"Position error" of outflow valve B737-300/-500 (4th altimeter)
A little experiment from the last sim-session:
Problem: A B737-300 in IMC. Loss of all air data. Bare CAT I weather. Now bring her down.
Basic flying is no problem thanks to pitch & power. Biggest concern is altitude. VSI is operative (source: IRS) but you only get a rate. The ground echos from the weatherradar work quite well for a crude altitude readout at higher levels (tested in real life). But closer to the ground a more exact, preferably barometric, altitude is desirable.
We came up with the following: Below 10.000ft make the ship bleedless, dump the cabin pressure and make sure the outflow valve stays in its full open position. Then use the cabin altitude indicator as altimeter (not tested in real life - at least by me).
Is there anybody out there who can share some information on the position error of this improvised altimeter as the sim may not be entirely accurate in this respect. I couldn't find anything in my official documentation either. Any other ideas how to solve this problem?
Regards,
Badente