Volcanic Ash — Operational Procedures

Volcanic ash is an acute hazard to flight safety — silicate microparticles that can be transported thousands of kilometres in the atmosphere. The 2010 Eyjafjallajökull eruption caused the largest European airspace closure since 1945.

Source: ICAO Doc 9974 Flight Safety and Volcanic Ash, ICAO Doc 9691 Manual on Volcanic Ash, Radioactive Material and Toxic Chemical Clouds. (Met aspects in Subject 050 lesson "SNOWTAM/ASHTAM/VAA".)

What happens during an ash encounter

Engine (main problem):

Ash particles melt at about 1100 °C (above combustion temperature).
Vitrification on turbine blades → altered aerodynamics, RPM drop.
Flameout possible within seconds to minutes.
After leaving the ash cloud: glass can flake off with cooling → restart possible.

Pitot/static: clogging → false speed/altitude indications.

Cockpit: sandblasting on windscreen → vision impairment to blindness.

Avionics: fine abrasive dust inside.

Fuselage: paint damage, antenna abrasion.

Real teaching cases

BA Flight 9 — 24 June 1982, Mount Galunggung (Indonesia)

B747-200 at FL370 over Java.
All 4 engines failed sequentially within about 13 min.
Crew initiated emergency descent from FL370 to FL120.
Outside the ash cloud: 3 of 4 engines restarted.
Emergency landing Jakarta-Halim with engine 4 failed again on final.
Source: UK AAIB final report.

KLM Flight 867 — 15 December 1989, Mount Redoubt (Alaska)

B747-400 in climb to Anchorage.
Ash cloud encounter at FL250.
All 4 engines failed → 4 min glide until restart.
Source: NTSB final report.

Both incidents: lucky outcomes, but taught ICAO that ash avoidance is absolutely mandatory.

Pilot procedure on suspected encounter

Immediate 180° turn away from ash cloud.
Reduce engine thrust, but keep engines warm (don't shut down in the cloud — makes restart harder).
Engine anti-ice ON (prevents ash deposition in inlet).
Cabin air OFF / recirculate (avoid ash ingress).
Oxygen masks (in case of pressure loss from filter blockage).
Mayday with position, ash concentration, altitude loss.
Descend as fast as possible to below-ash layers (typ. < FL100).
No restart in the cloud; restart attempts after leaving.

Pre-flight with VAA activity

Check Volcanic Ash Advisory (VAA) and SIGMET VA.
NOTAMs of the relevant FIR.
Planned route with wide deviation — rule of thumb: at least 50 NM lateral from ash cloud boundary.
Altitude choice: ash often in mid to high flight levels; VFR usually uncritical, but in major eruptions also < FL100 affected.
Alternate in ash-free region.

For PPL VFR

Rarely relevant — volcanoes in Central Europe seldom active.
During an eruption (e.g. Eyjafjallajökull 2010, La Soufrière 2021): VAA in briefing required.
With active ash in flight area: cancel flight, do not try to "go through quickly".