On November 29, 1991, a Piper PA-31-350 (registration N354AC) operated by Alpine Air, Inc. was involved in an aviation accident near Denver, CO. Investigators recorded the probable cause as: The left main landing gear down lock switch froze due to ice accumulation. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot performed a gear-up landing after being unable to confirm the left main landing gear was down and locked. Postaccident testing found ice had frozen the downlock switch. Icing conditions and up to 3 inches of ice were present on the aircraft.
Event Details
During the approach, the pilot could not obtain a gear-down-and-locked indication for the left main landing gear. The pilot subsequently elected to land with the landing gear retracted (gear-up landing). This resulted in substantial damage to the bottom of the fuselage.
Weather and Ice Conditions
At the time of the accident, weather conditions included icing, low ceilings, and low visibility. Prior to the accident, the pilot reported accumulations of moderate ice. Following the accident, ice accumulation of up to 3 inches was found on the aircraft.
Postaccident Findings
Postaccident tests revealed that the left main landing gear down lock switch had frozen due to an accumulation of ice. The freezing of the switch prevented the pilot from obtaining a positive down-and-locked indication.
Probable cause
The left main landing gear down lock switch froze due to ice accumulation.