Cessna P210 N4769K accident near Daggett, California

Probable cause

The pilot’s failure to detect the tripped alternator circuit breaker in flight, which resulted in a drained battery that prevented the landing gear from fully extending to the down-and-locked position. Contributing to the accident was the improperly installed hardware on the landing gear extension handle, which prevented the extension of the handle and operation of the system.

NTSB analysis

The pilot reported that during the flight the primary flight display started to flicker and did not read correctly. While he attempted to troubleshoot the problem, the radio and transponder shut off. He attempted to call air traffic control (ATC), and he set the transponder to 7600 but soon realized that the radios and transponder were not working. The pilot then positioned the landing gear handle to the down position and confirmed from the landing gear inspection mirror that the nose landing gear was down and locked, but the main gear had stopped in a transient position. The pilot reported that he attempted to use the emergency extension handle but was unsuccessful. The pilot landed with the main landing gear in the transient position, resulting in substantial damage to the left horizontal stabilizer and elevator.

During the postaccident examination with the airplane on jacks, turning the master switch to On immediately actuated the landing gear pump, moving the landing gear into the down-and-locked position. It is likely that the resting battery had enough electrical power to run the landing gear pump. The airplane was positioned on the ground and the battery was soon out of power. The airplane was set up for an engine test run and the mechanic found the alternator main circuit breaker had been opened. It is likely that the breaker opened before or during the accident flight, which prevented the alternator from charging the battery. Without a charge from the alternator, the avionics would have drained the battery and prevented the full operation of the landing gear hydraulic system. After the mechanic reset the breaker and then turned on the split-rocker master switch, voltage was observed. The engine started normally and charge was observed on the ammeter gauge. With the engine running at about 1,700 revolutions per minute (RPM) the voltmeter read 28.5 to 28.8 volts direct current (VDC) with all lights and avionics working normally. During the test run there were no shorts to ground or defects noted. The mechanic could not duplicate the tripping of the alternator breaker.

During the postaccident examination, the landing gear emergency extension pump handle could not be extended from its retracted and stowed position. When the screw attaching the inner handle retaining spring was backed out, the inner handle extended normally. It is likely that incorrect hardware was used during maintenance, which prevented the handle from extending during the accident flight.

Text from the NTSB. Open the NTSB docket for WPR24LA157 for the full record.