Airbus Question (A 320 -100)

[Sean Dell]

Does anyone know what may have caused the following?

Before engine start I noticed on the F/O's PFD that the pitch down graduations were visible (as well as the normal pitch up indications) along with a Rad Alt indication (fluctuating). We reset the cb's for both rad alts with no success. In the end we dispatched with Rad Alt 2 c/b pulled and hence were Cat 2 capable only (with wx deteriorating at destination - hence 3 tonnes xtra taken!). On approach for a Cat 2 landing we received a spurious 'hundred above' and 'minimums' call at around 2500' followed by the correct auto callouts at the right time.

Was this just simply a rad alt failure or something else?

[Zeke]

More thn likely one or more of the four rad alt antennas were faulty

[Iceman49]

Or possibly a problem with the FWC, Flight Warning Computer.

[Busta Level]

Sounds more like the FWC - The erroneous pitch indications on the PFD would support that view. Normally, if resetting the radalt c/b does not work, trying the FWC reset (only on the ground and parked of course!) will solve most problems like yours.

Computers are wonderful things! A United mechanic I was talking to the other day said that the difference between Boeings and Airbuses was that most things on a boeing could be fixed by hitting them, while most things on the airbus could be fixed by resetting the computers and then hitting them if they still did not work!

[IMA Conehead]

Sounds like RF leakage between the Rad Alt Antennae causing spurious ramping. The rad alt's only track down so if a spurious signal(leakage) is recieved (100 call @ 2500')the rad alt will then try to resynch on the actual ground return signal.

I seriously doubt the problem to be related to the FWC this will only process the audio call outs from signals received from the RAD ALT (In This Case)
Hope this helps Conehead.

[ 13 January 2002: Message edited by: IMA Conehead ]</p>

[CaptA320]

As far as the pitch error I would definitely suspect IR2 since it provides attitude information to the F/o's PFD and hence on the gound I would most likely do a realignment. As far as part two of your question I had exactly the same experience two years ago on a CATI ILS and it was associated with the Collins Radio Altimeter. Did you arm the approach push button above 5000 ft on that approach?
Collins needed a modification two years ago because it did a self test at 5000 and if you armed the approach p/b prior to the self test (above 5000) there was the posibility of errors. However this mod has been implemented a long time ago. Chech what make of Radio altimiters are installed on your aircraft.

[Sean Dell]

Thanks for all your comments. This damn aeroplane still puzzles me at times! In answer to your question A320 we did not arm the approach above 5,000'. I will however next time do a realignment on the ground.

Cheers

[Millenium Falcon]

On the -200 we used to get weird indications / Callouts, on the approach. We were subsequently told that the Rad Alts can get confused when operating in heavy rain. It was reported that in certain circumstances spurious Double Eng Fail ECAM warnings had occurred, on approach at about 2500'...All associated somehow with RAD ALTs???? <img src="confused.gif" border="0">

[mcdhu]

FCOM 36/2 'Radio Altimeter Anomalies During Adverse Wx Conditions' is worth a read although not relevant to the original post.
heers
mcdhu <img src="confused.gif" border="0">