Page 7 - Volume 18 Number 6

Socata’s
TBM 900
by LeRoy Cook
Back in 2006, Socata’s already-speedy TBM 700C2 turboprop single was upgraded to the TBM 850; replacing the 700-shp PT6A-64 engine with an 850-shp PT6A-66D markedly boosted climb and cruise performance. The TBM 850’s certification, however, limited takeoff horsepower to the original 700 shp, using a torque limiter that engaged when the flaps were extended to the takeoff detent. After the flap lever was moved forward, the throttle could be opened up to the 850-shp limit.
This worked, delivering max cruise speeds of 320 knots, but it eventually became clear that the TBM could benefit from further development. When Daher-Socata announced a new TBM 900 last spring, there was presumption that it was to be a 900-hp variant of the same airframe. Nothing could have been further from the truth.
First, the TBM 900 retains the 850-shp PT6A-66D of the TBM 850; the engine can actually produce 1,825 thermodynamic horsepower, so it’s more than adequate for the airplane. It is, however, no longer restricted from utilizing its max-power rating during takeoff, and its operation has been greatly simplified by engineering a single-lever (almost) power control system. There’s still a separate manual-control power lever, which can be brought into play if the primary fuel controller malfunctions. Otherwise, a hefty throttle bar does it all; the propeller just hums along at a constant 2,000 rpm, and to feather the prop the single power control is moved through a gated shift pattern on the quadrant. The similarly-absent condition lever’s fuel cutoff is reached by further movement aft of feather.
Secondly, even with no horsepower increase, the TBM 900 is a much-enhanced performer, thanks to a host of aerodynamic and thrust augmentations. The TBM 900 can cruise as fast as 330 knots, and it generates this added speed at higher fuel-saving altitudes.
JUNE 2014 TWIN & TURBINE • 5
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