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Volcanic Ash: Guidance for Flight Crews

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Article Information
Category: Weather Weather
Content source: SKYbrary About SKYbrary
Content control: Air Pilots About The Honourable Company of Air Pilots
WX
Tag(s) Volcanic Ash

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°C2,012 °F
    1,373.15 K
    2,471.67 °R
    ). 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

Related Articles

Further Reading

ICAO

Flight Safety Foundation

UK CAA

Airbus

Boeing

ALPA

Volcanic Ash

Volcanic Ash: An Aviation Hazard of Explosive Proportions.