Edinburgh Diverts last night

[pbrookes]

Does anyone know why there were a load of diverts at Edinburgh last night? The explananation on the BA flight was that the ILS was u/s and visibility was poor, but people on the ground reported good vis.!

[Jetstream Rider]

The ILS was U/S on 06 a couple of days ago. The approach is then either an NDB/DME or a visual. The NDB for us has a descision altitude of 710 feet (yes it is a descision and not an MDA), so no matter how good the vis, if the cloudbase is 500 feet you may well not see the runway.

ILS was OK on 24, but the wind precluded its use.

That does not answer why there were diverts last night though, as I don't know.

[Wheelybin]

Your assumptions were indeed correct J.R. There is a new localiser that has been installed for runway 06. This needs to be thoroughly flight tested before it can be brought into use cat 1 ( it will then have to run for 300 hours with no problems before it can be declared cat 3). In the meantime the required approach to runway 06 is an NDB/DME procedure.
Of course, as was expected, the law of sod started to apply. As soon as the old localiser was dismantled and the flight checker crew arrived, the wind swang to an easterly direction and the gloom descended to such an extent that the flight check crew could not safely complete their runs.
With particular regard to yesterday evening, the weather deteriorated rapidly at about the time of the last rush Northwards. Although the met visibility only went down to approx 5000 metres in moderate rain showers, the cloud base descended to being broken at 200 feet, well below the decision altitude/height on the procedure (710 ft QNH or 600 ft QFE) 4 aircraft made an attempt but all went around. Some decided to divert immediately, whilst others chose to hold at the UW or Tweed whilst the last departures went off 06 so we could switch the ILS on for runway 24. However the surface wind at the time was 060 at between 10 and 15 knots with the winds up top even stronger easterly.
It was at this point that the night shift arrived and were handed over a lovely situation to deal with whilst the rest of us retired home to lie in darkened rooms! At the time that I left 6 aircraft had elected to divert whilst there was still at least 12 others in the holds or due in the next few minutes, so I am unsure of the total number that diverted in the end.

[keithl]

That's two posts now referring to Decision Alt/Ht on an NDB.
At the risk of 'topic drift', may I ask for amplification? Particularly from JR as he made special emphasis of it not being an MDA/H.

I teach this stuff and I do like to keep up to date...

[brain fade]

Speaking as one of those who went to GLA......
Nowadays they don't like the idea of folk descending to MDA then flying along to the MAP. The idea of an a/c flying level in the landing config is seen as unstable. I don't really want to into the ins and outs of this sort of thinking. It's their train set not mine. Never bothered me before flying level but there you go.
Nowadays 'they' expect you to treat it like a home made precision app. Lateral tracking as before, NDB, LLZ or VOR.
More carefully flown vertical profile to bring you down to 'MDA' at more or less the same point you'd be at were you at this alt/height on a ILS. When you get to 'MDA' on one of these you are in the corrrect place, at the correct height and in the landing config. (subject to you having made a nice job of it!) So at the call 'decide', you either land or GA. No flying level, no descending (obviously).
Thats it.:ok:

Edited to add: When we got to GLA although there seemed to be diverts everywhere, got pretty much a straight in, we taxiied straight onto stand, someone met us, there was a GPU right there for us, pax disembarked promptly, engineers over to say hello straightaway. In short better handling by far on a divert to GLA than we get at EDI when we\'re on time! Well done GLA! (no comment on edi).:E

[mjtibbs]

i dont wont to side track either but just 2 Q's

1 - where were the aircraft diverted to?

2 - when people talk of NDB/DME approach does it mean using the normal NDB and the DME from the ILS?

its just i dont think NDB'S have DME equipment built in (or do they)?

my fs2000 is just a little out of date LOL.

-tibbz

[152wiseguy]

If you've got a set of Jepps you can read about the constant angle non-precision approach (CANPA) in there. Its down to the operator whether this is the method used to fly a non precision approach.

[brain fade]

mjtibbs.
1. Glasgow. maybe some went to Prestwick as well. We went to GLA.
2. Last night it was the 'UW' NDB and the ILS's co located DME (I-VG) to make an NDB/DME to 06

[Groundbased]

Out of interest, what backup gear do the crew checking a new ILS installation have in case it is all wrong?

[Right Way Up]

KeithL,
I think the DA that Jetstream Rider refers to is what we call in our company, a Company Decision Altitude. The legalities of the MDA is that you must not descend below that altitude unless you are visual. However if you make the decision at MDA whilst descending, you will bust that altitude. Therefore most companies add an increment (normally 50 ft) and call it a decision altitude.

[M609]

Out of interest, what backup gear do the crew checking a new ILS installation have in case it is all wrong?



Don't know about you crazy Brits, but us noggies do all calibration as VFR flights.

[Spitoon]

I'll show my ignorance first - what's a noggie?

And in my experience in the UK flight checking is done in visual conditions - although not necessarily VMC - but the flights are usually, technically at least, IFR. Like you say, crazy Brits!

[M609]

what's a noggie?

...a person living in a rocky, cold country NE of Shetland :E

[Jetstream Rider]

KeithL - exactly as above. The way I was taught it is that with a DA, you DECIDE at that alt and if you go around you may dip below it. An MDA on the other hand is a MINIUM and as such must not be busted without visual reference. Some operators then add a certain amount and call it a decision altitude. It works really well, no trogging around level and then diving to the field to land. It also means you can fly a constant descent approach and not upset the locals by putting power on at low level (unless you go around of course).

It is amazing - I partialled my Instrument Rating test for getting to 80 ft above MDA on an NDB approach, rather than to within 50 ft. My tracking etc was spot on, but I was told I was too high at the missed approach point and had to do it again. In real airline life, I would have been around decide. Ironic.

[keithl]

Thanks for the very clear replies, particularly Right Way Up and Jetstream Rider. It's always such a relief on this site to get rational (as opposed to "outraged") responses.

The phrase "Company Decision Altitude" clears up all my doubts.

[LYKA]

Roll on LNAV/VNAV approaches!

[Downwind.Maddl-Land]

"Crazy Brits" my ar$e! UK Flight Inspection is done with exteme skill, cunning, tons of experience and Big Balls - and an incredibly well developed sense of self-preservation. Otherwise nothing would ever get done!

The UK King Airs have some seriously clever kit on board and the guys really know what they are doing - you have to when the occasional ILS is turned on for the first time and comes out upside down and back to front!

[DB6]

Keithl, to further amplify on the subject of CDAs, MDAs etc., many airlines operate to what are called 'stabilised approach' criteria - typically at 500 feet: within +/- 5 degrees of apporach QDM, within half-scale GS deflection or +/- 50 feet of target alt, and not more than Vref + 20 kts. If you were to level off at MDA and then become visual at a later stage it would be very difficult, if not impossible, to complete the approach in a stabilised manner. The 'penalty' for becoming unstable is to go around anyway so the pragmatic approach is to add 50 ft to MDA and make the decision at that point as levelling off would bring no benefit.

[MANAGP]

Vref+20!!!! That's very generous :-)