AIRBUS Dual RA fault & Flight control laws

[SumFingWong]

Hi - Wondering if any Airbus experts can help me with the following:

When both RAD ALTS fail on the bus, I understand the flight control laws revert to direct law (flare law?) for landing.

My question is; on approach, when the gear is selected down and the AP turned off, and the 330 flight controls revert to FLARE LAW, will there be a "direct law" ECAM triggered ? (and subsequent approach/landing distance procedures).

I ask as I imagine it could pop up at a very inconvenient time during approach and would be much easier delt with prior to comencing an approach.

Any thoughts ?

Cheers.

[Founder]

You make a good point. this is actually only relevant if you're making cat 2/3 approaches. What happens is as you said, the aircraft reverts to Direct Law when landing gear down. There is no inhibition of the RA's warnings during approach until touchdown so what you get is a Autoland degradation from for example CAT3 DUAL to CAT1 SINGLE and the autopilots will disconnect.

GPWS and Automatic callouts will also be inop so hope that the weather is good =)

But there is no LDG DIST PROC Application for this failure since it doesn't affect the aircrafts ability to fly. Just its capability for accurate landing.

You can read more about it in FCOM1 (1.34.40 P2) and FCOM3 (3.02.34 P12)

Kind Regards
Tim

[C433]

I disagree with Founder there is a landing distance factor and procedure for direct law. The procedure requires you to land Config 3 Vref +10 and a landing factor of 1.35 dry runway. F/CL DIRECT LAW 3.02.27 P9 and 3.02.80 or QRH.
If you have prior warning of the dual RA fault this is my you should refer to the FCOM 3 after completing ECAM. 3.02.34 P12, this then will refer you to the direct law page and associated procedures and factors. I hope this helps?

[elac2]

Cannot arm the APP mode????? Think about that one.

elac 2

[ironbutt57]

Good point..many miss the direct law checklist:ok:

[groundfloor]

This is a cut and paste from the Airbus 330/340 FCTM (Flight Crew Training Manual)

"DUAL RADIO ALTIMETER FAILURE

The Radio Altimeters (RAs) provide inputs to a number of systems, including the GPWS and FWC for auto-callouts. They also supply information to the AP and A/THR modes, plus inputs to switch flight control laws at various stages.

Although the ECAM procedure for a RA 1 + 2 FAULT is straightforward, the consequences of the failure on the aircraft operation require consideration.

Instead of using RA information, the flight control system uses inputs from the LGCIU to determine mode switching. Consequently, mode switching is as follows:
· At take-off, normal law becomes active when the MLG is no longer
compressed and pitch attitude becomes greater than 8°
· On approach, flare law becomes active when the L/G is selected down and
provided AP is disconnected. At this point, “USE MAN PITCH TRIM” is
displayed on the PFD.
· After landing, ground law becomes active when the MLG is compressed and
the pitch attitude becomes less than 2.5°
It is not possible to capture the ILS using the APPR pb and the approach must be flown to CAT 1 limits only. However, it is possible to capture the localiser using the LOC pb.
Furthermore, the final stages of the approach should be flown using raw data in order to avoid possible excessive roll rates if LOC is still engaged. Indeed, as the autopilot gains are no longer updated with the radio altitude signal, the AP/FD behaviour may be unsatisfactory when approaching the ground.
There will be no auto-callouts on approach, and no “RETARD” call in the flare
The GPWS/EGPWS will be inoperative; therefore terrain awareness becomes very important. Similarly, the “SPEED, SPEED, SPEED” low energy warning is also inoperative, again requiring increased awareness."

Nice document the Airbus FCTM ;). LGCIU = Landing Gear Control Interface Unit.

[SumFingWong]

Thanks for your comments !

I have reviewed FCOM 3 "NAV RA 1+2 FAULT" (and the FCTM) and whilst they detail how the flight control laws will change to "flare law", there is no reference to "direct law" or the associated direct law checklists/approach procedures.

Should I read into this that since "flare law" is subtley different from "direct law", and there is no mention of direct law, I wont have any nasty ECAM surprise and approach procedure to apply late in the approach ?

[C433]

No the dual RA is one of those got you type problems. You will get a direct law ECAM when you lower the landing gear. As I mentioned in my previous post always review FCOM 3.02 after you have completed your ECAM. In this case 3.02.34 P12 will then lead you to 3.02.27 direct law. If there are notes in section 3.02 they are worth reading to prevent surprises or highlight why you are doing certain procedures. And of course sometimes there aren't any notes for simple ECAM procedures. I hope this helps?

