IMC Minima (sorry...)

[Shunter]

I'm sure this has been done to death somewhere, but despite searching I can't find it spelt out in black and white anywhere. Instructors, websites, textbooks, forums, all saying different things. I was especially concerned at having seen an IMC exam question which I believe took the advisory, not the legal position. So...

1. MDH - 200ft for precision, 300ft for non-precision. Many sources state 500ft/600ft respective absolute minima for IMC. Advisory, or law?

2. 50ft Position Error Correction for precision approaches. Advisory, or law?

3. You must be clear of all cloud at or above your min decision height, even that tiny little puff of FEW001 you might fly through at 100ft AGL having long since become visual with the airfield. Advisory, or law?

Thanks

[bookworm]

1. MDH - 200ft for precision, 300ft for non-precision. Many sources state 500ft/600ft respective absolute minima for IMC. Advisory, or law?

Absolute and recommended, not law. "Absolute" means "not relative" not "mandatory".

2. 50ft Position Error Correction for precision approaches. Advisory, or law?

The PEC is the error in your altimeter (and should be detailed in your AFM -- 50 ft is an "I couldn't be bothered to look it up" number). Think of it like your car speedo -- the requirement is to remain within the speed limit, and you need to take account of the errors in your speedo in doing so. In the same way, you need to pay attention to the PEC, as it's your only way of measuring that legal 200 ft or whatever.

3. You must be clear of all cloud at or above your min decision height, even that tiny little puff of FEW001 you might fly through at 100ft AGL having long since become visual with the airfield. Advisory, or law?

[shall not] descend below the relevant specified minimum descent height unless ... from such height the specified visual reference for landing is established and is maintained.

Feel free to fly through the cloud as long as you can still see the runway environment or approach lights while in it.

[Shunter]

Thanks for that. Answers pretty much everything.

I shall duly, yet respectfully, inform my instructor that he ought to revise his figures :ugh: Not that I plan to go out and start flying minima approaches, but since a lot of aviation is about dotting the I's and crossing the T's, it's nice to know the solid facts.

[Contacttower]

I'd agree with all the above...just to add that for Non-ILS approaches 600ft is the minium or add 200ft to the published whichever is higher. So if a published MDH is say 500ft then an IMC holder would go to 700ft.

[High Wing Drifter]

It is all here: http://www.ais.org.uk/aes/pubs/aip/pdf/aerodromes/30101.PDF

[tmmorris]

Contacttower,

No, no, no! We've argued this endlessly.

There is no requirement for IMCR pilots to add that 200ft. It is recommended, not mandatory, like the 500ft/600ft minima. Personally I work to an absolute minimum of 800ft, because I don't fly often enough to trust myself below that; but I practice to lower and legally I can do it (ILS minimum at my home field is 230ft).

And the 600ft is not for non-ILS approaches: it's for non-precision approaches. Precision approaches include ILS, MLS and PAR, and probably others I've forgotten...

Tim

[Fright Level]

I didn't think there was any limit for non public transport flight? With an IMC rating, you're unlikely to be operating public transport so could, technically, use any minima you like.

[tmmorris]

From the AIP reference quoted above:

1.3 Under the provisions of the Air Navigation Order 2005, public transport aircraft shall observe AOM, non-public transport aircraft
shall observe AOM when conducting an approach to a runway with a notified Instrument Approach Procedure (IAP).

Tim

[Fright Level]

Thanks for the reference Tim. Not that I'd every consider going below published minima in any case.

[212man]

Sorry to be a pedant, but it's DH for a precision approach, not an MDH!

[Shunter]

Thanks for the AIS link.. this is what I was after...

3.3.2.1 Pilots with a valid Instrument Meteorological Conditions (IMC) Rating are recommended to add 200 ft to the minimum
applicable DH/MDH, but with absolute minima of 500 ft for a precision approach and 600 ft for a non-precision approach. The UK IMC
Rating may not be valid outside UK territorial airspace, therefore IMC Rated pilots should check the validity of their rating for the State
in which they intend to fly. If the rating is not valid pilots must comply with the basic licence privileges, subject to the regulations of that
State.

[Contacttower]

No, no, no! We've argued this endlessly.


I didn't actually say that it was a requirement....I was merely quoting the IMC Confuser which granted isn't LASORS but is what a lot of IMC rating students use.

[Fuji Abound]

I was merely quoting the IMC Confuser

Must be why it is called the IMC Confuser. :)

[Blinkz]

ok there seems to be a lot of confusion here. First MDA(H) is ONLY for non-precision approaches, for a precision approach there is a DA(H).

The minima for each is dependant on a number of factors, the actual approach being used (eg. a CAT3 ILS has lower DH then a CAT1 ILS) and also the OCA(H). So the higher of the two will be used obviously...

For each approach there will be a plate with the relevant procedures on with the heights/altitudes for that specific approach. The position correction is used for precision due to the possibly low DH and relatively inaccurate altimeter.

[IO540]

There are no higher IMCR minima in the law.

However, the CAA IMCR exam papers do contain false questions. You have to quote the recommended figures to pass the exam. A bit naughty!

But then a lot of the CAA exams are word plays anyway, which is why the PPL Confuser is so good.

[DFC]

To put it clearly as per the AIP:

You are recomended to add 200ft to the published DH/MDH however, the absolute lowest DH you use is 500ft and MDH is 600ft.

Thus what many regular IMC users do is;

Precision approach - DH 500 ft or the published DH whichever is higher,

Non-Precision approach - MDH 600ft or the published MDH whichever is higher.

People will agrue to death that the IMC rating permits operation to IR minima but they will not fly to IR minima when they are renewing the IMC rating because they know they will fail.

There has never been a complaint to the CAA about an examiner failing an IMC test candidate for busting "IMC minima" on the basis that they did not bust IR minima.

The CAA did previously publish a CAP which clearly explained the calculation of minima for private flights. When the AIP was changed to the current position, it was binned but perhaps it is time to bring it back again.

Regards,

DFC

[Dr Eckener]

Not quite the same as IR minima, as RVR required is 1800m, no exceptions. And before anyone says anything, I know RVR is only quoted when below 1500m.

[bookworm]

To put it clearly as per the AIP:

You are recomended to add 200ft to the published DH/MDH however, the absolute lowest DH you use is 500ft and MDH is 600ft.

You think you're putting it "clearly" but you've actually rephrased it to nudge the meaning further towards ambiguity. "Absolute" does not mean "mandatory".

People will agrue to death that the IMC rating permits operation to IR minima but they will not fly to IR minima when they are renewing the IMC rating because they know they will fail.

There are many things that it is my legal right to do in an aeroplane that I would not do on a proficiency check for fear of displaying poor judgment to the examiner. Given the choice of demonstrating an approach to IR minima or recommended IMC minima, wouldn't you pick the latter too?

Not quite the same as IR minima, as RVR required is 1800m, no exceptions.

1800m in-flight visibility, not RVR. RVR can be considerably greater than visibility, depending on lighting etc.