Piper PA-31 Cheyenne

The two pilots and three passengers were conducting a cross-country flight over the ocean from South Carolina to the Bahamas. About 30 minutes into the flight, while climbing through 24,300 ft to 25,000 ft about 95 miles beyond the coast, the pilot made a garbled radio transmission indicating an emergency and intent to return. At the time of the transmission the airplane had drifted slightly right of course. The airplane then began a descent and returned on course. After the controller requested several times for the pilot to repeat the radio transmission, the pilot replied, "we're descending." About 15 seconds later, at an altitude of about 23,500 ft, the airplane turned sharply toward the left, and the descent rate increased to greater than 4,000 ft per minute, consistent with a loss of control. Attempts by the air traffic controller to clarify the nature of the emergency and the pilot's intentions were unsuccessful. About 1 minute after the sharp left turn and increased descent, the pilot again declared an emergency. No further communications were received. Search efforts coordinated by the U.S. Coast Guard observed an oil slick and some debris on the water in the vicinity of where the airplane was last observed via radar, however the debris was not identified or recovered. According to recorded weather information, a shallow layer favorable for light rime icing was present at 23,000 ft. However, because the airplane was not recovered, the investigation could not determine whether airframe icing or any other more-specific issues contributed to the loss of control. One air traffic control communication audio recording intermittently captured the sound of an emergency locator transmitter (ELT) "homing" signal for about 45 minutes, beginning near the time of takeoff, and ending about 5 minutes after radar contact was lost. Due to the intermittent nature of the signal, and the duration of the recording, it could not be determined if the ELT signal had begun transmitting before or ceased transmitting after these times. Because ELT homing signals sound the same for all airplanes, the source could not be determined. However, the ELT sound was recorded by only the second of two geographic areas that the airplane flew through and began before the airplane arrived near either of those areas. Had the accident airplane's ELT been activated near the start of the flight, it is unlikely that it would be detected in the second area and not the first. Additionally, the intermittent nature of the ELT signal is more consistent with an ELT located on the ground, rather than an airborne activation. An airborne ELT is more likely to have a direct line-of-sight to one or more of the ground based receiving antennas, particularly at higher altitudes, resulting in more consistent reception. The pilot's initial emergency and subsequent radio transmissions contained notably louder background noise compared to the previous transmissions. The source or reason for the for the increase in noise could not be determined.

The airline transport rated pilot and passenger departed on a cross-country business flight in a twin-engine, turbo-propeller-equipped airplane in day, visual meteorological conditions. Shortly after takeoff, the airplane banked left, descended, and impacted terrain about 1/2 mile from the end of the runway. There was not a post-crash fire and fuel was present on site. A postaccident airframe examination did not reveal any anomalies that would have precluded normal operation. Examination of the left engine found signatures consistent with the engine producing power at impact. Examination of the right engine revealed rotational scoring on the compressor turbine disc/blades, and rotational scoring on the upstream side of the power vane and baffle, which indicated that the compressor section was rotating at impact; however, the lack of rotational scoring on the power turbine disc assembly, indicated the engine was not producing power at impact. Testing of the right engine's fuel control unit, fuel pump, propeller governor, and overspeed governor did not reveal any abnormities that would have accounted for the loss of power. The reason for the loss of right engine power could not be determined based on the available information.

On April 17th, at 11:04 UTC, the aircraft turboprop Piper PA-31 Cheyenne II, registration HBLTI, private property, took off from runway 17 of the Cascais aerodrome (LPCS) bound to Marseille airport (LFML), IFR private flight, with 1 pilot and 3 passengers on board. According to several eyewitness testimonies, after takeoff, the Swiss twin-engine started to put the left wing down and consequently to turn left while climbing slowly to about 300’ feet of altitude. The left bank1 increased and the speed decreased leading the aircraft to stall. The aircraft entered a steep dive and impacted the ground next to a logistics dock of a local supermarket, located southeast of the airfield. The crash occurred 700 m from the end of the departure runway. Following the impact, the aircraft exploded and caught fire affecting a logistic dock, a house and a truck. The aircraft was destroyed by impact force and the post-collision fire, all the four occupants were killed. The driver of the truck affected by the explosion of the plane was also killed. The fuselage, wings, the engines and propellers were severely damaged by the impact force and post-impact fuel-fed fire. The structural damage to the aircraft was consistent with the application of extensive structural loads during the impact sequence, and the effects of the subsequent fire. No pre-crash structural defects were found. All aircraft parts and control surfaces were located at the site. The flaps and the landing gear were found retracted at the time of impact.

The airline transport pilot departed in the twin-engine, turbine-powered airplane on an air ambulance flight with two medical crew members and a patient on board in night visual meteorological conditions. According to a witness, during the initial climb, the airplane made a left turn of about 30° from the runway heading, then stopped climbing, made an abrupt left bank, and began to descend. The airplane impacted a parking lot and erupted into flames. In the 2 months before the accident, pilots had notified maintenance personnel three times that the left engine was not producing the same power as the right engine. In response, mechanics had replaced the left engine's bleed valve three times with the final replacement taking place three days before the accident. In addition, about 1 month before the accident, the left engine's fuel control unit was replaced during trouble shooting of an oil leak. Post accident examination revealed that the right engine and propeller displayed more pronounced rotational signatures than the left engine and propeller. This is consistent with the left engine not producing power or being at a low power setting at impact. Further, the abrupt left bank and descent observed by the witness are consistent with a loss of left engine power during initial climb. The extensive fire and impact damage to the airplane precluded determination of the reason for the loss of left engine power.