The Power of the Eyes
This is an article published in Aerokurier by Gerhard Berwanger, for many years Manager of the Oerlinghausen Soaring School.
Time has not diminished the validity of his observations.
“See and be seen” is a simple basic rule to avoid collisions in visual flight rules. That it is not always this simple is shown by the scary accident statistics of last years. This is why we should investigate what we can see, where the limits of our vision are, and the correct attitude.
While Günter Groenhoff had to peer through holes in the wooden sides of his “Fafnir”, modern sailplanes offer a panoramic view. Not only can the airspace be observed all around, but the pilot can enjoy a vision of the landscape below him in its full beauty. But de we really see like the birds? Do we recognize potential dangers properly and timely when they enter our field of vision? Why do we still have collisions?
Any experienced pilot can remember scary instances when he suddenly saw another airplane whose approach he had not realized, even though it did not approach from the dead angle of vision. It is simply not true that we always have a complete, colorful spatially correct and sharp image of the airspace and interpret it correctly. But we think we have and that can be a dangerous mistake.
Vision is a very complex action, which does not take place primarily in the eye but in the brain. We do not see with the eyes, but through the eyes. The performance of our brain must be learned and practiced. This already takes place in early childhood. But every later experience had to be learned again, and that is especially true when completely new experience take place, such as flying.
It is therefore profitable for every pilot to study the complicated actions of visual recognition and to understand them.
The eyes are equivalent to a stereo camera. By thickening or thinning the lenses we can focus on short distances and get a clear image. In addition to aiming the camera by head movements the eye muscles add small movements of the pupils. Why is this necessary?
The retina is not built up equally, but has various densities of light sensitive cells. There are two kinds of receptors, the color sensitive ones and the and the light-dark sensitive systems. In the center are mostly color sensitive ones, and towards the edge are more dark-light sensitive ones. The center ones need strong light stimuli, that is why we see less color at dusk, and at night only light / dark contrast. In the center, the so called yellow Spot the color sensitive ones are very dense and there are no light-dark sensitive cells. The center of our vision is night blind, and the edges are not color sensitive. Where the vision nerves pass through the rear of the eye we have no receptors – we have a blind spot.
But this is still not enough incompleteness. Only in the yellow spot does each receptor pass its information to the brain via a nerve strand. Toward the outer edges the receptors are bundled together. Only in the center do we achieve maximum acuity. Toward the edges the grain of the film increases and the picture is less sharp.
Sharp vision seems to be the main function of our eyes. The flight surgeon test this with tablets of letters. Vision is sharp if we can read the letters at an angle of five minutes and a stroke width of one minute. Disease or age can diminish these values.
Subconsciously we let the pupils wander restlessly.
The best acuity is in the center of the field of vision in a range roughly equal to the beam of a flashlight. We have to really look if we want a sharp picture. The outer rim is less sharp, fudged, colorless.
But why do we think the entire field of vision is in focus and don’t realize the deficiency?
If you follow the movement of the pupils you realize that the eyes are restlessly moving irregularly and unsystematically. The composition of many small sharply focused pictures produce a comprehensive, sharp image in the brain. The color information is stored and released back into the picture so that we do not recognize the weak colors on the edges of the eye.
For good vision we not only need the quality of the camera but also the aiming of the camera and the processing of the information in the brain computer
There are two processing steps in the diencephalon and the main brain. The preliminary evaluation in the diencephalon ensures that only the important visual images are passed to the main brain for final processing. This filtering process can be learned and trained for. The aiming of the vision is also a function of the diencephalon. It steers vision always to the important information. The eyes do not wander around unsystematically, but are steered so that a comprehensive picture forms as quickly as possible. This seemingly chaotic eye movement is very efficient and much better than the systematic scanning in mechanical scanners. But we have to learn through experience what is important and what isnt.
