Contemplate the worst scenario that might confront a pilot during a flight. What comes to mind? Fire? Flight control failure? Engine failure? Perhaps it’s flight crew incapacitation, explosive decompression or severe structural damage.

No doubt about it, those all fall into the Very Bad Day category. But there’s one that can be even worse: a mid-air collision. That’s because it can involve all the problems listed above — at the same time. And since the parties involved aren’t aware of the impending crunch until it’s too late, the mid-air is usually accompanied by a violent element of surprise, confusion, and initial denial.

You might think fatal mid-airs are rare events, and from a purely statistical standpoint I’d have to agree. According to the 2010 Nall Report, a fatal mid-air occurs about once every 8 million flight hours. Think of it as the roughly the same odds as winning the lottery or being struck by lighting. Doesn’t sound so bad, does it? A typical GA pilot might accumulate but thousand or so hours over a full lifetime of flying.

So what’s there to worry about? Plenty. The “big sky” theory may sound good, but it doesn’t hold up very well under close scrutiny. It’s true that the navigable atmosphere over the United States alone is massive — about 20 million cubic miles — and there are relatively few airplanes in the sky. Even on those occasions where a collision is possible, modern tools such as radar, TCAS, VHF communication, and anywhere between two and four sets of eyeballs almost always succeed in averting the disaster. If aircraft were equally distributed throughout the atmosphere, the “big sky” idea would be pretty comforting.

But airplanes cluster near airports, large cities, and on thin slices of the sky known as “airways”. For the VFR types, airspace and terrain often crowd planes into small swaths of the air in places like the Santa Ana Canyon or Banning Pass. The sky is much like the ground: vehicles stick to relatively confined spaces and that makes collisions a serious hazard.

Since we’re on the topic of statistics, let me give you a few of my own: I personally know two people who have been struck by lightning, and a winning lottery ticket was recently sold not 300 feet from my front door. Hey, crazy stuff happens. But unlike lighting strikes and golden tickets, we’re not all facing the same odds. The risk profile varies widely depending on the type of flying you’re doing.

For example, flight instruction is frequently a factor; thirty-seven percent of mid-airs occur with a CFI on board. Many instructional flights happen near airports, and as previously mentioned, that’s where other airplanes tend to congregate. On the other hand, if you fly airliners, your risk of a mid-air is rather low because the aircraft itself is large and easy to see, you’re always flying IFR, and the most sophisticated traffic avoidance hardware available is always installed. Airliners also spend most of their time in cruise and are in constant radar contact with ATC.

Think it can’t happen to you? Think again. Some very talented, capable, and well-respected pilots have been involved in mid-air collisions. I know a guy who was involved in one while flying a large-cabin, TCAS-equipped business jet under Instrument Flight Rules. Alan Klapmeier, the founder of Cirrus Aircraft, was in one too. Richard Collins, famed Flying columnist, was in a mid-air. Speaking of Flying, the recent Editor-in-Chief owns a very nice Cirrus SR-22 which was in a mid-air. And lastly, a decade ago I was in a mid-air collision myself.

I’ll save the blow-by-blow (no pun intended) on that for another day. The point I’m trying to make is that the odds of a mid-air are probably greater than you think, especially if you live in a populated metropolitan area and fly VFR. If you’ve ever had a close encounter with another airplane in flight, you were only separated from “those who have” by nothing more than a miniscule sliver of plain old luck.

Think about that for a moment.

This may be hard to believe, but there is some good news. For one thing, mid-airs are not always fatal. It seems intuitive that most collisions would involve fatalities, but all the people I cited above survived, including (obviously) myself. Also, technology is rapidly advancing, from cheap TCAD boxes to airframe parachutes to super-bright LED exterior lighting.

The question we should all be asking ourselves is how we avoid ending up in a mid-air, fatal or otherwise. If you refer to official guidance from the FAA, the answer is to simply look out the window and spot the other airplane before it hits you. This technique, referred to as “see and avoid”, is still considered adequate for preventing collisions. Here are a couple of passages from Chapter 1 of the Airplane Flying Handbook:

The “See and Avoid” concept relies on knowledge of the limitations of the human eye, and the use of proper visual scanning techniques to help compensate for these limitations. The importance of, and the proper techniques for, visual scanning should be taught to a student pilot at the very beginning of flight training.

Proper clearing procedures, combined with proper visual scanning techniques, are the most
effective strategy for collision avoidance.

Other FAA publications, ranging from the Aeronautical Information Manual, to Advisory Circulars like AC-90-48 (“Pilot’s Role in Collision Avoidance”) will give you the same spiel: “see and avoid will keep you safe”. And it will! Until it doesn’t.

