On 24 June 1982, British Airways flight 9 was cruising at 37,000 feet over the Indian Ocean south of Java when all four engines failed one after another. The Boeing 747 had flown into an ash cloud from the erupting Mount Galunggung. Nobody aboard knew that, because volcanic ash does not show on weather radar and it was night.
What the crew could see
The first sign was St Elmo's fire — an electrical glow flickering along the windscreen and leading edges, unusual enough that the crew took notice. Then the cabin filled with a smell of sulphur and a haze that passengers initially took for smoke. Then the engines began surging and flaming out, one at a time, until all four were out.
A 747 at 37,000 feet with no engines glides. Captain Eric Moody, First Officer Roger Greaves and Flight Engineer Barry Townley-Freeman turned towards the coast and began working the restart drill while descending.
The announcement
Moody's message to the cabin has become the most quoted passenger announcement in aviation history: "Ladies and gentlemen, this is your captain speaking. We have a small problem. All four engines have stopped. We are doing our damnedest to get them going again. I trust you are not in too much distress."
It is quoted for its composure, but it is also a good example of what cabin communication is for: passengers who can see engines out and smell sulphur will invent something worse than the truth if nobody tells them the truth.
Why the engines restarted
Molten ash had been drawn into the engines, melted in the combustion chambers and solidified on the turbine blades, choking them. As the aircraft descended and the engines cooled, the glassy deposits cracked and broke away. Below about 13,000 feet the crew got three engines started, then the fourth. They climbed away and landed at Jakarta.
The windscreen had been sandblasted opaque by the ash. Moody landed effectively by looking through a narrow strip of less-damaged glass, with the runway lighting barely visible.
What changed
BA9, and a similar KLM encounter over Alaska in 1989, established volcanic ash as a category of hazard the industry had not been managing. The response was the creation of Volcanic Ash Advisory Centres — nine centres worldwide that track ash clouds and issue warnings to aviation, coordinated internationally.
Procedures for an ash encounter were written and are now trained: reduce thrust, turn back on the reciprocal heading, descend out of the cloud, and expect engine restarts to become possible as the deposits cool and shed.
The wider lesson stuck too. Ash is invisible to weather radar. The system that protects aircraft from it is not onboard equipment but ground-based observation and communication — which is why the 2010 Eyjafjallajökull eruption closed European airspace rather than being flown around.