Executive summary
On Friday 30 August 2002 at 2120, ZK-NBS (flight NZ 2), a Boeing 747-419, took off from runway 23 at Auckland International Airport for Los Angeles. On board were 355 passengers and 17 crew, including 3 pilots on duty in the cockpit.
During a left turn shortly after departure at night, with the flaps still extended to the take-off setting, about 70% of the right inboard trailing edge fore flap separated from the aircraft. The pilots did not receive any cockpit indications of anything untoward and only felt some slight bumps they thought to be from turbulence. The crew were unaware of the separation until the landing approach at Los Angeles some 12 hours later, when the flaps were selected for landing. The pilots took the appropriate action and carried out a go around procedure. The aircraft was repositioned for a further approach and landed safely. The safety of the aircraft and its occupants was not compromised by the incident. No one was injured.
The flap separated because its inboard attachment link failed. The link failed because a pre existing stress corrosion crack had grown to a critical size, probably in a short period of time. The operator had inspected the flap assembly routinely and specifically as the aircraft manufacturer required, but neither the start of the crack nor its growth could be detected during those inspections.
A safety issue identified was the design adequacy of the fore flap attachment links. The aircraft manufacturer has completed a design change to overcome the limitations of the links.