Cessna 172RG N9415B accident near Martinsburg, West Virginia

Probable cause

A hydraulic leak in the right main landing gear actuator, which resulted in the main landing gear not extending.

NTSB analysis

The flight instructor stated that he and the private pilot were about to make their seventh landing, but when the pilot extended the gear, the gear down-and-locked light did not illuminate. A visual check revealed that the nose gear was extended but the main gear was not fully extended. The flight instructor used the emergency gear handle to try and pump the main gear down, but there was insufficient hydraulic pressure in the system. The flight instructor landed the airplane with the nosewheel extended, but the airplane’s left wing dropped, which resulted in substantial damage to the left wing and the elevator. After exiting the airplane, hydraulic fluid was observed pooling under the airplane and along the side of the empennage. Postaccident examination of the airplane revealed that an O-ring inside the right gear actuator failed and was leaking hydraulic fluid. Because the landing gear is extended/retracted by hydraulic pressure, the leak likely prevented the system from having adequate pressure for the electric pump and the manual gear handle to extend the gear.

Text from the NTSB. Open the NTSB docket for ERA18LA067 for the full record.