Altitude Testing of Flight Instruments

I calibrate altimeters and similar pressure indicating devices. I have never encountered a situation where someone wants to measure pressure below zero feet altitude. Could you explain further?

The customer is requiring based on the following:

MIL-HDBK-310 "GLOBAL CLIMATIC DATA FOR DEVELOPING MILITARY PRODUCTS"

(1050 mb = -1000 ft.)

5.1.16 High Atmospheric Pressure. A pressure of 1083.8 mb (32.01 in. Hg) was observed at Agata, Siberia

on 31 December 1968. Station pressures over 1050 mb have occurred in the contiguous United States.

Design for the extreme value of 1083.8 mb should not present difficulties. Therefore, frequencies of occurrence and long-term extremes are not presented.

Hi there,

I have never heard of this requirement before. Please keep us posted?

If I remember correctly you will have to look for ISA temperature ratings. You could get this from any flightsim website.

I do not know if the temperature will work with the inverse though. i.e. Temperature at sea level (0 Feet) and pressure 2992 inches is ISA temperature 15 Deg C. and then for every 1000 ft positive pressure change add 1.98 Deg C.

In your case - minus 1000 FT = 15 Deg C - 1.98 Deg C = 13.02 Deg C

You then need to look at the ISA charts to compare your pressure altitude with your calculated temperature etc etc.

As for the requirements - I am sure the ISA would have something on this.

Anyways - Please keep us advised as this is a very curious case.

Regards,

Craig