E3D ZH101 Altimeter in Inches
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E3D ZH101 Altimeter in Inches
Can any of you aircrew answer this question? Today, I (a humble air trafficker) spoke to an E3D (as it had a UK Mil reg and was a 8/23 sqn aircraft), and although it was a Brit aircraft (albeit with a non-UK sounding pilot (exchange?)), its altimeter was in inches rather than Mb. Can any one explain? Cheers.
If it has an altimeter with an electronic subscale the subscale decrements in discrete steps, rather than continuously as did older clockwork altimeters.(e.g. as in the Vickers FunBus - 3 clicks per millibar if I recall correctly - or alternatively in precise 0.01 inch Hg intervals as it had both options).
Given the relatively coarse assessment of touchdown zone QFE at most military bases (usually derived from standard correction applied to a value obtained from the Met Office up to an hour aga, the error displayed at the threshold using QFE may well put an RVSM-compliant altimeter out of limits if mB are used, whereas with precise inch Hg values, the greater precision may put it inside limits as you have 1, not 3 subscale alternatives.
The solution is to have instantaneous exact QNH inch Hg values available, plus accurately surveyed parking position elevations. So that you can check whether or not your altimeter is really within limits. But that would cost monry, so just fudge it and hope - as with most military compliance with current rest-of-the-world requirements.
Given the relatively coarse assessment of touchdown zone QFE at most military bases (usually derived from standard correction applied to a value obtained from the Met Office up to an hour aga, the error displayed at the threshold using QFE may well put an RVSM-compliant altimeter out of limits if mB are used, whereas with precise inch Hg values, the greater precision may put it inside limits as you have 1, not 3 subscale alternatives.
The solution is to have instantaneous exact QNH inch Hg values available, plus accurately surveyed parking position elevations. So that you can check whether or not your altimeter is really within limits. But that would cost monry, so just fudge it and hope - as with most military compliance with current rest-of-the-world requirements.
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Oh, it reads in inches because the E-3 was bought at short notice pretty much 'off the shelf' following the AEW Nimrod fiasco. Unlike so many other US (as opposed to U/S that is) bits of kit, 'we' didn't have time to meddle with it, at great expense, to convert to UK standard.
Sadly, many, if not most, E-3 crew don't perform their own conversions.
Not so much in the UK, but certainly in europe, I've had many an air traffic agency convert mb to inches incorrectly. I have seen E-3 crews accept an incorrect a/t figure rather than trust the conversion out of the FIH. W@nkers.
Sadly, many, if not most, E-3 crew don't perform their own conversions.
Not so much in the UK, but certainly in europe, I've had many an air traffic agency convert mb to inches incorrectly. I have seen E-3 crews accept an incorrect a/t figure rather than trust the conversion out of the FIH. W@nkers.
When I was struggling to get through the Buccaneer OCU at Honington back in 1976-77, we were told one day about an incident which had happened the previous night involving one of Uncle Spam's finest going into Mildenhall. He had been passed nine-nine-something as the 'altimeter' setting and had set it as twenty nine-point-nine something inches. As a result, he was hundreds of feet too low and I'd actually heard him going past Honington very low indeed...
We were told that, had Mildenhall been on the other RW, he would probably have hit the ground.
Of course this was long before radar altimeters and GPWS were fitted to all military heavies......wasn't it
?
We were told that, had Mildenhall been on the other RW, he would probably have hit the ground.
Of course this was long before radar altimeters and GPWS were fitted to all military heavies......wasn't it
?
1. This has happened before, F4J subscale was inches; I roamed around uk and yurap '84 to '88 and got inches on request (used to know a girl like that!).
2. Landing on QNH is not natural, you have to do sums.
nothing matters very much, most things don't matter at all.
2. Landing on QNH is not natural, you have to do sums.
nothing matters very much, most things don't matter at all.
I don't own this space under my name. I should have leased it while I still could
LJR - no, the rest of the world does not use QNH.
In UK Civil Aviation uses QFE for instrument approaches if I remember correctly.
As far as trying QNH, at great expense Lady Belinda Buck's lover introduced QNH in the RAF and we had to try it.
Once his flies failed we then reverted to QFE.
One the inches/mb question, on the Vulcan the rule was quite simple. If an American controller, being helpful, gave a setting in Millibars we had to ask for it in inches and then two of the crew would convert it to millibars.
Now we use hectopascals I guess it may all be different.
In UK Civil Aviation uses QFE for instrument approaches if I remember correctly.
As far as trying QNH, at great expense Lady Belinda Buck's lover introduced QNH in the RAF and we had to try it.
Once his flies failed we then reverted to QFE.
One the inches/mb question, on the Vulcan the rule was quite simple. If an American controller, being helpful, gave a setting in Millibars we had to ask for it in inches and then two of the crew would convert it to millibars.
Now we use hectopascals I guess it may all be different.
On Nato E3As (which have the altimeter baro scale in InHg) there is a conversion chart InHg to mb/HPa on the grey plastic between the pilots windscreen and the eyebrow windows, fixed with clear sticky back plastic in the best of Blue Peter traditons.
Originally Posted by Pontius Navigator
In UK Civil Aviation uses QFE for instrument approaches if I remember correctly.
BEagle's 'Mildenhall' incident, and others tales of mb/inch confusion, reinforce the need to specify "millibars", especially when the pressure is less than 1000 mb. Guidance in CAP 493 requires that UK civil ATCOs do so.
