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Airbus RVSM - Why Flap Mode Off?

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Airbus RVSM - Why Flap Mode Off?

Old 29th Jul 2002, 19:30
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Question Airbus RVSM - Why Flap Mode Off?

I believe the initial RVSM guidance from Airbus indicated that the EGPWS Flap Mode should be selected off when entering RVSM airpspace (A320). However, the reference quickly disappeared from our manuals. I not so sure it wasn't removed because nobody could give us a clear explanation.

Any theories or confirmations of why the Flap Mode would be disabled for RVSM? I have a rather convoluted theory, but would like to see what you think, or what other information is out there.


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Old 30th Jul 2002, 08:10
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The EGPWS Flap mode switch has no effect in RVSM airspace, turning it off allows one to land with non-normal flaps settings otherwise you'd get the TOO LOW FLAPS warning . This mode only functions below 1000ft (well below the RVSM airspace) and is taken form the Captains baro setting.

I cannot see how this affects RVSM unless it is added in error the first time.
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Old 31st Jul 2002, 19:24
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Airbus RVSM

This question came up on another message board. It was explained that prior to the implementation of a SB, the GPWS FLAP MODE PB could degrade the accuracy of the ADIRUS. It would be best to check with your company's maintenance department to see of the SB is applicable for your aircraft, and if it has been completed.

Since this limitation was buried in the FCOM, AI may have missed deleting it. I don't have an FCOM, but I have been told that the limitation is being removed from the appropriate manuals. Unfortunately, I do not have the number of the SB. I hope this helps.

The Kid


During a "flap mode Off "command performed with GPWS/FLAP MODE pushbutton switch to simulate flaps extended condition , the GPWS/FLAP MODE pushbutton switch grounds the GPWC AB9C terminal but also the flap extended discretes of the ADIRUS 1&3 .
Then because of this situation the ADIRUS 1 and 3 use anemometric and clinometric corrections normally used when the aircraft is really in flaps extended conf.

To prevent the unjustified grounding of the flap extended discretes of the ADIRUS this SB recommends to add a diode between......

Accomplishment of this SB prevents erroneous modification of the anemometric and clinometric data in ADIRU's 1 & 3 during a "flap mode off"command.
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