What happened
During the climb to cruise altitude, the crew of a McDonnell Douglas DC-8 cargo airplane retracted the landing gear. Following the retraction, the crew notified Air Traffic Control that the landing gear had failed to retract properly.
While the crew attempted to verify that the landing gear was in the down and locked position, a loud bang was heard. Simultaneously, a resident of a nearby single-family home reported that a metal object had penetrated her roof and become embedded in the floor. The aircraft subsequently returned to land without any further incidents; there were no injuries or fatalities reported.
The investigation
An on-scene investigation determined that the right main landing gear retract pin had separated from the landing gear leg. Investigators found that portions of the gear leg retract pin boss area had also separated and were wedged alongside the gear assembly.
A metallurgical examination revealed that the pin boss area contained metal fracture features consistent with an overload. One of these features was identified as being consistent with a pre-existing fracture area. The investigation further discovered that the pin boss area had been previously over-bored and chrome plated before the aircraft returned to service. According to the aircraft manufacturer, the pin boss bore should not undergo chrome plating.