Volcanic Ash and Jet Engines: What Actually Happens
British Airways Flight 9 wasn't a drill. It was a four-engine wide-body flying through something that shouldn't have been there, and what happened next changed how the aviation industry treats volcanic ash for decades. The aircraft, a Boeing 747-200, was cruising at about 35,000 feet on a flight from Auckland to Perth when the crew encountered an ash cloud from the eruption of Mount Galunggung in Indonesia. The pilots initially thought it was light snow. That was their first mistake, though honestly, anyone would have made the same call. Volcanic ash is not ice crystals. It's pulverized rock, mineral particles, and glass fragments, often sub-micron in size. When it gets sucked into a jet engine, the inside the combustion chamber — roughly 1,400 to 1,700 degrees Celsius — melts the silica in the ash. The molten particles stick to the turbine blades and nozzle guide vanes, changing their aerodynamic profile. That's called deposition. Within seconds, you lose airflow through the engine. The engine can't maintain pressure ratios. It flames out.
The Day The Sky Fell British Airways Flight 9 And The Terrifying Truth Of Volcanic Ash
All four engines on BA9 suffered the same fate. The crew lost thrust from engines one, two, three, and four. The aircraft went from a powered jetliner to a glider with a wingspan of 64.4 meters. Captain Eric Moody, who had 17,000 flying hours, immediately declared an emergency and started the descent. The plane dropped from 35,000 feet to 15,000 feet in a controlled glide. At that altitude, the engines were clear of the ash cloud, and the cooler air allowed the melted deposits to cool and harden — sometimes breaking free on their own, sometimes not. Two of the four engines restarted. All four eventually came back online as they descended further into clearer air. There were no fatalities. Everyone on board survived. But the aircraft was damaged. Windshields were sandblasted to opacity. Pitot tubes were clogged. Engine cores had ingested thousands of kilograms of ash. The repair bill was significant, and the aircraft was grounded for weeks. What most people don't understand is that the real danger isn't just the ash cloud itself. It's the fact that ash clouds are nearly invisible to pilots at night or in darkness, they don't trigger any onboard weather radar, and commercial radar systems simply reflect off moisture. Dry volcanic ash doesn't show up. You're flying blind into something that can kill all your engines in under two minutes.
How the Industry Responded After BA9
Before 1982, there was virtually no coordination between meteorological services, volcanic observatories, and aviation authorities when it came to ash threats. After BA9, the International Civil Aviation Organization (ICAO) pushed for the creation of Volcanic Ash Advisory Centers (VAACs). There are now nine of them worldwide, each responsible for a specific region. They monitor volcanic activity, track ash dispersion using satellite data and atmospheric modeling, and issue advisories that filter through to flight dispatchers and air traffic control. The color-coded alert system — green, yellow, orange, red — was standardized. Green means no volcanic activity. Yellow means an eruption is occurring or suspected, and ash clouds are forming. Orange means a significant eruption is underway with ash clouds reaching altitudes relevant to flight levels. Red means a major eruption with ash clouds at high flight levels and significant disruption expected. It's not perfect, but it's better than nothing. Engine manufacturers also redesigned certification requirements. Modern high-bypass turbofans are tested against ash ingestion to a degree that didn't exist before the early 1980s. The test involves running an engine in a chamber filled with synthetic ash particles at specific concentrations and particle sizes, then measuring performance degradation. The goal isn't to prove the engine can fly through an ash cloud — no engine can guarantee that. The goal is to define thresholds where the engine loses thrust predictably rather than catastrophically.
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What Pilots Are Told to Do Today
If you receive a volcanic ash advisory, the recommended action is simple: avoid the cloud entirely. Commercial aviation operates on the principle that prevention beats recovery. You don't try to fly through ash. You go around. The problem is that ash clouds can spread over thousands of square kilometers and drift with upper-level winds. A single eruption can close an entire airspace for days, as happened with Eyjafjallajökull in 2010, which grounded over 100,000 flights across Europe and cost the industry an estimated 1.3 to 1.6 billion euros. For the rare case where a pilot ends up in an ash cloud despite best efforts, the procedure is straightforward. Full thrust on remaining engines if any are still operating. Descend quickly to escape the ash layer — the idea is that the ash concentration drops at lower altitudes. Don't attempt to restart an engine until you're below the ash cloud because the hot engine components can remelt fresh ash and cause further damage. This is counter-intuitive for pilots trained in standard engine-out procedures where you attempt an immediate windmill or starter-assisted restart. I worked with a dispatch team that had to reroute a freighter around an unexpected ash plume from a eruption in the Kamchatka peninsula. The VAAC had issued an advisory, but the model output lagged behind the actual satellite imagery by about three hours. By the time our route options were calculated, the cloud had shifted east and a second flight was already sitting on the tarmac in Anchorage wondering if they should fuel up or wait. We ended up routing them through a corridor that added 47 nautical miles and eight minutes of flight time. Not glamorous, but it kept everyone out of trouble.
The Limitations Nobody Talks About
VAACs are good, but they're not omniscient. The advisory centers rely on satellite data, and not all satellites have the spectral resolution to distinguish volcanic ash from regular cloud cover, especially in the initial hours of an eruption. There's also the problem of low-level eruptions. A small eruption that only reaches 10,000 to 15,000 feet might not be detected until it's already drifting into a busy air corridor. The systems work best for large, sustained eruptions that send ash high into the stratosphere. Those are the ones that get global attention. The smaller, more frequent eruptions are the ones that create the narrow escape moments. Another issue is that the color-coded system, while useful for quick communication, lacks granularity. An orange alert and a red alert might both describe the same ash cloud at the same altitude, but one signals "significant disruption expected" while the other says "ash clouds reaching flight levels." In practice, the difference between orange and red often comes down to political and economic pressure rather than pure meteorological assessment. Airports close earlier and longer than the science strictly warrants because the liability risk of an incident outweighs the cost of a premature closure. That's understandable, but it means the system errs on the side of overreaction, which is fine for safety but terrible for efficiency. The hardest truth is that no amount of technology removes the fundamental risk. You can have the best VAAC coverage, the most advanced satellite detection, and engines certified to ash ingestion standards, and you can still end up in a cloud you didn't know was there. The 1989 KLM flight that encountered ash from Mount Redoubt in Alaska is another example. The crew saw nothing on radar. They only realized what was happening when the engines started flaring. They descended, restarted the engines, and landed safely. Two more examples. Same pattern. Different aircraft, different century, same underlying problem.
BA Flight 9 proved that a gliding 390-ton aircraft could be controlled and landed with all four engines dead. It also proved that the atmosphere around an active volcano is a place where commercial aviation simply wasn't designed to operate. The systems we have today exist because of that flight. They're imperfect, they have gaps, and they won't prevent every encounter. But they're the reason no one has repeated the BA9 scenario with the same outcome since 1982.
