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Egbert Drenth

Transition Level - FO resets baro

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Hi,

 

I have a question/remark about the transition level...

As far as I know when passing the transition level, the FO should set the baro from standard to QNH.

Currently the FO is doing it at TL.

So when cleared by ATC to descent to TL the baro should be still left on standard.

Only when leaving (or passing) TL the baro should be set to QNH.

 

Therefore maybe you should trigger the FO to reset to QNH at TL - 500 ft, thus when the TL is passed by a few hundred feet.
(I would keep a marging of a few 100 feet, because the AP may not capture the TL exactly and pass through it by 200/300 feet and then climb a little again)

 

Is my assumption correct about TL?

 

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Theorically, you should set your baro when or before passing the TL, not below. Don't forget that in some places TL and TA are at the same altitude (e.g.: Most airports in France: TL 050 / TA 5000ft). So in this case, if you wait to have past the TL for a couple of handred feet, you may be in an awkward situation with the ATC.

Practically, you may set the baro to local QNH as soon as you are clear for an altitude. 

Let's say the following: TL 070 / TA 6000.

The ATC clears you to descent to FL070, then you keep your baro to std.
The ATC clears you to descent to 6000ft, then you set your baro when the instruction is received and the AP will stop perfectly at 6000ft.

Now imagine, the following:

TL 035 / TA 3000. QHN 1000.

If you wait to have passed FL035 - 500ft (so 3000ft) to set your baro and you have been cleared to 3000ft, by the time you set your baro, you may find yourself well below 3000ft and will have to explain yourself...

 

Personnally I have changed the options and don't let the FO change the Baro, I prefer doing it myself. 

Anyway, in real I would not see a FO changing the baro setting of the captain... I think it would be awkward.

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Personnally I have changed the options and don't let the FO change the Baro, I prefer doing it myself. 

 

Ahhh... problem solved

I didn't realize it was an option. I'll put if off as well.

 

BTW:

Isn't is strange that in some countries the TL apparently is the same?

A departing aircraft that is cleared to climb to 5000ft is using QNH and an aircraft that is cleared to descent to FL50 is using 1013.

Doesn't make sense to me.

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BTW:
Isn't is strange that in some countries the TL apparently is the same?
A departing aircraft that is cleared to climb to 5000ft is using QNH and an aircraft that is cleared to descent to FL50 is using 1013.
Doesn't make sense to me.

 

Well I'm not a commercial pilot so I can provide a verified answer but at least on IVAO in France, I 'm always cleared to the 5000ft and never to FL050 whether I climb or descent.
I cannot say for real world though but I guess it would be the same as it is what makes sense the most.

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