Primarily for general aviation discussion, but other aviation topics are also welcome.
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By kanga
#1893907
CloudHound wrote:Radio Counter Measures?


Sorry, yes: he was a specialist jamming operator (comms and radars); there was a 'regular' WOp carried as well

The jamming equipment was so big and heavy that

a. they had to taxi over a pit to load it into the bomb bay: it could not be slid underneath the fuselage on a bomb trolley, given the low ground clearance of a Liberator

b. they were lighter on the return to UK only by the weight of fuel used, not by the release of bombs, so could not fly much higher than outbound unlike the returning bombers.
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By Rob P
#1893924
kanga wrote: they were lighter on the return to UK only the weight of fuel used, not by the release of bombs, so could not fly much higher than outbound unlike the returning bombers.

The same issue that made the YB-40 (Massively armed B-17 Fortress that was meant to escort the bombers) a total failure.

Rob P
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1893958
JAFO wrote:My favourite was QRM but I never had the opportunity to use it.


It's used in amateur radio a lot as there's often some sort of interference.

Not in that sense...
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By David Wood
FLYER Club Member  FLYER Club Member
#1893967
BoeingBoy wrote:
There is no requirement for you to use the semi circular rule +500' when VFR, but it's no bad thing to to.


No-one has ever been able to explain to me why following the semi circular (especially when in IMC) is ever a good thing.
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By Paul_Sengupta
FLYER Club Member  FLYER Club Member
#1893999
kanga wrote:often, in my experience, misused, when QRN was meant </radio geek :oops: >


Sometimes it's difficult to differentiate. Would you call interference from a switched mode PSU in an LED bulb as QRM or QRN? A high level of background noise could be LED bulbs or other electrical noise, or it could be atmospheric.
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By BoeingBoy
#1894124
No-one has ever been able to explain to me why following the semi circular (especially when in IMC) is ever a good thing.


It caters for the situation where ATC is not always as available as it is in Europe and also for random flights in IMC outside controlled airspace.

Two flights unable to contact ATC (maybe just due to terrain or poor reception) have a fighting chance of not hitting each other. Don't forget it's a global concept so caters for countries with problems different to here in Europe.
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By David Wood
FLYER Club Member  FLYER Club Member
#1894139
BoeingBoy wrote:
No-one has ever been able to explain to me why following the semi circular (especially when in IMC) is ever a good thing.


It caters for the situation where ATC is not always as available as it is in Europe and also for random flights in IMC outside controlled airspace.

Two flights unable to contact ATC (maybe just due to terrain or poor reception) have a fighting chance of not hitting each other. Don't forget it's a global concept so caters for countries with problems different to here in Europe.


Hmmm. Unfortunately that just doesn't make sense. I don't mean to sound rude, but it doesn't.

A moment's consideration will show that confining traffic into a series of levels only increases the risk of collision. It does nothing to decrease it. That is especially so in areas like the UK where there are often relatively few levels that a GA aeroplane can take up between the ground and any overhead Class A.

The was a whiff of merit to the argument you make in the days of the Quantrantal Rule, under which all traffic at a particular level would be flying in a 90 degree arc and therefore all flying in roughly the same direction. But the move to the Semi Circular Rule where the traffic is flying in a 180 degree arc blows that argument out of the water.

As an example, if you are flying roughly north or south (as I do, IFR on business quite often) you could quite conceivably meet traffic just a few degress off the nose, converging, at the same level.

The best way of minimising the risk of collision would be to allow traffic flying OCAS to fly at any level. The semi-circular rule has no merit, in my view, and should be scrapped.
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By BoeingBoy
#1894165
Hmmm. Unfortunately that just doesn't make sense. I don't mean to sound rude, but it doesn't.


Firstly you are right that allowing total freedom of cruising altitude and direction reduces the risk of collision, that's why many global ATC authorities are working on 'free flight' programs and why all ATC routes in Scotland in upper airspace have been scrapped. However that's predominantly to cope with high density airspace like Northern Europe and the States.

Now let's go to Africa and less well developed regions where ATC is minimal to say the least. If the authorities do not allow 'free flight routing' and restrict passage to airways you need to have a built in system of protection for aircraft travelling in opposing directions. That includes the 359/181 degree conflicts.

To put it into context, several years ago I took a 757 down to the Gambia. We were put down to a non standard level under radar control by Canaries. Trouble is we lost VHF contact with them before they could clear us back up. Using the 'All radio' public broadcast system we heard a Scandinavian aircraft coming Northbound at our level. As we couldn't raise the local ATC I had to take the decision to revert to our standard 'semi circular' level without any clearance. Just as we levelled off he shot underneath us, whinging like hell and threatening to file an air miss.

However, closer to home are IFR flights operating in regions like Wales and Scotland. Sods law says that if two aircraft are in opposing directions at the same level in Class G airspace they'll find each other eventually. At least putting some protocol in place to protect against that is what the Semi Circular rule is for.
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By kanga
#1894167
BoeingBoy wrote:... We were put down to a non standard level under radar control by Canaries. Trouble is we lost VHF contact with them before they could clear us back up. ..


