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A320 FPV and unreliable airspeed

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A320 FPV and unreliable airspeed

Old 21st Aug 2020, 07:59
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A320 FPV and unreliable airspeed


The above is a para from FCTM UAS chapter. I don't understand how the FPV is affected along with the barometric altitude. It may be recalled that ADR provides barometric altitude and FPV is supplied by the IR part. UAS is a resultant of pitot/static blockage and not related to IR failure. How is FPV affected in this case? Any thoughts?
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Old 21st Aug 2020, 08:10
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A common misconception. The bird is primarily IRS derived but also has a static input. See below from the FCTM (my bold).


FCTM > Aircraft systems > Bird

RELIABILITY

The bird is computed from IRS data and is affected by inertial errors. During the approach, the flight crew may detect a small track error, usually up to +/-2 °.

The bird is also computed from static pressure information. Therefore, if the altitude information is not reliable, the flight crew must consider the bird as not reliable.
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Old 21st Aug 2020, 09:47
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Thanks for the reply T-T-O. I have reviewed that in the FCTM. My doubt was based on the below info from FCOM and FCTM.

Here is an excerpt from FCOM

And here is an excerpt from FCTM...
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Old 21st Aug 2020, 12:39
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You might be over thinking this. The FCOM is notoriously sketchy with its information, giving you only what Airbus think you need to know. If the FCOM stated that the bird DID NOT have a static feed while the FCTM said it did then I would obviously go with the FCOM. However in this case I believe that the FCTM is adding information to that given in the FCOM rather than directly contradicting it.
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Old 21st Aug 2020, 12:59
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Originally Posted by CMpilot1 View Post

The above is a para from FCTM UAS chapter. I don't understand how the FPV is affected along with the barometric altitude. It may be recalled that ADR provides barometric altitude and FPV is supplied by the IR part. UAS is a resultant of pitot/static blockage and not related to IR failure. How is FPV affected in this case? Any thoughts?
Answer is HERE.
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Old 21st Aug 2020, 16:14
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Thanks A33Zab and sonicbum. Now when the instructor asks me to "switch on the f******" bird!" (on an old sim) for an approach/landing following an unreliable speed incident, I can wipe his nose through this paragraph
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Old 21st Aug 2020, 18:49
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Originally Posted by sonicbum View Post
Answer is HERE.
So only after the BUSS activation, is the FPA solely reliant on the IR information? Do I have that right? What about planes without BUSS?
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Old 22nd Aug 2020, 17:33
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Originally Posted by Check Airman View Post
So only after the BUSS activation, is the FPA solely reliant on the IR information? Do I have that right? What about planes without BUSS?
the BUSS is Air Data (Not IR)
​​​​​​—AoA data (as a red/green/red IAS tape and GPS altitude.
i think by definition IR data can’t be trusted...
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Old 22nd Aug 2020, 17:57
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Originally Posted by Check Airman View Post
So only after the BUSS activation, is the FPA solely reliant on the IR information? Do I have that right? What about planes without BUSS?
I will link You to the rest of the thread where A33Zab explains it perfectly !

HERE
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Old 22nd Aug 2020, 19:45
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Appreciate it. Will have a read
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