On November 21, 1999, a Cessna 210D (registration N3928Y) was involved in an aviation accident near Sheridan, WY. Investigators recorded the probable cause as: The partial failure of the engine driven hydraulic pump. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot experienced right main landing gear failure after failing to obtain a positive gear down indication. Postaccident inspection revealed hydraulic pump pressure was far below normal.
Incident Overview
The accident involved a general aviation aircraft on its first flight following an annual inspection. During the approach for landing, the pilot extended the landing gear handle but did not receive a positive gear lock light. The pilot then cycled the landing gear multiple times in an attempt to achieve a positive down-and-locked indication. He also attempted to manually pump the gear down, but still no positive indication was obtained. Despite the lack of a gear-down light, the pilot proceeded to land the airplane. During the landing roll, the right main landing gear collapsed.
Postaccident Findings
Examination of the engine-driven hydraulic pump after the accident revealed that its output pressure was only 200 pounds per square inch (psi). According to maintenance personnel who had worked on the airplane, the normal pump pressure output should have been 2,725 psi. The hydraulic pump was subsequently replaced, and afterward the landing gear cycled normally during ground testing.
Probable Cause
The source does not explicitly state a probable cause for the accident.