Colour Vision in Aviation: Part 2
At the very dawn of aviation, the use of colour was introduced to convey information and orders to airborne and taxiing aircraft. Such directives as "do not land", "cleared for take-off' and "cleared to land" were passed to pilots by the use of coloured lanterns, flags and pyrotechnic flares. These techniques were adopted largely from the maritime services of the time. The use of radio in aviation was undreamed of, so there was no other reliable means of providing pilots with these important operational directives. It followed naturally that a pilot who was unable to interpret these signals could cause chaos in such an environment, so it made sense to exclude such "colour defective" individuals, even from daytime flight.
However, with the advent of radio and its use in ground to air communications the colour coded systems of signalling became redundant, all the more so as radio equipment developed in sophistication and reliability. This has resulted in the present day anomaly, whereby the colour coded light signals from tower to aircraft are still printed in the AIP and VFG but are poorly understood by most pilots.
Going back to early aviation, the early administrators saw fit to adopt another maritime convention, namely that of placing different coloured lights on the wingtips and tail of night flying aircraft. The assumption seems to have been made that such a system would aid in the recognition of the flight path of an aircraft when no other clues were available. The system of red port, green starboard and white tail lighting has never seriously been questioned. It may (questionably) work for ships, but does not work in the aviation environment, as will be shown. In fact, the system has some rather serious drawbacks. Keep in mind during this consideration that the supposed purpose of the navigation lights is to aid in COLLISION AVOIDANCE.
Let's look at the navigation light system more closely. If we place an imaginary aircraft at the centre of a circle, the navigation lights are required to be visible in specified sectors of that circle, so that the green (starboard) light covers the arc from dead ahead to an angle of 110 degrees to starboard. The white tail light then covers from 110 to 250 degrees and the red (port) light completes the circle with a red sector from 110 degrees to port to dead ahead. There may be, but need not be, a small amount of overlap between the various sectors.
It is obvious that a pilot who sees a coloured light, say a red one, may be seeing another aircraft that is doing anything from pointing almost straight at him to pointing away at an angle of up to 60 degrees to the line of sight. Such information is of no use whatsoever. The visual tasks involved in collision avoidance are far more sophisticated than the recognition of coloured wingtip and tail lights on aircraft. Let us look at what really is involved.
To avoid a collision the first task is to recognize that the object under observation is another aircraft. This is aided by the bright anti-collision and strobe lights. The next step requires an assessment of the distance separating the aircraft from the observer and whether that distance is GETTING SMALLER. This is called "MOTION IN DEPTH" and is a fundamental component of the overall task. In the entire blurb put forward by the DOA that I have read, the task of assessing motion-in-depth is completely ignored. The third and equally important component of assessing collision risk is that of determining the RELATIVE BEARING of the other aircraft. In essence, when an aircraft maintains a constant relative bearing in relation to the observer's fore-aft axis, then a risk of collision exists. When the two are combined, namely a constant relative bearing and motion in depth toward the observer, then a collision is guaranteed unless evasive action is taken by either or both pilots. The colours of the lights being observed are immaterial to the imminence of a collision. They will only tell you which side of the other aircraft you will hit.
There are of course many areas within the cockpit and outside of it where colours are used to convey information. These include hypsometric tinting of maps, coloured arcs on instruments, coloured warning and safety lights on the panel, runway and taxiway lighting, parking guidance lighting at major terminals, coloured components of landing guidance systems such as T-Vasis, airport identification beacons and more. These won't be gone into in' detail because there is a mass of evidence that indicates that the colour defective pilot is at no disadvantage in using these systems.
There is however, one use of colour that the DOA is trying to use to justify the continued restriction of the colour defective pilot and that is in the new CRT instrument displays now becoming more and more widely used in modern aircraft. Despite the fact that the manufacturers of these instruments state that the colours used in this type of instrumentation are REDUNDANT, DOA has spent big dollars trying to prove otherwise. It is alarming to me that the experimental techniques used in the testing of these instruments are unscientific. Equally, should the results show that the colour component is not redundant; the consequences could be devastating for the colour defective pilot. It is conceivable that newer restrictions be introduced to exclude colour defective pilots from even daytime flying.
In my appeal to the Administrative Appeals Tribunal, soon to be heard after two years of preparation, the DOA has made it clear that their primary concern is the issue of collision avoidance at night. In the third part of this series next month, I will discuss the inconsistencies of the DOA’s arguments.
FOOTNOTE: There has been a recent hearing before the full Tribunal of, the Administrative Appeals Tribunal on
Wednesday 18th February. The question being considered is whether it has the jurisdiction to hear the appeal by Dr Pape against the DOA's Colour Vision Policy. The outcome of the hearing will have enormous implications regarding the power of the Secretary of the Department of Aviation and the right of individuals to appeal against the DOA's policy decisions.