Airbus A320 Radio Altimeter

[Bagoongathipon]

Is there such a thing as "discrepancy between the two RAs" in the Airbus A320? is the values the same between the two RAs? if not, What are the tolerances and effects of these discrepancies?

If there is, where can I find it in the Airbus training manuals? Because to the best of my knowledge, there isnt any of this.

Secondly, in general aviation knowledge, is there any discussion regarding this matter?

I would appreciate if any comments are backed up by a source that can be studied about.

Thanks

[Superpilot]

As far as an official statement goes describing the RA limitations and tolerances I also can't find anything in the FCOMs. However,

1.) Looking at the RA antenna placement on the aircract, under normal circumstances there should not be a difference between the two RA readouts and therefore no computed adjustment to either.

2.) "The Autoland light illuminates when the difference between both radio altimeter indications is greater than 15 feet." - FCOM1 - Autoland

Generally speaking (Airbus FCOM bulletin No 812/1), RAs are prone to errors due to reflections from hail clouds or heavy precipiation. Which could obviously be dangerous at low levels.

[PappyJ]

Unofficially, they often miss-read. However, it's only for a brief time when in flight. On the ground they can often miss-read as well, and may do that for greater lengths of time.

On the ground, it can be caused by a vehicle being parked under the aircraft. Depending where it's parked, one or the other radio altimeters miss-reads.

In flight, it will normally be a very short time when the aircraft is changing pitch, rolling, etc. The difference won't be much during flight, and will sort itself out when the aircraft is in equilibrium.

Again, that's unofficial observations from over 15 years on Airbus 320'2, 321's and 330's.

[shortfuel]

RA discrepancy tolerance is known for autoland as mentionned by Superpilot.
For approaches based on baro-referenced MDA, no clear ECAM/CAUTION will appear to tell you that you have a discrepancy.
Having said that, a discrepancy could be a consequence of an errouneous RA; and for that, Airbus sent a RED OEB:

http://nsa14.casimages.com/img/2010/04/09/100409030604766742.jpg (http://www.casimages.com)

http://nsa15.casimages.com/img/2010/04/09/100409031201169085.jpg (http://www.casimages.com)

http://nsa15.casimages.com/img/2010/04/09/100409031244857141.jpg (http://www.casimages.com)

[mrtickle]

unbelievable, airbus are so complicated, a paperless aircraft that has to have the encyclopedia airbus attached to it to explain everything.

The RA can cause a stall ?? what a pile of steaming vile these a/c are.

[shortfuel]

An erroneous RA can cause a stall on a 737 too...we know that for sure :suspect:.

[Bagoongathipon]

thanks for these information especially to that OEB.

Last question,
RAs used radio waves to determine its actual height. Does these kinds of equipments need calibration(any kind of calibration)? (just like barometric instruments wether a pilot or ground crew calibrates these instruments).

My question leads to, if it requires calibration, then even if RAs are in perfect condition but not properly calibrated, it might give a discrepancy between them because it might not be properly calibrated.

[shortfuel]

In the AMM, there is no RA calibration task.
You can either do a system test (correct ops of RA transceiver) or a ramp test (verify auto call-out height correctly announced) on the ground (CFDS menu).

But am not an engineer so just my 2 cents...

[Jim Croche]

This Airbus OEB arrived some considerable time after the Boeing 737 stalled in Amsterdam. It appears that up to that accident, Airbus hadn't considered all the possible effects of an RA failure (and neither had the rest of us). Evolutionary learning - usually from accidents - helps us to stay alive to make the new mistakes that nobody had considered! The ability of the human being to find new ways to f*ck up knows no boundaries I'm afraid.

[captmilo]

HI , For the answer look ito indicating and recording systems in fcom vol 1 chapter . ull find you answers


thank you
captmilo

[I-FICO]

Hi guys,

I was looking for a post talking about RA 1+2 fault. Maybe this is the right one.
I have just completed my A320 type rating and I am trying to figure out what happens during take off if both RA fail. I undesrtood that when LND GEAR it goes in direct law (directly). Ok everything clear for landing. What about during take off?
Will it revert to normal law?
Thanks in advance...

[MD83FO]

Yes you go back to normal law after gear is up and or engage the AP

[max nightstop]

RA failures don't cause stalls, excess AOA causes stalls...if you fail to react to the first you might get the second.

[I-FICO]

THX MD83FO!

Where I can find this information on the FCOM?
Another question..Will the A/THR engage normally? I'm asking like that because I don't understand it clearly due to the fact that the OEB#38 report that the LVR CLB message will not appear on FMA during go-around. I understood that the LVR CLB message will appear at the altitute selected on the FMGS during cockipt preaparation. So it should not be linked on RA operations..
Where did I screw up?

[Chouman]

I can’t found radio altemeter fans in A320 MEL
its go item or no

[vilas]

There appears to be complete misunderstanding about double RA fail. Double RA fail doesn't cause anything so aircraft remains in normal law. With gear down it is put in direct law to give conventional feel during flare and landing because normal law flare mode requiers RA inputs which are not available.

[Dan Winterland]

RA faults can also occur when the cabin crew pour coffee and red wine down the forward galley sink. The residue can cover the lower rear fuselage and the aerials, and disrupt the signal. More common on the A321.

[goeasy]

This is also a reason to note the ‘LAND’ annunciation even on cat 1 landings as it verifies rad alt integrity test. Just another backup.