Saturday 18 May 2013 09:00 UTC
This forum is for anything to do with light aviation
If you're descending "for the purposes of landing" then either you are descending VFR in VMC or are using an approved approach in IMC. So isnt a DIY let down therefor not possible to be "for the purposes of the landing" as it is not VFR or "published IAP". If that logic holds then the descent is for enroute navigation to enable VFR and so breaks the 1000ft rule?
Believe Lufty was using short-hand for AGL as it's largely about cloud bases, and for simplicity assumed no obstacles other than usual (ie below 300ft).
Now I'm more confused than before. I thought Bookworm's cryptic answer was that "normal aviation practice" not required for the 1000ft/5nm rule. So if the mountain in the south is not an issue anymore, why move 1nm north (which may not be possible due to airspace) and not just break-cloud somewhere over the airport?
The IFR cover the descent, that is 1000' above anything within 5nm.
Rule 5 does not kick until 500'.
The hill is 4nm south, so 1 nm north allows you under the IFR to descend to 300' (what the OP said was the highest ground in that direction) plus 1000' = 1300'.
As the cloud base is 2000' there is no need to descend to minima, so I stuck in a fudge factor and called it 1500'. 1500' is also more convenient for a join. I could have nominated anything between 1999' and 1300'.
The cloud break over the airfield would be within the IFR if it was for the purpose of landing. That descent could then be continued below 500' if it was according to normal aviation practice.
There is an awful lot of confusion and misinformation in this area. The rules are actually very straightforward.
But these days we have to bear in mind that the IFR were written for Ernest Gann and his mates in the 1940s or earlier. Then 5nm was a reasonable distance to estimate when in cloud. These days we know where we are to 5m and the IFR are quite outdated.
If you have got the GPS wrong, you are as likely to be 50nm as 5nm from where you thought you were.
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Just to be pedantic, why not!
I was trying to be provocative and state that a "descent for landing" is different to enroute descent. Thus a descent for approah or landing sector can only ever be VFR eg overhead join, VRP etc or a published let down in IFR to a fix.
Therefore the only thing a DIY let down can be is an enroute procedure in order to subsequently be able to fix visually for landing. If during that descent you break the 1000ft rule you and neither "descending for the purposes of landing in VFR" nor "descending for the purposes of landing with an accepted (read published) aviation let down".
Is the bit that is self evidently not true. If you have set up a "Point in Space" at the corner of a big field in which an aeroplane has never landed before, but in which you are intending to land today, and then descend using GPS OBS and a CDA calculated on distance to run to the corner of the field, and the cloud base is 100', then it is clearly true to say that you are "descending for the purposes of landing" and equally not true to say that "you are descending VFR in VMC or are using an approved approach in IMC."
I am more than a little puzzled as to why you think that you are.
You are using an unapproved approach in IMC.
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And that is the essential question. The FAA make it crystal clear in their world that one of the rules of IFR are you must be above the MEA MAA MOCA MSA or be on a leg of a published approach - so your statement is true in the US.
However, the CAA specifically choose not to use such language and only to require an intent to land with no mention of approved (by whom), published, documented etc. approach. There (TMK) is no case law of this issue being considered. As an aside, the language is slightly bizarre in that it seems to require an intent to land, which would mean an intentional missed approach (where you descended on the procedure in IMC but intended to go around) doesn't seem to have a legal basis as you are IMC below 1000 ft and not intending to land, therefore in contravention of the rules (but clearly not the CAA's intent or the long established operational practice).
The CAA published a proposal a few years ago which would outlaw unpublished approaches.
The PDF is still out there somewhere.
It was abandoned reportedly because it would have also outlawed the numerous "private IAPs" which the UK is littered with e.g. those used by air ambulances and the police. Most airfields today which don't have ATC and thus cannot have a published IAP but do have a navaid there (a sole NDB will do) do in fact have a private IAP for use by some commercial operator. That operator owns the intellectual property in the IAP (what a joke, eh? especially as it is prob99 the same public IAP which was there before the said airfield lost its ATC) so it cannot be published. The diagrams are widely used by local pilots and the MDHs are so generous (say 600ft) that knocking up your own version is hardly rocket science.
