Historic Incidents

Photo of Clark Air Base, Philippines, June 10,1991 provided by FAA Aviation Safety Journal

Photo of the base on June 24, 1991, after the eruption of Pinatubo that occured on June 15,1991

In order to live well in the present we must look at our past, therefore it is important to note and understand the historical incidents of aircrafts entering ash clouds. These incidents have occurred at an alarming rate, there have been over 80 reports of aircrafts entering ash clouds in the past 20 years. By determining what the crew did correctly and incorrectly during the emergency it better enables advisory agencies to make recommendations if similar situations occur. Some of the volcanoes where aircrafts encountered ash are:
Gallunggung, Indonesia
Pinatubo, Phillipines
Sakurajima, Japan
Pacaya, Guatemala
Galeras, Columbia
Hudson and Lascar, Chile
Mt. Spurr, Alaska
Nyamuragira, Zaire
Sheveluch, Russia
Manam, Papua New Guinea
Redoubt, Alaska
Augustine, Alaska
Kluchychevskoi, Russia
It must be stressed that this is a small list of the incidents that have occured between aircrafts and ash clouds. For more information about the incidents consult your local library.
The incident at Redoubt volcano is one of the most famous and dramatic accounts of an airplane entering an ash cloud. The following excerpt, by Campbell, should provide you with an idea of the sense of confusion and panic that abounds during such an emergency.

Photo of KLM Flight path (heavy black line) provided by Casadevall

Redoubt volcano, near Anchorage Alaska, began erupting on December 14, 1989. On the following day, a 747-400 airplane powered by GE CF6-80C2 engines entered an ash cloud at 25,000 ft. and experienced flameouts on all four engines.

During descent to 25,000 ft., the airplane entered a thin layer of altostratus clouds when it suddenly became very dark outside. The crew also saw lighted particles (St. Elmo's fire) pass over the cockpit windshields. At the same time, brownish dust with a sulfurous smell entered the cockpit. The Captain commanded the Pilot flying to start climbing to attempt to get out of the volcanic ash. One minute into the high-power climb, all four engines flamed out. Due to the volcanic ash and dust in the cockpit. The crew donned oxygen masks.

The Pilot Flying noticed the airspeed descending, initially at a normal rate (given the airplane's altitude) but suddenly very fast. All airspeed indications were then lost due to volcanic dust contamination in the pitot system. At the same time, there was a stall warning and the stick shaker was activated with no signs of buffeting. The Pilot Flying rather firmly put the nose of the aircraft down to avoid a stall and initiated a turn to the left in a further attempt to get out of the volcanic ash.

The crew noticed a "Cargo Fire Forward" warning and deduced that the fire warning was caused by the volcanic ash, so no further action was taken.

As the engine spooled down, the generators tripped off and all instrument were lost except for instruments powered by the batteries.

During the time the engines were inoperative, the cabin pressure remained within limits and no passenger oxygen masks deployed. The crew elected not to deploy the masks because the passenger-oxygen-mask system would have been contaminated by volcanic dust in the cabin air.

An emergency was declared when the airplane passed through approximately 17,000 ft. The crew stated that total of seven or eight restart attempts were made before engines 1 and 2 finally restarted at approximately 17,200 ft. Initially, the crew maintained 13,000 ft. with engine 1 and 2 restarted, and, after several more attempts, engines 3 and 4 also restarted.

After passing abeam and east of Anchorage at 11,000 ft, the airplane was given radar vectors for a wide right-hand pattern to runway 06 and further descend to 2,000 ft. The Captain had the runway continuosly in sight during the approach; however, vision throught the windshields was impaired due to "sandblasting" from the volcanic ash in such a way that the Captain and the First Officer were only able to look forward with their heads positioned well to the side. Finally the airplane did land safely, but approximately 80 million dollars was spent to restore the plane, which included replacing four engines. The in-depth account of this incident helped researchers devise a procedure of what a crew should do when they encounter an ash cloud.

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