Thursday, 13 July 2017
Acknowledgements: THE UK CAA’S AIRPROX SAFETY MAGAZINE 2017
Every year there’s an increase in Airprox occurrences as the better weather arrives. It’s probably no coincidence; those who aren’t hardy winter flyers get back into the cockpit, perhaps a little rusty after a bit of a lay-off, and as a result there’s a great temptation to focus on getting hands and minds recalibrated rather than looking out. We see something like one mid-air collision per 60 Airprox occurrences, so take a couple of minutes to remind yourself before each flight of the risks and causes of Airprox, and when airborne use THE MOST USEFUL INSTRUMENTS IN YOUR COCKPIT as much as possible - your EYES.
How long do you reckon it takes from seeing another aircraft to hitting it – 30 seconds to a minute, maybe? NO! lf you’ve been unlucky enough to have had a very close encounter you’ll know you have nowhere near as long as 30 seconds to take action; a bit like a slow-motion train crash, everything seems to take a long time until the last few moments when it all happens in split seconds. Research shows that in normal circumstances the average pilot and aircraft needs anything from nine to 12.5 seconds from spotting another aircraft to processing the closure geometry and avoiding a potential collision.
So, take two PA-28s meeting head-on at around 90kt each; there’s around ten seconds from the most eagle-eyed pilot being able to spot the other aircraft and impact. The crucial thing here is that in the first five seconds little seems to happen with not much change in the size or motion of the oncoming PA-28 - it’s only in the last five seconds that it suddenly blooms in size; the mind then takes a couple of seconds to recognise it as a threat, leaving just three seconds or so to take action. Naturally, the odds of spotting a potential collision reduce in relation to time spent looking out, and the best rule of thumb is 80 percent of the time looking out and just 20 percent inside the cockpit in small chunks.
A recent collision between two PA-28s shows just how looking down into the cockpit can lead to trouble. The two aircraft were flying on a converging track, and while one pilot looked down to set QFE on his altimeter in preparation for landing, the other looked down at his map – moments later they collided. They were lucky, and both were able to land safely. The AAIB concluded: ‘It is likely that poor into-sun visibility, the constant angle between the tracks of the aircraft, and the fact that the attention of both pilots was inside their respective cockpits before the collision, contributed to the breakdown of the see-and-avoid.’
So, looking for other aircraft is vital, especially before going head-down in the cockpit, but just ‘looking’ isn’t enough. Even in a featureless sky eyes tend to focus somewhere, but if there’s nothing specific to focus on they revert to a relaxed intermediate distance, which means you don’t necessarily see anything that’s going on out there. Movement is a very important attention-getter, and with no visual clues there’s a tendency to focus at a point in space one to two metres away; so, you’re not necessarily going to see something at a distance. A periodic glance at objects such as the wingtips will stop this ‘empty field myopia’.
Colliding aircraft have a relative bearing constant to each other until impact. The collision threat remains in the same place on the canopy, so moving your head relative to the canopy or windscreen is an important aid to a successful lookout.
A collision threat’s size on the retina roughly doubles with each halving of the separation distance, so colliding aircraft stay relatively small until shortly before impact when it all happens rather quickly! This underlines the importance of apportioning the correct amount of time for a systematic and repetitious scan pattern. ‘Lookout’ should be performed using a series of small eye and head movements with intervening rests, and whilst carrying out regulated scans might sound a bit formulaic they do work. For example, the RULE OF 3s which involves dividing your field of view into 3 zones, with 3 areas in each. Start scan on centreline (greatest threat); return scan to centreline (greatest threat). First look at centre 3, then 3 hops left; back to centre, 3 hops right; back to centre, look inside.
No one is immune from mid-air collision, but an understanding of the limitations of vision, collision geometry and visual scanning technique will help to avoid one.
Other important aids to airprox avoidance include:
· Ears – communicate by talking/listening on the radio to make your intentions clear and maintain situational awareness of others.
· Foresight – fly defensively, with vigilance, courtesy and consideration for others (aka airmanship).
· Insight – review your understanding of ATC services, rules of the air, circuit patterns and procedures.
· Advertise – make your presence known through conspicuity measures (electronic and visual).
· Prioritise – time-share cockpit tasks and avoid distractions compromising your lookout.