Piper PA-31 Cheyenne

The pilot had filed an instrument flight rules (IFR) flight plan for 25,000 feet mean sea level (MSL), and he amended it to 27,000 feet MSL en route. About 36 minutes after the altitude change to 27,000 feet, the pilot advised air traffic control (ATC) that he had lost cabin pressurization and needed an immediate descent. About 20 seconds later he was cleared to 25,000 feet, then 15 seconds later to 15,000 feet. Shortly after the pilot acknowledged the lower altitudes, the radio communications deteriorated to microphone clicks with no carrier. The aircraft started a shallow descent with slight heading changes, then was observed to make a rapid descent into desert terrain. About 10 months prior to the accident the aircraft had been inspected in accordance with the Piper Cheyenne Progressive Inspection 100-hour Cycle, event No. 1. According to the servicing agency, the aircraft inspection was completed and the aircraft was returned to service with a 12,500 feet MSL altitude restriction due to unresolved oxygen system issues. The last oxygen bottle hydrostatic check noted on the bottle was October 1989. The oxygen system was in need of required maintenance and the masks were in a rotted condition. The pilot failed to report his severe coronary artery disease condition, medications, and other conditions to his FAA medical examiner for the required flight physical.

The flight was on a practice nondirectional beacon (NDB) approach to Great Falls runway 34 in visual conditions. Abeam the final approach fix, the aircraft was 4 miles right of course. Upon being advised of this by ATC, the pilot corrected back to final with a 60-degree intercept angle, rolling out on course 3 miles from the runway. When the pilot called missed approach, the local controller (a trainee) instructed the pilot to make a 360-degree right turn to enter right downwind for runway 3, and the pilot acknowledged. The controller trainee then amended this instruction to a 180-degree right turn to enter right downwind for runway 21, then to a 180- degree right turn to enter right downwind for runway 3. The crew did not acknowledge the amended instruction. Controllers then observed the airplane had crashed. Witnesses reported the airplane entered a steep descent from a right turn and impacted the ground at a steep angle. The flight was described as recurrent training required by the owner's insurance; however, the second aircraft occupant's airline transport pilot and flight instructor certificates had been revoked, and he held only a private pilot certificate. Investigators found no evidence of aircraft malfunctions.

The pilot, sole on board, was descending to Paris-Orly in poor weather conditions when he informed ATC about control problems. The twin engine aircraft entered an uncontrolled descent and crashed in a field. The pilot was killed.

During an attempted takeoff, the airplane collided with a taxiway sign, a fence, a light pole and came to rest between two buildings. According to the pilot in command (seated in the right seat), a preflight and run-up inspection was completed successfully. He stated that a pilot rated passenger (in the left front seat) was following along with a placard checklist. He stated that the airplane was accelerated for takeoff on runway 7, and at 500 feet down the 2700 foot long runway with the airspeed at redline, rotation was initiated and the airplane veered to the right. He stated that shortly thereafter the right engine surged and he noted the matched power levers, but he did not record the engine power instruments. A passenger (seated in a forward facing seat behind the pilot in command) reported that the pilot rated passenger's hand was on the throttle(yellow-knobbed handles) at the time of the accident The reported visibility was 1/8 mile in fog. The prescribed takeoff minimums for that airport is 400 feet and 1 mile visibility. Post accident examination of the engines and their systems revealed no evidence of preimpact mechanical malfunction. The pilot reported that there was no mechanical malfunction.

After the completion of scheduled maintenance and a normal ground run up, the airplane departed the airport for a local test flight. Witnesses observed the airplane in a nose high attitude, turn to the left, and then saw the nose drop toward the ground approximately 1 1/2 miles from the departure end of the runway. The airplane impacted hilly terrain and was consumed by a post impact fire. Detailed examination of the airframe, engines, and propellers revealed no defects or anomalies that would have contributed to the accident.

While descending to Arequipa-Alfredo Rodríguez Ballón Airport, the crew encountered poor weather conditions when the twin engine aircraft struck the slope of Mt Chachani located about 17 km north of the airport. The aircraft disintegrated on impact and all five occupants were killed.

The twin engine aircraft was completing a liaison flight from Campo de Mayo AFB in Buenos Aires and General Villegas. On approach to General Villegas Airport, the crew encountered very bad weather conditions with thunderstorm activity, heavy rain falls and turbulences. Control was lost and the aircraft crashed few km from the airfield, killing all four occupants. The aircraft had the dual registration GN-705 and LV-OIF (civil).