Primarily for general aviation discussion, but other aviation topics are also welcome.
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By Maverick
#72837
Timothy wrote:
Dunk wrote:
    Between GA aircraft
    In VFR
    In good weather
    In the circuit (80% or which on final)
    With a Certified Flight Instructor on board

Which is why the "you must never go in cloud without radar" brigade are so misguided.


I agree with you Timothy. I would summarise as follows:

There is undoubtedly a risk of collision in IMC and undoubtedly an increased risk without a radar service but the risk is still very low and massivley lower than the risk when flying in good VMC. If you're worried about flying in IMC without radar then you should be so worried about flying in good VMC that you should never do it.

...and people fly around in good VMC with their eyes closed (metaphorically) all the time :!:
By bookworm
#72852
The problem with such inference about flight in IMC, as I posted elsewhere I think, is that it's not possible to distinguish between the proposition that the risk is low, and the proposition that the aggregate exposure to such risk is relatively small.

That there are few collisions in IMC may indicate that either:

a) that the risk of a collision in IMC is low or
b) that few people are daft enough to fly in IMC without a radar service :)

All the supporting (experimental, not statistical) research I've seen suggests that the probability of detecting another aircraft on a true collision course in VMC with enough time to do anything about it, is uncomfortably low without help from artificial systems like RIS or TCAS.
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By buzzman
#72866
I was flying with my instructor, north from Brookmans Park towards Cambridge in IMC at 2400 under RIS when Stansted radar says "traffic 12 o'clock, 4 miles, similar height, not under my control".

A few moments later he says "traffic 12 o'clock, 2 miles, similar height, closing, not under my control"

What to do?

Should we climb? descend? turn? ...and what if the other pilot was on radar with, say, Luton and he did the same as us?

My instructor and I looked at each other until we heard "traffic clearing in your 6 o'clock". We were in full IMC the whole time and never knew how close we were.
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By Dunk
#72870
Maverick wrote:Dunk,

I'm sure your post is light-hearted ..... but ......Saying "most collisions occur with an instructor on board" is not the same as saying "you are more likely to have a collision if you have an instructor with you".



Yes it was intended to be light-hearted, and yes you are absolutely right about the nuances.

bookworm wrote:
Do you have a reference to the paper please, Dunk?



Certainly, but it'll be a dog to get hold of

    Approaching Equivalence: UAV See and Avoid System Reliability Requirements, Ryan J Shaefer, SRA International Inc, presented at the Nineteenth International Conference on Unmanned Air Vehicle Systems


The topic will be quite scary to many - how do you fancy sharing the skies with unmanned drones, either autonamous or remotely controlled? Various people are developing collision avoidance systems for UAV's.

Of course you can't make a perfect automatic system to do this, but you don't have to - it only has to be as good as or better than the Mark One Human Eyeball. Unfortunately that means that the "average GA pilot" is used as the not very good yardstick for UAV designers to aim for.

Dunk
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By Steve Morley
#72876
Well Dunk. I saw your joke as a joke and it made me laugh. :D Plus the main thrust of your post provoked a really good debate! Double whammy there!
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By Vince C
#72877
You may also find that almost every pilot involved in a collision was wearing shoes. So for absolute safety, remove your shoes before flight. 8)

You may think this sort of silly-think is absurd, and so it is. But it's surprising how much it is used in presenting statistical cases, especially by government departments and quangos.

Vince
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By Steve Morley
#72879
Stats, like oral contracts, are not worth the paper they are written on generally.

They just reinforce the opinions they were commissioned to uphold.

That's according to a recent poll, of course :wink:
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By Keef
#72911
There is no example of a minister of religion in full choir dress flying VFR in the UK being involved in an air accident. I've got my safety plan well stitched up ;)

PS: nor of him being "done" by the CAA for any infringement. :twisted:

Aren't statistics wonderful!
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By Maverick
#72934
bookworm wrote:That there are few collisions in IMC may indicate that either:

a) that the risk of a collision in IMC is low or
b) that few people are daft enough to fly in IMC without a radar service :)


Clearly the case, but I think this is a redundant distinction.

