IMC currency

[IO540]

FlyingForFun

If flying IFR the last people I would talk to would be London Info; they are mostly used by PPL students and people going abroad (flight plans).

I would talk to the nearest place with a radar, e.g. Exeter, Solent, Thames, Boscombe, Cardiff. Even a "flight information service" from them is worth a lot more than anything I get from london Info (in my view).

Scheduled traffic does fly in VMC and IMC without an RIS, outside CAS, to some places, amazingly, especially when the radar is down.

[2Donkeys]

I think the cure for some of this discussion is to go out and get a little experience.

If you don't have much time in real IMC, or if as in some cases, you are not even rated yet, it can seem daunting to fly around in IMC not talking to anybody. From postings in the recent past, some people find the concept of flying around in VMC without talking to anybody difficult to stomach.

Once you have flown a little in IMC, you will realise that this is a non-problem. For the vast majority of the time, thre will be an ATC facility able to offer some form of limited radar service to you whilst you are in IMC. For the rest of the time, you will fly, and survive remarkably well.

Get a visit in to LTCC or your local radar unit. Some of you will be surprised I suspect by quite how few blobs there are around outside controlled airspace on IMC days. There are not an enormous number around comparatively on VMC days unless you plough the deep furrow between the South of England and Le Touquet on a sunny weekend.

As somebody else wrote earlier. This is about risk assessment. You engage in far riskier activities every day than you do when you fly without a radar service in cloud.

You are far more likely to be killed by running a tank dry or losing an instrument and crashing, than you are by a midair in IMC.


2D

[bookworm]

See and avoid is a remarkably over-rated talent on the part of most GA-pilots.

The only scientific research I've seen in this area reinforces the point quite markedly. It was commissioned after the Cerritos accident.

24 GA pilots flew Bonanzas on 45 min flights with an observer/safety-pilot in good VMC. They were briefed that the exercise was about single-pilot cockpit technique and asked from time to time to rate their workload. They were asked to call any traffic seen. A C421 conducted intercepts aiming for zero horizontal separation and 200 to 500 ft vertical separation.

The results: in 64 intercepts, the C421 was seen just 36 times, at an average range of 1 nautical mile.

(J W Andrews, Modeling of Air-to-Air Visual Acquisition, Lincoln Lab Journal Vol 2. no. 3 (1989))

Most of us have also had one or more scares in good VMC where we didn't see the other guy until the last minute.

I wonder how many went completely unseen?

[Keef]

Think that's true, bookworm.

Several times, I've seen another aircraft that's crossed my track (in VMC) relatively close, and given no indication whatever of having seen me (ie if I hadn't altered course, we might have collided).

I'm sure that I've also been the one who didn't see the other aircraft on a few such occasions.

What I have noticed very clearly is that some folks are better than others at spotting traffic. One colleague who flies quite often with me will spot other aircraft long before I do.

[bookworm]

What I have noticed very clearly is that some folks are better than others at spotting traffic. One colleague who flies quite often with me will spot other aircraft long before I do.

Yes, but I do wonder how relevant such data is. Some people are better at seeing movement against a cluttered background, which allows them to spot other aircraft in the vicinity. Unfortunately, those aren't the ones that are going to hit you in an enroute midair. The dangerous ones are the ones with no relative lateral movement, which are altogether harder to see.

[IO540]

It is probably a lot easier for a passenger to spot other planes. That's what I usually find

I think the hardest thing to spot would be another plane on a closing track from one side. You've got to be doing an awfully wide scan to see one of those.

TAS/TCAS and compulsory Mode C+ would be nice but all the statistical data shows that one could fly blindfolded (EN-ROUTE) and would still die of old age.

[andrewc]

The interesting thing about flying with TCAS, as I do,
is that the skies are far busier than you ever
thought they were when you were flying without
it's assistance.

You are far more aware of external traffic - in particular
you know where to look for a potential conflict.

-- Andrew

[englishal]

I agree that meeting traffic in IMC in Class G in the UK is unlikely, but the risk is there, and no doubt it'd prove to be terminal.

Out of interest how many of you use a mode C transponder while flying in IMC / IFR? (I do) I'm curious as I'm wondering on the usefullness of these portable "TCAS" units (www.avshop.com). Although they don't tell direction they will tell you differential altitude and range, which are the important things and I'd be happier flying IMC in the UK without a RIS if I had some means of traffic avoidance.

Cheers
EA

[bookworm]

The interesting thing about flying with TCAS, as I do,
is that the skies are far busier than you ever
thought they were when you were flying without
it's assistance.

