At first, a low flying toy drone would seem to be little threat to a commercial jetliner. However, during landing and takeoff, a drone buzzing around an airport can get sucked into the jet engines. This can result in catastrophic damage. Additionally, due to uncontained engine failures the damage can spread to the wing (which can have fuel tanks) or even the fuselage and cabin.
Simulations by researchers at Virginia Tech have shown that the impact of an eight-pound unmanned aerial vehicle (UAV) with a nine-foot diameter turbofan engine would result in shrapnel and debris flying around at speeds of 715 mph. This shrapnel tears through the rest of the engine causing catastrophic engine failure in 1/200th of a second in this scenario.
Personal drone takes out multiple turbofan blades. Image courtesy of Virginia Tech.
“Because the damage is spread to a large section of the engine, it is unlikely that it will be able to maintain thrust,” said Javid Bayandor, an associate professor of mechanical engineering at Virginia Tech.
Current jet engines are designed to contain the failure of a few turbofan blades within the engine’s casing. However, a UAV strike would cause the failure of the majority of the blades, and, as seen in the simulation, could turn the engine casing into Swiss cheese. At that point, the fear of debris ripping through the fuselage, wing or fuel tank and causing potential electrical damage, fire and personal injury becomes real.
Investigative report into Qantas Flight 32 by the Australian Transportation Bureau.
Though it is difficult for a drone to fly high enough to cause this failure while the aircraft is pressurized, causing this damage during landing, or worse, take off (when the fuel tanks are full), could cause a significant emergency situation.
Virginia Tech’s drone collision simulation started as a bird study about three years ago. However, the study moved towards drones after their popularity grew and pilots started to see them within commercial airspace. In fact, in California a firefighting aircraft recently was unable to battle a forest fire due to drone interference.
“Because of the unprecedented damage a small or even micro unmanned aircraft systems can inflict on a passenger aircraft, pilots cannot risk flying in the same airspace where there are drones,” said Bayandor. “While strict regulations are already in place to isolate drones from operations in controlled airspace, their enforcement has proven challenging due to the anonymity of drone users.”
Currently, regulations require that aircraft be able withstand soft airborne objects like birds and bats. However, the industry has yet to account for the damaging effects of drones. This has Virginia Tech researchers worried.
“As of yet, there are no specific certification requirements to account for procedures to be executed by pilots to remedy such a situation,” said Walter O’Brien, professor of mechanical engineering at Virginia Tech. “Drones create a new dimension in aircraft foreign object impact challenges that we need to address.”
Unfortunately for the aviation industry, predictions suggest that pilots will face increasing drone threats in years to come. The Association for Unmanned Vehicle Systems International predicts that sales in the U.S. should rise to $13.6 billion by 2019 and $82.1 billion by 2025. That translates to a lot of potential aerial mines for pilots to look out for.
The Virginia Tech team is looking into solutions to potential drone and aircraft collisions. For instance, they note that different aircraft and relative impact velocities can have significantly different collision outcomes.
However, Virginia Tech notes that their team isn’t enough. To prevent this sort of disaster, the aviation industry really needs to get cracking.
Is your aircraft design team taking drones into consideration for your engine designs? What regulations are needed to ensure passenger safety? Comment below.