A320 autoland with failures

[PhilRabbit]

Hi there!
Being an air traffic controller I had an interesting discussion with a collegue about the A320's autoland functions/features.

What happens to FD and AP if the aircraft is in LOC-G/S, LAND, FLARE or ROLLOUT modes and e.g. the LOC or G/S signal is lost (aircraft receiver failure or ground transmitter failure)?
I understand that these FD modes guide the aircraft to a fully automated landing using localizer, glideslope and RA data. But what happens if some of the vital data are suddenly lost, especially when the aircraft is close to touchdown (e.g. LAND, FLARE, ROLLOUT)?

Thanks for any help!
Phil

[michelda]

It depends of your height.
Until 200 ft you can loose loc/gs signal or 7 second without caution or degradation of your landing capability. After this time you have a degradation of capability.
Below 200 ft one (or two) red NO AUTOLAND light comes up and if you don't have adequate ground references you have to go around.
I try to semplify as much as possible the system; I don't know if I was able to do it

ciao

[PhilRabbit]

Thanks guys!

So with or without landing capability degradation...will the AP(s) disconnect and FD(s) revert to basic modes?
I have read somewhere that LAND mode remains engaged (below a certain height?). But how can it when vital data are not available? Does it somehow memorize the last received data and use it for further guidance?

@michelda: you do not have to simplify things...I do have some (basic) knowledge!

Thanks again!

[Airbus Girl]

Put simply, those modes will only come up if everything is working properly. Lets assume you are doing a Cat 3b approach ( don't know anyone who does Cat 3c). You need 75m forward viz. If you lose a signal higher up you get an autoland warning and you go around. We have plenty of warnings to let us know if something has failed, usually something flashing on the FD!! If we don't get Land mode we go-around if not visual. We call "alert height" at 100' which is our final check. Depends on the problem really. We can also go-around from any point, even if the wheels have touched.

[Clandestino]

There will be no autoland warning if G/S signal is lost below 100ft RA or loc signal is lost below 15 ft RA - autoland will use inertial reference instead of ILS beams. However if one has a really bad day and both main and stby localizer transmitters pack up just at touchdown, autopilot has to be disengaged after touchdown and manual rollout has to be done - not an easy task with 75m RVR, but not impossible either.

[PhilRabbit]

Many thanks to Airbus Girl and Clandestino!!

autoland will use inertial reference instead of ILS beams

Ahhhh, THIS is what I didn't know. So AP/FD will remain in LAND mode, do "its best" using internal/inertial reference and warn the pilots via the autoland lights, correct?

Stupid question:
Will the system continue its ("inertially guided") autoland until touchdown if the pilots do NOT initiate a go-around and simply ignore the autoland warnings (I know, why should they?)? Why doesn't it simply disengage APs and revert to HDG-V/S, forcing the pilots to do something?

[TyroPicard]

Phil - just to tidy up the loose ends..

Above 200'RA if the LOC or GS signal is lost for more than 7 seconds, the AP's disengage (with aural and visual warnings) and the FD's revert to basic modes, HDG V/S or TRK FPA. This would prompt a go-around, which is nice.

Ahhhh, THIS is what I didn't know. So AP/FD will remain in LAND mode, do "its best" using internal/inertial reference and warn the pilots via the autoland lights, correct?

Correct. Below 15'RA it can cope with no LOC signal, below 100'RA it can cope without G/S, in those cases there is no warning. From 200'RA down to those heights a big red AUTOLAND light comes on - prompting a G/A unless sufficient visual reference for landing.

[PhilRabbit]

Many thanks for your help, TyroPicard!
That makes sense...interesting, what the auto system is capable of!
But I guess that a loss of both RAs would cause the AP to disconnect and FD revert to HDG V/S or TRK FPA in any case, right?

[FlightDetent]

Loss of both RA automatically degrades the "guidance" capability. To CAT I manual landing. This will be announced on FMA and if under specific height also by "Autoland" warning light.

In fact, there is no need for AP to disengage and I would guess it doesn't. The guidance mode changes but AP is still well capable of following any FD modes that remain available after the downgrade.

FD (the un-real)

[jb5000]

Unfortunately to further complicate matters a double RA failure will put you in alternate law, going to direct law with the gear down.

The AP would drop out as it is not available in direct law, Triple Click, FDs would revert to basic modes, Autoland light, 'Use Man Pitch Trim' etc.

All quite exciting, but thankfully having a simultaneous dual RA failure is quite unlikely.

[dkz]

jb5000 - actually in dual RA you would stay in normal law and you will get the direct law when the gear is down (with AP1+2 inop included in the package)

(also you cannot arm the ILS Appr mode however you have LOC)

[jb5000]

Ahh of course, of course. Apologies!

[TyroPicard]

Simultaneous double RA failure unlikely - agreed.
But in the event of a CAT 2/3 approach with one RA Inop - if the serviceable one fails with the gear down it leads to an interesting go-around in Direct Law, worth being aware of and briefing the possibility.

[PhilRabbit]

Many thanks for your help, guys!!

[batman123]

-below 200 ft, the mode become a combined mode like LAND. FLARE...(replace the 2 mode for alt and track)
the only way to go around is to move the throttle to his G/A position.
if you see no flare before 50 ft, you have to flare manauly, or you will land very hard.better to keep a hand on the stick and be ready....

-in combined mode you can not change your altitude by pushing/pulling the alt knob on the FCU(open or managed climb)

-I presume if you lose your ILS signal above 200 ft, you will have a warning, the plane will revert back to a normal rate of descent of 5%, or 3 degrees.

try this in the sim...