Master Altimeter Allocation on Instrument Approaches

[SIXTYRULEOK]

I have, since Shawbury, been taught to conduct a final Altimeter Cross-Check at 1000' and allocate a Master Altimeter (lowest) for use at DH(DA)/MDH(MDA). However, I cannot find any UK documentation Military or Civil that requires it. Does anyone know where this requirement is laid down (if at all)?

[TorqueOfTheDevil]

Shouldn't your handle have changed to SIXTYRUEOK in August?:oh:

[A and C]

Your aircraft altimeters should not be such that any error take you outside the safety limits for an IFR approach.

Picking up altimeter errors should be part of your SOP but I would argue that 1000 ft be it QNH or QFE is too low to do anything but discontinue the approach and sort the problem out above the MSA.

We have a robust altimeter checking system, with a check on the ground before engine start, a check when setting STD in the climb, a check in the cruise ( that is recorded for RVSM reasons ) a check when setting QNH and another check when the RAD ALT comes alive at 2500 ft AGL.

There is also a check at the final approach fix ( usually at about 1000 ft AGL ) any significant error at this point would result in a go-around if not VMC, in my view nominating a master altimeter at this high workload point would only distract from far more vital things to do and compromise the safety of the aircraft for the so called safety advantage of going around a few feet higher.

In short your altimeter checking and troubleshooting should be done long before you get to 1000ft on an approach and the check at 1000ft should be a simple go/no go decision on continuing the approach.

[212man]

ICAO Doc 8168 Part 1 makes no such references, and I've not heard of the term 'master altimeter'. As said, the master is the one the PF is using! Eurocontrol, Skybrary and the Flight Safety Foundation have lots of useful documents about altimeter checking, and best-practice procedures, and none mention doing what you suggest. Typically, the only formal checks done at low altitude are the Outer Marker (or equivalent) crossing height and the "500 feet above (DA/MDA)" call.

As an aside, some operators suggest doing the OM crossing height check thus: "passing the OM at xxx ft - that's correct". I would suggest the safest way to do it is "passing XXX ft - and overhead the OM". Think about it.....

[charliegolf]

What the OP describes was always the case back as far as the 80s on the SH fleets.

[ShyTorque]

It was also the case in the 1970s.

It came under "airmanship" rather than rule following per se.. "Master altimeter" is certainly a military (RAF) term, at least I've never heard it used/written in the civilian world in the last twenty two years since I handed back my blue uniform.

For those who haven't experienced it before, remember that just because you have been used to one way of doing things, it doesn't mean to say all the other ways are wrong, eh? ;)

[ShotOne]

Good point well made, shy torque, although in this instance the change seems very much for the better. 1000ft is very late in the day to be deciding which altimeter you should be looking at!

[SIXTYRULEOK]

1000ft is very late in the day to be deciding which altimeter you should be looking at!

Just to confirm, this is the last of a number of altimeter cross-checks (top-of-drop, every 5000' above 10,000' and every 1000' below). If the opposite Altimeter reads lower, you don't start flying a cross-cockpit scan, you mentally adjust for the discrepancy whilst flying on your own. You could not do this much earlier because the errors between altimeters can increase with height (hence the absolute requirements for an altimeter cross check before entering RVSM airspace).

E.g. On an ILS with a DH of 200'. At 1000' I compete a cross check and find that the other Altimeter reads 960' (within limits). If I were to ignore this and the other Altimeter is correct I would erode my safety factor by 10%. Instead, I mentally adjust my Altimeter indications to make my decision at 240' (200' on the other Altimeter and, for all I know, agl):

[charliegolf]

In ShyTorque's case, he'd usually have to be going up to see a 1000', not down!

[ShyTorque]

Good point well made, shy torque, although in this instance the change seems very much for the better. 1000ft is very late in the day to be deciding which altimeter you should be looking at!

Gents, in no way was 1,000 feet intended to be the first time the altimeter check was carried out! Rather more of a final cross check that both are serviceable and together before final descent on the approach. Bear in mind that military operate under a different set of requirements and priorities and that approaches in helicopters don't always end at an airfield.

I still do the check to this day, as I suspect a large number of other military trained pilots do.

[juliet]

Same procedure on the Herc J fleet in the 2000's.

Descending though transition a cross check was done with whichever altimeter showing low becoming the master. Usually a comment along the lines of "20 low, mines the master". If the monitoring pilots altimeter was the master then you just called your own heights during an approach. If the flying pilots altimeter was the master then the monitoring pilot would just take 20', or as needed, off their indications.

Worked well and I still make note of it today.

[Aynayda Pizaqvick]

Was still standard on SH a couple of years ago, but of course that might be a result of the Shawbury training. I disagree that it is too late in the approach for helicopters; all our current platforms have good APs and we hardly go fast down the approach so workload really isn't that high at all. It could also be argued that due to type specific helicopter type allowances that an earlier check before you were in on an approach profile would be a waste of time.
As an IRE I would have expected altimeter cross checking every time they were changed, and a cross check at 1000 ft, but provided they pretty damned close then you're good to just fly off what is in front of you. My type didn't actually have any prescribed altimeter cross check limits, but if it was greater than 30 ft between them I would be using the lower one on the approach as a matter of good airmanship. I'm pretty sure the 1000 ft check was in SOPs, but again, there was no guidance on what to do if they disagreed or how accurate they should actually be, nor a requirement to nominate a 'master'. There are less and less outer markers these days, so a cross check then is getting less likely; personally I think a check at FAF would be best.