1013 or 2992?
 

Hi there.

When setting STD on an analogue altimeter which has both HPa and In as the sub scale, which gives a more accurate FL readout, 1013 in the HPa window or 2992 in the In window? I have noted that 1013 and 2992 don't exactly match up in the sub scale windows. I have a feeling that this maybe because STD is exactly 1013.25HPa, and possibly that is why the two never sit perfectly in line in the sub scale window.

A bit pedantic I know, but its been bugging me for a while lately as I do those RVSM checks!!

Thanks.

29.92" is what we set on the B777 standby altimeter.

Hi genius747,

Not at all pedantic, :ok:(in my opinion) I set 29.92 for std and 29.91 for a QNH of 1013 mbs (Hpa) thereby providing a clue for r/t purposes that I'm talking FL against Altitude.

Regards

HH

I would think that in Europe (and anywhere that uses HPa) that setting 1013 would be appropriate.

In airspace where In is used, set 29.92

Always set 29.92 as it is easier to set than the CORRECT setting of 1013.2.

A quick back of envelope sum says that 1013.25mb/hPa = 29.921in.Hg, so 29.92 would give you about 0.9ft error.

Setting 1013 when 1013.25 is technically correct is, according to my calibrated back of envelope, would give you 6.75ft error.

So, I'd say that 29.92 in.Hg is definitely more correct.

G

Lets face it folks...inches work properly, every time.
IE: 29.92

However, having said this, 1013.2 is.....close enough.
Don't have a cow over this, relax and enjoy the view.:ok:

"Setting 1013 when 1013.25 is technically correct is, according to my calibrated back of envelope, would give you 6.75ft error." - and that could ruin a good beat up:)

When the aeroplane that you are in is more than one hPa thick what does it matter? :cool:

Regards,
BH.

Maybe it is just a poor reflection on the aircraft I fly, but when I set any QNH on both altimeters, there is always a slight difference (<30ft) between the pilots and the co-pilots side...

OK, I'm not flying RVSM aircraft, but I wouldn't get too pedantic about 0.25 hPa.

Airbus has a "STD" button which I presume gives it exact whichever units you have selected when you deselect STD!:p

... and this presumes that no-one EVER forgets to set standard going through transition ... ?

bit like wheels up landing, I suspect ....

Interesting new units of measurement Bullethead, aircraft thickness measured in hPa! A nice change from the media's common use of "football field" units for aircraft length / wing span.

I like it:ok:

Regards,

Old Smokey

J_T

Was taught many moons ago-reset to STD when cleared above the transition altitude and reset, at least, the stby to local QNH when cleared below the TLv. Drives other Yanks nuts, but is very effective.

GF

... no-one EVER forgets
 

Any thoughts on which is more likely to be miss-set?
28.92, 30.92 vs 1003, 1023, 1033 ?

For those who always set 1013.2, is the quest for precision more likely to act as a trigger for detecting an incorrect entry?

Well, I hope nobody is doing instrument beatups then :E

Seriously, the inherent inaccuracy in the measuring system (instrument), and static vents is going to be a lot more than 6.75 ft.... I've not seen an altimeter where you can accurately set .2 hpa either.

Was taught many moons ago-reset to STD

Have had colleagues who did likewise .. I get uncomfortable if more than standby is reset in anticipation .. most of us have been caught with a revised clearance to maintain on the way up ... and either forgotten, or been at risk of forgetting, to reset the clocks. Right or wrong, I put my faith in rigorous attention to transition scan so that, even if we got distracted and the scan/check was delayed, the matter would be fixed sometime in the next few thousand feet .. on the way down, our routine check at F150 was considered close enough (and unlikely to set us up for being caught out) to transition (in Oz and local, anyway) to set QNH in anticipation ...

- 'tis indeed pedantry, but the question was asked in post#1 and Flight levels ARE defined on 1013.25MB/29.921".

Many airlines, BA included, refer to "1013" as 'Standard" (presumably to reduce printing costs:)) but Boeing and Airbus at least view it as 1013.2mb/29.92 in the 'auto' setting. The point being, if you are going to set it, set it properly! For Alf, the act of confirming both '1013 and a bit'/29.92 on the subscale goes along way to eliminating the error.:ok: I have yet to see it mis-set in 45 years+.

Doesn´t that depend on which airspace you are flying in?
On my a/c you can switch between hPa and In, but as we usually don´t cross the atlantic, I never touch it. Changing the unit of measurement to gain 6 feet of accuracy, just to be irritated when I have to set the QNH in hPa again sounds odd to me.

According to our Flight Ops Inspector, 2992 should be set.
73NGs also have the STD button, which makes things so much easier.