On May 29, 2005, a Mooney M20K (registration N928MB) was involved in an aviation accident near Englewood, CO. Investigators recorded the probable cause as: the pilot's failure to maintain control of the airplane and the pilot's improper use of unusual attitude recovery procedure. Contributing factors were the failure of the HSI and the clouds. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot reported HSI failure in IMC leading to spatial disorientation, unusual attitude, loss of control, and overstress during recovery. A mechanic later found a stripped plastic gear in the HSI.
Event Description
According to the pilot, he was in instrument meteorological conditions and climbing to his cruise altitude when the horizontal situation indicator (HSI) failed. Following the failure, he became disoriented, the airplane entered an unusual attitude, and he lost control. When the airplane subsequently broke out of the clouds, it was descending rapidly. The pilot pulled back hard on the control yoke in an attempt to arrest the descent. During this recovery maneuver, the airplane's structural limitations were exceeded, resulting in overstress.
Maintenance Findings
In a telephone interview, a mechanic who replaced the HSI at Duncan Aviation, a repair shop located at APA, reported that a plastic gear in the HSI was "stripped" and that the heading bug caused the compass card to "hang-up."