I'm a Scientist... / XKCD strikes again
Thoughts on Exam Questions

Ashclouds, Airplanes, Engines and Risk

74sq.jpegOnce upon a time, in a previous career, I was an Engineering Officer in the Royal Air Force.

Fun times. At a young age I was asked to sign for 15 x F4-J Phantom Aircraft which were, technically, the property of Her Majesty - but I was led to understand that she was busy looking after three Corgis and so it fell to me to take responsibility for these aircraft. They were worth roughly GBP50 million each in today's money. And, yes, I had to sign for them. Nearly a Billion Dollars worth of hardware. Because, well, someone has to sign for these things - the rules are very clear.

My job was to keep these aircraft flying. I had 150 of the RAF's finest technicians to help me, all of whom knew a great deal more about the hardware than I did. But they were all specialists: engine specialists; armament specialists; radar specialists. And I, blessed as I was with an Oxford degree, was - of course - a specialist in absolutely nothing. Which meant that what I actually did was to ask questions. Lots of questions. Lots of very stupid questions. The sort of questions that only a graduate, with no useful knowledge whatsoever, could possibly ask...

So it was that I learned about the subtle art of "gentle persuasion".

I was looking at the exhaust of a General Electric J-79 engine. The F4-J Phantom is driven through the air by two of these beasts. They are huge. They consume a ridiculous amount of aviation fuel. And they can accelerate an aircraft from 0 - 600 mph in about the time it will take you to finish reading this sentence. These engines are the va-va-voom of the fast jet world...

Unfortunately, this particular engine wasn't about to voom anywhere. Not even if... well, you get the general idea.

ze362.jpegThe pilot who had returned this particular engine had decided to fly the aircraft upside down whilst slamming the throttle from "idle" to "reheat" - and back again - whilst simultaneously taking the Phantom through the sound-barrier. I kid you not, dear reader. The engine, in turn, had decided to expire.

"How", I asked, "are we going to fix it ?"

"Oh, don't worry Sir. A little gentle persuasion will soon have this fixed." replied Sgt Paul Leslie - a man who knew everything there was to know about engines - and a bit more besides.

"Ah yes" asks I, "but what are we actually going to do ?"

"Well, just a bit of gentle persuasion Sir. Have it fixed in no time. Back flying by this afternoon."

"Ah yes" says I, "but what EXACTLY are we going to DO ?"

"Well Sir" said Sgt Leslie "we're going to hit it with a bloody hammer." Although he didn't actually use the word "bloody". Because this is the military and you have to swear a lot more aggressively than that.

The aircraft got fixed. I got educated. And the world moved on.

The point of the story is that engines break. Aircraft break: bits fall off; birds fly into the windscreen; tyres burst. These things happen - and they get fixed. With a bit of luck we all live to fight another day.

But it isn't luck, is it ? It's risk management. It's professionals making rational decisions based on good evidence and a clear understanding of risk.

Which brings me to the ash cloud. We all know what an ash cloud can do to an aircraft - because we've all read about British Airways Speedbird 9 which flew through volcanic ash, lost all four engines and flew on silently for fourteen long minutes before Captain Eric Moody and his crew finally managed to relight one engine.

IcelandVolcano.jpgBut I still like asking questions and so I have a few questions about the current volcanic ash saga. Specifically:

1. What is the chance of any one aircraft encountering ash whilst flying between England and Continental Europe ? - I'm guessing "relatively low".

2. What is the likely damage that would be sustained by a modern aircraft if it did encounter such conditions ? - I'm guessing "tolerable"; these are modern aircraft with fault tolerant engines.

3. If the worst did come to the worst, and all the engines stopped working, then how difficult is it to land a modern commercial aircraft - deadstick - no thrust - given that the starting point is 20,000 feet above mainland Europe ? - Bear in mind that every Shuttle landing is a deadstick landing - and the Shuttle flies like a brick. Bear in mind that we can land aircraft in the Hudson River. Bear in mind that technology is getting better. Bear in mind that there are airfields all over the place.

Well, I just don't know. I'd like to see it done in the simulator a few times. I'd want to talk to a few Captains.

But I'm guessing, and this is just a guess, "easier than it was in 1960".

And that, it seems to me, is an important yardstick. If the level of risk - properly and professionally assessed - is no greater than the risks that passengers routinely assumed in the 1960s - then it's a risk we might all reasonably assume in 2010.

This isn't politics. This isn't PR. But it may be a rational assessment.

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