CATIII FO to CATIII FP vis requirements question

[billonearth]

:confused:A senerio came up in a recent PC involving a CATIII Fail Operational approach being degraded to a CATIII Fail Passive due to system failure. The reported vis on the field was 100m. We had the required vis for the Fail Operational mins (50m) but did not have the required vis for the Fail Passive mins (175m). We were inside the FAF during the system failure. Does the rule about being able to continue the approach inside the FAF if the vis goes below minimums apply to this situation?

[411A]

It depends on the specific regulatory authority, and, in many cases, the specific airlines operations specifications...for our ops, the answer is Yes.
Type, L1011.

[Mansfield]

The rule applies, however it isn't really a get-out-of-jail-free card. You are still required to have the necessary visual references in sight by the time you reach the DH; in this case, you'd be looking for the TDZ lights or markings. If you can see those, then you meet 121.651(c)(3) and, I would also think you'd have a pretty strong argument that you had the flight visibility specified in 121.651(c)(2).

Another consideration is what did you brief prior to the approach? Some operators will accept a blanket sort of CAT III briefing that allows you to degrade during the approach. My current employer does not; if the system downgrades from FO to FP, the approach must be missed, re-briefed and re-flown, unless you are using your emergency authority.

[FatFlyer]

Hi, a similar question which I am unsure of, we have Cat111b
75m rvr required and no decision height. If via drops to say 50m after final fix/1000ft, the rules say we can continue to DH and land if visual, but no visual reference needed. Though it is sensible to go around, is it permitted to continue? Can't find answer in ops manual.

[lion-g]

If it's Fail Passive, the landing cannot be continued with an autoland as how i understand it! Is it allowed in some places ? Saw a post on the minima required for a "FP" RVR.. is that for CAT3B downgraded to CAT3A or CAT2 ?

My understanding of FP is that there is no significant deviation in flight path BUT AUTOLAND capability is LOST. Am I missing something here ?

As for the CAT3B approach, we have a 100m RVR requirement a stated by our company policy.

Any comments or critics ?

Cheers,
lion-g

[rudderrudderrat]

Hi billonearth,

We have to take note of the RVR before the 1,000 ft gate. Any RVR received after that position is for "information only" and we may continue the approach provided our landing capability is still good.

Your aircraft down graded to CATIII FP (CatIII single) after the 1,000 ft point - but the RVR you were using before the 1,000 ft point was only 100m and therefore not good enough. We would have to GA.

Hi FatFlyer. You may continue in your case, because the RVR received after 1,000 ft gate was "information only". You were still capable of No DH - therefore you don't need to see anything - just the runway turn off when trying to vacate.

Hi lion-g, Fail Operational (CATIII B) has at least two separate autolanding autopilots engaged. If one fails after alert height (100 radio) the other continues seamlessly. If one AP fails before 100R - then you will be alerted.

Fail passive (CATIII single) - only 1 autolanding AP needs to be engaged. (2 APs may be selected on - but unless they are independently compared to each other e.g. separate electrical source - then it doesn't qualify). Therefore the pilot has to verify all is going OK by looking out of the window using the required visual clues.

[Denti]

We had the same rules as ruderruderrat about information only value of any RVR received after the limiting point (outer marker or 1000ft), however with the introduction of fail operative 737s it got changed and any RVR below 75m after passing the OM or 1000ft is a mandatory go-around. Justification is that with fail operational we still have to get a visual segment at 50ft and thus ensure proper touch down and more importantly rollout and leaving the runway whereas with the fail operational we do not need a visual segment until the nose gear has touched down and the 75m RVR is required to be able to notice any rollout malfunction.

[411A]

Slightly different with other types, and operators.
L1011, fail operational, dual/dual out of the factory, forty years ago.
Both dual channel autopilots need to be engaged for CATIII landings.
Previously, if one A/P became unserviceable during the approach, CATII minimums were reverted to...this was a company procedure, not an aircraft limitation.
Now, if below 1000 feet baro height, if one A/P becomes unserviceable and/or the RVR drops below minimums, we are allowed to continue with the automatic approach/landing (provided DLC remains operational), no questions asked.
Autothrust desired, but not strictly required.