top of page

What the eye doesn't see, the heart doesn't grieve over.

The so-called "Big Sky Theory," which once claimed that there was always enough space for everyone, no longer holds true. The skies have significantly evolved since the days of aviation when the "see and avoid" principle was conceived. Originally tailored to the speeds of aircraft of that era, this concept now lags behind the era of high-speed aviation and congested skies. And then, there are us, the pilots, while intelligent beings, we cannot perfectly “see”.

Speaking of which, let's take a closer look.

That was then, and this is now.

Research dating back to 1970 clearly illustrates the gap between yesteryears and tomorrow. It claimed that "see and avoid" could prevent 97% of potential collisions at low closing speeds.

Recent research however conducted by John Andrews in the United States provides compelling evidence against "see and avoid."

Even motivated pilots participating consciously in these trials often failed to spot conflicting traffic, achieving a meagre success rate of 56%. 

These trials expose the uncomfortable truth that our reliance on this outdated concept is dangerous and could even jeopardise lives.

Why? Because we are ‘only’ human.

The "see and avoid" process is far more complex than meets the eye. It involves multiple steps, including looking outside the aircraft, scanning the visual field, detecting objects, identifying them as aircraft, deciding on evasive action, and executing control movements. At each step, human factors cast shadows over the chances of success. These limitations are not signs of 'errors' or 'poor airmanship' but are inherent in the limitations of human vision and information processing, affecting all pilots to varying degrees.

Speed and Vision: A risky combination.

Picture yourself aboard a typical general aviation aircraft. It's a machine capable of reaching significant speeds (averaging 120 knots, and up to 200 knots for high-performance models), and it can be approached from any direction at varying speeds. However, there's a catch: speed significantly reduces the field of vision.

On average, a person has a field of vision of about 180 degrees, but as speed increases, this field drastically diminishes, dropping to just 30 degrees at 130 km/h! 

Not to mention that when two aircraft approach each other, their speeds add up, turning their approach into a veritable race.

But there's more to it. A pilot's view is most restricted on the side farthest from their seat. For left-seated pilots, aircraft approaching from the right pose a particular threat.

Who would have thought that your choice of seat could have such a profound impact on your safety?

Race against the clock.

FAA data delivers a stark message: recognising an approaching aircraft and executing an evasive manoeuvre demands approximately 12.5 seconds, provided the target is detected promptly. 

Picture those critical seconds slipping away as you struggle to spot a potentially converging aircraft. Limited time is not on our side in the skies. Early detection is the key that separates life from tragedy. We'll revisit this later…

The unforgiving march of time.

Age may bring wisdom, but it also brings vision challenges.

After 35, your field of vision starts to narrow. For men, deterioration even accelerates after 55. 

These are in a nutshell the lain challenges that humans pose to the "see and avoid" concept. But there's another aspect to consider: the aircraft itself can also restrict your field of vision.

Rage against the machine.

In the cockpit, pilots juggle increasingly complex instruments, radio communications, and critical tasks. These demands can divert their attention from essential external scans. Talking, thinking and even daydreaming all occupy mental processing capacity.

Did you know that VFR flight pilots spend only about 50% of their time monitoring traffic outside the cockpit? 

Near airports, where air traffic is high, workload reaches its peak. Now let that be precisely where vigilance is crucial, as most collisions occur there, as confirmed by the recent Safety Report from the European Union Aviation Safety Agency (EASA).

The pitfalls of visual obstructions.

There are many obstacles in the cockpit that can obstruct a pilot’s a pilot's field of vision. These may include window-posts, unsightly bug splatter on the windscreen, sun visors, wings partially obstructing the view, front seat occupants, and instrument panels. These physical barriers are apparent, but there are also subtler forms of visual interference such as…

… The hazards of glare.

Ah, the allure of a radiant sunset! Yet, glare, whether direct or reflected, significantly reduces visual effectiveness. Even glare half as intense as the general illumination reduces visibility by 42% at a 40-degree angle. At only 5 degrees off the line of sight, visibility dramatically drops by a staggering 84%.

It's a reminder that beauty can obscure danger...

But there is hope.

In our human frailty, we are subject to physical limitations so it's crucial to be alerted to potential convergence as quickly as possible because, as described above. But what if we could turn back time? In particular, the 12.5 seconds needed to recognise convergence and execute evasive manoeuvres? Am I converging or diverging, what's the closure rate, what action to take?

We said it before: Early detection is the key that separates life from tragedy. Guess what, that’s exactly what SafeSky allows you to do by being alerted already 60 seconds before convergent traffic approaches, well before those crucial 12.5 seconds even begin!


Lady Luck alone is no longer sufficient to avoid mid-air collisions, it is a reckless gamble. Don't get us wrong. "See and avoid" has served us well and continues to do so, preventing countless collisions. But as our skies fill up, our aircraft become faster and more complex, and our pilots face ever-increasing demands, it's time to seek assistance. And that assistance exists. Let SafeSky be your assistant, or your second pair of (electronic) eyes if you prefer.

🎧▶️ Also listen to Emmanuel Davidson's recent presentation at the Mondial de l'ULM 2023: "See and avoid: the human eye wasn't built for that."



Limitations of the See-and-Avoid Principle
Download PDF • 880KB

Aviation Safety Spotlight
Download PDF • 715KB


Back to top

bottom of page