The seemingly improbable threat of being taken out by a giant frozen lump of human waste falling from the sky gained currency as a genuine risk this month when a 10-kilogram frosty poo-ball landed in a village near the Indian city of New Delhi.
Initially thought to be an extra-terrestrial object, authorities eventually decided it was most likely something known as blue ice — frozen sewage that leaked out of a commercial aircraft waste system mid-flight.
With anything up to 10,000 commercial planes airborne at any one time, the media focus on this event prompted some to start gazing skyward with a heightened sense of urgency whenever they heard that familiar jet engine roar.
While it might be enough to foster spontaneous coprophobia — that fear of faeces — in the hardiest of ground dwellers, CQUniversity aviation expert Ron Bishop said people could rest assured events like this were actually quite rare.
"It's not as common today as it once was," he said.
While waste is normally disposed of once an aircraft has landed, Mr Bishop said leaks could occur in the air.
Frozen human waste very occasionally forms around worn overflow outlets for aeroplane toilets and then falls to earth.
"I don't think I'd be running around like Chicken Little, but it does happen once in a while," Mr Bishop said, citing developments in aviation waste-storage technology.
"Luckily no deaths have ever been reported."
Mr Bishop, a pilot and senior aviation lecturer, said incidents have become less common since the mid 1980s when commercial airlines began using vacuum waste-disposal systems.
"From 1979 to 2003 there were at least 27 wads of blue ice [big] enough to tear through roofs, smash cars, one even took out a church in England," he said.
"Now we're getting more efficient."
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The vacuum toilet system was patented by American inventor James Kemper in the mid-1970s and was first installed by Boeing in 1982.
Mr Bishop said the advancement was one of the biggest in the history of commercial aviation.
"The old system used to flush liquid into a tank much like a [camper van]," he said.
"But it's very cold at the altitude where aircraft fly so the liquid would often leak and freeze up."
Mr Bishop said the topic of how to best dispose of human waste was an important one.
"It's not an easy topic to discuss," he said.
"But the governing [aviation] authorities around the world take it very seriously."
