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Flight crews should follow company approved procedures and manufacturers guidance, regarding the conduct of the flight and management of aircraft systems, in the event that the aircraft encounters volcanic ash clouds
This article considers some aspects of airmanship which are applicable generically to all aircraft and situations.
Routes should be planned laterally and vertically to take account of active eruption plumes and clouds of dispersing volcanic ash notified by appropriate meteorological information, for example SIGMET charts. Other planning considerations include allowances for additional route fuel and allowances in the crew rest schedule. Night flights in regions known for regular explosive volcanic activity should be undertaken with especially careful pre flight planning because of the possibility that dangerous ash plumes, from new eruptions which have not yet been detected and notified, could be encountered.
Note that weather radar cannot detect the small particle sizes of which ash clouds are composed.
A combination of some of the following will occur if a significant concentration of volcanic ash is encountered:
On 24 June 1982, a Boeing 747-200 had just passed Jakarta at FL370 in night VMC when it unknowingly entered an ash cloud from a recently begun new eruption of nearby Mount Galunggung which the crew were unaware of. All engines failed in quick succession and a MAYDAY was declared. Involuntary descent began and a provisional diversion back to Jakarta, which would necessitate successful engine restarts to clear mountainous terrain en-route was commenced. Once clear of cloud with three successful engines restarts and level at FL120, the diversion plan was confirmed and completed with a visual approach from the overhead.
On 15 December 1989, a Boeing 747-400 positioning for a planned en-route stop at Anchorage with crew awareness of a significant volcanic eruption in progress some 150 nm upwind entered volcanic ash during descent north northeast of the airport. When an attempt to climb out of the ash using full thrust was made, all engines failed. After repeated and eventually successful engine restart attempts as a 13,000 feet loss of altitude occurred, the fight was completed. The Report of the comprehensive NTSB Investigation remains unpublished with only a brief factual report containing neither Safety Recommendations nor Safety Actions issued.
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