What happens if an airliner’s jet engine were to swallow up a drone?

Air traffic safety has been a hot topic of debate surrounding the Federal Aviation Administration’s long awaited drone regulation proposal. Fear of drones colliding with airliners has prompted the agency to devise a new set regulations that would inhibit drones from flying past 500 feet in elevation or near airports. Nonetheless, enforcing these laws is difficult as there’s no tangible way to catch the rogue that disregards them. So, what exactly happens if a drone were to collide with an airliner?

To answer that question, the IEEE Spectrum contacted George Morse, founder of Failure Analysis Service Technology, an aviation consulting firm that specializes in analyzing foreign-object damage to airplanes. Morse, an expert who’s examined over 4,000 cases over the course of his career, hasn’t yet encountered any drone-related collisions (thankfully), but he has investigated plenty of collisions with unlucky birds similar in size and weight to drones.

Morse explains that the danger in a collision scales with the velocity of the two objects involved [we know this from automobile collisions and because the amount of kinetic energy released is equivalent to the square of velocity, K = (½)(mass * weight)^2 ]. However, the environment within a turbo engine is unique, and the relative velocity of the colliding objects doesn’t factor nearly as much as the engine’s power-level, that is to say that the speed of engine’s spinning fan blades increases with regards to the engine power. 

To demonstrate, Morse recants two examples of bird collisions in which the end result varied completely. In the first instance, an MD1 passenger jet taking off from Portland International ingested a one-kilogram herring gull in 2001 and was forced to abort the flight after the engine’s fan blade sustain heavy damage while running at full power. By contrast, a flight landing in Orlando swallowed a two-kilogram bird into its engine but only sustained minimal damage due to its low-power setting.

Now in the case of drones, Morse believes that the small drones will disintegrate and pass right through with little to no effect on the engine, whereas the drones the size of the DJI Phantom II will be treated like a bird strike. “There’s a good chance it’ll take the engine out at high power,” he suggests, but that’s not guaranteed. Most bird strike-related emergency landings are caused by collisions with a portion of the flock, not a single animal, so in a sense, a singular drone may in fact be less hazardous to the engine than the birds.

It’s worth noting that contemporary airbuses are built to resume flying even with the loss of an engine (even if most were constructed in the 60s). The aircraft will not suddenly plummet, but descend in such a way that a skilled pilot will be able to perform an emergency landing. Recall that in 2009, a US Airways flight piloted by Chesley B. Sullenberger III, performed an emergency landing in New York’s Hudson river after colliding with a flock up birds a few minutes of takeoff. 

What about the lithium-ion batteries within the drone? Won’t the volatile components end up in the combustion chamber? Morse agrees that batteries are hard, but he offers that ice can be hard too, and that doesn’t necessary debilitate engines. Similarly, the batteries inner-workings are likely to be burned up by the engine. 
Even if lives are spared in drone collisions, the immediate inspections and repairs that follow are likely to be expensive. “I’d be more concerned about hitting the windscreen,” exclaims Morse, as a collision with the windscreen centers more on kinetic force and velocity than object composition.

Nevertheless, the number of drone sightings is steadily increasing, with 193 sightings on record for 2014 alone.

Source: Gizmodo via IEEE Spectrum