What does surprise me a bit is that the pilot didn’t see the inbound. At one mile he must have had the landing light on, so should have been visible even against the clutter of a built-up area (which is a problem at many US GA airports, as they are often in the middle of urban sprawl).
This is a common assumption that a landing light being on in the pattern helps with acquiring the position of a target aircraft. In most cases during the day, this is incorrect. The eye is able to distinguish an aircraft by the contrast with the background. If your aircraft is at the same altitude or lower than the target, then the bright sky is the background and the landing light or strobes are not visible until well after acquisition of the target. What the eye detects in this case is the dark aircraft against the bright sky. Since most pilots are trained to use their landing light when in the pattern, try this experiment at a local airport during the daytime. Spot the aircraft on final approach. Note what you are able to see. Determine when you are able to make out if the landing light is on or not.
During the early part of WWII, the US did not have radar that was small enough to work in aircraft. They used B24’s to spot U boats off the coast of the US and attempted to bomb them when they were on the surface. This was largely unsuccessful early on because the U boats could spot the bomber and dive for protection under the sea. To make the B24’s stealthy, they were outfitted with landing lights along the leading edge of the wing and turned on. This made them virtually invisible to an observer on the surface as it eliminated the contrast with the sky.
There is an excellent study prepared by the Australian Transport Safety Bureau titled “Limitations of the See-and-Avoid Principle” that documents the usefulness of landing lights and Strobes. It says:
There have been frequent suggestions that the fitting of white strobe lights to aircraft can help
prevent collisions in daylight.At various times BAS1 and the NTSB have each recommended the
fitting of white strobe anticollision lights.
Unfortunately, the available evidence does not support the use of lights in daylight conditions.
The visibility of a light largely depends on the luminance of the background and typical
daylight illumination is generally sufficient to overwhelm even powerful strobes.
Here is more quoted from the same study.
Field trials have generally confirmed the ineffectiveness of strobes in daylight. The following
U.S. military trials are outlined in a US Air Force report (Schmidlapp 1977).
1. In 1958 the USAF Air Training Command conducted flight tests to compare strobe anticollision lights with rotating beacons. It was concluded that in daylight conditions, no lighting system could be expected to prevent collisions.
2. Further tests in 1958 at the U.S. Air Force’s Wright-Patterson Base again found that strobe lights were ineffective in daylight.
3. A major U.S. Army study was conducted in 1970 in which observers on a hilltop were required to sight approaching helicopters equipped either with strobes of 1800, 2300 or 3300 effective candela or a standard red rotating beacon. It was found that none of the lights were effective against a background of daytime sky, however strobes were helpful when the aircraft was viewed against the ground.
4. U.S. Air Force tests in 1976 found extremely poor performance of strobe lights on aircraft. In all cases, the aircraft was sighted before the strobe. In addition, it was found that after two years service on aircraft, strobe lights were about half as intense as expected.
5. Extensive trials in 1977 by the US Air Force Aeronautical Systems Division used strobes fitted on a tower and observers at various distances and viewing angles. The results indicated that in daylight, even a strobe of 36000 candelas was not particularly conspicuous. However, strobes were more visible when the background illumination was less than 30 candelas per square metre, equivalent to a very dark day.
FAA studies have also concluded that there is no support for the use of strobes in daylight. A 1989 FAA study of the effectiveness of see-and-avoid concluded that ‘Aircraft colours or lights play no significant role in first directing a pilot’s attention to the other aircraft during daytime’ (Graham 1989).
An earlier FAA study considered that there was ‘little hope that lights can be made bright enough to be of any practical value in daylight’ (Rowland and Silver 1972). A major FAA review of the aircraft exterior lighting literature concluded that ‘During daytime, the brightest practical light is less conspicuous than the aircraft, unless there is low luminescence of background …’(Burnstein and Fisher 1977).
In conclusion, while strobes are not likely to be helpful against bright sky backgrounds, they may make aircraft more visible against terrain or in conditions of low light.
NYCYankee, thanks, that’s very interesting. However, I was under the impression that the accident pilot was above or at the same altitude as the inbound and would therefore see him (or not) against the background clutter. From personal experience in the L.A. basin, I can definitely make out the moving landing light (not the strobes!) against the visual clutter of the built-up background in similar situations.
[Bold bit fixed up – an odd “feature” of the text editor :) – if you want to apply two attributes on top of each other, you have to re-swipe the text]
I have heard of that US tactic with leading edge lights – clever!
Here, the RAF painted their training turboprops (the Tucanos) black, for better visibility.
Unfortunately I think “plastic” planes have to be white, to stop the material getting too hot when parked in a hot sunny place.
The whole visual contact thing is massively overdone. I know that in VFR conditions, “see and avoid” is all you have, but that doesn’t mean it is much good. Just because a problem has only one solution, doesn’t mean that solution works well.
If you get an active TCAS system that really opens your eyes to how much traffic there is which you (or your passengers, if you ask them to look out also) have never seen. Some of it gets very close – I would say 90% of near misses never become visual and that is after the system pretty damn well tells you where to look. I have done a number of go arounds against TCAS traffic. It does irritate 1 or 2 people (one instructor gave me a bollocking in front of his students for having used the system to avoid his aircraft – no kidding) but the system has never produced what looks like phantom returns, and one should never bet against known odds! One also often sees traffic which is reporting from a very different place to where they actually are.
Don’t all new SR22s come with TCAS? I would think Mode C transponder usage is a lot higher in the USA than in Europe – due to all the TMZs in the USA. Here, TCAS doesn’t do much for you unless you are above about 2000ft (most of the nontransponding community flies below that) – or you are in the circuit and then you can sometimes get more returns than you can take into account.
NYCYankee, thanks, that’s very interesting. However, I was under the impression that the accident pilot was above or at the same altitude as the inbound and would therefore see him (or not) against the background clutter. From personal experience in the L.A. basin, I can definitely make out the moving landing light (not the strobes!) against the visual clutter of the built-up background in similar situations.
Although it is not clear who was lower, the same report has an extended discussion on the difficulty of picking out an aircraft amongst a complex background. Unless the conditions are fairly dark, spotting a landing light on an aircraft is very difficult, above or below.
Don’t all new SR22s come with TCAS?
AFAIK yes and maybe a traffic alert made him panic enough to take this evasive action which eventually proved lethal.
I agree, but there’s on thing that makes this situation a bit different – you know where to look. The final approach path is a pretty clearly defined area (unless someone does a really tight turn-and-dive arrival, which wouldn’t be normal ops). Other than that, I know how hard it is to spot an airplane against a cluttered background.
