[Casadevall & Budding, in prep.]

Class

Criteria

0

Acrid odour [e.g. sulfur gas] noted in cabin
Electrostatic discharge [St Elmo’s fire] on windshield, nose, engine cowls
No notable damage to exterior or interior

1

Light dust in cabin; no oxygen used

2

Heavy cabin dust; "dark as night" in cabin
Contamination of air-handling systems requiring use of oxygen masks
Some abrasion damage to exterior surface of aircraft and engine inlet and compressor
Frosting of windows due to impact of ash
Minor plugging of pitot-static system; insufficient to affect instrument readings

3

Vibration of engines owing to mismatch; surging
Plugging of pitot-static system to give erroneous instrument readings
Contamination of engine oil hydraulic system fluids

4

Temporary engine failure requiring in-flight restart

5

Engine failure leading to crash

References

Casadevall T. J., and Budding K., in prep., Volcanic ash and aviation safety; database for encounters between aircraft and ash clouds, US Geol. Surv. Bull. 2XXX