B744, en-route, Alaska USA, 1989

Summary: 

On 15th December 1989, a KLM Boeing 747 encountered a Volcanic Ash cloud over Alaska, USA. the ingestion of ash led to compressor stall of all engines; the engines were subsequently relighted successfully and the aircraft landed safely.

Event Details
When: 
15/12/1989
Event Type: 
Day/Night: 
Day
Flight Conditions: 
IMC

18646

Flight Details
Operator: 
Type of Flight: 
Public Transport (Passenger)
Intended Destination: 
Actual Destination: 
Take-off Commenced: 
Yes
Flight Airborne: 
Yes
Flight Completed: 
No
Phase of Flight: 
Descent
Location
Approx.: 
near Mt. Redoubt, Alaska
LOC
Tag(s): 
Loss of Engine Power, Environmental Factors
WX
Tag(s): 
Volcanic Ash Effects
Outcome
Damage or injury: 
Yes
Non-aircraft damage: 
Yes
Non-occupant Casualties: 
No
Off Airport Landing: 
Yes
Ditching: 
Yes
Causal Factor Group(s)
Group(s): 
Aircraft Operation
Safety Recommendation(s)
Group(s): 
None Made
Investigation Type
Type: 
Independent

Description

On 15th December 1989, a KLM Boeing 747 encountered a Volcanic Ash cloud over Alaska, USA. the ingestion of ash led to compressor stall of all engines; the engines were subsequently relighted successfully and the aircraft landed safely.

Synopsis

During Descent through FL260 the aircraft flew into a volcanic ash cloud (the result of an eruption of Mount Redoubt). Ash and smoke entered the cockpit and the crew donned Oxygen masks and applied maximum power in an attempt to climb back out of the cloud. One minute later all 4 engines lost power, there was electrical power interruption, a loss of airspeed indication (caused by blocked pitot tubes), and a fire warning alarm for the forward cargo area (caused by the smoke rather than a fire). After 8 or 9 attempts and descent to 13,300 feet, the crew were able to restart the engines and the flight made a safe landing.

The NTSB determined the probable cause as:

"Inadvertent encounter with volcanic ash cloud, which resulted in damage from foreign material (foreign object) and subsequent compressor stalling of all engines. A factor related to the accident was: the lack of available information about the ash cloud to all personnel involved."

Effect of Volcanic Ash on Jet Engines

The following is taken from the proceedings of the First International Symposium on Volcanic Ash and Aviation Safety, 1991:

"Ingestion of volcanic ash by high performance turbofan engines at operating conditions melts glass shards and some of the minerals that make up the ash. Volcanic glass compositions can show wide variations and still be melted upon ingestion into the engine because of high engine operating temperatures. Operating temperatures must be lowered below the lowest melting temperature (c. 1,000 deg C for glass) to prevent melting of ingested volcanic ash. Reduction of engine operating conditions to idle settings (c. 600°C) will prevent melting of ingested volcanic ash", an interesting summary of earlier Alaskan aircraft events and a review of the precise ingestion effects on the GE engines in the KLM 744 - "The primary cause of engine thrust loss…was the accumulation of melted and resolidified ash on the stage- 1-turbine nozzle guide vanes. These deposits reduced the effective flow of air through the engine causing compressor stall. Reduction of thrust level while in an ash cloud significantly reduces the rate of engine-performance degradation"

Related Articles

Further Reading

NTSB

  • For further information on this particular incident, see the NTSB Accident Report which contains brief details of the event.

ICAO

US Geological Survey

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