That the guided vision has to be learned and practiced is of critical importance in flight training. Investigations in road traffic have shown that driving students have too much delay in their vision. Their eyes do not reflexively take in the important information, but cling too long to individual sights and then jump uncertainly to the next point.
The picture shows the vision of an inexperienced student pilot. First he looks at the airfield to his right, then jumps to the horizon when the instructor reminds him, stays there without observing the remaining airspace, and then jumps to the sailplane flying on his right, and when the instructor calls Airspeed he looks at the instrument panel and stays on the ASI.
His brain cannot form a usable and comprehensive total picture composed of the important information. This student is looking through a pipe to see only individual pictures.
Only as he gains experience does he use the dynamic panning of the experienced pilot, as shown in the next picture. Without consciously steering his vision his eyes take in all the important images on the ground and in the air and the weather, and includes the instrument panel without staring at it. The pilot forms a comprehensive picture of his environment in a relaxed manner.
The constant visual intake requires not only movement of the pupils, but also of the head. One can observe from the back seat how an experienced pilot moves his head in an apparent random fashion. The beginner does not do that, he still has to learn it. Tiredness, disease or age can diminish this ability, critical self-examination is indicated. The largest part of our vision does not take place in the eye or the diencephalon, but in the main brain. A square millimeter of the retina is serviced by about 10 000 square millimeters of the main brain. Here we can only give some examples of the output of this Video camera that are important for the pilot.
To interpret the received information properly and to recognize what is seen it is necessary to compare this input with information already in memory. Of course we will never get exactly the same picture in size, color and layout before us. That is why we have developed the ability to recognize the basic structures of the image again and again. As an example we can use reading. The young student has difficulty distinguishing between U and V, but the adult has memorized the basic structure to such a degree that he can recognize it instantly even in poor handwriting. No computer has yet mastered this type of recognition to the same degree. Problems can arise when the perceived information is insufficient and can then be misinterpreted.
In the picture cover up the two sailplanes on the bottom and look only at the silhouette on top. Its easy to recognize a sailplane. Does it fly towards you or away from you? The correct interpretation can be life saving. We need more information. The bottom two pictures we see both variants, distinguished by the distribution of the shadows. To make the correct interpretation the small details are important. But that takes sufficient acuity. The ability to recognize shapes is developed by experience and can be improved by conscious vision.
In order to recognize other aircraft against a camouflaging background this ability if especially important. White sailplanes in front of the rocks or glaciers of the mountains are a good example. An experienced mountain flyer will recognize them faster than a novice.
A Panoramic View:
A human eye has a field of vision of about 210 degrees, but only the center section, about 60 degrees, is seen by both eyes. Only here does the central acute vision guided by eye movement take place.
In the outer periphery we only see through one eye. Here the retina does not deliver a sharp image, but somewhat blurred optical information. But this area is superior to the center in one respect. We can detect movement faster and more certain. Why? The nerves of several vision cells are bundled. A weak light impulse or a slight change, such as a movement might be to weak to be transported through the center of the eye, and can be lost. In the periphery the bundling of the nerves strengthen the impulse and relay it to the brain. The construction of the nerves in the periphery cause somewhat blurry vision, but instant recognition of even slight movement.
This is an important safety feature, developed long ago to recognize stalking predators. The eyes periphery reports a movement, the brain thinks its important, and the vision is automatically centered on the threat. It is so imprinted on us that we cant do anything about it, and shouldnt.
As pilots we need the ability of peripheral vision and should value the recognition of danger, and, if possible, develop it further.
Both eyes together vive us the panoramic vision that is so important for early recognition of danger signals. But do we need both eyes for spatial vision, to see our movement in three-dimensional space properly. Not necessarily so.
Only for short distances to a maximum of 100 meters do we see stereoscopically because of the difference of the two pictures observed by the eyes. In flying that is only important within the cockpit.
The space recognition of a pilot functions first of all because of perspective. Near items are large, distant items are small.
For example: lines of telephone poles converge in the distance.
