BEECH V35B — Novato, CA

What happened

While en route to the destination airport on an instrument flight rules flight plan in dark night conditions, the instrument-rated private pilot declared an emergency, advised the air traffic controller that the engine was losing power, and stated that he needed to divert. The controller first issued instructions to an airport about 20 miles behind the airplane's position, then offered an airport about 14 miles abeam the airplane's position. The pilot initiated a turn to the first airport, then to the second airport, accordingly. During these transmissions, the controller referred to the positions of these airports as "radials" from the airplane, despite the pilot's repeated request for headings.

As the airplane maneuvered, it descended from its cruise altitude of 6,000 ft mean sea level (msl) to about 2,000 ft msl. The controller contacted the airplane and stated that it had descended below the minimum vectoring altitude for that area. About a minute later, the pilot stated that the engine had regained power, again asked for a heading to the diversion airport, then stated that he had "lost [the] compass." Over the next 3 minutes, the airplane climbed to about 3,100 ft msl before entering a gradual descent. The controller provided the pilot with vectors, and the pilot asked how far the airplane was from the airport. The controller first provided an incorrect distance of 7 miles, then corrected himself, stating the airplane was 9.7 miles from the airport. Shortly thereafter, the pilot asked whether the airport was under visual meteorological conditions, to which the controller replied, "affirmative." The pilot then stated that he was in the clouds and asked the controller if there were "any hills" between the airplane and the airport. The controller did not answer the pilot's question, but instead provided the current weather conditions at the airport. The last transmission from the accident airplane was the pilot stating, "one thousand feet," followed by a series of microphone clicks, indicating that the pilot may have been attempting to activate the airport's pilot-controlled lighting system.

The airplane impacted terrain at an elevation about 700 ft msl about 7 miles from the airport. Examination of the airplane indicated that the landing gear was extended at the time of impact. No mechanical malfunctions or anomalies were identified with the engine, airframe, or gyroscopic flight instruments that would have precluded normal operation; therefore, the investigation was unable to identify the reason for the pilot's reported loss of engine power and "lost compass." It is likely that, following the emergency declaration, the pilot began to shed tasks and became completely dependent on the controller for providing orientation. The inaccurate and varying communications from the controller, including the use of the word "radial" rather than "heading," could have contributed to a loss of situational awareness. Further, had the controller issued a safety alert to the pilot or provided him with the elevation of terrain located between the airplane and the airport, the pilot may have been able to take action to avoid the terrain.

Given the radar track of the airplane and the evidence that the landing gear was extended at the time of impact, it is likely that the pilot had configured the airplane for landing and elected to continue the airplane's descent in an attempt to locate the airport. However, despite the automated weather observation indicating the airport was experiencing visual meteorological conditions, witness accounts and additional sources of weather data indicated the presence of heavy fog in the vicinity of the accident site about the time of the accident. It is unlikely that the pilot was able to obtain visual contact with the ground or the airport environment, and descended into terrain as he attempted to do so.

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