NTSB Identification: IAD00LA002
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Thursday, October 28, 1999
Probable Cause Approval Date:
Loral Corp. GZ-22, registration:
Injuries: 1 Minor, 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The pilot of the fly-by-wire airship flew several traffic patterns and approaches from both the pilot and co-pilot stations. After he departed the traffic pattern and leveled the airship, it entered an uncommanded, descending left-hand turn. The control panel displayed no indication of a malfunction, and emergency and troubleshooting procedures failed to regain control of the airship. The airship landed in trees, and both the pilot and the technician on board escaped injury. Metallurgical examination of the actuators that convert electrical signals to mechanical flight control inputs revealed that the splined shafts on the output side of the starboard actuator were almost completely stripped, and provided no flight control input. The gear teeth of the splined shafts on the output side of the port actuator were worn to 25 percent of their original thickness, and did not provide full flight control input. Hardness testing revealed the output shafts of both the port and starboard actuators did not meet the manufacturer's specified hardness requirement. The manager of the airship fleet said the one-of-a-kind airship would not be rebuilt.
The National Transportation Safety Board determines the probable cause(s) of this
The failure of the flight control system manufacturer to meet design (hardness) specifications that resulted in stripped splines.