Another example: railway lines where distant items are covered over by near items.
Another example: clouds in the sky. Seeing in perspective is first of all a result of experience, of life long learning. Layout of the approach path, the runway and sideways divergence from the center path are easily recognized by the experienced pilot; beginners often have difficulties with them. He still has to gather visual experience and store it. That is easier with the panoramic view of both eyes. But with experience we could do it with one eye, since stereoscopic vision is not essential. It is therefore understandable that a student with only one eye is not allowed to qualify, but an experienced pilot is allowed to continue flying with one eye.
Vision, that most important input for a pilot, is a multi-layered and fascinating procedure. Now lets look at an analysis of real situations and their practical application.
|Both pilots stated that they did not see the other airplane until the collision took place. This or similar statements can be read in almost every collision accident report if they were minor enough to have the pilots survive.|
Was the other airplane really not visible before the collision, or was he just not recognized although he was clearly within the field of vision? Its hard to imagine, since we are used to take everything in with our alert pilots eyes. But in some situations its easy to overlook something. The enormous confidence in our ability to see is relative, so we will now see if we can draw useful conclusions from specific examples.
Just how important it is in collision avoidance to see other airplanes timely and correctly can be demonstrated by some typical sequences of events and their impact on vision. The near picture shows in real size the progress of a frontal approach at about 100 km/h. To get the proper perspective you should hold the picture about one meter from your eyes. 23 second before the collision the other sailplane is so small it could be hidden by the yaw string. Just six second before a collision the fuselage could be hidden behind the yaw string tape. Only the wings would be small, white lines. The picture shows that the approaching airplane does not alter its relative position to our straight flight. Its almost like nailed to the canopy and grows slowly and then increasingly faster. That is true for any straight-line approach that would lead to a collision if an avoidance maneuver is not initiated. But frontal collisions are relatively rare.
The picture at right shows several collision courses based on a speed of 100 km/h. The relative approach speeds between the airplanes, and their distance ten seconds before impact are shown. It is important to realize that the angle of vision from the cockpit of our airplane does not change throughout the sequence of events. The approaching sailplane remains at the same angle and the same spot of the canopy.
The next picture is not to scale. It is valid for different airspeeds, Jet or sailplane, when distance and direction are such that the airplanes converge at a certain point. The other airplane blooms like an ice flower on the canopy, without changing its direction.
Other airplanes which we observe are considered to be on a collision course except when the other sailplane is on an exactly parallel course at the same airspeed, or is flying exactly the same turn at the same speed.
In the next to last picture let us look at the various approach speeds. Although it makes mathematical sense it is still surprising that an airplane approaching at a 60 degree angle from the right has an approach speed of 100 km/h. That mean we approach a collision with this airplane as if we were flying into a fixed obstacle.
The airplane enters the outer field of vision is we are looking straight ahead or at the instrument panel. In this area of vision the acuity is poor and we will not necessarily see an unmoving, slowly blossoming object in time. Only sufficient scanning of the airspace, only the sliding dynamic look can protect us from a collision. We see how important the peripheral vision is, and how useful it is that we recognize movement in the outer area quicker than in the center.
In soaring more collisions occur in thermalling than in straight flight. Like moths to a light, soaring pilots are attracted to thermals. But discovering a thermal can detract the attention from other things, and another sailplane in the thermal or about to join, is overlooked.
Of the many possible collision courses in circling flight lets look at the examples in the next pictures: in the first one two sailplanes fly parallel at the same height and about 300 m lateral separation and make contact with the same thermal. Both turn inward (position 1). From the start of the turn they have 15 seconds to collision if they don’t see each other.
Pilot A can see B only if he searches and looks 130 degrees to the rear. If he is reasonably attentive he will recognize the danger only at position 2, at 90 degrees. Both have only 11.5 seconds to do something. Until avoidance becomes impossible in position 3 they have only 8 seconds.
The situation in the next picture is even more critical.
