Everyone remembers the great Volcanic eruption of 2010. The Icelandic volcano, Eyjafjallajökull made headlines not for its rarity or magnitude, but for the number of people who rued the day it was ever created. The relatively small volcanic eruption caused enormous disruption to air travel across western and northern Europe over an initial period of 6 days last April, but for travelers, those days felt like a lifetime. About 20 countries closed their airspace (a condition known as ATC Zero) and it affected hundreds of thousands of travellers who were left stranded in the wake of the volcano's ash cloud.
On June 6th 2011, it happened again, only this time in Chile. A volcano in the Puyehue-Cordon Caulle chain of south-central Chile erupted after lying dormant for more than 50 years, throwing ash more than 6 miles into the sky. Planes across South America were grounded by the ash and places as far away as Australia and New Zealand continue to experience ongoing flight cancellations.
The volcano is still effecting flights and it may for some time to come. Because the volcano and its ash are unpredictable, in many areas, it is unclear when passengers will be able to fly again.
So, why can't planes fly through ash? After all, planes fly through lightning storms, heavy fog, rain, snow and the occasional flock of geese and come out on the other side just fine.
The short answer?
You will literally fall out of the sky.
The long answer?
The problem is the tiny volcanic ash particles. They are extremely fine and if they get into a jet engine, it can block up the ventilation holes that let in cooling air. They accumulate, melt and form molten glass inside, causing damage and raising engine temperatures to almost 2,000 F (1,093 C) -that's lava in your jet engine, which can lead to the engine cutting out completely.
The ash particles also erode the body and windscreens of the plane, making it impossible for the pilot to see to direct the plane. Furthermore, the particles can clog the fuel system.
None of this is something you want to happen when cruising at 30,000 feet (9,150 meters).
Even if your plane does come out on the other side of the cloud, it would cost millions of dollars to repair, if it's not completely totaled already. This spells out bad news for the airlines.
A few brave souls have tried to out-smart the ash to disastrous results.
In 1982, a British Airways flight lost all of their engines when they flew into an ash cloud over Indonesia. At the last minute, one engine started. But, the forward windows had been too badly abraded by ash and the pilot had to land blind. A KLM flight had a similar experience in 1989 over Alaska.
If that's not enough to make you think twice before trying to strong-arm an airport employee into getting you onto a flight, I don't know what is.