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How to set the two altimeters under IFR

In my IFR training, I learned to always set the primary and the standby altimeter to the same setting, i.e. QNH if flying on QNH and standard (1013,25 hPa) when flying flight levels. At one point, I had done a flight with another IR rated pilot, who told me that I should leave one altimeter on QNH when I changed to flight levels at the transition altitude, and to me it was clear that he thought I was doing it wrong by wanting to change both altimeters.

On some planes (like the SR22 with Perspective avionics), the standby altimeter is even slaved to the primary, so when you set the primary baro, the standby altimeter is set to the same value automagically.

So how do you handle this and why?

Last Edited by Rwy20 at 14 Apr 09:15

Rwy20 wrote:

In my IFR training, I learned to always set the primary and the standby altimeter to the same setting, i.e. QNH if flying on QNH and standard (1013,25 hPa) when flying flight levels. At one point, I had done a flight with another IR rated pilot, who told me that I should leave one altimeter on QNH when I changed to flight levels at the transition altitude, and to me it was clear that he thought I was doing it wrong by wanting to change both altimeters.

On some planes (like the SR22 with Perspective avionics), the standby altimeter is even slaved to the primary, so when you set the primary baro, the standby altimeter is set to the same value automagically.

So how do you handle this and why?

I always set the altimeters to the same pressure and cross-check. The cross-check is for me the important thing and with different settings you can’t do that. (Well, not unless without changing and changing back.)

ESKC (Uppsala/Sundbro), Sweden

First of all, maybe stating the obvious, but there are no “rules” about how the second altimeter is handles (even if some characters might think so). Everybody can do what he likes. My advice: stay away from people who fiercely state what is universally right or wrong.

Personally, I also handle the two altimeters as one, i.e. the second one is just a backup indication of the first one. Having different settings would confuse me.

Mainz (EDFZ), Germany

Luckily I have now three altimeters, two classicals and one came in as integrated part of the Sandia Quattro. So I do have two altimeters set on standard QNH for the crosscheck and one set on the last known QNH on ground.

EDDS , Germany

Rule #1: find out how your examiner likes it set and use that

Otherwise, I use

  • both to QNH if messing about low level VFR
  • both to QNH when flying cleared at altitudes
  • main to FL and #2 to last known QNH (for emergency obstacle clearance) when flying cleared at FLs

There is also GPS altitude immediately available, from a yoke mounted Garmin 496. This is the most accurate; no QNH needed.

Administrator
Shoreham EGKA, United Kingdom

I agree with Peter – horses for courses.

Fwiw, in my case – both on QNH for take-off. Primary to 1013 when cleared to a flight level. Both to 1013 when in high level cruise. Second one to QNH after receiving the destination ATIS. Primary to QNH when cleared to an altitude.

This covers all bases escept for a “stop descent a FLxx” amended clearance in the descent.

Biggin Hill

For private flying, altimeter setting is up to the pilot’s discretion (with one exception, see below). If flying commercially or under training however, altimeter setting procedures are mandated by the operating or training manuals. And wherever I received training, trained and flew commercially, the rule was to set the altimeters to the same pressure setting. With no exception. Otherwise the whole concept of redundancy and cross-checking capability would not work.

When using RVSM airspace, having the primary and secondary altimeter set to standard and cross checking them before airspace entry and inside is a legal requirement. For everyone.

Last Edited by what_next at 14 Apr 11:03
EDDS - Stuttgart

SOP at my training organisation was QNH on 2, 1013 or QNH as per cleared altitude on 1, all the time.

Biggin Hill

what_next wrote:

And wherever I received training, trained and flew commercially, the rule was to set the altimeters to the same pressure setting. With no exception.

Same here, except I’ve never flown commercially

LDZA LDVA, Croatia

It seems to me that all the UK pilots here use the “QNH on standby” method, and the rest the “same setting on both altimeters”. Is that impression correct?

It could then have to do with the widespread practice of uncontrolled IFR in the UK, which isn’t really done much in the rest of Europe (except Sweden, but where you get a sort of radar service in class G anyway if I understood this correctly). Where you would of course also be particularly interested in maintaining your own separation with terrain.

Last Edited by Rwy20 at 14 Apr 12:49
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