Murphy's Law: The UAV Collision Myth


July 13, 2013: A recent opinion survey in the United States found that 57 percent of the population favored the use of UAVs (Unmanned Aerial Vehicles) in general (anywhere in the U.S.), 88 percent favored UAV use for search and rescue, and 63 percent for fighting crime. Many countries outright forbid the use of UAVs for any reason (even military training). But some, like Israel, have allowed their use for decades with no problems. Most civilians instinctively recognize the benefit of UAVs, but the bureaucrats in charge of air safety are very risk averse. They gain nothing by backing UAV use and risk hurting their careers if a UAV collides with a manned aircraft or otherwise hurts people. So many nations follow their cautious air safety bureaucrats and ban the use of UAVs anywhere except in air space reserved for military operations.

This is all about fear trumping reality. For example, air travel has long been much safer than it appeared to be. That paranoia has been extended to UAVs despite no lives lost to UAV collisions in Iraq, Afghanistan, or anywhere else. There is a potential danger with collisions involving large (over 50 kg/110 pound) UAVs, as these can inflict enough damage to bring down manned aircraft. Yet in a decade of heavy use in Iraq and Afghanistan there has been only one such collision and in that incident there was no loss of life. But fear of such collisions has led to heavy restrictions on UAV use in disaster relief operations, which the military is often called upon for overseas and inside the United States. The American military must receive permission from the Secretary of Defense before using UAVs off the battlefield. That’s not really an issue at the moment because most recent disasters the military got involved in there were sufficient manned aircraft to look for survivors, assess damage, and so on. Nevertheless, disaster relief experts point out that in the early hours and days after a major disaster you can’t have too many eyes in the sky.

The one actual UAV collision took place two years ago, when a U.S. Army RQ-7 UAV and a U.S. Air Force C-130 transport collided. The RQ-7 hit a wing of the C-130, between the two engines. The RQ-7 was destroyed, while the C-130 had the skin of the front of that wing torn open and some of the interior spars bent. One of the props on the inboard propeller was destroyed (and that engine had to be turned off). But the C-130 was able to land safely, and the air force promptly had parts and technicians flown in to repair the C-130 where it was.

An RQ-7B Shadow 200 weighs only 159 kg (350 pounds), compared to 70,000 kg for a loaded C-130, so the outcome of this collision was not surprising. Shadow is small, being 3.5 meters (11 feet) long with a wingspan of 4.1 meters (12.75 feet). Most UAVs in the air over combat zones are even smaller. Indeed, over 90 percent of them are the tiny two kilogram (4.4 pounds) Ravens. Witnesses in Iraq and Afghanistan have seen a few of them destroyed, or simply knocked out of the air by a passing aircraft, usually a helicopter. Raven operators suspect that many of those that were lost for unknown reasons were similarly hit or caught in the backwash of low flying aircraft. A few have been seen getting attacked by birds. There have been very few recorded collisions.

The small, plastic Raven does not do much noticeable damage to an aircraft. The pilots and crew of helicopters hit by Ravens apparently don’t notice it at all. After landing ground crews may notice a new dent and wonder where it came from. The Shadow collision was understandable because the Shadow is the largest UAV that often operates at low altitude (under 300 meters) and uses military airfields to land and take off.

In light of all this, the army is developing a new radar system (GBSAA or Ground-Based Sense And Avoid) to increase safety for UAVs. GBSAA is mainly a software system using existing radars to track UAVs and manned aircraft and alert UAV operators when their UAVs are too close to other aircraft (manned or unmanned). GBSAA can be expanded to use transponders (which commercial aircraft have been using for a long time) and more flexible software. But the basic idea is to insure that UAV operators are no longer “blind” to what is in the air nearby. GBSAA had its first field test a year ago and it was a success. The first GBSAA will be deployed next year.

GBSAA will likely be more in demand by potential civilian UAV users. Battlefields have much lower safety standards than civilian air space, what with all those artillery and mortar shells, plus the bullets and rockets. But civilian air space has a lot of small aircraft and helicopters, so UAVs are generally banned. GBSAA could change that and make battlefields safer as the UAV traffic becomes denser. 




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