The first-ever reported collision between a drone and a commercial airliner has rattled the aviation world and led to the realization that engineers know almost nothing about how a drone could damage a turbojet engine — an unlikely but potentially deadly scenario.
After years of warnings from aviation experts, a drone struck a British Airways jet as it approached London's Heathrow airport this past weekend.
The jet landed safely and all 132 passengers and five crew were fine. But the collision comes as pilots around the world are reporting record numbers of drone sightings, often close to busy airports.
In this instance, the drone made contact with the nose of the Airbus A320 during the plane's descent. The jet was inspected after landing and engineers cleared it to resume flying that same day.
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It doesn't surprise Dylan Thomas, chief pilot of London Air Services, that the plane was able to withstand the collision without sustaining any damage. Thomas told CBC News that he believes the Bombardier-built Learjets he flies would likely withstand a blow from a recreational drone undamaged.
"Where the critical point comes is in the engine. If the drone was ingested by the engine, there's a very strong chance that the engine would fail," he said at the company's hangar in Richmond, B.C.
Airliners are certainly built to withstand adversity, but what would happen if a drone was sucked into a turbojet engine?
It's a question that, at least currently, is surprisingly difficult to answer.
'There's just not a lot of data'
"I'm concerned that it could be catastrophic," Aaron McCrorie, an aviation enforcement official with Transport Canada, told CBC News.
"We don't have definitive information, but I am concerned it could cause an airplane to crash."
When it comes to life and death in the skies, aviation engineers usually test for every eventuality, but the popularity of recreational drones has outpaced both regulation and safety research.
There are an estimated 500,000 drones or Unmanned Aerial Vehicles (UAVs), in the U.S. alone, a fact that has sent the Federal Aviation Administration (FAA) scrambling to write new regulations. Transport Canada is also updating regulations, with new rules expected next year.
Tossing drones into multi-million dollar jet engines to see what happens is an exceedingly expensive undertaking and that may be a factor in how little is known about their potential effect on aircraft, experts say.
"It's true that there's just not a lot of data about what could occur in that kind of situation — if a drone were to hit a manned aircraft where it is more susceptible," says Jeremy Laliberté, an aerospace engineer at Carleton University who frequently uses UAVs in his research.
'A bird is one thing, a drone is another'
The closest analogy is bird strikes, which are not uncommon, particularly below 3,000 metres as planes take off and land. The most significant danger is from flocks of birds, especially if they're relatively large. Remember, it was a skein of Canada geese that caused both engines of US Airways Flight 1549 to fail, eventually leading to the "miracle on the Hudson" in 2009.
The weights of many 'micro' hobby drones currently available on the market, less than a kilo or so, are comparable to that of small or medium-sized birds, so academics have used bird strike logs to estimate the relative danger that these kinds of drones may pose to commercial airliners.
An extensive 2014 analysis of 25 years of FAA bird strike data, for example, found that about nine per cent of reports indicated damage to the aircraft. Fewer than 0.2 per cent of all incidents involved injury or harm to people.
While the comparison is somewhat helpful for hypothetical analysis, its value is limited.
"It's important to remember, of course, that a bird and a drone are not made of the same things. Drones have batteries, which are flammable and volatile, and they have motors," Laliberté says. "And it's not clear yet how that would affect a jet engine. A bird is one thing, a drone is another."
Sense and avoid
As more data is collected, it will likely spur fundamental changes in the drone industry, according to Mark Aruja, a policy strategist with Unmanned Systems Canada.
Many drones, including hobby and commercial models, will eventually be outfitted with a satellite positioning system known as Automatic Dependent Surveillance - Broadcast (ADS-B). It's a "sense and avoid" technology that would help commercial jets and air traffic controllers monitor every drone in a particular airspace.
It is already a standard technology in commercial aviation, but until recently has been prohibitively expensive or too bulky to affix to many drones.
"Everything is advancing so rapidly right now, this is something that could be a reality in the coming years," says Aruja.
While Canadian regulations stipulate that drones must stay at least nine kilometres from any airport and fly no higher than 90 metres — which should, at least in theory, be enough to prevent any collisions — ADS-B would help ensure the safety of commercial airliners in a sky increasingly filled with drones.