What happened
On 10 April 2004, a Boeing McDonnell Douglas MD-11, registration PH-KCG, was operating a scheduled passenger flight from Vancouver to Amsterdam Schiphol Airport. Approximately 46 minutes into the flight, the crew observed a level 1 alert indicating generator 1 had turned off. This was accompanied by a momentary blanking of all six cockpit display units and several brief alerts. The crew determined that a fault in the integrated drive generator #1 had likely caused a generator relay to open, but they decided to continue the flight as the aircraft's autoland capabilities remained intact.
During the approach phase, while passing 1500 feet on the instrument landing system, the aircraft experienced a more significant disruption. All six cockpit displays blanked for several seconds, causing the autopilot and autothrottle systems to disengage. The crew initiated a manual go-around at approximately 1200 feet. As the displays recovered, several alerts remained, including 'AC TIE 2 OFF', 'EMER PWR ON', and 'EPGS FAULT'. The crew could not find specific guidance for these alerts in the emergency checklists.
On a second approach, the crew encountered an unsafe gear warning despite hearing the mechanical sounds of gear extension. Suspecting an electrical indication error, they performed another go-around at 60 and initiated a third approach. After consulting with the airline, the crew re-selected the gear, which then showed a down and locked indication. The aircraft landed safely, though a further electrical disturbance occurred during taxi-in when starting the auxiliary power unit.
The investigation
The investigation focused on the electrical reconfiguration process of the MD-11. During an automatic approach, the electrical power control unit (EPCU) reconfigures the system to separate power sources for the flight control computers. The investigation examined the power relays responsible for these connections.
Findings
- Testing of two relays from the incident flight revealed several faulty contacts.
- The specific type of power relays used in the MD-11 fleet were found to be susceptible to contact point erosion, making them unreliable.
- The airline's relay test device was often unable to detect this specific type of contact degradation.
- The unsafe gear indication was determined to be a coincidence and not related to the electrical failures.
- A secondary electrical failure during taxi-in was attributed to a depleted aircraft battery.
Safety action
- The investigation highlighted that the MD-11 electrical system is vulnerable due to these unreliable power relays.
- The event demonstrated that existing emergency checklists did not provide effective solutions for the specific alerts presented during the electrical failures.