pressure ALTITUDE

[Captain_BH]

hi all

if your indicated ALT is based on 1013
and the area used QNH is 1023
You've been asked to level off at 4000ft
which one is correct
u level off at 4300 or 3700

[de facto]

Is that a tricky question Captain?:p

Ps:light hearted comment before framer,kramer and the rest jump my bone about my crm.:E

[ATCast]

You would set 1023 and level at 4000' wouldn't you?

If you would then set 1013 again, your reading would be lower, 3700 would be about it.

[keith williams]

It depends on how we interpret the question.

Using the generally accepted lapse rate of 30 hPa per 1000 feet, the 10 hPa difference between 1013 and 1023 equates to about 333 feet. The author of your question appears to have rounded this off to 300 feet, so let’s use that figure.

With 1013 set the altimeter will indicate altitude above the 1013 hPa pressure level. This is above the 1023 hPa pressure level, so with 1013 set the indicated altitude will be less than the actual altitude.

If you keep 1013 set and level off at 4000 feet indicated your actual altitude will be about 4300 feet.

If you keep 1013 set and level off at an actual altitude of 4000 feet your indicated altitude will be about 3700 feet.

If you select 1023 and level off at 4000 feet indicated your actual altitude will be about 4000 feet.

[Captain_BH]

In dual FCU failure in A320
your PFD ALT wil be based on STD 1013
So if ATC clears you to desend 4000 with QNH 1023
would maintain 4300 or 3700 with STD

[BOAC]

Standby altimeter?

[de facto]

Stanby altimeter and then deal with failure.
At the correct altitude of 4000 ft,your standby will show 4000 and your pfd on standard will show about 3700 ft.
HIGH to LOW watch out BELOW:p

[BOAC]

your standby will show 4000 only if set on 1023. See OP if your indicated ALT is based on 1013 - a bit too vague, I think.

[de facto]

If he follows the standby i hope he sets the correct qnh:}

I think the OP is saying that his PFD altimeter resets to 1013 during the failure,therefore if he were to follow this erroneous altimeter reading,would he have to descend to 4300 or 3700.
:oh:

[Ralis]

If in doubt draw it out :ok: