CAT III localizer unusable for rollout guidance

[None]

There are two airports that I know of that have a CAT III ILS with this note.

The question often asked is may I shoot an autoland to this runway (the only method to shoot a CAT III for the jet I fly)? My response is that I believe an autoland is OK, but that the autopilot must be disconnected after nosewheel touchdown.

The AOM does not indicate that rollout guidance is a requirement for either a CAT III ILS or an autoland in the ILS airborne equipment requirements table.

To date, leadership agrees with this, but others are not convinced. Do you have experience with this CAT III ILS note?

The published minimums are RVR 175m (600ft) at one airport, and RVR 200m (700 ft) at the other. Other parallel CAT III ILS approaches at the same airport include minimums of RVR 75m (300ft). Perhaps this implies that the minimums are higher due to the unusable rollout guidance. It might also simply indicate that those two runways present totally different environments, not just localizer guidance problems.

[bobrun]

With the airplane I know, auto-rollout is required for Cat3B, but only preferred for Cat3A. Often Cat3A requires a RVR of 200m, and Cat3B requires RVR 75m.

[BelArgUSA]

A Cat III approach without rollout guidance for autopilot is flown with Cat IIIa minimums.
Unless there is a note preventing all Cat III operations.
If the approach has Cat III rollout guidance, it is a CAT IIIb approach.
Boeing 747 classics can be certified to Cat IIIa... but not Cat IIIb.
Yet their autopilots were capable if they had that option, but never were certified.
xxx

Happy contrails

[Mansfield]

Early autoland systems did not have rollout capability, which limited the original CAT III ops in the US to an RVR of 700 feet. Once rollout guidance was implemented, CAT IIIB minimums were approved. Since that time, there has been some finessing of the requirements, and current US requirements limit CAT III operations without rollout control to 600 RVR. Because of this softening of RVR requirements, the traditional definitions of CAT IIIA and IIIB have little value anymore...what really matters is whether the aircraft is fail-passive or fail-operational, and whether it has functioning rollout guidance.

Your MEL may provide some insight on this. For example, with respect to the 757/767, it is possible to defer the rudder pedal nosewheel steering. However, if you do this, you should be restricted to at least 600 RVR because the rudder pedal steering is how the autoflight system tracks the centerline. No rudder pedal steering, no rollout guidance.

With that in mind, if the localizer signal is unusable during some portion of the rollout, the runway should be restricted to at least 600 RVR.

[WX-T]

Rollout control guidance. Does this mean ground based guidance and/or A/C based guidance?

So, if you are flying to CAT IIIb minima (100m RVR) and you don't get the FMA mode changing from LOC to ROLLOUT at 5', can you continue to land?
You have no rollout guidance and no reversion to CAT IIIa minima.

[411A]

So, if you are flying to CAT IIIb minima (100m RVR) and you don't get the FMA mode changing from LOC to ROLLOUT at 5', can you continue to land?
You have no rollout guidance and no reversion to CAT IIIa minima.

Indeed, an interesting question.
Now, in the 'ole TriStar, there is no doubt (in the described scenario) you are going to land, but without rollout guidance, you could, I suppose, end up in the weeds.
In personally performing well over 800 autolands in the Lockheed three holer, never once has rollout not been annunciated (and provided), however, if the LOC (ground facility) trips off at the least opportune time...well, this would definitely not be good if the visibility was severely restricted.

[stilton]

With inadequate visibility to ensure centreline tracking No roll out guidance is cause for an immediate go around.

All you have to do on the 75/76 is select TOGA, for a completely automatic go around, whether you have touched down or not, pitch limiting is provided for initially to prevent tail strikes.

The GO Around option is available until reverser deployment.

[FE Hoppy]

For no rollout your talking about a dual failure in a very small time frame.

[Henry VIII]

Totally agree with stilton.

[763 jock]

Thread drift here.

Can anyone explain why on the 75/76 you can get GA thrust at the same time as Flare/Rollout? The alternative is Idle thrust with GA GA annunciated. I know how it happens, by why did Boeing design it as such?

Any ideas?

[Mansfield]

I also agree with Stilton. However, this can be a bit tricky with the 767/757 design. Rollout captures at 5 feet RA. If the airplane is at or below 5 feet RA for more than 2 seconds, the automatic go-around is disarmed. Need to be quick, and as always, prepared to complete the go-around with manual control if need be.