PPRuNe Forums - Change to standard pressure

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Change to standard pressure

In the initial climb when do you advise to change to 1013 - at MSA or the published transition level? Common sense would suggest to me that the transition level is the best and the MSA seems a bit premature though I've heard it done both ways - just wanted to see what is the consensus.

It’s a good question and one that comes up seemingly frequently (see other threads).

In a multi-crew operation with high rates of climb, the consensus appears to be “when cleared to a flight level and above acceleration altitude”. In any case, the standby altimeter can remain on QNH until above MSA and Trans Alt.

In a slow climber, without a standby, maybe there would be more chance of getting a revised clearance to stop at an altitude and thus it might be better to wait until Trans Alt.

UK AIP ENR 1.7 Altimeter Setting Procedures:

Quote:

5.1.4 Within Controlled Airspace a pilot should set one altimeter to the latest Aerodrome QNH prior to take-off. While flying at, or below,
the Transition Altitude vertical position will be expressed in terms of altitude based upon the Aerodrome QNH. When cleared for
climb to a Flight Level, vertical position will be expressed in terms of Flight Level, unless intermediate altitude reports have been
specifically requested by Air Traffic Control.

5.1.5 Outside Controlled Airspace, a pilot may use any desired setting for take-off and climb. However, when under IFR, vertical
position must be expressed in terms of Flight Level on climbing through the Transition Altitude.

This is based on ICAO PANS-OPS (Doc 8168) Vol I, Part III (Aircraft Operating Procedures), Sec 1 (Altimeter Setting Procedures), Ch 1:

Quote:

1.1(c) The change in reference from altitude to flight levels, and vice versa, is made:
1) at the transition altitude, when climbing; and
2) at the transition level, when descending.

The transition altitude is published. The transition level is determined by the aerodrome QNH. The altimeter subscale setting for flight levels is strictly 1013.2 hPa and not 1013 or 1013.25 hPa.

In the US and Canada the standard altimeter setting is set on the Standard Pressure Region side (which can be entered in level flight).

Quote:

Originally Posted by eckhard (Post 10251339)

The first two paragraphs are great advice. I’d steer clear of the third, much more likely not to get stopped off and to forget or be distracted than to be stopped off; stopping off is itself a cue to ANC and resolve the potential problem.