altimeter setting
Join Date: Jun 2006
Location: Brisbane
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Yes, but your FMC is basing it's altitude restrictions on your primary altimeters (assuming you have an FMC).
So if on departure, say TA is 10,000', you have a SID with an "at or above 8000" at a waypoint, and your clearance is to climb to FL140.
I have trouble with how the FMC (or you for that matter) complies with the "at or above 8000" if you have already selected the primary altimeter reference to STD prior to passing 8000'.
There is in fact a STAR in YBBN that has a limiting* descent restriction of "at or below FL120" with a TL of FL110. Your typical clearance at this point is to descend to 9000'. This can really catch you out if you go to QNH early.
*I use the term "limiting" here to indicate that (depending on runway) this waypoint is below the normal descent profile so is the "controlling" waypoint for the descent, meaning correct altimetry at this waypoint is vital.
So if on departure, say TA is 10,000', you have a SID with an "at or above 8000" at a waypoint, and your clearance is to climb to FL140.
I have trouble with how the FMC (or you for that matter) complies with the "at or above 8000" if you have already selected the primary altimeter reference to STD prior to passing 8000'.
There is in fact a STAR in YBBN that has a limiting* descent restriction of "at or below FL120" with a TL of FL110. Your typical clearance at this point is to descend to 9000'. This can really catch you out if you go to QNH early.
*I use the term "limiting" here to indicate that (depending on runway) this waypoint is below the normal descent profile so is the "controlling" waypoint for the descent, meaning correct altimetry at this waypoint is vital.
Well as far as I remember, the Airbus FMGC is clever enough to comply with altitude restrictions as entered, despite having a different setting on the altimeter. Don't know about Boeings, although I should!
The STAR at YBBN is an example of poor ATM, whether by design or subsequent modification of the procedure. I think it is unacceptable in today's busy environment to 'design in' potential traps for unwary pilots and controllers.
The low transition altitudes in the U.K. are another example, especially if the SID clears you to a Flight Level.
Procedures and airspace design should be as simple as possible and subject to several 'test flights' in the simulator before being released. Perhaps they already are but sometimes one is left wondering, 'who on earth came up with this idea?'
The proposed raising of the Trans Alt in the U.K. to 18,000ft is a welcome move. Let's hope that the rest of the world follows suite. That will still leave the CIS, Mongolia and China (and N Korea) to get with the programme and ditch Meters and QFE (and mmHg)!
The STAR at YBBN is an example of poor ATM, whether by design or subsequent modification of the procedure. I think it is unacceptable in today's busy environment to 'design in' potential traps for unwary pilots and controllers.
The low transition altitudes in the U.K. are another example, especially if the SID clears you to a Flight Level.
Procedures and airspace design should be as simple as possible and subject to several 'test flights' in the simulator before being released. Perhaps they already are but sometimes one is left wondering, 'who on earth came up with this idea?'
The proposed raising of the Trans Alt in the U.K. to 18,000ft is a welcome move. Let's hope that the rest of the world follows suite. That will still leave the CIS, Mongolia and China (and N Korea) to get with the programme and ditch Meters and QFE (and mmHg)!
Join Date: Jul 2013
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Derfred: follow the rules and you cant go wrong.
" On departure change to std setting when passing TA and on arrival change to QNH on passing TL".
By all means stick std into a spare altimeter on departure but dont refer to that altimeter until passing TA. Ditto on descent, stick qnh into the spare but dont refer to it until passing TL.
" On departure change to std setting when passing TA and on arrival change to QNH on passing TL".
By all means stick std into a spare altimeter on departure but dont refer to that altimeter until passing TA. Ditto on descent, stick qnh into the spare but dont refer to it until passing TL.
Well as far as I remember, the Airbus FMGC is clever enough to comply with altitude restrictions as entered, despite having a different setting on the altimeter. Don't know about Boeings, although I should!
