Piper PA-30 N373JT accident near Roanoke, Texas

Probable cause

The pilot’s failure to follow the published emergency procedures to lower the landing gear following a loss of electrical power.

NTSB analysis

The pilot said he was on a cross-country flight and he noticed that the alternators were producing about 9 volts. He tried to troubleshoot the problem, and he switched the alternators off and on a “number” of times, but he was unable to get them to indicate more than 8 to 9 volts (the pilot used the term "alternator" and "generator" interchangeably in his statement). He said that he heard a “squeal” coming through the headset, and when the right alternator was switched off, the noise would stop. He said that he eventually lost radio communication capability while en route to his destination, and he diverted to an alternate airport. The pilot lowered the landing gear on the downwind leg, and he observed that the nose landing gear was extended by its reflection in the spinner. The landing roll was “normal” until the right main landing gear collapsed, and then the left main landing gear collapsed.

A postaccident examination of the landing gear did not disclose any evidence of a mechanical malfunction. The pilot reported that he lost all electrical power due to a loss of one or both alternators. It is likely that the right alternator failed, so when the pilot turned off the right failed alternator, the noise stopped; however, the left alternator could not put out enough voltage to power the radios and other electrical demands. By the time the gear was lowered, there was not enough power to lock the left and right main landing gears in place, so they both collapsed during the landing roll. Had the pilot realized that he had lost electrical power and followed the emergency checklist, he could have verified the locked status of the landing gear and followed the emergency landing gear procedures to extend the gear.

Text from the NTSB. Open the NTSB docket for CEN12LA204 for the full record.