To further address the question I think a distinction has to be drawn between flights that are not receiving a radar service, but are nevertheless in radio contact with an ATSU and are following published procedures, and flights that are just buzzing around in IMC. The former is not unusual since there are many airfields that have IFR procedures published outside controlled airspace at airfields that do not have radar. In these circumstances I would say that the risk of collision between participating aircraft is intrinsically low. There remains a risk that someone will stumble into the region, IMC and not in radio contact and on a collision course but this is very unlikely just because it is very rare. The answer in this case is therefore a) and b). In the latter case, whilst I would certainly not advocate it for any length of time, it is probably still true that the risk is very low simply because very few people will be doing it in the same place at the same time i.e. a) because of b).

I think much of the debate stems from the fact that different people have different scenarios in mind. If you are an IMC/IR rated pilot who flies in IMC regularly you will know that you cannot always get a good radar service. Provided you obey the rules and use the radio sensibly I think you can be confident that even when not receiving a radar service your risk of collsiion is very low and less than that when flying VMC on a sunny day in the circuit. This is quite different from the image of a thousand IMC rated PPLs all doing unusual attitudes in IMC below the TMA north of London and not in radio contact with anybody - clearly not desirable but presumably not reality. If it were then we would obviously have to rethink.
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By wonko the sane
#73034
Dunk wrote:Presumably therefore, if a mid-air is imminent you should reach over for the instructor's door and tip him out. The statistics say so.


This is why you should always carry a bomb onto a commercial flight when you're travelling. Statistically speaking, there's something like a 2 million to one chance that the aeroplane you're on has a bomb on it. But there's something like an 80million to one chance that there's two bombs on it. Therefore ....
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By Timothy
#73036
...and indeed why you should never go to bed. More people die in bed than anywhere else.
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By rodan
#73043
buzzman wrote:I was flying with my instructor, north from Brookmans Park towards Cambridge in IMC at 2400 under RIS when Stansted radar says "traffic 12 o'clock, 4 miles, similar height, not under my control".

A few moments later he says "traffic 12 o'clock, 2 miles, similar height, closing, not under my control"

What to do?

Should we climb? descend? turn? ...and what if the other pilot was on radar with, say, Luton and he did the same as us?


Request avoiding action? Make a right turn as per the rules of the air?
By Guest
#73049
On a practical point it is sometimes nigh on impossible to get a radar service quickly enough anyway. The last thing a pilot needs when running into cloud and being buffeted about is trying to negotiate a radar service.


I can't remember the last time there was any negotiation. Either a service was granted, or not. Occasionally, the service has up- or down-graded as circumstances have dictated.

In Buzz's example of two aircraft outside controlled airspace on a converging heading, the real answer would go something like this

Where the other traffic is working Luton.

Essex Radar - "Traffic in your 12 O'Clock range 4 miles converging at the same altitude working Luton -would suggest a turn onto heading nnn to keep you clear"

Or more interestingly where the other traffic is not working Luton and you are under a RIS

Essex Radar -"There is traffic in your 12 O'Clock range 4 miles on a converging heading indicating same level unverified"

G-ABCD: "Errrr Roger"

Essex Radar - "Previously reported traffic now in your 12 O'Clock range 2 miles, are you happy to maintain your own separation?"

G-ABCD: "Errr mumble errr mumble"

Essex Radar: "Avoiding Action Turn Left heading nnn G-ABCD Radar advisory service"

Or something along those lines (apologies in advance to the ATCOs)

An ATCO watching you on radar has a duty of care to you, whether they like it or not, and if equipped to prevent you from hitting another aircraft, this will override the limitations of the service that you are being offered, to the extent that this is technically and operationally possible.
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By Dave Phillips
#73075
Top Tip - for a start don't fly at 2400ft underneath the TMA; every other idiot is at the same alt.