Piper PA-31 Cheyenne

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.

About 13 minutes after takeoff for a medical transport flight, while climbing through about 14,900 ft mean sea level (msl), the pilot reported to air traffic control (ATC) that he was smelling smoke in the cockpit and would be returning to the originating airport. The flight was cleared to return with a descent at pilot's discretion to 9,000 ft msl. The pilot replied, "okay," and said that it looked like he was going to lose some power shortly. The pilot then stated that he had smoke in the cockpit, declared an emergency, and requested that ATC contact the fire department. About 1 minute 15 seconds after the initial report of smelling smoke, the pilot made the last radio transmission of the flight stating that he had three people on board. The wreckage was located about 9 hours later in an area of brush and heavily forested terrain. Portions of the burned and fragmented wreckage were scattered along a debris path that measured about 2,400 ft in length, which is consistent with an inflight breakup. The center fuselage and cockpit areas were largely intact and displayed no evidence of fire; however, there was an area of thermal damage to the forward fuselage consistent with an inflight fire. The thermal damage was primarily limited to the floor area between the two forward seats near the main bus tie circuit breaker panel and extended to the forward edge of the wing spar. All exposed surfaces were heavily sooted. Some localized melting and thermal-related tearing of the aluminum structure was present. The primer paint on the floor panels under the right aft corner of the pilot seat and the left aft corner of the co-pilot seat was discolored dark brown. An aluminum stringer in this location exhibited broomstrawing indicating that the stringer material was heated to near its melting point prior to impact. A single wire located in the area exhibited notching consistent with mechanical rubbing. The main bus tie circuit breakers were partially missing. The remaining breakers were heavily sooted on their aft ends, and one breaker was thermally discolored. Areas of charring were on the backside of the panel. Examination of the wiring in this area showed evidence of electrical arcing damage. Four hydraulic lines servicing the landing gear system were located in this area, and all the lines exhibited signs of thermal exposure with melting and missing sections of material. Six exemplar airplanes of the same make and model as the accident airplane were examined, and instances of unsafe conditions in which electrical lines and hydraulic lines in the area of the main bus tie circuit breaker panel were in direct contact were found on all six airplanes. Some of the wires in the exemplar airplanes showed chafing between hydraulic lines and the electrical wires, which, if left uncorrected, could have led to electrical arcing and subsequent fire. Based on the unsafe conditions found during examination of the exemplar airplanes and the thermal damage to the area near the main bus tie circuit breaker panel on the accident airplane, including broomstrawing of the aluminum structure, electrical arcing damage to the wiring, and melting of the hydraulic lines, it is likely that an electrical wire near the tie bus circuit breakers chafed on a hydraulic line and/or airplane structure, which resulted in arcing and a subsequent in-flight fire that was fed by the hydraulic fluid.