One part of Andrews's paper I didn't describe was a comparison of the 'unalerted' visual acquisition capability with the TCAS equipped equivalent. The results were, as you would expect, vastly better. 57 of 66 targets were acquired, and 5 were not acquired because avoiding action prevented a visual sighting. Moreover, targets were sighted earlier giving the pilots a much better chance to assess the threat and take avoiding action. In the terms of the paper, the probability of sighting per unit time per unit solid angle of target was increased by a factor of about 9.

The problem with the portable collision avoidance units is that they don't give any azimuthal indication (i.e. relative bearing to the target). It's that that is the main contributor to increasing acquisition probability. Simply knowing that something is out there and getting closer doesn't help much unless you know where to look.

[IO540]

englishal & andrewc

I can see that TCAS must be an eye-opener and I also know (simply from flying under an RIS) that there are many more planes around which one never sees (even when told roughly where they are).

The HUGE problem is the number of people who fly without a transponder, or with it switched off, accidentally or deliberately. This is immediately apparent when getting an RIS. Many that one does spot are far from being bits of old junk.

I would not spend any money on a box which does not tell the direction in which to look. Most of the alarms one will not be able to act on at all.

So I could spend about £25k on kit which would help by perhaps only 30%. The other 70% won't show up.

[2Donkeys]

I am with IO540 on this

I too fly with TCAS, and in the controlled airspace environment of airways flying it is perfect. In principle, everybody has a transponder, and TCAS provides both situational awareness clues as well as a degree of protection if used correctly.

Outside controlled airspace, there are too many non-squawking aircraft, Mode A targets and other bits and pieces floating around for it to be as effective. I switch to TA-only mode under those circumstances so that at least I get some clues as to where traffic might be visually acquired. More than that is deeply unreliable.

The TPAS units I have seen advertised look like a monumental waste of money. I played with one in a friends aircraft, and apart from inducing panic that an aircraft might be close, it did little to help.

My experience was that it had big difficulties spotting the difference between traffic at the same level half a mile ahead, and traffic over the top of us 2000+ feet above.

2D

[Flyin'Dutch']

Interestingly I did a trip to Holland earlier this year and flew a few days around there. It is now mandatory for all traffic above 1200ft to have Mode C. That is all traffic apart from gliders.

So even with the TCAS in the Cirrus it remains paramount to keep a good lookout.

It is very illustrating to go and fly in a TCAS equipped machine and find out how much traffic you miss even when you do your best to keep a good lookout. Even when the TCAS points out to you where the others are it takes some good looking to see it against some backgrounds.

FD

[englishal]

I did wonder about the usefulness of these TPAS units. Sounds like a good idea, but as pointed out, no azimuth info will probably just create unnescessary worry......so I'll save my money.

Cheers
EA

[FlyingForFun]

For anyone who hasn't noticed, I've started a related thread in the Questions forum to find out what our commercial friends do when flying through uncontrolled airspace in IMC without any radar coverage.

The initial responses seem to be along the lines that

Quadrantals protect you against collision

I have previously said that I won't fly in IMC without any radar coverage. But if it's acceptable in the commercial world (even without TCAS in the case of at least one poster, although that was before TCAS was common on commercial aircraft) then I could be pursuaded to change my mind. I haven't been pursuaded yet, but I could be.

FFF
---------------

[Flyin'Dutch']

TCAS is a help but not a panacea.

Before being exposed to it I was playing with the idea of getting one of these handheld TPAS units.

Would not bother now as:

1. In the open FIR (where you are least likely to have a meaningful service) most bogeys will not have a TXPDR so they are not going to show up anyway.

2. Without azimuth and bearing information you will just get worried sick, swivelling your head in any direction to find it, potentially interrupting a 'good can' and detracting from conflicting traffic in your path.

When not able to get a RIS/RAS in the open FIR it still pays to talk to a meaningful station as most sensible people will do the same.

FD

PS: Relying on quadrantals for protection is the same as trusting the 'big sky theory'

[IO540]

Relying on quadrantals for protection is the same as trusting the 'big sky theory'

I must be missing something obvious here, but surely the quad/semi rules do nothing at all apart from reducing the speed at which traffic on a recip or roughly-recip track is likely to meet each other.

The collision speed would still be high enough to destroy both planes, in most cases.

Is there another reason for this system?

In IMC it might help with procedural separation but that requires radar assistance to start with, or control of departure times and speed.

[Flyin'Dutch']

IO wrote:

I must be missing something obvious here,

Well if everybody would stick to them and nobody had to climb to the 'opposing' traffics altitude/levels it would provide additional separation.

Alas non of the above assumptions are facts of real life aviating so it is nothing more than an aid to separation.

Maybe invented by the people that claim: 'Every little helps'

FD

[IO540]

Well if everybody would stick to them and nobody had to climb to the 'opposing' traffics altitude/levels it would provide additional separation.

Only by dispersing traffic, by taking more advantage of vertical spacing. So the benefit is only statistical. There is no increase in separation.