Volcanic eruptions that expel volcanic ash into the atmosphere are actually expelling gas and bits of volcanic glass and pulverized rock. This gas, glass and rock can be invisible to the naked eye, yet can be in enough concentration to wreak havoc on jet engines, enter the cabins of aircraft to choke the people inside, and can come as a total surprise.
The famous “Jakarta Incident” of June 24, 1982 was a surprising event. Inititally, there was no visible reason for all of British Airways Flight 9 engines to go into a string of sudden surges, flameouts and eventual failures. Mount Gallunggung, 110 miles away, had erupted, but the only indicators were increasingly sulphurous smoke in the cabin and an effect upon the windscreen that was similar to “St Elmo’s fire”.
There were no indications of any atmospheric phenomenon on radar, which only detected wet substance. Volcanic ash is dry, and did not register.
On 15 December, 1989, KLM Flight 867 had multiple engine failure when flying through the ash cloud from the Mount Redoubt volcanic eruption, making aircraft and ash a bad combination that is nothing new.
When considering the process of jet propulsion, the problems that are created by volcanic ash that interferes with the combustion cycle become quite clear. First, there is an enormous amount of air that is taken in, then there is compression, followed by injection of highly volatile fuel into the compressed air. Next is the ignition of the fuel, followed by the ejection of the vastly compressed and heated air, which thrusts the attached body of the aircraft forward.
An old joke summarizes the process as “suck, squeeze, pow!, boom!”
This process is made possible by incredibly engineered and finely tuned sets of both stationary vanes and sets of super fast rotating blades.
Incredible amounts of heat are generated in jet engine combustion. This heat melts the particles of rock and volcanic glass which will collect and fuse to various parts of the engine, especially the parts of the rotating masses. The rock melts at about 1,100° F. The heat in a jet engine commonly reaches at least 1,400° F. To add to the problem, jet engines are set up to increase power when they develop a failure cascade, which ramps up the compression and heat to melt and fuse more melted rock to the engine parts.
The ash can deplete oxygen, which is a major component of the fuel/air mix in jet engines. Engine temperature sensors can fail or be tricked into giving false readings. Simple clogging at the air compression stage by a large volume of ash can cause flameouts or stalling due to not enough air getting through.
The rotating masses have “blades” that are hollow and finely balanced. The hollows can fill with ash and cause the blades to become overheated or out of balance, resulting blade failures that are incredibly dangerous, given the rate at which those huge blades whack around. In a catastrophic blade failure, the huge blades can crash into each other, break apart and go slicing through the parts of the aircraft in many directions and at very high speed.
Volcanic ash creates more problems. The aircraft windshield can be turned opaque, thanks to a micro-sandblasting effect that only can occur at high speed and with fine particles of jagged rock and glass. This blinds the pilots and can even jeopardize the aircraft’s landing rights.
Other systems are in jeopardy. The pitot tube speed indicator systems, radio systems, cabin air quality, and even the essential health of the essential crew can be jeopardized by the volcanic ash that seems to get in everywhere.
All of these hazards, plus the real events that served as warnings, serve as sound reason for the extensive shutdown of flights that were anywhere near the path of the material from Icelandic volcanic ash eruption.
Wikipedia, “British Airways, Flight 9”
