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Revisiting collision avoidance


Seven years ago I wrote about scanning methods for collision avoidance and how to enhance your visibility to other aircraft. Since then the topic has arisen sporadically in both my column and other columns in COPA Flight.

Given the recent Hudson river mid-air collision between a helicopter and small airplane, leading to the loss of nine lives, it seems appropriate to review that material once again.      

In 1988, Fred G. DeLacerda published a nice little book called “See and Avoid.” While, in my opinion, the material in this book served as a compilation of material that could be found piecemeal from other sources, Fred presented that material in a way that made you think hard about the very real problem of seeing traffic and avoiding it.

Perhaps the most poignant comment he makes in the book is, “The perfect scan pattern is absolutely worthless unless it is used.” That sentence really made me think about what I had written back in 2002.

I talked about scan patterns; what was effective and what was not, etc. But I don’t think I did a really good job of driving home the idea that scanning for traffic is a two-step process.

Step 1 is knowing how to scan, while step 2 actively involves scanning for traffic. Seems intuitive doesn’t it? Well, apparently it’s not so intuitive to everyone, or else we would see far fewer collisions every year.

If you read Pilot’s Primer back in 2002, you may recall that I endorsed a sweep or sector scanning method as most efficient. These two methods have been endorsed by other organizations and recent research supports the claim of efficiency.

However, one key aspect of any scan pattern is understanding how the eye actually spots traffic. And for that, the eye needs some reasonable level of focus, especially if the target (aircraft) is small or quite distant.

In order to properly focus, the head needs to be stationary. That is to say, that if you are moving your head, everything in the visual field will be somewhat out-of-focus. In order to focus on an object, accommodation must take place. This is where the eye’s lens actually changes shape to allow focus to take place.

The process of accommodation is quite similar to focusing a camera lens so that the desired scene can be clearly seen. Try moving na automatically focusing camera around while you try to take a picture. If you press the button with the camera in motion your result will be a nice picture of blurriness, since the camera was not stationary long enough to know what to focus on. Human eyes work the same way.

Bearing all that in mind, now let’s go on a flight that requires some level of scanning for collision avoidance. The ideal method to support focusing on a potential target would involve not moving the head, but this method is flawed since the traffic would have to move into the current stationary visual field in order to be detected.

As a result, we need to sequentially move our view to different areas outside and fixate on those locations long enough to focus on any object that might be present.

One can imagine how much time it might take to thoroughly scan all of the available outside world for potential targets when using this method of scanning.

It might just take every bit of the 70-75% of your time that many sources recommend be devoted to scanning for traffic when in visual conditions. Are you spending that much time looking outside?

Ok, so you say you are spending enough time looking for traffic, and your proof is that you’ve never come too close to another aircraft while airborne. That’s fine, but let me promote the idea that shear luck might be involved as well.

While I do not personally subscribe to the “big-sky” theory of collision avoidance, I have to admit that most of the time it seems like I could keep my head in a sack while flying and never run into anything. Obviously there are other times where this is not the case, but it does seem like aircraft are few and far between once out of the vicinity of the airport.

But let’s consider the airspace where the recent midair along the Hudson occurred.

Lots of traffic, lots of stuff to look at! Imagine how hard it is to fly in an area with so many interesting things to look at yet stay focused on looking out for traffic. I think I’d have difficulty devoting the recommended time to that task, but that’s just me!

As I’ve discussed in earlier articles, the potential of a traffic conflict is dependent on several factors: 1) the expected density of traffic in the immediate vicinity, 2) the actual observed traffic in the immediate vicinity and, 3) the workload of the pilot; whether or not that workload is artificially imposed.

All this presupposes that the pilot has normal vision as well. Any problems with visual acuity or field of vision can easily impact the ability to see and avoid traffic. For example, not wearing sunglasses when the conditions call for it can lead to squinting which reduces the field of vision and impairs focusing ability.

That may seem to be a contradiction since squinting often makes reading that next line on the doctor’s eye acuity chart possible. While that’s certainly true in the doctor’s office, it’s not the same viewing environment as when squinting due to the glare from bright sunlight.

So assuming we do everything just right there’s a very good chance that traffic will be detected in time to make an avoidance maneuver. But maintaining the optimum scanning strategy is difficult even under the best of circumstances. For instance, research has shown that once a traffic threat is observed that the pilot may change their scanning technique to focus more on the current threat at the expense of the rest of the outside world where new threats may go unnoticed.

This behavior is not entirely unexpected, but the consequences of focusing attention on such a narrow portion of the outside world should be obvious. I wonder if something like this happened in the Hudson River midair. But regardless of what really happened, just how many potential conflict aircraft can the average pilot keep track of simultaneously?

There is reasonably solid research to show how many aircraft an air traffic controller can keep track of simultaneously so we can make some predictions about a human’s general ability to monitor and interact with multiple aircraft. However, there are substantial differences between a controller and pilot’s job.

While both jobs are vigilance tasks to an extent, the workload each experiences during that task of monitoring traffic varies considerably. For instance, a controller is monitoring aircraft from a static position, and while the aircraft he or she is controlling can potentially conflict with each other, there is frequently some level of control exerted over those aircraft. The controller may also have information about speed, direction of flight, as well as altitude in many cases.

On the other hand, the pilot who is not under air traffic control is on their own to make these determinations. He must make his own judgment about the other aircraft’s speed, direction, and altitude prior to determining the conflict potential. Further, this conflict potential is constantly changing and two aircraft may have to be quite close prior to making an accurate conflict threat assessment.

Now multiply that process by the number of aircraft that might be visible at any one time and we have quite a vigilance task to engage in while simultaneously flying the aircraft. To date, I have seen no practical research that would predict how many aircraft a pilot can effectively track while flying. Some researchers have made valiant efforts to study this problem, but there are simply too many variables in the real world of flying to make any statements of certainty.

In the end, the best a pilot can do is to spend as much time as possible looking for traffic when flying in visual conditions. Of course the pilot should spend only as much time looking outside as allowed by the need to control the aircraft.

For many flights there is very little time, if any, to sightsee. And always bear in mind that most sights worth seeing will attract other aircraft, all with the same sight-seeing intentions.

If sight seeing is indeed the intention, then consider getting someone else to fly the airplane so you can look at the sights. Of course there have been cases where neither aircraft pilot(s) in a midair collision were faulted for failing to see and avoid.

However, I’ve generally come to the conclusion that in most of these cases both aircraft pilots could have done something differently thus avoiding the crash.

Hindsight is 20/20, but perhaps we can use some of that 20/20 acuity to increase our ability to see and avoid prior to having that midair!

This month’s Pilot Primer is written by Donald Anders Talleur, an Assistant Chief Flight Instructor at the University of Illinois, Institute of Aviation. He holds a joint appointment with the Professional Pilot Division and Human Factors Division. He has been flying since 1984 and in addition to flight instructing since 1990, has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and Army. He has authored or co-authored over 180 aviation related papers and articles and has an M.S. degree in Engineering Psychology, specializing in Aviation Human Factors.