[Captain Marvel]

On the A330, you will not get the FCTL DIRECT LAW ECAM on landing gear extension with a dual RA fault, this may be different to other Airbus. Thus I do not believe you need to refer to the direct law procedure.

It is the same as ELEC EMER CONFIG, again you do not refer to the driect law procedure and do not get the ecam on gear extension (Emer Elec shows ALTN LAW: PROT LOST on the status page)

FCOM dual RA does not say refer to direct law procedure, unlike IR DISAGREE, where it specifically refers you to the direct law procedure.

The direct law ecam will show on the status page DIRECT LAW: PROT LOST. and also FCTL PROT on the inop systems You do not get this on the dual RA ECAM.

[SumFingWong]

Thanks !!!

[SIDSTAR]

The 320 paper checklist states "CREW AWARENESS"

This is a nasty problem if you're not ready for the implications. Imagine:-

1. Direct Law for landing - therefore flap 3 and a landing distance increment of 1.35. Not something to discover when you put the gear down.

2. APP pushbutton u/s (LOC will work for a while!)

3. No Autopilot

4. No autocallouts

5. No GPWS
Basically much of your normal backup systems for a anormal approach are gone and it can really throw pilots.

I have seen numerous pilots in the sim totally screw up this problem simply because either they weren't aware of the implications of a seemingly innocuous failure or didn't read FCOM 3. Every time you have a failure get out FCOM 3 after you've finished the ECAM procedure to see what gems may be hidden in the notes etc.

Nice a/c the 320, until you see the problems that such a simple failure can create. In most other types you would merely lose your GPWS and Cat 2/3 capability.

In the 320 it virtually puts you into an emergency situation and you'd better be ready for it. Thankfully, most reputable 320 operators that I know, drill this into their crews in recurrent training.

[FlightDetent]

This is a nasty problem if you're not ready for the implications. ...
Every time you have a failure get out FCOM 3 after you've finished the ECAM procedure to see what gems may be hidden in the notes etc.

Words of wisdom.

[Admiral346]

My question is; on approach, when the gear is selected down and the AP turned off, and the 330 flight controls revert to FLARE LAW, will there be a "direct law" ECAM triggered ? (and subsequent approach/landing distance procedures).

The point is: Without the RAs there is no way for the computer to know, when to go into the Flare Law. Therefore you cannot engage the Approachmode at all, and it will revert to manual flight at gear down (so it is smart to get it on speed and correct descent rate when lowering the gear, to keep the trim requirements down)

Nic

[TyroPicard]

SumFingWong
Different Airbi have different control laws in this situation - does your question relate to A330/340 or A320?

[jyan_zhang]

If A319 aircraft got the failure message that "RA1+2 fault" identified by EFCS1&EFCS2 at phase befor 6 inclusive(eg.phase 2)
My question is :
:confused:When approaching and before L/G is down, can the APPR mode be engaged normally ?

[bond2002]

Can any one explane why Approach can not be armed in a Duel RA failure.

[rudderrudderrat]

Can any one explain why Approach can not be armed in a Dual RA failure.

I guess it's because during the "AP/FD common modes" (FCOM 1.22.30. AP/FD ) Approach modes on the ILS, "LAND FLARE & ROLL OUT" are armed. Since there is no RAD ALT information - the FMGC can't compute LAND & FLARE so "APP" is rejected.

On a previous aircraft (L1011) the AP/FD "Approach" mode was separate to the "A/L" (autoland) mode, so we could do an auto coupled approach to CAT 1 minima with no RAD ALT information. PFM.

[TyroPicard]

Also, from the FCTM.. (A320)
"The final stages of the approach should be flown using raw data in order to avoid possible excessive roll rates if LOC is still engaged. Indeed, as the autopilot gains are no longer updated with the RA signal, the AP/FD behaviour may be unsatisfactory when approaching the ground."
So that's two reasons.

[OATNetjets]

My 2 pennies about this...

