Incident Overview
The crew of KLM Flight 867 was advised before takeoff of a volcanic eruption located approximately 100 miles southwest of the destination. During the en route phase, the flight received notification of another eruption. As the flight prepared for arrival, it was cleared to descend from flight level 390 at the pilot's discretion. Air traffic control provided vectors to avoid the last known area of the ash cloud.
Ash Cloud Encounter
While descending through flight level 260, the aircraft encountered an ash cloud. Ash and smoke entered the cockpit and passenger cabin. The crew donned oxygen masks and applied maximum power to climb. One minute later, all engines lost power, with rotational speeds dropping to 28-30% RPM. The aircraft experienced an interruption of electrical power, loss of airspeed indication, and a fire warning alarm for the forward cargo area.
Engine Restart and Landing
After 8 to 9 restart attempts and a descent to 13,300 feet, all engines were successfully restarted. The flight continued to a safe landing.
Aircraft Damage
Inspection revealed damage to the external surfaces of the aircraft and to the high-pressure turbines of all engines.
Additional Information
The Boeing 747-B2-4 had been advised to avoid volcanic activity. In the event of an encounter, retarding thrust to idle was recommended to reduce buildup in the engine and improve stall margin. ATC radar could only detect volcanic ash for 5 to 10 minutes after an eruption, and aircraft radar was not designed for ash detection. The ash cloud was forecast to move north-northeast at 60 knots, but satellite data later showed it moved at approximately 120 knots. KLM had no established procedure for a 747 encounter with an ash cloud, and no additional instructions were given to KLM crews.