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NTSB: Stall Warning Sounded Before Phenom 100 Crash


Downloaded cockpit voice recorder and flight data recorder preliminary information from an Embraer Phenom 100 that crashed 1 mi. short of the runway at the Montgomery County Airpark outside Washington D.C. on Dec. 8 revealed that the aircraft’s automated stall warning system sounded continuously for the final 20 sec. of the flight, according to NTSB board member Robert Sumwalt.

The accident killed the pilot and the two passengers on the jet as well as a woman and her two children in one of three houses struck by debris.

The pilot, who owned the aircraft, had an air transport pilot rating as well as a flight instructor rating and about 4,500 hr. flight time. In March 2010 he experienced a landing accident at the same airport on the opposite runway in a Socata TBM 700 after having directional control problems on the landing. The aircraft was destroyed but the pilot was not injured.

Sumwalt said Dec. 9 that a passenger in the Phenom 100 was in the co-pilot seat of the aircraft during the 57-min. flight from Chapel Hill, North Carolina, and during the GPS approach to Runway 14 at the airport. He says there was "minimal conversation during the arrival." The Phenom 100 is certified for single-pilot operations.

At 32 sec. before landing the aircraft passed through 500 ft. above-ground altitude with flaps and landing gear configured for landing on a straight-in approach to the runway. At 20 sec. before the end of the recording, the aircraft’s audible "stall stall" warning triggered, indicating that the wing’s angle of attack was approaching aerodynamic stall, which for the Phenom 100 generally occurs at 77 kt. with full flaps and landing gear extended. Sumwalt said the lowest recorded airspeed from the flight data recorder was 88 kt. "At that point, there were large excursions in pitch and roll," he said. Two seconds later, the pilot added power and the engines responded. Standard recovery technique for a stall warning in the Phenom is to add power and lower the pitch attitude (to decrease the angle of attack). He said there was no indication that the engines had been damaged by bird ingestion or had caught fire or suffered any type of uncontained failure. Sumwalt did not have information on when the lowest speed occurred in relation to the stall warning activation.

Three instructor pilots were in the vicinity when the accident occurred, two on the ground and one flying a downwind leg to the runway, preparing to turn on the base leg. Two of the pilots, including the one in the air, told investigators they saw a "series of pitch-and-roll excursions" with large pitch angles. The descriptions match what eyewitnesses in the accident area described seeing, and would appear to match the general behavior of an aircraft in an aerodynamic stall.

Due to the aircraft’s handling in a stall, Embraer was required to install a "stick pusher" system that automatically reduces the pitch angle (by mechanically pushing the yoke forward) at the point where the aircraft reaches aerodynamic stall, typically at 77 kt. The overall stall protection system is designed so that the audible stall warning should occur before that point so that the pilot can recover before the stick pusher activates.

According to the FAA Flight Standardization Board (FSB), the stick pusher "is effective and aggressive." While the aircraft "has no unusual flight characteristics if recovery is initiated at first indication of a stall," and there will be minimal altitude loss, the FSB cautions that if an aerodynamic stall occurs at the same approximate airspeed as stick pusher activation, the loss of altitude during the stall recovery will be 300-500 ft. "As a consequence, flight crews, training personnel and evaluators should be aware of the consequences of low-altitude stalls," the FSB says.

Editor's note: This post has been updated.

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