Cessna 210 N9540T accident near Chino, California

Probable cause

The failure of the engine-driven hydraulic pump, which resulted in the main landing gear not fully extending and locking into place during landing. Contributing to the accident was the failure of the emergency gear extension system for reasons that could not be determined.

NTSB analysis

The pilot reported that the accident flight was the first flight since the airplane had undergone recent landing gear maintenance. While in the airport traffic pattern, he extended the landing gear; however, he noticed that it would not lock into the down position. Despite multiple attempts to cycle the landing gear, which included using the emergency landing gear extension procedure, he was unable to obtain a positive down and locked indication. While landing, both main landing gear collapsed and the left wing and left horizontal stabilizer impacted the runway surface, which resulted in substantial damage to the left elevator and horizontal stabilizer.

Postaccident examination of the airplane revealed that the engine-driven hydraulic pump was not operational. No mechanical damage was observed within the engine’s accessory case. No evidence of any preexisting mechanical malfunction was observed with the airframe or emergency gear extension system. Examination of the engine-driven hydraulic pump revealed a torn section of an oil seal that surrounded the pump drive shaft. The oil seal was hard, brittle, and torn, which resulted in an oil leak that prevented the pump from holding pressure, which likely prevented the landing gear from fully extending and locking into place during landing. The reason for the emergency gear extension system not functioning could not be determined.

Text from the NTSB. Open the NTSB docket for WPR20LA288 for the full record.