History of Flight
On December 10, 2021, about 2330 eastern standard time, a Swearingen SA-226AT, registration N54GP, was destroyed in an accident near Bedford, New Hampshire. The commercial pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 135 on-demand cargo flight.
According to the Federal Aviation Administration, the airplane was conducting an instrument landing system approach to runway 6 at Manchester Boston Regional Airport (MHT), Manchester, New Hampshire. During the approach, the pilot reported an engine failure at 2330:42 but did not specify which engine. Radio and radar contact were lost at 2330:51, when the airplane was about 1/4 mile from the runway. Review of ADS-B data revealed that during the last 9-second period, the airplane's groundspeed slowed from 99 knots to 88 knots, as it descended about 400 feet in a slight left turn to impact.
Video from a residential security camera recorded a portion of the approach, but only the airplane's navigation lights were visible in the distance. A sound spectrum study performed on recorded engine noise indicated constant engine noise at about 2,000 rpm. The last reliable audio data was recorded at 2330:28, 14 seconds before the engine failure report.
Personnel Information
The pilot had a total flight experience of 2,257 hours, including 496 hours in multi-engine airplanes and 118 hours in the accident make and model. According to the operator's flight and duty report, the pilot had 14.8 hours of off-duty rest before reporting for work at 1930.
Aircraft Information
The most recent maintenance inspection was a 100/150, 200, and 450-hour inspection completed on November 30, 2021, 10 days before the accident. At the time of the accident, the left engine had accrued 15,419 total hours of operation, with 3,339 hours since major overhaul. The right engine had accrued 12,155.5 total hours, with 2,871 hours since major overhaul (time between overhaul was 5,400 hours). The published minimum controllable airspeed (Vmc) on the airplane's airspeed indicator was 92 knots.
Wreckage and Impact Information
The wreckage was located on a river sand jetty, oriented north. A postcrash fire consumed the cockpit, cabin, and both wings. No debris path was observed. A crater about 6 feet long, 3 feet wide, and 2 feet deep was found at the beginning of the sand jetty. The left aileron was recovered in the water near the crater. The empennage remained intact with the elevator and rudder attached and undamaged except for the right elevator tip. The right wingtip was near the empennage, and an outboard left-wing section was located 60 feet left of the main wreckage. Three landing gear were near the main wreckage, and the radome was at the end of the sand jetty in water. Elevator control continuity was confirmed from the elevator to the cockpit area. Rudder control continuity was confirmed from the rudder to the cabin area. No aileron cables were identified.
The left engine was in the main wreckage; its propeller had separated and was partially embedded in mud. All three blades remained attached. The right engine was forward and left of the main wreckage; its propeller remained attached, with all three blade roots attached and charred. Both engines and propellers were retained for examination.
Engine and Propeller Examinations
Teardown examination of the left engine revealed that a 1st stage turbine blade had separated mid-span. The fracture surface exhibited varying levels of oxidation; the investigation could not determine if the blade separated during the accident flight or a prior flight. Microscopic examination showed the 1st stage operated near 1,700°F and the 2nd stage near 2,200°F for 10 to 100 hours. The 2nd stage operating at a higher temperature than the 1st stage was consistent with engine degradation over time. The 2nd stage turbine stator assembly was missing vane material from the 6 to 12 o'clock positions, consistent with thermal damage over time. Rotational scoring was present throughout the engine, including the propeller shaft, compressor impellers and shrouds, and turbine rotor blade tips. Sand debris was observed throughout the gas path.
Teardown examination of the right engine revealed no anomalies that would have precluded normal operation. Rotational scoring was documented at multiple locations, and sand debris was observed throughout the gas path, with accumulation in the combustor and outer transition liner.
Teardown examination of both propellers revealed no anomalies that would have precluded normal operation. All blade angles were mid-range (not feathered) and exhibited evidence of little to no powered rotation.
Additional Information
The pilot operating handbook for the make and model airplane contains a warning: "IN THE EVENT OF AN ENGINE FAILURE OR POWER LOSS, THE ENGINE NEGATIVE TORQUE SYSTEM (NTS) ONLY PROVIDES PARTIAL DRAG REDUCTION BUT NOT TO THE EXTENT OF A FULLY FEATHERED PROPELLER. PILOT MUST TAKE ACTION TO FULLY FEATHER THE PROPELLER (ON THE AFFECTED ENGINE) TO REDUCE PROPELLER DRAG." The first step listed is to pull the ENGINE STOP AND FEATHER CONTROL for the failed engine.