1/2 mile vis

[mastermags]

Sounds like an interpretation issue. Sort of like the old argument about autopilot in RVSM - do you have to have it available in working order or actually have to have it engaged.

Our book says must be engaged.

And what's all this nonsense about a fed on the ground determining flight visibility?

 

[152SIC]

At my 121 carrier (and at least one other that I know of) you would be violating company procedures as well as having a hard time explaining how you complied with OpSpec C052 (b)(2) if you saw the runway but landed with RVR lower than required for the approach.

In other words, if the RVR dropped below mins after the FAF, and I continued and saw the runway before DH and landed, I would be illegal.

The POIs at both of those 121 carriers are confused. I believe that the opspec in question talks about RVR being controlling. Is that where the confusion lies?

 

[Autothrust Blue]

I've worked for five airlines and that wouldn't be true at any of them

Two airlines and untrue.

 

[wheelsup]

Great feedback everyone, this made for a great discussion with fellow CFI's hanging out in the FBO the other day. Ultimately we digressed the discussion to "what's legal" versus "what's safe" and we discussed why sometimes just because it's legal doesn't mean it's the best course of action.

This is an old thread but FWIW.

I have seen 1800 RVR (lowest limit of 1/2 mile) and at 200' you barely make out the lights (but they are there). At 150' you just start to see the runway beginnings (think about 3:1 rule, 300' per mile).

I have seen 1600 RVR and all you see at 200' is a glow (like a city at night, not individual lighting system). The extra 200' RVR makes a HUGE difference.

The way the systems are designed, if you actually do have the approach lights in sight at DH, you've at least got close to 1/2 mile vis. This is probably why @BobDDuck said what he did (without putting words in is mouth).

If you attempted to land in 1/4 mile (1200 RVR) you wouldn't even come close to adhering to 91.175. The discussion is mostly academic in nature and has no practical application IMO...

 

[BobDDuck]

The way the systems are designed, if you actually do have the approach lights in sight at DH, you've at least got close to 1/2 mile vis. This is probably why @BobDDuck said what he did (without putting words in is mouth).

Pretty much. I have no way of knowing what the up to the second RVR is when I'm in the last few hundred feet of an approach. The only number that matters to me in the DH/MDA/MAP. The way the approach is built will dictate what RVR is needed to see the runway environment and safely land. I have done one approach where we did get the approach lights right at mins but never picked up the runway environment in the next 100 feet so we went around. I'm guessing it was less than 1800 RVR that day.

 

[smig]

The POIs at both of those 121 carriers are confused. I believe that the opspec in question talks about RVR being controlling. Is that where the confusion lies?

Yes, the opspec states that rvr is controlling for approach and landing.

 

[152SIC]

The opspec in question can be pretty confusing sometimes, even for POIs. I should know, I used to be one.

Here is the answer: http://fsims.faa.gov/PICDetail.aspx?docId=8AA798FD4885F5C886257A8400600E10

paragraph 4-280

Hope this helps. It really had me confused for a while!

It'd be great if you could show confused POIs the correct reference in the 8900.1 as well.

 

[Itchy]

People keep talking about going down a 100ft lower if the terminating bars are in sight. Just semantics for most approaches, but the rule is 100 ft above touch down, not decend down another 100 feet.

Discussion topic in the pilot lounge the other day; how to determine if you legally have a half mile vis.

Discussion started during a conversation regarding 135 ops and when it's legal to shoot the approach, but also, when is it legal to land if the wx goes lower than 200 & 1/2 during an ILS. You have to have you're flight visibility so the question was, "How do you know if you have you're 1/2 mile visibility or not?"

At 200' on the ILS, and you have the approach lighting system, you can descend to 100' below the DA, and then if you pickup the runway environment, great, but how do you determine your half mile?

The best answer that I came up with was that on a 3 degree glide slope, at approx 140' agl, you are about 1/2 mile away from the thousand foot boxes on the runway, so if you can see them, you've got your half mile. But is there some other way to use the MALSR/other ALS to determine your 2650' visibility? It would seem that if you're on the ILS at 100' and all you can see is the runway #'s, that's not good enough to land? I know we might be thinking "Hell, if I can see the tarmac, I'm putting it down!" The question is, though, is that legal under 135/121?

This came up on an interview, too, so I thought this might be good discussion here.

Thanks for your participation in advance!

People keep talking about going down a 100ft lower if the terminating bars are in sight. Just semantics for most approaches, but the rule is 100 ft above touch down, not descend down another 100 feet from your present position.

 

[z987k]

The opspec in question can be pretty confusing sometimes, even for POIs. I should know, I used to be one.

Here is the answer: http://fsims.faa.gov/PICDetail.aspx?docId=8AA798FD4885F5C886257A8400600E10

paragraph 4-280

Hope this helps. It really had me confused for a while!

It'd be great if you could show confused POIs the correct reference in the 8900.1 as well.

The 8900 should be referenced more by pilots. For all intents and purposes is the FARs continued... or maybe "explained better". I find it a LOT more difficult to navigate and find what I'm looking for in it though.

Here's the directly relevant part, but you should read the whole thing at the link 152sic posted. -
Part 135

C. Parts 125 and 135 Controlling Minimum. The controlling minimum concept for parts 125 and 135 differs in application from part 121. Part 91 applies to all parts 125 and 135 operations whether they are conducted in foreign countries or the United States (see part 125, § 125.23(b) and § 135.3(b)). Operations conducted under parts 125 and 135 must also be in compliance with §§125.381 and 135.225 (which applies to all operations within the United States, U.S. territories, U.S. military airports, and foreign airports). For parts 125 and 135 operations, the controlling minimum concept must be used at all airports (with the exception of a part 135 “eligible on-demand” operator who is permitted to start an approach without weather reported above landing minimums (see §135.225 (b)). As a consequence, §§ 125.381(b) and 135.225(b) prohibit parts 125 and 135 operators from conducting look-see approaches at any airport. The controlling minimum concept, however, allows for a pilot to continue a CAT I approach to DA/DH or MDA if the visibility/RVR was reported to be at or above the controlling minimum when the pilot began the FAS, even though a later visibility/RVR report indicates a below-minimum condition. The controlling minimum concept also allows for a pilot (upon reaching DA/DH or MDA and before passing the MAP) to continue the approach below DA/DH or MDA and touchdown if the requirements of § 91.175 are met, even though the visibility/RVR is reported to be below the controlling minimum.

Part 121

Part 121 Controlling Minimum. The controlling minimum concept for operations conducted under part 121 is implemented by § 121.651(b). For these operations, the controlling minimum must be used at civilian airports within the United States and its territories, and at U.S. military airports, unless the provisions of § 121.651(d) are met. Section 121.651(d) permits a pilot to begin the FAS even though the reported visibility/RVR is below the controlling minimum if the approach procedure is an ILS and the flight is actively monitored by a PAR. Therefore, pilots are not constrained by the controlling minimum on runways with ILS and active PAR facilities, provided the provisions of § 121.651(d) are met. The controlling minimum concept allows for a pilot to continue a CAT I approach to DA/DH or MDA NPA if the visibility/RVR was reported to be at or above the controlling minimum when the pilot began the FAS, even though a later visibility/RVR report indicates a below-minimum condition. Upon reaching DA/DH or MDA and before passing the MAP, the approach may be continued below DA/DH or MDA to touchdown if the requirements of §121.651(c) are met even though the visibility/RVR is reported to be below the controlling minimum.