Secondary instruments

[forthbridge]

Having a look at some cockpit shots, I've noticed a couple of boeings where, on the deck, the Pilot's altimeter reads lower than the copilots' by 10 feet. Another, a Kc-135 in a turn at FL130, has the Pilots's showing 13980 ft, and the copilots' 14020 feet - with the altitide alerter not 'showing' but set at 14000 ft.

Any reason for this?

[Garry Russell]

Cold it just be the barometric pressure setting been updated on one??

Garry

[DispatchDragon]

Garrys correct - your supposed to both reset at the same time - well at least every where I have worked - If they were european - I would say that one has the pressure set for the transition and one for QNH :lazy: but what do I know

Leif

[Hot_Charlie]

It's actually nothing abnormal - certainly with a split of less than 50ft. In the VC10 for example, you can often have quite a split between the two with the same setting (even with In. Hg rather than mb set).

[forthbridge]

cheers guys

[Motormouse]

Indeed as 'Charlie' says above, its' nothing unusual for the accuracy to be 'out' especially with purely 'steam driven'
instrumentation; reasons for this are usually hysteresis within the gauge itself,coupled with density ranging error (instrument getting less sensitive as air density decreases with altitude) and/or static source error,(position of the static port on the airframe causes error).

Modern instruments systems incorporating an air data computer to convert static pressure into
electrical signals which then 'drive' servo altimeters don't suffer as much.

ttfn

Pete

[DispatchDragon]

Dont know what the RAF goes by - but we have to do a static check if there is a split of 150 feet or more

Leif

[Erick_Cantu]

For me, probably bass, although I do want to learn to play drums.

Hm, maybe I misinterpreted the topic at hand...

[Garry Russell]

Airplane........flying on instruments

Garry

[Hot_Charlie]

Dont know what the RAF goes by - but we have to do a static check if there is a split of 150 feet or more

Leif

Ours are checked an logged on the ground (on the VC10 that's both pilots precision digital altimeters (with either QFE or QNH set depending on the location), the analogue standby (QNH)) by the Nav. As you would expect they are then checked (but not logged) before again take off (primarily to ensure both primarys are set correctly), and then on each altimeter setting change after that and before landing. The only other time they are logged after that is on entry into RVSM airspace, where they are checked and compared along with the standby to ensure RVSM compliance (+/-200ft).