Last time I wrote on this topic, the ATCOs who moderate this forum rubbished me thoroughly (but offered no more info) so I won't say any more
But it's clear that the CAA is well aware of the situation and all its implications and is content to leave it as it is. There is very little evidence that hordes of pilots are getting killed on DIY IAPs. Many more plain PPLs get killed scud running or CFITs, and a fair few experienced IR holders are getting killed flying dodgy VFR in solid IMC...
Practically, if you design a DIY IAP you need to design a missed approach procedure also. Most people don't do that; they just descent on a long final down to X feet and then if not visual they climb out in a sort of straight ahead direction, which may be OK or maybe not (look up TB20 N700S in N Ireland). I would also test it in VMC.
But anybody can descend down to the MSA for whatever purpose, 100% legally.
That's essentially my point. I am not saying it's not practical nor am I saying I wouldn't do it, however you can use the CAA wording to support my position:
The accepted aviation practice for safety is to a) join a circuit visually or b) position yourself using a published procedure c) divert somewhere where you can do a) or b).
A DIY let down is a means by which to get to a) that is to say join visually. However until you are visual you cannot safely have an intent to land. All you are doing is deliberately descending below MSA/1000ft rule.
I would do it, everyone else does it and the use of GPS etc makes it a non issue in my opinion. All I'm saying is that I Dont seeing anything that explicitly makes it "ok" in CAA land as the wording is open to interpretation.
The FAA rules are crystal clear. There's very little room for confusion. In many ways, it's a pity NIH prevented EASA from taking them over, lock stock and barrel - but that's a different argument.
In comparison, the CAA has been quite deliberately vague. If you do something silly, then they can prosecute for "endangering an aircraft" and it would be hard to defend against that if whatever you did ended up in tears. So the relaxed rulemaking includes "don't do anything silly".
There are places where only the most skilful would attempt a DIY or non-published IMC approach. On the other hand, in the wide open flatlands of East Anglia, for example, it may not be so silly to descend to (say) 600 feet AGL in IMC using a proven GPS, with the intent of landing if you become VMC at that point. Clearly, you wouldn't go down to 50 feet, and your DIY approach would be one you'd worked out with a chart and flown in VMC to check it out - including the missed approach part.
Would I have done that in pre-GPS days? Based on a remote NDB - no way. I once flew the NDB20 procedure at Shoreham in poor VMC, and quickly gave up, and asked for the 02 even with a 5 knot tailwind. I really do not like NDB procedures unless every other option has failed.
A VOR radial: just maybe, if there's a suitable VOR close. It would have to be pretty close!
Moderatio in omnibus
I used the word "MSA" so yes, MSA=MSA
There is no such thing as e.g. "MSA is 2000ft but there is a tower sticking up over there to 3000ft so you have to be careful to not hit it". In that case, MSA would be 4000ft.
I do find it a bit of a laugh that a commercial AOC operator, carrying paying passengers with a high expectation of safety, can legally operate via an NDB IAP (with its 20-30 degree error being pretty routine) whereas some criticise any idea of a DIY IAP no matter how carefully designed. But this charade is all over the place, from the UK all the way to some little Greek island.
The point that you're missing here is that there's nothing special about a published IAP from the point of view of Rule 33. The exception "(a)it is necessary for the aircraft to do so in order to take off or land;" is required just as much for the ILS on 27L into Heathrow in IMC as it is for unpublished procedure.
Don't underestimate the safety value of the procedure designer's work, nor the regulator in approving it. But whether or not that work is necessary to bring risk down to an acceptable level every time an aircraft wishes to descend below 1000 ft in IMC is very much open to debate.
But it would be much better if we didn't have to have these debates because an LPV approach was available to each end of each runway we ever wanted to use in IMC.
UK Law is that you don't need anything that explicitly makes it "ok" in CAA land.
The absence of anything that explicitly PROHIBITS it in CAA land means that it is allowed.
There are two ways to argue with a woman.
Neither of them work!
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