Two sailplanes approach each other head on, with about a 400 m lateral separation. Both make contact with the same thermal and immediately turn to the right. They have 15 seconds to collision. Pilot A can see the other sailplane if he turns his head 130 degrees rearward and searches for the other sailplane. But only in position 2 can he see the sailplane B about 90 degrees to his right, and in frontal view it is difficult to see. If he does not see it he has 7.5 seconds to impact. After a further 4 second impact is unavoidable. Even in this hopeless situation sailplane B is only visible to A in his outer field of vision at about 60 degrees. In this situation pilot B has the better viewing conditions, but can we rely on that?
Both scenarios show that the danger of collision creeps from the outside into the field of vision, which means it is not enough to just scan forward, but one must especially be conscious of dangers coming from the outer rim. One can play these scenarios in many variations, but the end result is always the same. Frontal approach collisions are so that we can apply the following basic rule:
A sailplane with which I can potentially collide is at first small, with slow movement in the outer rim of my field of visio
|Collisions in the air usually end in tragedy. Seven deaths and three injuries were the result of collision that are described here. They took place a few years ago. The accident investigation reports of last season are not yet available. But one thing is obvious already: with 7 mid-air collisions the year 1995 had scary dimensions.
At the Bartholomea-Amalienhof airfield a pilot is killed in a mid-air in July 1994. An LS-4 and a ASK-21 circle in the same thermal. Their radios are different frequencies so that radio communication is impossible. When the LS-4 leaves the thermal the pilots in the ASK-21 assume he has departed. But the LS-4 returns. The pilot does not join up in accordance with the standard procedure. A situation arises where the two pilots cannot see each other. The LS-4 is slightly higher and collides from behind with the ASK-21. He is slightly damaged and can land on the airfield. The LS-4 however suffers a broken fuselage just in front of the vertical fin. The pilot jumps, but his parachute tangles and does not open. He is killed.
In April 1993 a tragic accident happened at Brandenburg Schauplatz. A Two-Seater Bocian and a single seat Pirat report their positions. The two-seater is about 50 m higher and in a position where they cannot see the Pirat. It is probable that the Pirat pilot did no pay sufficient attention to the Bocian. Because of the inferior performance the Bocian descends on the Pirat. Just before they turn onto base leg they collide. The Bocian can land in a nearby lake, but the Pirat pilot is killed when his parachute cannot open in time.
In May 1994 there were 5 deaths in a collision over Görlitz. The pilot of a Piper PA-28 was on a local flight with three passengers. He flew near a Bocian that was circling in a weak thermal because one of his passenger was a relative of one of the Bocian crew. They collide. The Bocian pilot jumps, but the passenger does not although he had been briefed in exiting the aircraft. The four people in the Piper were killed.
At first glance it seems improbable that two airplanes meet in the same space at the same time, given the wide expanse of sky, and that both pilots do not properly look out. But the high number of collisions and near misses tells a different story. That is why it is of life-saving importance to observe the surrounding airspace. Especially in the landing circuit caution is warranted because of the increased traffic. Radio communication can be helpful before one gets too close. Near an airfield one should listen to the radio traffic. And when thermalling it is essential that all observe the ground rules.
But the peculiarities of peripheral vision offer us good protection. Danger, small movements or collision course we can recognize quite fast and safely.
The sudden appearance of moving object lead is into a closer look. We move our head, recognize the oncoming aircraft and can react in time. But that only works as a functioning reflex if we trained our vision filters for this special flying situation. While flying the entire landscape below us moves, and within it many single objects, such as cars, people, cloud shadows.
The diencephalon must have learned to filter out only the important movements in the airspace, and to guide our eyes to it. Constant and conscious training can improve and condition these subconscious mechanisms.
