A TBM 700 Experiences A ‘Torque-Induced Stall,’ Part 1

The left-turning tendency of propeller driven airplanes is no secret. Student pilots learn about P factor and experience that left turning tendency on every takeoff, even in small training airplanes. However, when those novice pilots move up to much more powerful airplanes like the Daher (Socata) TBM 700 single-engine turboprop, the performance can catch them by surprise. The left turning tendency of the airplane when it is in a high-thrust, low-speed flight regime is very strong.

That’s what happened to a TBM 700 in Lansing, Michigan, on Oct. 3, 2019. The airplane, registration N700AQ, crashed during an attempted go-around from an approach to Capital Region International Airport (LAN). When the pilot applied thrust, the airplane banked to the left and stalled, striking the ground 0.3 mi. west-northwest of the approach end of Runway 10R. The pilot and four passengers were killed and the airplane was wrecked. One passenger survived.

When the NTSB produced its analysis of the case, the agency declined to make the connection between torque and the stall. The board said: “although an increase in thrust is required for a go-around, the investigation was unable to determine how rapidly the pilot increased thrust, or if a torque-roll occurred during the aerodynamic stall.”

The investigators were being cautious. Without a flight data recorder (FDR) to support a performance analysis, understanding all the forces on the airplane was too difficult to attempt. But I think it’s important for pilots of these airplanes to understand what happens in this situation, so I am coining the term “torque-induced stall.”

You won’t find the term “torque-induced stall” in any FAA handbooks. If someone else has used the term already, I will gladly cede the credit for it. I use it here because I think it helps to explain what has happened in a number of loss-of-control accidents in the TBM and similar airplanes. 

The Accident Flight
The airplane departed Indy South Greenwood Airport (HFY), in Greenwood, Indiana, at 0800 EDT and climbed to flight level 190. Thirty-four minutes after takeoff, the airplane began a gentle cruise descent. At 0853, Great Lakes Approach said: “TBM zero alpha quebec, five miles from FAMLI, turn right, ah, right heading zero seven zero, maintain three thousand until established on the localizer, cleared the ILS one zero right.” 
 
The pilot replied: “Zero seven zero, ah, we’re cleared for the ILS ten right into, ah, Lansing.” After the approach controller switched him to the tower, he said: “Tower, seven hundred alpha quebec with you on the ILS, ah, one two right.”

The tower said: “Seven zero zero alpha quebec, Lansing, ah, tower, the winds are calm, one zero right cleared to land.” The pilot’s last transmission was “cleared to land, ah, ten right, seven hundred alpha quebec.” 

ADS-B data showed the airplane’s calibrated airspeed was 196 kt at 0855. The flight passed the FAMLI final approach fix (FAF) 29 sec.  later. At 2303 ft. MSL, it was 97 ft. low, and at 166 kt calibrated airspeed (CAS), it was 81 kt faster than the TBM’s prescribed approach speed of 85 kt.

FAMLI is 4.5 nm from the runway 10R threshold. In that distance, the pilot slowed from 166 kt to 84 kt. while descending on the glide slope. The ceiling at LAN was 400 ft. and the visibility was 1.25 mi. He arrived at 400 ft. above the airport at about 1.3 nm from the threshold. His airspeed was still 84 kt at 180 ft. AGL and .5 nm from the runway, but at that point he entered a shallow climb and began turning left.

As the pilot added power for an apparent go-around, the airplane banked left and the airspeed fell to 74 kt. It stalled and descended to the ground, landing hard in a level attitude. 

The initial impact area was in a large grassy area. The ground scar extended 135 ft. along a heading of 060 degrees. A lower antenna, gear door and flap track fairings were left along the debris path. 

The fuselage, wings and empennage were relatively intact when the airplane stopped, but there was extensive damage. Safety investigators checked all flight control surfaces and cable continuity and noted that both fuel tanks had ruptured. The engine and propeller were heavily damaged, but they gave no indication of pre-accident malfunctions. Investigators ruled out mechanical failures as a factor in the accident.

The spoilers were retracted and the rudder and elevator trims were neutral. The flap selector was up and locked, but the actuator jack screws were halfway between the takeoff and landing positions. The landing gear selector was gear-up and the nose gear and left main landing gear were fully retracted, but the right main landing gear, while retracted, had not yet arrived in position on its actuator uplock.

The throttle was in flight idle, the prop lever full forward, and the condition lever also full forward.

Overloaded And Tail-Heavy 
The airplane was overloaded and tail-heavy. Based on the reported weight of the pilot and five passengers and the fuel load of 202 gal., the takeoff weight was 7,626 lb. That was 232 lb. above the maximum allowable takeoff weight of 7,394 lb. The takeoff CG was 196.18 in., 2.53 in. past the aft limit. The airplane’s weight upon arrival at LAN was still 126 lb. above the maximum landing limit of 7,024 lb., and the CG was still 2.95 in. aft of the aft limit.

Excess weight increases stall speed, of course, and aft CG reduces stability and ability to recover from a stall.

The TBM 700’s stall speed increases with bank, as we describe in Part 2 of this article.