1°) Normal law is a load factor control law, which means that the pilot stick or the autopilot are "asking" for a certain Nz demand, that is then computed using a number of information (like mass, CG, flaps configuration, dynamic pressure or mach number...) to give the adequate change of trajectory.
2°) Direct law is a control law that uses no information (or very little) but the gains have been set by defaut to "safe" value. It's a fixed gains mode that is adequate for a range of speeds although precision of flying is degraded and the flight domain may be restrained. Its use is related to failure modes.
3°) Normal Nz law on ground is "catastrophic" while direct law is not.
4°) The flare law is a direct law with additional damping and an additional pitch down term (increasing with time to give the pilot a "natural aircraft" behavior) that is equivalent to a direct law ajusted for low speed (no need to have it valid for 250 kt) that are activated based on RA. No RA => no flare law as such

Based on that if we loose the RA's:
1°) If landing gear is up the aircraft is entitled to think that it is not about to land and therefore there is no reason not to keep the load factor control law, whose gains do not depend on RA information.
2°) A good way to determine that landing is coming is to use landing gear information, then I do not know what the ECAM's or procedures say but the aircraft will be in direct law (or equivalent) since flare law is not available and normal law is not adequate to land.
3°) In normal mode the autopilot gains (pitch and roll) are not valid anymore (too sensitive) due to loss of RA and thus the FD information as well, which explains the loss of the APP functionality.
4°) In direct law the autopilot would still be asking for Nz while the control law is not controlling Nz anymore. Therefore it is not available either, and the "no APP mode" is sensible.

Pierre

[fantom]

Different Airbi have different control laws in this situation - does your question relate to A330/340 or A320

Point of order: should be 'Airbii', Latin. Or 'Airbusartum' Or Airbusos (Gr).

[Dani]

You have to make your decision before you start your approach. You are not allowed to start a Cat II or III without RAs. Some airlines provide you with complete lists of things you need for approach. RAs are two of them.

Dani

[IflyA320]

On A320 you can't engage App mode. Only Loc Mode is available.

[I-FICO]

Guys what happens during take off? Will it revert from direct law when landing gear up?

[A4]

From FCTM:

At take-off, normal law becomes active when the MLG is no longer
compressed and pitch attitude becomes greater than 8°


On approach, flare law becomes active when the L/G is selected down and
provided AP is disconnected. At this point, “USE MAN PITCH TRIM” is
displayed on the PFD.

A4

[IFLY_INDIGO]

The GPWS/EGPWS will be inoperative; therefore terrain awareness becomes very important.
[/FONT][/FONT]
I found in simulator that terrain display on ND is not affected at all. May be only the EGPWS alerting system is inoperative.

[Rocket3837]

On A320.....
upon L/G selection during app, Directl law activates and at this point the ECAM (STS) will ask for flaps 3 & spd & ldg dist increment....
After takeoff with RA 1+2 fault, Direct law is active until L/G is selected up.
If I remember correctly, A330/A340 behave the same way..

[vilas]

May be only the EGPWS alerting system is inoperative It's not may be but it is inoperative. Without RA inputs the system will not know the clearance from terrain. These inputs also go to FWC. More interestingly why should it take ten years to discuss such a simple failure.

[FlightDetent]

Whether inside the A320 the GPWS and EGPWS are in fact two separate systems, or - as the acronym would suggest - the enhanced functions are built atop the core GPWS is not known. There are no technical reasons why RA failure should affect EGPWS. I am not saying they don't on the aeroplane, that's down to internal logic.

[Bahruz]

Hello guys!
At the moment, I am in my type rating program on A320. That is why, i want to ask about DUAL RA FAILURE (RA 1+2 FAULT).
The question is, should I fly as the same LOC G/S out, using FPA ? (on the final stage)

[FlightDetent]

Yes, LOC+FPA. The A/P should not be left engaged too long (it is written), however. Then FD=off.

Good luck with your training, enjoy the aeroplane!

[vilas]

A330 and 320 differ in redundancies. As someone said A330 is not a big A320. In A320 Approach mode cannot be armed as it requires inputs from RA. An easier way to fly ILS is treat initially as an NPA. With AP on and TRK/FPA, arm LOC. After LOC capture configure to Flap 2. Then put the gear down AP off, FDs off, set RW track and then on fly raw data ILS.

[tubby linton]

I have often wondered how the Flight Guidance would perform for an Rnav approach with a double RA failure. I know that it is not good with an ILS as it uses the RA to tune the sensitivity of the LOC as you get closer to the ground, but I wonder if the same logic is used for an RNAV (GPS)?

[Check Airman]

I have often wondered how the Flight Guidance would perform for an Rnav approach with a double RA failure. I know that it is not good with an ILS as it uses the RA to tune the sensitivity of the LOC as you get closer to the ground, but I wonder if the same logic is used for an RNAV (GPS)?
I'm guessing it would do fine, as the guidance is all internal. No evidence to support my theory though.

[FlightDetent]

Would there even be a need for any such logic? The LOC is getting more narrow closer to the runway (and ground), hence the FD-AP (do not remember which one) gains need to be adjusted to avoid over-controlling. I think this may not apply to the internal guidance at all.