What possibilities does an instructors have to help a student develop the correct pilot senses? He must develop his ability especially for flying situations, he must help him to develop the sight and movement filters need in flying, and to develop a serene and dynamic viewing habit. An added complication in soaring is the fact that an instructor cannot really see where the student is looking. The tandem seats allow only verbal communication, so the instructor has to try to communicate the sight training to his student and pass on his trained viewing habits. That can only be done by constant reminders. The instructor announces what he sees, where he is looking, and the student confirms that he sees the same thing. And the student must be encouraged to announce what he sees.
Because it is not easy to communicate ones findings fast and in few words, a certain scenario should be used.
In the beginning of training the instructor announces his target by stating designation, altitude, and where applicable, movement. For example: Helicopter, at 4 oclock, under the horizon, from right to left. As soon as the student has seen the target he announces Got it. If he sees it first, he announces his observation. Although one cannot always rigidly adhere to this procedure, it is a valuable guideline.
In a Two Seater announce direction by the clock!
Directional instructions can often be misunderstood if they are announced by right or left, and that should be avoided. It is also difficult to describe direction and course movements that way. The safest and most effective direction indicator is the face of a clock. And for altitude one should use the horizon as a guide. That is especially important because the biggest danger comes from airplanes who are roughly on the horizon, meaning at the same altitude as us.
Only at very high altitudes can this guideline not be used. Because of the curvature of the earth one sees an airplane at the same altitude above the horizon.
The exchange of visual information between instructor and student has to become a normal occurrence, and cant hurt experienced pilots either. Four eyes see more than two, and the visual education never stops. For some instructors that may be inconvenient, but it is necessary.
The scanning method advocated in the US has not proven to be very practicable. They practice airspace observation by systematic scanning. But that contradicts the efficient natural method of chaotic seeing . And the best method to learn this is by exchanging information between the instructor and the student.
If the student finally sees objects before the instructor, the instructor can be satisfied that he has taught well. The student has unlearned the zigzagging view and has adopted the relaxed dynamic panning, and sees everything of importance. An experienced and observant instructor will recognize this from the back seat: The head of the student follows in small movements his view, seemingly without system, but always in the direction where something important is happening.
Proper airspace observation only works if we do not restrict our field of vision unnecessarily and remember the importance of a large field of vision. Eye glasses with broad frames, or worse, snow glasses with side shields, large-brimmed hats or hair-dos that fall into the face, have no place on a pilots head.
A dirty canopy combined with a tired pilot can hinder proper airspace observation. Its not so much because of interference with the view but more because of the tendency of tired eyes to focus on near objects. The distant airplane is only a blurred image. A compass on the canopy, or an overly large yaw string can have the same effect.
Very critical is the unnoticed shrinking of the field of vision. The eye is a very sensitive organ that can be influenced by small disturbances. Tiredness and some diseases can diminish the field of vision without the pilot being aware of it. Critical self-examination is necessary when such influences are a possibility. If one is overly tired or sick, takes certain medication or is under severe stress he should not be in the cockpit.
A special warning about the nerve poison nicotine. A smoker has a narrowed field of vision and the pupils become lazy. He lives more dangerously.
Lack of Oxygen Narrows Vision
Lack of oxygen can become a problem in as little as 1500 m altitude, and restricts the field of vision noticeably. Above this altitude the field of vision can narrow dramatically without extra oxygen. The danger of collision increases.
Vision is a most important sense for a pilot and has an irreplaceable technical function in piloting an airplane. We don’t fly blind, because even IFR the pilot has to reply on his eyes.
Flying is a visual experience. We should not forget that. Alert eyes and senses make our sport not only safer, but also much more pleasant.
translated by Albin Schreiter, CDN
All glider pilots share a common and not entirely unjustified fear from high performance military jet aircraft.
However, the military are very much aware of this potential danger and train their pilots accordingly.
The following was written by an expert of the German Air Force (Luftwaffe):
SEE AND AVOID
by Major Heß, LwA-AbtFISichhBw
According to § 1 Luftverkehrsordnung (LuftVO – German rules of the air) the airspace can be used by anyone.
