PIPER PA 32R-300 near McGrath, AK — 2016-11-21

Probable cause

The failure of the nose landing gear to extend and lock due to the failure of the alternator and reduced battery power due to the cold ambient temperature, which prohibited the electrically-driven hydraulic pump from supplying adequate hydraulic pressure to extend the nose landing gear. The cause of the left main landing gear collapse could not be determined, as there were no postaccident anomalies or malfunctions found when the landing gear was actuated following replacement of the alternator and battery.

NTSB narrative

The on-demand passenger flight was approaching its destination airport when the commercial pilot noted that the two main landing gear extended, but the nose landing gear did not extend and lock. The pilot diverted to a larger airport, where ground personnel verified that the nose landing gear was not down and locked even after the pilot completed the manual gear extension procedure. The pilot elected to land the airplane with the engine off, and he stated that the touchdown was uneventful. He held the airplane's nose off the runway for several hundred feet; the left main landing gear then collapsed and the nose wheel extended. The airplane slid about 200 ft before coming to rest. A witness reported that the touchdown was smooth and when the left main landing gear collapsed, the airplane gradually slowed to a stop on the runway. An examination of the airplane revealed that the alternator became inoperative during the flight, and, due to the cold temperatures, the battery was unable to accommodate the electrical load required by the system. In addition, the grease on the nosewheel was thick, which, combined with the cold temperatures, can increase its viscosity and reduce its effectiveness. Because the nose landing gear extends into the relative wind direction, it would be more difficult for it to extend and lock with the low battery power and increased viscosity of the grease. Further, because the landing gear was not in the "up" position when the emergency extension control was activated, the hydraulic fluid had already been released, thus rendering the emergency procedure ineffective. After landing and with a reduction in the relative wind, the gear was able to lock in place; however, the reason for the collapse of the left main landing gear could not be determined. When the alternator and battery were replaced, the airplane was placed on jacks and all three landing gear actuated as designed. A review of the passenger's injuries revealed that the fracture of the transverse process of L2 vertebrae was "age-indeterminate," which means that it could not be definitively determined when the injury occurred.

Analysis

Primary failure mode

Mechanical failure

First missed decision gate

Pilot could have opted for a go-around instead of landing with known gear issue.

NTSB coding

• Electrical system malf/failure · Enroute-descent

Evidence available

• Photos
• 5 docket documents

Docket documents5

• Passenger Statementinterview
• Pilot's Emailed Statementinterview
• Pilot's Statementinterview
• Witness Statementsinterview
• Photosphotos