Volcanic Ash: Guidance for Flight Crews

Volcanic Ash: Guidance for Flight Crews

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General

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.

Avoidance

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.

Indications

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:

  • St Elmo's Fire caused by electrical discharges as small electrically charged rock particles impact the metal surface of the aircraft may be seen around the flight deck windscreens and on the leading edge of engine nacelles
  • a “search light” effect may be observable at the engine intakes - as if a light is shining from within the engines through the fan blades
  • the appearance of very fine dust haze within the cabin and the possible visible settlement of dust on surfaces.
  • an acrid electrical or sulphurous smell from the air conditioning system.
  • engine surges and power fluctuations especially when occurring on more than one engine. There is a possibility of engine flame out.
  • unexplained fluctuations or erroneous readings in Indicated Airspeed (IAS) on more than one displays, attributable to partial blockage of Pitot Tubes with ash.

Actions

  • Oxygen. Use of flight crew oxygen masks may be advisable if the dust and sulphurous smell is strong.
  • Reduce thrust. Engine core operating temperatures of jet engines must be reduced below the temperature at which silicate ash particles melt (around 1,100°C). Reduction of engine thrust to flight idle is the only reliable way of achieving this in the absence of more precise guidance. If this action is not taken at or before the first signs of engine malfunction then flame out is likely to follow if clear air cannot be regained.
  • Reverse track and /or descend. Clear air must be regained as soon as possible. Terrain permitting, a descending 180 degree turn is likely to be the fastest way out of the contaminated air. Under no circumstances should a climb be attempted as an escape option.
  • Prepare aircraft systems for recovery from potential engine failure. Follow company/manufacturer’s guidance which may include advice on increasing the flow of bleed air to improve engine stall margins, and operation of the Auxiliary Power Unit (APU) within Aircraft Flight Manual (AFM) limits to provide a source of bleed air and electrical power in the event of multiple engine failure.
  • Monitoring. The engines will need careful monitoring, particularly the Engine Exhaust Gas Temperature (EGT) which may climb dangerously if there is significant ash contamination in the engine. Monitor aircraft attitude and airspeed remembering that airspeed indications may become unreliable if blockage of the pitot-static system occurs. Good awareness of the Ground Speed and head/tail wind component can be useful to help spot if indicated trends are genuine or not.

Accidents and Incidents

B742, en-route, south southeast of Jakarta Indonesia, 1982

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 volcano, 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. 

B744, en-route, north of Anchorage AK USA, 1989

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.

Volcanic Ash (SKYclip)

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Volcanic Ash (SKYclip)

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Further Reading

ICAO

Flight Safety Foundation

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Airbus

Categories
Weather, Volcanic Ash, Aircraft Emergency & Unusual Situations, Guidance for Flight Crews

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