Whoever uses the airspace has to make sure that he/she poses no danger or obstacle to anyone. The rules for collision avoidance are set in §§ 12 and 13 LuftVO. VFR flights in uncontrolled airspace are to be carried out following the rule see and avoid.
However, even though the procedures for collision avoidance are generally understood, mid-air collisions still happen – not only to civilian, but also to military aircraft. Between 1987 and 1999 the German Bundeswehr reported 15 collisions of German military aircraft, 6 of which also involved civilian aircraft. Over the same time-span NATO aircraft were involved in 5 mid-air collisions in German airspace and two incidents with consequential damage. Three of these cases involved civilian aircraft.
Collisions between military jets and other aircraft are usually fatal because of the high speeds, and are a particularly controversial issue if civilian persons are the “victims” of such collisions. As soon as two or more aircraft share the same airspace there is a risk of a collision. Mid-air collisions can have a number of causes.
One aspect is probably the non-compliance with rules, regulations and NOTAMs. Another cause might be the lack of attention, the belief that he who travels faster is safe, and of course the “luck” factor. One critical factor is however the fact that the performance of modern aircraft together with complex deployment situations can conflict with the limited adaptability of the human physiology. Collision avoidance is entirely based on the timely recognition of the other aircraft and the resulting action.
Recognition and avoidance
The following example (taken from: U.S. Naval Aviation Safety Bulletin) shows the time-span between seeing another aircraft and starting the appropriate avoidance manoeuvres:
Seeing an object on the canopy 0.1 Sec.
Identifying the object as an aircraft 1.0 Sec.
Recognizing the risk of a possible collision 5.0 Sec.
Decision to take collision avoidance measures 4.0 Sec.
Delay due to reaction and aircraft’s inertia 2.4 Sec.
Total approx. 12.5 Sec.
These times are the result of scientific models and assumptions.
They are therefore not generally valid.
It is a very useful basic estimate however of the time-lapse until a collision depending on the relative speed and distance. Based on this knowledge the time until a collision between two aircraft 5 km apart and with a relative closing speed of 480 kts (jet: 450 kts, glider: 30 kts) will be approx. 18 seconds and the time for successful avoidance measures will be approx. 5.5 seconds.
The detection of another aircraft is influenced by both physical (obstacles like struts or instruments in the cockpit) and physiological limitations. Visual acuity is only good in a small, central area of the retina, the so-called fovea. Even at very small angular departures from this central area, acuity drops off alarmingly to a small fraction of the central acuity. This means that if we are looking for a small object and this object never happens to fall on the area of the fovea we will probably never see it,
particularly if the target has no relative movement. If there is no motion the eye can follow, it will only move in fast jerks with interposed rests. Only when the eye stops can we see something.
Slow, systematic movements are useful when the target also moves at the same rate and can be tracked by the eye. The human eye can only detect a moving target if it has a minimal perceived size of 2 mrad (2 mm in 1 m distance). In straight flight a Cessna with a wingspan of 11 m and a length of 8.5 m for example presents the biggest relative surface from one side and the smallest surface viewed from the front or back. In particular the head-on approach of two aircraft is a great danger as here you have the highest relative closing speed combined with the lowest perception. Let me explain this with an example:
With a civil aircraft moving at a speed of 100 kts and a jet aircraft moving at a speed of 420 kts the relative closing speed is 520 kts or 267 m/sec.
At a distance of 3,210 m the size of the Cessna’s silhouette is 2.8 mrad and the time until a collision is 12 seconds.
4 seconds before a collision the distance is 1,070 m and the size of the Cessna 8.5 mrad.
2 seconds before a collision it is only six times bigger than in the beginning, but with only 0.5 seconds left it is suddenly 23 times as big.
