A320 RA 1+2 Fault

[Boyington]

In the A320 in the case of RA 1+2 Fault the Approach cannot be armed. So in case we need to do an ILS approach, the option is to either switch off the FDs and fly the ILS raw data or use the FDs by selecting V/S.
My doubt is this: In case we are following the FDs using the V/S selector knob should we use the minima (visibility) applicable for FDs available or FDs not available as it is not as precise as arming the approach.

[EGPFlyer]

What's the difference between minimas? It's still cat I

[vilas]

Minimums are not based on FD,s availability. Minima depends on type of approach, precision or non precision. With double RA failure the recommended method is you fly like a LOC approach for interception and gear down then fly Raw data ILS. Then you can use ILS minima. If you use HDG/VS it will become an NPA, a localiser approach with higher minimum.

[Cough]

If you use HDG/VS it will become an NPA, a localiser approach with higher minimum.

Why? You still have permanent g/s guidance available full time. Though why use V/S? LOC-FPA is a far more appropriate...

The parallel for me is a PAR approach, whereby the crew know nothing about the approach except the spoken words from ATC. Yet this is still a precision approach...

[Boyington]

In Delhi for ILS RWY 29 the RVR required for CAT I is 750 m and the chart also mentions RVR 550 with Flight Director or Autopilot or HUD to DA.

[Boyington]

Minimums are not based on FD,s availability. Minima depends on type of approach, precision or non precision. With double RA failure the recommended method is you fly like a LOC approach for interception and gear down then fly Raw data ILS. Then you can use ILS minima. If you use HDG/VS it will become an NPA, a localiser approach with higher minimum.

In Delhi for ILS RWY 29 the RVR required for CAT I is 750 m and the chart also mentions RVR 550 with Flight Director or Autopilot or HUD to DA.

[vilas]

Thanks! Indeed it is so but coming back to the point your AP/FD is not capable of tracking GS and therefore it becomes LOC approach with minima of higher than ILS. If you fly raw data it will be ILS DA which is lower albeit with higher RVR of due manual flight.

[Denti]

Interesting, the LIDO chart i have here just shows the 550m visibility, nothing else. So it would be 960ft, 550m in my company, flying raw data.

[akindofmagic]

Thanks! Indeed it is so but coming back to the point your AP/FD is not capable of tracking GS and therefore it becomes LOC approach with minima of higher than ILS. If you fly raw data it will be ILS DA which is lower albeit with higher RVR of due manual flight.

This isn't correct.

If you were intent on using automation (in this case the FDs), you could just follow the raw data (G/S) using FPA or VS. Until you put the gear down, you can do this with the AP on. Afterwards, the PM would presumably make the required corrections to keep on the G/S. The relevant minimum would be CAT I.

Personally however, I find it far easier to just go FDs off.

[EcamSurprise]

I agree.

You could use the FD in selected V/S guidance using Cat 1 minima. The latest by gear down i'm usually flying it myself with FD off though, because it's just simpler but there is no need to use NPA minima.

[tubby linton]

The LOC mode becomes unusable at low level due to the loss of the radalts. The radalts apply a smoothing correction to the guidance. At minimums with this failure you are flying raw data, so if necessary adjust your minima accordingly.This is described in the FCTM.(AO-34 Dual Radio Altimeter Failure)

[RUMBEAR]

The answer to the question should be found in the AIP in the country in question. In my experience to use the published CAT 1 minimum visibility the required equipment includes an FD that is tracking a LOC and GS signal. So if using the FD with LOC/FPA or FD off would require the visibility to be increased to 1200m.

[FlightDetent]

RUMBEAR has a point. In EASA-land, the use of 550 RVR for CAT I minima, as opposed to ICAO's standard of 750 m, is based on a set of conditions, and FDs are one of them. Except it is not AIP, but the operator's OM-A written i.a.w. applicable (pan-)national regulations. The didactical quality, as well as depth of understanding of OM-A, naturally vary. :E

The OP's question is very valid. According to my LIDO OM-C, the regulatory reference is AMC5 CAT.OP.MPA.110.

RVR of 750 m or less .... may be used
- for Cat 1 operations to runways with FALS, RTZL, and RCLL;


I only quoted the non-FDs section. My personal memory trick to remember is:
. CAT II lights > no FDs required
. Simple ALS > FDs are required

[vilas]

Boyington
As correctly pointed out by tubby linton autopilot/FD is not capable of proper guidance in later part of the approach and that is why it is not approved procedure to use AP or FD for this approach. So you will have to fly raw data once on glide slope and thereby CAT1 minima without credit for FD should be used. Quoted below from FCTM:



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 altimeter signal, the AP/FD behaviour may be unsatisfactory when approaching the ground.

[Goldenrivett]

As correctly pointed out by tubby linton autopilot/FD is not capable of proper guidance in later part of the approach and that is why it is not approved procedure to use AP or FD for this approach.......


Please can someone tell me how the AP behaviour is "unsatisfactory when approaching the ground" when I'd be in Direct Law? (Unless, of course, I was attempting to land with the gear up.)

[whitelabel]

Flying a cat 1 approach or a loc approach does NOT depend on your level of automation. With this failure (RA1+2) you can use raw data, HDG/VS, TRK/FPA but of course the easiest is LOC/FPA. Many people here are confused that you now revert to a non precision approach but you are still following a glideslope. So vertical guidance and therefore normal CAT 1 minima as you can fly in you basic c172!

[CL300]

Like in ALL autopilots the RadAlt induces a bias for sensitivity ( read microvolts) from acquisition of ground return to the certified minimum of A/P utilization ( indeed this can be ground contact).
As a consequence, and i think it is the case in the A320, the whole logic of flare, derogation, throttle etc..depends on Radalt.
However i do not see why F/D should be off for a cat 1? Is it like mandatory when flying manual to have the F/D OFF ?

[ACMS]

Just be a PILOT and hand fly the Jet, it's an Airbus with FBW so you ain't really doing anything that hard are you.:D

[vilas]

Golden
It is a generic statement in the FCTM. Obviously in this case only applies to use of FDs.