From my perspective as someone who’s been in a mid-air and who was using proper clearing and scanning techniques at the time, I take it as gospel that “see & avoid” won’t always do the trick. I’m just one guy, of course. But many others — some institutional in nature — just happen to agree with me.

For example, a couple of years ago Canada’s Transportation Safety Board issued an accident report on a mid-air collision between a Beech V-35B Bonanza and a PA-28 Cherokee over northern Virginia. Canada was tasked with performing the investigation because the pilots of the Bonanza were employees of the NTSB while the Cherokee was piloted by an employee of the FAA.

I won’t keep you in suspense. The conclusion from the TSB was that the “see and avoid” concept was inadequate. They even quoted a 1991 report produced by the Australian Transport Safety Bureau which provides an overview of the major factors that limit the effectiveness of the see-and-avoid principle in preventing mid-air collisions, as well as a 2005 scientific study published in Aviation, Space, and Environmental Medicine which came to the same conclusions.

The main points:

• Cockpit workload and other factors reduce the time that pilots spend in traffic scans, and even when pilots are looking out, there is no guarantee that other aircraft will be sighted.
• Visual scanning involves moving the eyes in order to bring successive areas of the visual field onto the small area of sharp vision in the center of the eye. The process is frequently unsystematic and may leave large areas of the field of view unsearched.
• A thorough, systematic search is not a solution as in most cases it would take an impractical amount of time.
• The physical limitations of the human eye are such that even the most careful search does not guarantee that traffic will be sighted.
• The pilot’s functional visual field contracts under conditions of stress or increased workload. The resulting ‘tunnel vision’ reduces the chance that an approaching aircraft will be seen in peripheral vision.
• The human visual system is better at detecting moving targets than stationary targets, yet in most cases, an aircraft on a collision course appears as a stationary target in the pilot’s visual field.
• An approaching aircraft, in many cases, presents a very small visual angle until a short time before impact.
• Complex backgrounds such as ground features or clouds hamper the identification of aircraft via a visual effect known as ‘contour interaction’. This occurs when background contours interact with the form of the aircraft, producing a less distinct image.
• Even when an approaching aircraft has been sighted, there is no guarantee that evasive action will be successful.
• Because of its many limitations, the see-and-avoid concept should not be expected to fulfill a significant role in future air traffic systems.
• Transportation Safety Board of Canada aviation investigation report A06O0206 identified that there is a high risk of mid-air collisions in congested airspace when aircraft are not alerted to the presence of other aircraft and rely solely on the see‑and-avoid principle.

There’s one more area of the TSB report which is worth of quotation. In it, they reference a British Royal Air Force study into mid-air collisions. If you’re keeping score, that’s the third sovereign agency to reach the conclusion that “see and avoid” is inadequate. Yet our own FAA, which oversees about 80% of the world’s aircraft and almost all of the high traffic density airspace, still officially proclaims that one can look out the window and see everything that needs to be seen.

This accident has demonstrated yet again that relying solely on the see-and-avoid principle to avoid collisions between aircraft operating under visual flight rules (VFR) in congested airspace is inadequate.

A number of international studies have addressed the overall issue of the effectiveness of the see-and-avoid principle, as well as the risks of collision associated with this principle. All acknowledged the underlying physiological limitations at play and that, when mid-air collisions occur, “failure to see-and-avoid is due almost entirely to the failure to see.”

One study stated that “our data suggest that the relatively low (though unacceptable) rate of mid-air collisions in general aviation aircraft not equipped with TCAS [traffic alert and collision avoidance system] is as much a function of the ‘big sky’ as it is of effective visual scanning.”

A British Royal Air Force study into mid-air collisions, which were deemed to be random, found that the probability of conflict is proportional to the square of the traffic density, and recommended avoiding altitude restrictions that concentrate traffic.

Measures such as improving aircraft conspicuity, pilot scanning techniques, and pilot traffic awareness can reduce risks, but they do not overcome the underlying physiological limitations that create the residual risk associated with a see-and-avoid method.

It’s obvious that “see and avoid” cannot, by itself, ensure our safety. If it could, there’d be no need for TCAS or most of our controlled airspace (both of which came about because of high-profile mid-air collisions, I might add!). I’m not necessarily in favor of mandating any additional equipment, airspace, or restrictions, especially on general aviation. But it’s clear that serious changes are needed in how collision avoidance is taught, especially as it concerns “see and avoid”. The concept has serious limitations which must be understood so the pilot-in-command can make educated decisions about how — or even if — they want to mitigate those risks.

I sincerely hope our nation’s regulatory and safety organizations will eventually acknowledge what we all know to be true: “see and avoid”, while a good start and certainly a vital part of collision avoidance, is simply not sufficient to ensure traffic separation.