PIPER PA 34-200T — Flagstaff, AZ

What happened

The airline transport pilot regularly used his twin-engine airplane to conduct volunteer flights for a non-profit organization dedicated to transporting medical cargo. On the day of the accident, he departed his home airport about 0945, made a planned interim stop at one airport, and then flew to a second airport, where he waited for his next cargo pickup. The cargo was delivered to him, as scheduled, about 2100, and he departed shortly thereafter on a night visual flight rules (VFR) cross-country flight. The air traffic control tower was closed at the time of the pilot's departure. The airport was situated in semi-rural, mountainous terrain, and both the sun and the moon had set about 2 hours before takeoff.

Ground-based tracking radar data indicated that the airplane departed to the southwest, turned west, then south, and then north before it descended rapidly and impacted trees and terrain about 2.5 minutes after takeoff. The first segment of the radar-derived trajectory was consistent with a normal takeoff and initial climb. About 1 minute after takeoff, some undetermined occurrence(s) or circumstance(s) interrupted the climb and resulted in the course deviations and the extreme descent.

Examination of the accident site indicated that the airplane was in a banked attitude when it impacted the trees. The available evidence indicated that both engines were developing significant power at impact, and that the propellers were operating normally. No evidence of a bird strike or an in-flight fire was observed. With the exception that one of the two instrument air pressure pumps were inoperative, the investigation did not discover evidence of any pre-impact mechanical deficiencies with the airplane or its equipment. However, the wreckage was highly fragmented, which could have masked or destroyed such evidence.

The artificial horizon and the directional gyro were two of the flight instruments that were driven by the air pressure pumps. Although the two air pressure pumps and associated valving were designed to provide automatic continued normal system operation in the event of a single air pressure pump failure, the severity of the damage precluded determination of the pre-accident functionality of the instrument air system. Therefore, it is possible that a failure of the valving system could have resulted in the loss of valid artificial horizon and directional gyro information, which in turn, due to the dark night and scarcity of ground lights, could have resulted in the accident.

Damage also precluded testing of the autopilot system. However, the pilot typically hand-flew the airplane to cruise altitude before engaging the autopilot; therefore, the accident was likely not due to an autopilot malfunction.

Although the departure airport automated weather observation reported 10 miles visibility with no clouds less than 10,000 ft above the airport, the heavy rain earlier in the day, combined with nighttime cooling and the lack of a temperature-dew point spread, suggested the potential for localized low altitude clouds or fog.

Given the dark night and the lack of significant ground lighting, pilot disorientation for a variety of reasons could not be discounted. The most likely possible reasons included:

- Distraction from some unknown event inside or outside the airplane

- Malfunction or failure of one or more flight instruments

- Inadvertent encounter with localized instrument meteorological conditions

The medical investigation of the pilot was significantly limited by the degree of injury, and it could not be determined whether the pilot experienced an acute medical event during the flight. Due to the pilot's age, his reported pre-existing medical conditions, and the paucity of autopsy findings, physiological impairment or incapacitation of the pilot could not be eliminated as a possible reason for the accident. Because it has no direct psychoactive effects, it is unlikely that the pilot's use of metoprolol contributed to the accident. The absence of ethanol in the kidney tissue indicates that the identified ethanol in muscle tissue was from post-mortem sources, and therefore did not contribute to the accident.

Although the pilot was the president of the organization for which he was flying, and that the organization published flight operations guidance intended to ensure a minimum level of operational safety, the pilot's history demonstrated repeated deviations from that guidance. One of those deviations concerned the number of pilots on board. On the accident flight, as well as on most of his other night missions for the organization, the pilot flew solo, even though the guidance recommended that night flights use two pilots. Although the investigation was unable to determine the specific reason for the accident, it is possible that a second pilot might have been able to assist in some way to prevent the accident.

An editorial "what led to it / how to avoid it" analysis for this accident is generated separately and will appear here.