Northwest Airlines Flight 85 was a regularly scheduled international passenger flight between Detroit Metropolitan Wayne County Airport and Narita International Airport.
On 9 October 2002, the Boeing 747-451 experienced a lower rudder hardover due to metal fatigue.
The crew turned the Boeing 747-451 around and landed safely in Anchorage, Alaska.
The Boeing 747-451
The Boeing 747-451 involved was registered as N661US and was built by Boeing Co for flight testing as N401PW. The aircraft was delivered to Northwest Airlines on 8 December 1989.
Northwest Airlines Flight 85
The Boeing 747-451 departed Detroit Metropolitan Wayne County Airport at 14:30 EDT. The incident occurred at 21:40 EDT.
At the time of the incident, Jr Captain Frank Geib and F/O Mike Fagan had taken control of the aircraft. Senior Captain John Hanson and F/O David Smith were on rest break. The incident occurred at 35,000ft (FL350).
The Boeing 747-451 abruptly and unexpectedly banked 30-40 degrees to the left. Geib initially believed one of the left engines had failed. Hanson re-entered the cockpit and continued to fly with Fagan. Geib declared an emergency and began a diversion to Anchorage, Alaska.
Despite being in the communications dead zone, Northwest 85 contacted Northwest Airlines 19, who relayed the mayday message to Anchorage.
The captain of NWA85 reported none of the emergency procedures could correct the issue. The pilots contacted Northwest Airlines at Minneapolis St Paul area, but no solution for the bank came out.
The pilots used asymmetric engine thrust and the upper rudder to guide the aircraft to land at Anchorage, Alaska.
The NTSB (National Transportation Safety Board) as well as Boeing launched investigations into the incident.
The investigations found a fatigue crack in the power control module. The crack could not be visually found. The lower rudder control module's cast metal housing had broken. The end portion of the control module housing had separated from the main portion.
It was also theorised the Boeing 747-451's testing may have been too much for the aircraft to handle. N661US was a Boeing 747-451 tester aircraft, but was given to Northwest Airlines.
Boeing issued ASB 747-27A2397, dated 24 July 2003. The company recommended Boeing 747 operators conduct ultrasonic inspections of pertinent high-time lower and upper rudder power control modules.
The FAA published an NPRM making the ultrasound inspection mandatory on Boeing 747-451, 451D, 451F aircraft.