Instruments checks on the ground

[Giulicor12]

Hi all ! These days I had some questions from my instructor concerning the checks of instruments while on ground. I've been looking for the answers but no results...

The questions are :

1) what is the maximum difference between the QFU and your compass when lining up for take off ?

2) the max difference between your compass and your heading on the HSI ?

3) In IFR, 2 altimeters are required, what is the max difference between both altimeters readings ?

Does someone can help me ? And most of all, does someone can give the source of the information found ? For example Jeppesen, ATPL books, ICAO annexes or whatever !

Thanks

[Capot]

1. Should be 5 degrees (the runway is designated to the nearest 10) factored by, if anyone thinks about it, the change in variation since the runway was designated. (I don't know of any runway redesignated for variation changes, but there may well be some.)

2. Assuming that the HSI is showing magnetic headings (is it?) there should be no variance. After all, a 1 degree error would have you 3 miles off track in 180 miles flown if you use the wrong instrument. Too much, if you have no other way of establishing your actual track flown.

3. 100 feet would be the maximum; if you average the two readings you'll not be more than 50 feet out, I think, which sounds acceptable.

Actually, I've totally forgotten, if I ever knew, what the "book" rules are. So ignore the above.

[foxmoth]

1. Should be 5 degrees (the runway is designated to the nearest 10) factored by, if anyone thinks about it, the change in variation since the runway was designated. (I don't know of any runway redesignated for variation changes, but there may well be some.)

Deviation?



Whilst I know these, I have not the time to double check them or get the references so am not happy to post them at present.

[BigEndBob]

And if you in the habit of taking off with the landing lights on, check how much the compass is affected when you line up. I've seen upto 20 degrees!

[phiggsbroadband]

Hi Capot, runways that have changed, local to me...

Manchester was 06/24 now 05L/23R 05R/23L
Hawarden was 05/23 now 04/22
Sleap was 01/19 now 36/18

Magnetic Annual change of Variation is -7 minutes, so look for some more
changed designations soon !

[Capot]

foxmoth, you are, of course absolutely right. I meant "deviation".

phiggs..., thanks for the info. I thought there might be some.

[mad_jock]

Also to note as well that in some places you won't get certain runway numbers because they are deemed unlucky.

Which I only just realised last year. When my heading was off by 12 degrees and after checking the plate found the ILS track was the same as what I was getting on the HSI via flux valve. FO came up with the idea that if they had called it the proper number that would have made it unlucky. Which is to be honest the only logical reason why they would miss that number out. They missed that floor number out as well in tall buildings.