Orval Fairbairn wrote:

You can count on an early overhaul, at best. During the 1980s, several
turbine aircraft, including a B747, encountered ash clouds in flight.
The ash is so abrasive that it eroded the compressors to the point of
flameout. The B747 descended to ~10000 ft before they got three engines
relit.


June 24, 1982, a British Airways 747 over Java.

The ash cloud also sandblasted the windshield nearly opague.
The flight crew had great difficulty making out the approach and
runway lights to land the aircraft. If the incident had occurred
during daylight hours, they probably would not have been able
to see out at all.