On May 1, 1987, a Boeing 707-323C (registration N8404) was involved in an aviation accident near Oklahoma City, OK. Investigators recorded the probable cause as: The pilot's decision to taxi without confirming that the airstart unit was fully disconnected, following the ground signalman's departure from the immediate area. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
After engine start, ground personnel struggled to disconnect an airstart unit hose. The signalman left the crew's view to help, and the pilot taxied without confirmation, resulting in a collision with the starting unit that caused substantial damage to the aircraft's right wing.
What happened
Following the completion of engine start procedures, ground support personnel encountered difficulties in disconnecting the hose connected to the airstart unit. During this process, the ground signalman departed from the pilot's line of sight to assist other team members in their attempt to detach the equipment from the aircraft.
Assuming that all connections were secure and the area was clear for movement, the pilot initiated taxi operations without further visual confirmation from the ground crew. As the aircraft began to move forward, it collided with the airstart unit still attached or partially attached to the airframe. This collision resulted in substantial damage to the right wing of the aircraft.
The investigation
The investigation focused on the sequence of events during the post-start ground handling phase. Investigators examined the point of contact between the moving aircraft and the stationary airstart equipment. The physical evidence confirmed that the right wing sustained significant structural impact damage consistent with striking the starting unit.
Findings
Substantial damage to the aircraft's right wing caused by collision with the airstart unit
Ground signalman left the view of the crew to assist others in disconnecting the unit
Pilot assumed clearance and began taxi without verifying the status of the ground equipment
Difficulty experienced by ground personnel in disconnecting the airstart unit hose
Probable cause
The pilot's decision to taxi without confirming that the airstart unit was fully disconnected, following the ground signalman's departure from the immediate area.
