BBC News Magazine

Page last updated at 11:25 GMT, Thursday, 9 July 2009 12:25 UK

What happens to ice falling from planes?

The Magazine answers...

In a freak accident a man in Bristol has been hit by a lump of ice falling from a plane. What happens to the ice that forms on aircraft?

David Gammon
The ice hit Mr Gammon on the thigh

It is the stuff of a spoof news report - an injury sustained from ice hurtling to earth after breaking off a plane.

Bristol pensioner David Gammon is badly bruised after a grapefruit-sized ice block fell from the sky and into his lap. He was in his garden, under the flight path of Bristol International airport.

The airport has found no proof the ice came from any of its planes, and its air traffic controllers calculate it could have fallen from another plane flying within a five mile radius.

In such incidents, the ice typically forms from water leaking from the aircraft, says Richard Taylor, of the Civil Aviation Authority. Unlike in The Day Today sketch where a woman is lanced by a falling urine icicle, toilet waste is not always to blame.

"The misconception is that a toilet has been flushed and the remnants, when falling to earth, have frozen," says Mr Taylor. Hence the name "blue ice", so called for the chemicals added to plane toilets to mask odour and break down solids.

Ice on planes usually thaws as it falls to the ground
It's leaking water - rarely toilet waste
In 40 years, just five UK cases of people being hit

"But toilets are not emptied until the plane is grounded."

While a leaking plane is not a particularly reassuring explanation, Mr Taylor says it is water seeping out that's to blame for these ice incidents. "It leaks from the galley pipes and seeps out of the aircraft, freezing quickly."

According to the Federal Aviation Administration, modern commercial aircraft cruise at high altitudes, and the sub-zero temperatures outside cause any liquid to freeze immediately.

The resulting ice then breaks off the plane, gaining speed as it falls to the ground far below. Most ice will break up on descent, says Mr Taylor.

"It is very rare, but sometimes the ice fails to thaw. As a rule it falls unnoticed and without harming anyone."

And for a person to be hit is extremely rare. Out of three million flights in the UK in the past year, there were just 35 reported cases of ice falling. And in the 40 years the CAA has been recording such incidents, there have been just five cases of a person being hit.

"That really puts this circumstance into perspective," says Mr Taylor.

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But there have been numerous reports of cars or buildings being damaged by falling ice.

In 2003 Chris Hastings was awakened by a large crash. He emerged from his house in Manitoba, Canada, to find a basketball-sized chunk of yellowish ice on the roof of his blue estate car.

And two years ago in California, an ice boulder punched a hole through the wall of a recreation centre, and shattered into fragments said to be as large as bowling balls. The local airport said the ice may have fallen from planes flying overhead.

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Ice falls from plane and hits man
08 Jul 09 |  Bristol


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