What happened
On the evening of August 30, 2002, a Boeing 747-419, registered as ZK-NBS, departed Auckland International Airport for Los Angeles. The flight, operating as NZ 2, carried 355 passengers and 17 crew members. Shortly after takeoff from runway 23, while the aircraft was performing a left turn at night with flaps set to the takeoff position, a portion of the right inboard trailing edge fore flap detached from the airframe.
During the separation event, the flight crew did not observe any warning lights or cockpit indications of a malfunction. The pilots noted only minor vibrations, which they attributed to turbulence. The structural failure remained undetected for the duration of the 12-hour flight. The crew only became aware of the missing flap component during the approach to Los Angeles when they attempted to select the flaps for landing. Upon discovering the issue, the pilots executed a go-around procedure and subsequently landed the aircraft safely. There were no injuries reported.
The investigation
Investigators focused on the mechanical failure of the flap assembly. The inquiry established that the separation was caused by the failure of an inboard attachment link. Detailed examination revealed that a stress corrosion crack had developed within this link. This crack had progressed to a critical size, likely over a relatively short duration.
While the operator had been performing routine inspections of the flap assembly in accordance with the manufacturer's requirements, the investigation found that the specific crack and its subsequent growth were not detectable through the established inspection protocols.