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I met someone the other day who owns a small plane and he was going to fly from Cambridge to the Isle of Wight. I asked him whether he had to file a flight plan and he said no.

Just wondering therefore how such collisions are prevented?

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Most air collisions in the uk seem to between military aircraft. –  RedGrittyBrick Aug 21 '14 at 13:58
@RedGrittyBrick formation flying is always dangerous, and a lot of the accidents involved trainer aircraft, so probably were formation flying training... –  jwenting Aug 21 '14 at 14:00

4 Answers 4

Small airplanes will be under VFR (Visual Flight Rules) which entails that the pilot looks out the window and is responsible for staying away from other aircraft and staying out of the clouds (the fog banks of the sky).

If you see another plane in your path then there are standard rules to avoid him see this question.

They can fly under IFR (Instrument Flight Rules) but that requires that Air traffic control monitors the airplane and steers it away from other planes.

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thanks. I'm quite surprised that it relies on pilots being vigilant... for example what if one plane is descending and another climbing... it's got to be difficult always to keep a visual watch in 3 dimensions... presumably there haven't been many collisions otherwise this system would have been called into question... –  mike rodent Aug 21 '14 at 13:12
@mikerodent The pilot must always be vigilant –  ratchet freak Aug 21 '14 at 13:24
@mikerodent There are quite a number of accidents and incidents involving small airplanes. Not only mid air collision but also cases of small aircraft straying unintentionally into controlled airspace. There is work going on to make it cost effective to equip small aircraft with ADS-B OUT and ADS-B IN so that an extra early warning for nearby traffic is possible. –  DeltaLima Aug 21 '14 at 13:40
@mikerodent Also bear in mind that there are very few planes in the air and, also, that it's much harder to hit something in three dimensions than it is in two. For example, if you were to drive from Oxford to Dover while your friend was driving from Cambridge to the Isle of Wight, your paths would certainly cross (ignoring the possibility of bridges) and you would crash if you both reached the crossing point at the same time. However, if you both flew, your tracks over the ground would have to cross but you might fly over that point at different altitudes as well as at different times. –  David Richerby Aug 21 '14 at 13:42
@DavidRicherby yes, that thought had occurred to me... and ultimately engineers deal in probabilities (e.g. that a wing won't fall off an A380)... but the VFR system described is, it seems to me, clearly sensitive/vulnerable to the number of people owning and using small aircraft, and to the restriction of usable areas if ever controlled areas are extended. Particularly in proximity to the runways where small aircraft take off and land. –  mike rodent Aug 21 '14 at 13:46

Glider student here.

There is no electronic or administrative system which can replace pilot vigilance. In the US (I am not familiar with the regulations anywhere else), the end responsibility to avoid other aircraft ALWAYS falls with the pilot in command, even when given clearance/directions from ATC.

There are systems to help though. Popular with glider pilots (especially in Europe, but increasingly in the US) there is a system called FLARM which broadcasts GPS and baromatric data. Other aircraft with FLARM units within range receive this signal and selectively warn the pilot of collision hazards. FLARM has a number of shortcomings which pilots must be mindful of; eg: aircraft without a FLARM unit are not tracked, it has limited range so it isn't very helpful for distant or fast-moving aircraft.

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According to Wikipedia: "In the UK the telecom authority and Civil Aviation Authority confirmed in 2007 that FLARM was acceptable and so it is also being adopted there." –  RedGrittyBrick Aug 21 '14 at 19:56

Whilst there isn't really a good all round on board system for GA aircraft in the uk. It's good practice to get a Lower Airspace Radar Service from a nearby unit if available.

The level of service depends on how busy the unit is, but generally you can get some form of deconfliction service which provides traffic information and avoidance steers.

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To add - you don't need to be IFR to get a LARS service. –  vectorVictor Aug 31 '14 at 7:27

As has already been mentioned, the primary method of avoiding other aircraft when flying VFR is to simply look out the window and don't fly into another aircraft. However, pilots in the same area are also usually in contact with each other by radio on a frequency that is determined by where the aircraft are operating. Pilots advise each other of their intentions by radio, which allows other pilots to know where they are and what they're planning to do.

The specific case of around airports was mentioned in a comment earlier. This is indeed the area where pilots have to be most vigilant in avoiding other traffic (because there's more of it around airports.) However, for uncontrolled airfields, there are specific, standard traffic patterns that pilots are supposed to fly when approaching or departing from a given runway. While pilots should always be vigilant in monitoring every direction, following this pattern allows pilots to know where to expect other aircraft to be around the airport and monitor those areas most closely. And, again, pilots approaching or departing from an airfield should advise other nearby pilots of their intentions via radio.

Of course, at controlled airfields, pilots are required to maintain radio contact with the controllers and follow their instructions so long as it's safe to do so.

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