.. ah, if you had been carrying a FRO and using HF Morse .. :wink:

[my last scrounged AIDU ERS, 2009, shows HF frequencies for 'Canaries Radio']
By A4 Pacific
#1894171
I’m afraid talk of flying through Africa may be another red herring. There is no radar coverage in much of that continent, yet it is relatively busy airspace.

By far the most effective means of avoiding MAC there is the use of SLOP, TCAS and the IFB.

Of course SATCOM (if fitted) can normally be used to contact ATC agencies should the radio be problematic.

Interestingly, if you must adjust altitude in the North Atlantic RVSM/datalink airspace without a clearance, (another procedurally managed area with no radar) then flying a FL plus or minus 300/500’ is mandated.

As for business trips flying North/South, at least the semi circular rule means you have a pretty good idea of where the most dangerous traffic is likely to be coming from, should you have any opportunity to acquire it!

Personally I think this discussion merely highlights just one of the potential dangers of flying IFR outside Controlled Airspace.

Inside CA, the semi circular rule works well for all parties at the table.
By Ibra
#1894174
Sorry what hard data we have on MAC in Golf? we can imagine plausible scenarios but not much can be supported by actual data:

There is a list here (about 337 are documented in the last 100years) with only a small fraction OCAS and a very tiny in cruise OCAS:

https://en.wikipedia.org/wiki/Mid-air_collision

https://aviation-safety.net/database/ev ... Event=COAI

I am sure there are plenty of airprox or aircraft spotting or loss of separation in Golf but that is nowhere near a “collision risk”? the formers are subjective (except separation which is well defined in ATC jargon but it is not offered or reported for flights OCAS), so I am sticking to the latter (collision is very objective), maybe there are load of undocumented collisions but you can’t hide two aircraft? Ok looking at the documented cases:

About order of magnitudes of x10 over 100 years were IFR/IFR in all in VMC on Airways on procedural ATC

The most notable one is this, flying IFR airway and visually avoiding CB & terrain from the same side, since then US Congress imposed controlled IFR and Echo airspace and radar everywhere for public transport

https://en.wikipedia.org/wiki/1956_Gran ... _collision

Once in 5 years, IFR vs VFR in VMC near controlled airports
Last ones were 6 months ago:
- in Denver, where an SR22 & Metroliner, no TCAS in both (theoretically, it should not happen if the VFR did fly a tight visual circuit with steep low power approach, you are nowhere at 800ft agl on 3nm final while VFR? or maybe it’s the case now as they teach VFR landings with ILS & PAPI and full power?)
- in Alaska, FAA was searching for “hit & run” from the surviving aircraft (it was a paraglider)

The most notable one was this one where TCAS was mandated for public transport in Part121, again by US Congress bill (TCAS is not yet mandated for Part135 as the Metroliner case show but still both aircraft had the mandatory ADSB :eye: )

https://en.wikipedia.org/wiki/Aeroméxico_Flight_498

Hundreds of MAC from VFR vs VFR near airports in VMC OCAS

Maybe millions of airprox?

No VFR/VFR collision happened in VMC above 5kft agl OCAS in the last 50 years

No IFR/IFR collision in clouds happened in IMC OCAS since 1940

The last two won’t change above FL50/5kft agl using semi-circular or random as there is not much traffic for it to happen (yes load of airporox may happen but you need to see 10000 airporox or loss of separation for collision to happen)

Where things get messy is if you ask everybody to fly under 5kft airspace at FL35, FL45, FL40, FL45, then I am sure assign in/out routes would be a great idea otherwise let it mix and leave maths & thermodynamic do it’s job, it’s far better than people when it comes to diluting probabilities :thumleft: just watch out when going to an airport or circuit or near cloudbase, that is where most of the risk sits, for cruise above 3kft OCAS you are most likely to lose the altimeter or have a random heart attack than hitting someone…

PS: when you cross French/Spanish border you have to swap from N-S semi-circular to E-W semi-circular, I bet zillions of people like me did not know this and still none has fallen out of the sky yet :lol:
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By David Wood
FLYER Club Member  FLYER Club Member
#1894181
A4 Pacific wrote:Personally I think this discussion merely highlights just one of the potential dangers of flying IFR outside Controlled Airspace.


What are the other potential dangers in flying IFR OCAS, may I ask? Do you mean flying in IMC OCAS or are you using the two terms to mean the same thing?

Personally I always feel much safer flying in IMC (under IFR) OCAS because 1) almost by definition I'm higher than 90% of GA traffic; and 2) I'm in a cloud where much of GA fears to tread. The risks of collision in IMC are tiddly-tiny, more or less negligible. My point was that they could be reduced even further from almost negligible if the tiny volume of GA traffic that is flying in IMC wasn't mandated to fly at a small number of set levels.

A4 Pacific wrote:Inside CA, the semi circular rule works well for all parties at the table.


I don't think I've ever flown by the semi-circular rule when inside controlled airspace. Why would one do that when being, by definition, controlled?
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