Incident Description
A Boeing 737 was being towed for repositioning by maintenance personnel when the nose landing gear collapsed forward into the wheel well. The nose landing gear remained attached to the airplane by its primary trunnion support and upper drag brace.
Examination Findings
Metallurgical examination of the nose landing gear lower and upper drag braces, and lock brace, revealed no evidence of preexisting cracking, and that they failed due to overstress. Examination and testing of the nose landing gear steering components did not reveal any pre-incident malfunctions.
Maintenance and Manufacturer Response
The maintenance technician in the cockpit reported that he was "riding the brakes" at the time of the incident. The airplane maintenance manual stated that at a minimum, applying airplane brakes while towing the airplane could shear the towbar shear pins; however, there was no visible evidence on the ground that the airplane's brakes had been applied during the tow. After the incident, Boeing issued a service letter that discussed six previous reports of 737 nose landing gear collapse that occurred between 2004 to 2006 during pushback or towing. It also addressed current towbar design, and provided recommendations for operators intended to minimize the likelihood of nose gear damage or collapse during towing/pushback operations.