Two more thoughts:
while the sequence described by vilas is perfectly fine, I reckon the type rating course will demonstrate LOC+FPA for this excercise.
Secondly, is there an agreement on how close is too close, so that the AP needs to come off? I always guessed 1500 ft-ish.

[tubby linton]

Thinking about it you would need to have a flight director to fly an rnav-gps as there is no raw data.I would still be interested to see how the guidance reacts with a double RA failure.

[Check Airman]

Secondly, is there an agreement on how close is too close, so that the AP needs to come off? I always guessed 1500 ft-ish.

At my last company, the only suggestion was to select landing flaps before extending the gear, so as to have normal law do as much of the trimming as possible.

Interestingly, some of our airplanes require F3 for landing in this case. For others, landing config isn't specified. Does anyone have any reason why this is so?

[FlightDetent]

Wow, I always thought DCT law was F3 by design requirement. And dual RA is that due to no flare mode, A330/340 included. Slap me if I deserve it, could it be a typo in the manuals?

With regards to F3 then gear-down: I remeber that as well in the past. Later, with a wider undestanding on what were the appropriate instructing philosophies, the company mantra changed - no tricks outside the book were recommended, only smart application of it. Hence for dual RA, unlike in G+Y HYD where the summary advises the swap, standard sequence would be used. But we would deccelerate to F speed before dropping the wheels, goal achieved. Vapp(f3) to F speed difference is insignificant.

[sonicbum]

The A320 has been landing CONF 3 in direct law for the past 31 years, not sure this is different today, unless the latest MSNs have a new F/CTL software. I have always highly discouraged configuring to CONF 3 then L/G DOWN in a DUAL RA, as the EMER CANC for a legitimate non spurious warning is against the Airbus philosophy.

[Goldenrivett]

I have always highly discouraged configuring to CONF 3 then L/G DOWN in a DUAL RA,
Like wise.
There is a perfectly serviceable trim wheel available - which for some reason Airbus pilots are reluctant to use.
Boeing pilots must be laughing their sox off.

[FlightDetent]

discouraged configuring to CONF 3 then L/G DOWN in a DUAL RA, as the EMER CANC for a legitimate ... warning ... Huh, an old leash scar on top of my left hand just opened up reading this, :) sweet memories of Toulouse. "Merci(*), what on Earth stops you from landing gear up after cancelling it?!"

Further study of the FCOM ABN L/G for that warning shows there's logic specifically designed to ensure with DUAL RA the bells go off with L/G UP and F3.

For landing F3: MSN 7000+ both CEO and NEO in our library have that for the landing.

---
* I am sure with the first syllable "mer", the following one not too much.

[vilas]

At my last company, the only suggestion was to select landing flaps before extending the gear, so as to have normal law do as much of the trimming as possible. This is debatable. When you do that you get a uncancelable gear up warning for a good reason. Using EMER CANCEL you are setting your self for Gear up landing. I wouldn't do that just to postpone direct law for 30 seconds. Besides whenever you lower gear the trim will change because thrust will change which has to be trimmed manually. So what's the point?

[vilas]

Hence for dual RA, unlike in G+Y HYD where the summary advises the swap, standard sequence would be used. Very true. There are only two exceptions to standard sequence. Both with double hydraulic. First in G+Y because if you drop gear at higher speed then when you reduce to Vapp the last elevator position will let the nose drop. So you will be flying with stick held backwards out of neutral. This reduces available side stick movement to raise the nose to 15° should you go around. Second is G+B where gear has to be lowered first before 200kts for better controllability with half elevator then configure all the way to three.

[sonicbum]

Huh, an old leash scar on top of my left hand just opened up reading this, :) sweet memories of Toulouse. "Merci(*), what on Earth stops you from landing gear up after cancelling it?!"

Further study of the FCOM ABN L/G for that warning shows there's logic specifically designed to ensure with DUAL RA the bells go off with L/G UP and F3.

For landing F3: MSN 7000+ both CEO and NEO in our library have that for the landing.

---
* I am sure with the first syllable "mer", the following one not too much.

Hehe exactly, that's the Toulouse style :-) Anyway for all the "EMER CANC" lovers the FCOM DSC-31-30 states :

Note: This pushbutton should only be used to suppress spurious MASTER CAUTIONS.

:D

[Bahruz]

Yes, LOC+FPA. The A/P should not be left engaged too long (it is written), however. Then FD=off.

Good luck with your training, enjoy the aeroplane!
Thanks a lot)