Visual Reference In CatIIIB

[Thridle Op Des]

A query was raised in 'Questions' about how many lights should be visible at a CatIIIA DH, however I would like to extend this to include CatIIIB, but rather that say how many lights, I would simply like to ask what visual reference should you have on touch down (if any). There seems to be some confusion certainly in my mind about the requirement and a few of my fellow pilots are experiencing the same thing. I know this is rather academic and the probability of actually having no visual reference at all is miniscule, but I would be interested in some guidance on the subject.

Just for info we have an interesting contradiction, our Ops Manual says 'At least one light is attained and can be maintained' but at 200' we announce 'Landing' (A330 Alert Height) and are being told that the visual reference at DH is now irrelevent since you are beyond the Approach Ban Point and the Auto Land light has not illuminated.

Regards

TOD

[Stretchwell]

Cat 3B no decision = nothing. Cat 3B with a decision height = ONE centreline light.

[Hotel Mode]

Depends if you are doing a Cat 3B (no DH) approach or just a CAT 3B approach. 3B no DH requires no visual reference and a normal CAT 3B requires 1 centreline light. Depends if you have Fail Operational (no DH) or Fail Passive (with DH) autopilots available. On 744 3 autopilots means no DH and if you lose 1 and become Land 2 you use 3B with DH and requirement for visual reference. On previous type we only had 2 autopilots so could only do approaches with 50ft DH/150m RVR. On both 744 and previous type in the fail passive (2 autopilot case) the aircraft trimmed back to allow safe GA in event of a (further) failiure.

[Popster]

Cat 3B with decision height

The requirement is as stated above to be able to see 1 centreline light at decision.
What puzzles me is how do you know its a centreline light when its the only one visible? !!

[MrBernoulli]

You don't know! Cat 3 is intended for autoland so you have to rely on the kit putting you on the centreline. You will never have sufficient reference to really allow a manual landing. The Cat 3A minima only allows the pilot to ascertain that the aircraft is landing (itself) in the touchdown zone (hopefully). A Cat 3B approach adds the safety of ensuring a rollout on the centreline.

ALL of the above assumes correctly operating (and operated) certified kit in the aircraft and on the airfield.

[howflytrg]

Cat 3A Visual Requirements

A segment of at least 3 consecutive lights being the centreline of the approach lights, or TDZ lights, or runway centreline lights , or runway edge lights, or a combination of these is maintained and can be maintained.

Descent below DH without adequate visual reference is prohibited.

in the trusty 737 any AP disconect/Nav set failure/ 2 or more deviation flashes or Stab out of Trim below 500R is a mandatory Go Around

[Clarence Oveur]

A bit off topic...

Originally Posted by Hotel Mode

Depends if you have Fail Operational (no DH) or Fail Passive (with DH) autopilots available. On 744 3 autopilots means no DH and if you lose 1 and become Land 2 you use 3B with DH and requirement for visual reference. On previous type we only had 2 autopilots so could only do approaches with 50ft DH/150m RVR. On both 744 and previous type in the fail passive (2 autopilot case) the aircraft trimmed back to allow safe GA in event of a (further) failiure.

Perhaps you could explain how you are Fail Operational with 3 AP, but not with 2?

[Hotel Mode]

Perhaps you could explain how you are Fail Operational with 3 AP, but not with 2?

Because with 3 you still have comparison/monitoring left when one fails. The 2 AP aircraft i've flown did not have sufficient self monitoring for this.

[NigelOnDraft]

Perhaps you could explain how you are Fail Operational with 3 AP, but not with 2?
Because with 3 you still have comparison/monitoring left when one fails

Not quite a simple as that. Unless I am much mistaken, I have yet to find AP3 on an Airbus (A320 etc., and A340 as I recall...), but we are quite happy doing CAT3B No DH etc...
NoD

[Human Factor]

For CAT 3b, you require rollout guidance in order to track the centreline after touchdown. For this, there needs to be an autopilot channel to the rudder. The 737 does not have this (although I understand it may be an option on the NG), whereas more recent types do. Certain failures in a 737 will leave you with one autopilot so you cannot Autoland. Similar failures in an Airbus will still leave you with two, although they may be downgraded. However, below 200' RA, you won't know there has been a failure until after you've landed (fail operational).

[foxmoth]

Not quite a simple as that. Unless I am much mistaken, I have yet to find AP3 on an Airbus (A320 etc., and A340 as I recall...), but we are quite happy doing CAT3B No DH etc...
NoD

Two autopilots each with 2 channels so 1 channel failure still leaves you 2 APs working.

[Captain Airclues]

Originally Posted by Hotel Mode

On 744 3 autopilots means no DH and if you lose 1 and become Land 2 you use 3B with DH and requirement for visual reference.

Probably a typo Hotel Mode but if you lose an autopilot on the 744 you revert to Cat 3A not 3B.

Airclues

[airwaya457]

CAT III b with a decision height one light is required

CAT III b with no decision height (alert height) there is no requirement to see anything prior to touchdown.

Could be wrong but that’s the way I understand it.