the engine rather than the earlier TBM700 model’s P3 outlet. This means that the bleed system doesn’t extract as much power from the PT6 to power the pressurisation.

The pressurisation system is automatically controlled and will maintain a sea level cabin atmosphere up to approximately 14,500 feet, increasing to 9300 cabin altitude at the maximum ceiling of 31,000 feet. At a normal cruise level around the mid 20,000 foot range, the cabin altitude is a comfortable 5500 to 6000 feet, about the equivalent of a modern jet airliner.

Exploring the cockpit
Squeezing my large frame through the gap between the forward seats into the cockpit wasn’t as hard as it looked. If access to the cockpit is going to be a problem for an owner/operator, SOCATA offer an option of a separate ‘pilot entry’ door.

Getting myself comfortable wasn’t a problem with the leather appointed seating and adjustable rudder pedals. Each seat is equipped with a yoke control. The TBM850 now comes standard with the Garmin G1000 avionics system, featuring two 10.5-inch screens (one for each pilot) and a massive 15-inch centre-mounted Multi Function Display (MFD) displaying all the engine, navigation and aircraft systems data.

Above the left Primary Flight Display (PFD) are the three standby instruments – an Attitude Indicator, Altimeter and Airspeed Indicator. Above the right PFD is a neat, small stowage that can accommodate a pair of sunglasses, approach plates or any other small items. Approach Plates? Well with the Garmin G1000 system you actually don’t need any ‘paper’ charts as all the relevant data and charts can be displayed on the MFD from the electronic database that is updated by way of SD RO M cards.

Below the left-hand PFD are the anti-ice controls and the gear handle and indicator lights. Above the centrally mounted MFD is the G710 Autopilot control and below it is the keypad for entering waypoint and other navigation data into the Garmin or entering aircraft performance data like weight and balance.

On the outboard side of each yoke grip is a group of switches that include the electrically operated pitch trim, rudder trim, press to talk and autopilot disconnect switches. The roll trim is on the centre pedestal. In the centre of the yoke is a small area with a clip that could be used to hold paper charts or a flight plan, the whole area being illuminated by an adjustable light. The centre pedestal contains the power lever, propeller control lever, engine condition lever, flap handle and fuel tank selector, along with the roll trim rocker switch.

The interesting thing about the flap handle is the extra position forward of the UP detent, the ‘850’ position that, when selected after airborne, removes some automatic torque limiting control of the engine and allows the PT6 to generate the flat rated 850hp to increase climb and cruise performance. In the TBM850 procedures manual this ‘850’ position is only selected after the flaps are up, climb is established safely and the engine torque is confirmed below 100 per cent. By selecting the ‘850’ position, engine torque will increase to a limit of 121.4 per cent. Recommended climb speed at this selection is 130KIAS.

The 850hp available gives awesome performance, and as a result care should be exercised with the planning and operating of the TBM850. As a precaution and because a number of automatic controls are removed to supply this power, the TBM test pilot explains he is cautious in selecting the 850 position on climb and usually only if the workload is lower and he has climb clearance from ATC so he can adequately monitor the engines limits without distractions.

Hitting the skies
After a brief pre-flight check of the all appropriate systems, it was time to fire up the avionics and after an initial boot-up period the Garmin sprang to life with the characteristic display that has been so common now in modern glass cockpits. After we entered the number of passengers and the passenger load that was onboard into the system, with its own measurement of the fuel load the Garmin was able to accurately calculate performance data.

Our planned track for the flight was loaded into the G1000 using the centre data entry keypad. Considering the weather at the time in the Ballarat area, we planned to climb up to a reasonably low altitude of about 8000 feet, where without too much trouble we could explore the handling qualities of this thoroughbred. Our return to YBLT would be via an RNAV Approach Runway 18 via the IAF at BLTND. This was loaded from the Garmin’s database into the legs of the nav system.

Selecting the IGNITION selector to AUTO and the STARTER ON, there was a quiet whirring from under the cowl as the electric starter rotated the gas generator section of the PT6. As the propeller just started to slowly rotate and with approximately 13 per cent rpm, the Condition Lever was opened to the LO/IDLE detent. The start procedures call for the monitoring of the ITT as it rose, avoiding the start limit of 870°C, which can be exceeded for no more than 20 seconds. The starter is normally selected OFF after achieving 50 per cent as the engine will then self-sustain and reach it’s idle rpm automatically.

After the start sequence was completed, the Condition Lever was advanced to the HI/IDLE position to taxi. Minimal power was required to get the TBM moving forward with our three occupants and around half fuel load. Visibility over the long nose didn’t seem to be a problem and the outlook to the sides was excellent as both pilot seats are situated just over the low-wing’s leading edge. Speed control when taxiing in a straight line over long distances could be controlled through use of the Beta prop range, which also helps to reduce brake wear. The TBM850’s normal procedures however warn against the use of reverse at taxiing speed.

