PIPER PA46 near Seattle, WA — 2016-06-02

Probable cause

The pilot’s failure to use the emergency procedures checklist for generator failures or for gear extension following a loss of electrical power due to the separated flag terminal of a diode in overstress, which resulted in a gear-up landing.

NTSB narrative

The pilot departed in dark night conditions for the cross-country flight. While air traffic control vectored the accident airplane for the instrument approach to the destination airport, both of the airplane’s generator circuit breakers popped out, but the pilot did not observe a generator failure light. He subsequently pushed both circuit breakers in and they remained in. Shortly thereafter, when given the final vector to join the localizer, the instrument panel went dark, and all post lights, backlit gauges, and engine instrument gauges went dark and failed. The failure also affected the three green landing gear down-and-locked lights and the landing gear warning horn. According to the pilot, it was too dark to see the position of all the circuit breakers; rather than troubleshooting the problem in the air, he elected to proceed with the instrument approach. The pilot subsequently landed with the landing gear retracted, which resulted in substantial damage to the undercarriage and the left wing. A postaccident examination revealed that a diode located between the left main electrical bus circuit breaker and the main bus was found to have a separated flag terminal, which caused an open circuit. As a result, it is likely that before the accident, the left tie bus and main bus circuit was not providing a conductive electrical path, which required the right tie bus and main bus circuit to carry the full load. When the right main electrical bus circuit breaker tripped due to an excessive electrical load, the electrical path from the tie bus to the main bus no longer provided power. Subsequent testing of the subject diode revealed that the solder joint had failed in overstress though the diode itself was functional. The pilot reported that he did not refer to or use the airplane's emergency procedures checklist for a generator failure, which directs the pilot to reduce electrical loads in the event of such a failure. Depending on how much the electrical load was reduced, the pilot may have prevented the right main circuit breaker failure and retained the ability to lower the landing gear. Additionally, the pilot failed to use the emergency landing gear extension procedure. The generator failure emergency procedures checklist contains a CAUTION that states, "Without electrical power, the landing gear must be lowered with the emergency extension procedure. The gear position lights, and the flaps will be inoperative." Had the pilot used the checklists for a generator failure and, subsequently, for gear extension, this accident would have likely been prevented.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Pilot did not use emergency procedures checklist for gear extension.

NTSB coding

• Electrical system malf/failure · Approach-IFR initial approach
• Checklist Use

Evidence available

• Photos
• 9 docket documents

Docket documents9

• JetPROP Service Information Letter No. 16-360-01 90-Amp Generator Circuit Breaker Upgradeform
• Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1form
• Release of Aircraft Wreckage, NTSB Form 6120.15form
• Record of Interview with Pilotinterview
• Checklists for PA46-350Pother
• Electrical Schematicsother
• Photos of damage to airplanephotos
• Duncan Aviation Examination Reportreport
• Systems Specialist Reportreport

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