novice
Posts: 90
Joined: Tue Aug 07, 2012 2:55 pm

Pressure Error

Wed Nov 07, 2012 8:40 pm

Can someone explain pressure error? in regard to one of the altimeter instrument errors

Cheers
 
flyingturtle
Posts: 4741
Joined: Mon Oct 31, 2011 1:39 pm

RE: Pressure Error

Wed Nov 07, 2012 9:44 pm

Altimeters should be pretty reliable... except some wasps decide to occupy the static port.

Does your question relate to pressure altitude? Temperature differences can cause wrong altimeter indications. Or do you mean the difference between QNH (standardized altimeter setting to maintain vertical separation between aircraft) and QFE (the correct altimeter setting in regard to the ground)?


David
Keeping calm is terrorism against those who want to live in fear.
 
User avatar
Jetlagged
Posts: 2562
Joined: Sun Jan 23, 2005 3:00 pm

RE: Pressure Error

Mon Nov 19, 2012 9:17 pm

Pressure error is the difference between sensed air pressure (static or pitot) and freestream pressure (static or total) . This occurs because the local airflow affects the pressure around the port. In relation to an altimeter it means that the sensed static pressure will give an incorrect altitude reading unless it is corrected. Air Data Computers have correction tables based on flight test data which apply a correction to the sensed pressure to give a corrected pressure, from which the indicated altitude is derived.

On some aircraft if you select alternate static source in flight you get an uncorrected pressure measurement (or perhaps a less sophisticated correction) which means the indicated altitude jumps to a new value.
The glass isn't half empty, or half full, it's twice as big as it needs to be.

Who is online

Users browsing this forum: AirstairFear, UltimateDelta and 9 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos