Altimeters tolerance
Thread Starter
Joined: Sep 2004
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From: France
Altimeters tolerance
FCOM Supplementary techniques:
ALTITUDE TOLERANCES PFD 1 or 2 at ground check : plus or minus 25 ft (8 m)
MAXIMUM DIFFERENCES BETWEEN ALTITUDE INDICATIONS ALTITUDE (ft) COMPARISON BETWEEN FL/SPEED ADR 1 and ADR 2 (on PFD) GND CHECK 20 ft(6 m)
So how do you interpret this ?What is the altimeter tolerance on A320 at ground check? 20 ft or 25 ft?
The wording is different , with OR & AND. initially they say PFD 1 OR PFD 2 -->25 ft
Then ADR 1 AND ADR 2 on PFD ---> 20ft
Can anyone shed light on this?
ALTITUDE TOLERANCES PFD 1 or 2 at ground check : plus or minus 25 ft (8 m)
MAXIMUM DIFFERENCES BETWEEN ALTITUDE INDICATIONS ALTITUDE (ft) COMPARISON BETWEEN FL/SPEED ADR 1 and ADR 2 (on PFD) GND CHECK 20 ft(6 m)
So how do you interpret this ?What is the altimeter tolerance on A320 at ground check? 20 ft or 25 ft?
The wording is different , with OR & AND. initially they say PFD 1 OR PFD 2 -->25 ft
Then ADR 1 AND ADR 2 on PFD ---> 20ft
Can anyone shed light on this?
Last edited by Citation2; 7th June 2012 at 12:05.
Joined: May 2005
Posts: 434
Likes: 8
From: Italy
Hello..
my understanding is that the two altimeters (ADR 1 & ADR 2) should not indicate more than 20ft difference in reading between them, at ground level. (this tolerance increases with your flight level).
Further, any of the two altimeters should not indicate more than 25ft discrepancy between the indicated altitude and your aerodrome altitude (ground check).
Ricky
my understanding is that the two altimeters (ADR 1 & ADR 2) should not indicate more than 20ft difference in reading between them, at ground level. (this tolerance increases with your flight level).
Further, any of the two altimeters should not indicate more than 25ft discrepancy between the indicated altitude and your aerodrome altitude (ground check).
Ricky
Thread Starter
Joined: Sep 2004
Posts: 161
Likes: 2
From: France
The tolerance with airport elevation is 75 ft:
FCOM special operations : RVSM
Check that the PFD altitude indication (QNH reference) of ADR1, and also of ADR2, does not differ from the airport elevation by more than 75 ft.
So I dont think that it refers to airport elevation
FCOM special operations : RVSM
Check that the PFD altitude indication (QNH reference) of ADR1, and also of ADR2, does not differ from the airport elevation by more than 75 ft.
So I dont think that it refers to airport elevation
Thread Starter
Joined: Sep 2004
Posts: 161
Likes: 2
From: France
There are 3 values for ground check: 20 ft , 25ft and 75 ft
The 75 ft is an old rule of RVSM regulation, that any altimeter should agree within 75 ft of airport elevation.
Is airbus more stringent and restrict it to 25 ft tolerance between any PFD and airport elevation ? In which case FCOM Special operation RVSM is wrong... Just reproduced an old generic rule not applicable anymore Stating " Check that the PFD altitude indication (QNH reference) of ADR1, and also of ADR2, does not differ from the airport elevation by more than 75 ft"
I am sure that the guy who wrote "FCOm special operation RVSM " is not the same author of "Supplementary NAV , altimeters tolerance"
I understand it like this : PFD 1 or 2 with airport elevation 25 ft
PFD 1 and 2 , should agree within 20 ft
And the 75 ft does not apply anymore
Or PFD 1 with airport elevation 75 ft
PFD 1 and 2 --> 25 ft
And I missed something about the 20 ft tolerance
The 75 ft is an old rule of RVSM regulation, that any altimeter should agree within 75 ft of airport elevation.
Is airbus more stringent and restrict it to 25 ft tolerance between any PFD and airport elevation ? In which case FCOM Special operation RVSM is wrong... Just reproduced an old generic rule not applicable anymore Stating " Check that the PFD altitude indication (QNH reference) of ADR1, and also of ADR2, does not differ from the airport elevation by more than 75 ft"
I am sure that the guy who wrote "FCOm special operation RVSM " is not the same author of "Supplementary NAV , altimeters tolerance"
I understand it like this : PFD 1 or 2 with airport elevation 25 ft
PFD 1 and 2 , should agree within 20 ft
And the 75 ft does not apply anymore
Or PFD 1 with airport elevation 75 ft
PFD 1 and 2 --> 25 ft
And I missed something about the 20 ft tolerance
Joined: Mar 2005
Posts: 1,338
Likes: 1
From: Uh... Where was I?
There is, apparently, a discrepancy, but I think it is not exactly a discrepancy:
if for instance PFD1 altimeter on the runway threshold differs 40 ft with respect to the elevation in the plate, you would be OK for RVSM, but anyway you would not be OK for flight, RVSM or not RVSM...
if for instance PFD1 altimeter on the runway threshold differs 40 ft with respect to the elevation in the plate, you would be OK for RVSM, but anyway you would not be OK for flight, RVSM or not RVSM...
Joined: Mar 2005
Posts: 1,338
Likes: 1
From: Uh... Where was I?
Yep, that's what I do every day.
But now thinking, the usual question: and what will we do if one day I see PFDs with a more than 20 ft discrepancy (with same QNH of course). And What if altimeters read more than 25 ft different than elevation (if accurately known and QNH is accurate, too, which is a lot of assuming).
Enter the MEL?
But now thinking, the usual question: and what will we do if one day I see PFDs with a more than 20 ft discrepancy (with same QNH of course). And What if altimeters read more than 25 ft different than elevation (if accurately known and QNH is accurate, too, which is a lot of assuming).
Enter the MEL?