Effectiveness of SEE AND AVOID
As a consequence of a collision between a Tornado GR1 and a Jetranger helicopter in June 1993 the British Ministry of Defence commissioned a report from DERA (Centre of Defence Analysis). The requirement was to carry out a survey on the effectiveness of the principle of see and avoid and to evaluate various measures to increase the effectiveness of this technique.
One of the main findings of the report, published in April 1997, is the fact that lookout is 95-99 % effective in avoiding a mid-air collision and therefore the most effective method.
The institute in Farnborough, UK, calculated a yearly collision rate of 0.118 between military jet aircraft, based on 1000 hours.
The collision rate between military jet aircraft and civil aircraft is 0.007.
Another result of the survey was that measures like changing the aircraft’s colour scheme, fitting the aircraft with high intensity strobe lights (HILS), forward facing lights and collision warning systems could improve the effectiveness of see and avoid significantly. Painting Hawk and Tucano aircraft for example could reduce the risk of a collision among these aircraft types by 27 %. Fitting Hawk and Tucano aircraft with forward facing lights could reduce the risk by up to 75 %.
High intensity strobe lights on all military aircraft would reduce the yearly collision rate by 15 % according to the report. A significantly reduced collision rate (approx. 66 %) could be achieved by integrating an electric collision warning system. Of course the implementation of the above features in civil aircraft, especially gliders, microlights and hang gliders would significantly reduce the risk of collision, but there seem to be insurmountable obstacles that prevent the technical and financial realization and the acceptance of technical alterations.
The RAF has already started a programme to modify all Hawk and Tucano aircraft. This modification will include a black paint scheme and forward facing lights. In addition to that the RAF plans to equip all military aircraft with a high-intensity strobe light. Within the next 3 years all military jet aircraft in the RAF will be fitted with a passive electronic collision warning (an external container similar to a flight profile recorder). The Airforce started fitting transport and special purpose aircraft with an airborne collision avoidance system (ACAS) for test purposes in 1999. Serial fitting of the system is supposed to start in 2000/2001. ACAS is not designed for the tactical deployment of fighter aircraft, and indeed at present it does not appear to be suitable for this purpose. A limited number of flight profile recorders (FPR) have been acquired as outer ballast for the flight mission assessment in fighter aircraft.
In addition to the processing of the data in a ground station FPR data transfer between aircraft in flight will be possible after a modification that will be carried out this year. Assuming that this modification includes the UHF transmitter, then collision warning between fighter aircraft with FPR will be possible via a voice output in the cockpit.
At present the Automatic Dependent Surveillance Broadcast (ADS-B), the future passive ATC system in Europe, looks to be the most promising collision warning system as it registers most aircraft by using the transponder mode “S”.
At the moment however the perception system “eye-brain” is the only effective collision warning device. Therefore it is useful to know the eye’s uses and limitations. The following hints are no guarantee that a mid-air collision will never occur, but observing these rules will significantly reduce the risk of a collision. Remember that the aircraft you might collide with is the one that seems to stay in the same place on the canopy.
- Remember that you are looking for a tiny object that will increase in size dramatically only when it is too late to avoid a collision.
- The area you would have to scan is big. However, the area from where a collision is more likely to occur is limited.
- Concentrate your search on the horizon in your flight direction.
- The time you spend not looking out (checking the instruments or the map) are potentially dangerous and should be kept as short as possible.
- Carrying out flight manoeuvres poses a risk, too, and requires an intensive lookout.
- Don’t think you can scan the sky thoroughly with smooth eye movements. Scan the sky with quick movements.
- Even small obstructions like thin struts in the cockpit can dramatically reduce the area of vision.
- Gliders and microlights are often difficult to spot in the sky because of their light colour (which is partly due to their construction) and extremely slim silhouette. Circling gliders and microlights will temporarily be invisible even though the distance might be comparably small (Note: in Germany approx. 9,500 gliders and motor gliders with an annual flying time of around 600,000 hours share the airspace with all other aircraft.).
translated by Claudia Buengen