Editor's Note: Bats and Air Traffic Control

Ever wonder how bats–thousands of bats–are able to fly within the confines of a pitch-black cave without bumping into each other? No?

Well, maybe you should–especially as a two-word phrase becomes more and more prominent in the discussion of future flight operations: "self-separation." Self-separation of aircraft is the capability promised with systems such as Automatic Dependent Surveillance-Broadcast (ADS-B). And self-separation is what the Mexican free tail bat (Tadarida Braziliensis) does intuitively.

"When an engineer needs to ‘think outside the box,’ it is often useful for him or her to examine how nature addresses a similar design problem," said Harry R. Erwin, explaining the purpose of his paper, submitted at last year’s Air Traffic Control Association (ATCA) conference. Erwin recently completed his Ph.D at the Computational Science and Informatics Institute of George Mason University, where he also teaches computer science. He also supports the Federal Aviation Administration in security and software engineering through TRW’s technical assistance contract with the FAA Office of Air Traffic Systems Development. His paper at the ATCA conference is titled "How Bats Do It: Biological Models of Air Traffic Control."

As it turns out, the Mexican free tail bat flies with amazing control amid traffic. Hundreds of bats fly nightly out of warm caves in the southwest United States to capture a late-night snack of flying insects. With their about 1-foot (0.3-meter) long wing span, they accelerate away from the caves to about 60 miles per hour (96 km/hour). Their spacing at the mouth of the cave, calculated from infrared photographs, gets down to about a foot (their wing span), according to Erwin. Despite this concentration of wing-flapping mammals, the engineer/professor claims "there is no accumulation of dead and wounded bats on the ground below."

Aw, but bats have some sort of sonar, or echolocation, for self-separation, right? Not totally, said Erwin. He believes this capability plays only a supplemental role, and the bats’ well-developed eyesight is their primary sense for separation.

So, it is apparent that integrated multiple sensors represent one factor that gives bats incredible situational awareness for self-separation. Rapid response time is another contributing factor–although Erwin claims it is not so fast as to be unlike human response time.

Bats "control their flight very much like human pilots," he told ATCA attendees. "Their motor reaction time is on the order of 0.1 to 0.2 seconds, about twice as fast as humans, and they seem to plan their maneuvers about 0.8 to 1 second in advance, which is comparable to the emergency response time for humans." In other words, Erwin claims that, "given comparable aerodynamic performance, the human pilot should be able match the bat’s flying performance."

But such performance assumes the pilot is readily aware of his or her situational awareness. Erwin said, "Given the large amount of sensory data to be processed, [the bats] need some mechanism for selecting only what is important..." Bats obviously possess such a mechanism; now the human-interface folks are tasked to develop one for pilots.

Erwin explained that the sensor data from the bat’s echolocation capability triggers two things: a match/mismatch process that filters the large amount of incoming data, and an extremely fast modeling process. So fast, in fact, that bats achieve a predictive capability. This fast modeling, Erwin added, is essential to "predict the future acoustic environment [using echolocation], rather than a memory to compare the immediate past with the present."

Erwin also said studies suggest that bats don’t fly willy-nilly, as some might suspect. Scientists have altered a bat’s environment and then noted that the change did not alter the animal’s flying routine or its return to its familiar perch. This indicates that bats maintain an internal "world model" (perhaps, like a flight plan), which is modified only when sensor data suggest a change, according to Erwin.

Rapid modeling for a predictive (or intuitive) capability. Situational awareness based on integrated multisensor input. Maybe we can learn from the lowly bat.

Results of biological studies of this flying mammal can "provide some insight into how to engineer air traffic control," Erwin concluded. "Even at high aircraft densities, the pilot has enough time to react to the developing situation as long as traffic can be relied upon to fly in approximate formation and the response to emergency situations is coordinated so that evasive actions do not create additional emergencies.

"The problem is that the data stream must be filtered so that an information overload is avoided..." That, of course, is not an easy problem to solve. Obviously, we can learn more from bats.