Unlike piston aircraft, the turboprop in the TBM850 only needs to run up to confirm the operation of the propeller system. After ensuring the condition lever is in the HI/IDLE position, the propeller lever is selected to FEATHER twice and then back to MAX rpm. The TBM850 G1000 system has a built in Caution Alerting System (CAS) that warns of any systems problems that need to be rectified.

With the torque of the 2.3m prop and 700hp, acceleration was rapid and with the pre-take-off rudder trim setting only a small extra amount of rudder pressure was required to hold the TBM straight. The rotate seemed to be quite abrupt at about 85KIAS. The gear was selected UP and the speed was allowed to accelerate to an initial climb airspeed of 110KIAS.

The torque was maintained at 100 per cent and speed accelerated to 130KIAS for a brisk climb. The climb could have been accomplished using the G710 autopilot which could either maintain a desired rate of climb or an indicated airspeed.

In and out of cloud during the climb, the anti-icing system was given a good workout. The visibility airborne, as on the ground, was excellent from the front seats. Roll control was reasonably light and very responsive thanks to the balancing and added power of the spoilers to aid roll rate. Roll reversals from 45° to 45° were accomplished in around three to five seconds. Initially it took some getting used to having the rudder trim on the yoke, but I soon appreciated the benefits. Every power change requires a change in the rudder, particularly with this amount of horsepower and torque and having the trim switch right under your thumb was a great help.

Bringing her in
Before long it was time to set up for the return to Ballarat via the pre-loaded RNAV Approach. When the route was activated in the nav system it was displayed on the MFD map display and LEGS display, with lateral and vertical navigation information appearing on the PFD. When established on the approach passing the IAF at BLTND, Rod selected the Jeppesen approach plate on the MFD, which replaced the topographical map. This showed our current position as a magenta aircraft symbol over the approach path down to the IF of BLTNI.

As we progressed further down the approach, we slowed our approach back to the minimum but still ended up having to break it off and overshoot to join the crowded circuit. The overshoot on this occasion was quite benign considering we discontinued our approach well above the MDA of the approach. It was more of a case of levelling off at circuit height and looking for the traffic visually.

The TBM was slowed to circuit speed of around 100-110KIAS and with the gear lowered we selected the flaps to the TO position. Slowing further to less than 100KIAS on base and finals, the flaps were selected to LDG and the speed allowed to reduce to 90KIAS.

The view of the aim point over that long nose was quite good and I now appreciate the design feature incorporated into the TBM that uses a negative floor angle so that on approach you have a better visual view of the approach. This approach was discontinued not because of the slightly steeper angle but because the aircraft in front spent a while on the runway.

The go-round was nothing short of impressive. With the power available from the 700hp in the PT6 and the instant thrust response from that Hartzell prop, acceleration was rapid and the climb rate back to 1000 feet similarly impressive. After raising the landing gear and making an early turn onto downwind, the next circuit was more successful both with traffic spacing and glide path control. The touchdown was reasonable after a couple of abortive early flares down to the flare height.

The TBM 850 is a truly awesome business aircraft with a very high standard of finish.Combine these aspects with a very generous worldwide service support and warranty and the TBM850 offers a very cost-effective form of business travel.

Wingspan: 12.68m
Length: 10.65m
Height: 4.355m
Wheeltrack: 3.874m
Wheelbase: 2.914m
Prop ground clearance: 0.207m
PT6A-66D Thermodynamic Power: 1825 SHP
PT6A-66D Nominal (flat-rated) Power: 850 SHP
Time to climb to 26,000ft/31,000ft: < 15 min/<20 min
Maximum cruise speed at 26,000ft: 320 KTAS
Economy cruise speed at 31,000ft: 252 KTAS
FAA Certified ceiling: 31,000ft
Take-off distance: 2840ft (ISA to 50 ft AGL)
Landing distance w/o reverser: 2430ft (ISA to 50 ft AGL)
Range at economy cruise (252 Kts): 1585 NM (ISA – 45 min reserve)
Range at maximum cruise (320 Kts): 1410 NM (ISA – 45 min reserve)
Basic empty weight: 4589lbs (2081kg)
Maximum Zero Fuel Weight: 6032lbs (2735kg)
Maximum ramp weight (MRW): 7430lbs (3370kg)
Maximum Takeoff Weight: 7394lbs (3353kg)
Maximum Payload: 1443lbs (654kg)
Maximum payload with maximum fuel: 931lbs (422kg)
Maximum Landing Weight: 7024lbs (3189kg)
Maximum Usable Fuel Weight (291.6 USG): 1910lbs (867kg)

My thanks to thanks to Rob Carratello from Executive Airlines for his help in preparing this evaluation, along with Daryl Chibnall from Aerovision for his help with photography.

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