Instrument approach minimums

B

bhp

Well-Known Member
I'm getting ready to take the instrument knowledge exam in the next 2 weeks and I have a question that hopefully someone here will be able to clear up.

So here's the scenario: You're en route to an airport with an ILS approach with minimums of 300AGL and 1/2 mile visibility. ATIS reports OVC002 and RVR of 2000 ft.

My understanding is that under part 91, it is legal to "go and take a look" and shoot the approach anyway, of course still observing the DH. Suppose that conditions are indeed slightly better than the ATIS indicates and you break out just at minimums and can see the MALSR ahead. The question is, what about the visibility? If it looks like the 2000 ft. visibility is still true (below minimums) do you have to go missed even though you have the "runway environment" in sight? Is it safe to assume that being able to see the lights at the DH with needles centered necessarily means that the required visibility exists?

If you couldn't tell, I'm new here, so If there's another section where this question would be appropriate, please advise.

Thanks,
bhp
 
My understanding of this is that in practice, the value is taken on the honor system. ATC might be reporting less than 1/2 mile, but really only the pilot is in a position to know the real figure at any given instant. If you honestly know you can land safely, I really don't think you can be questioned afterwards despite whatever was "reported".

That said, adhering to the published minimums is probably a good way to avoid getting killed.
 
If you have the runway environment in sight you don't have to go missed unless you lose it again.

Part 91 (for the most part) you can shoot the approach even if it is reported as 0 visibility or 1/4 or 600 RVR. Then on the approach if you get the runway you land... it wouldn't make any sense to get the runway in sight and then be like 'oh, the visibility is low... lets go missed.' Yeah, it's low... you just got the ATIS and it said 600 RVR right? You already know it is low.

Well, let me clarify that... if you get the runway environment in sight but say past the VDP (on a non-precision) then you wouldn't be able to make a normal approach to landing you might very well have to go missed. But on a precision approach if you get the runway in sight before the DH, why wouldn't you continue?
 
The only time I can really imagine attempting an approach reporting below minimums would be when conditions appear to improving and it's been nearly an hour since the time on the ATIS. Things can change significantly in an hour.

Here's a related question: I assume that at a towered field you can just ask for a minute-by-minute ceiling and RVR reading and use that for your decision. But if the tower closes at night, what happens to the ATIS? Does it revert to an AWOS type reporting?
 
You can fly the approach. If you don't have the visibility on the approach plate you cannot land, no matter how well you see the runway.

91.175.(c). Operations below DA/DH or MDA. Except as provided in paragraph (l) of this section, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—
...
(2) The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and
...
 
milski said:
You can fly the approach. If you don't have the visibility on the approach plate you cannot land, no matter how well you see the runway.

91.175.(c). Operations below DA/DH or MDA. Except as provided in paragraph (l) of this section, where a DA/DH or MDA is applicable, no pilot may operate an aircraft, except a military aircraft of the United States, below the authorized MDA or continue an approach below the authorized DA/DH unless—
...
(2) The flight visibility is not less than the visibility prescribed in the standard instrument approach being used; and
...
Click to expand...

But does ATC report "flight" visibility?
 
Holocene said:
I don't see why anyone would waste time trying to determine the flight visibility when they could be determining whether or not they can safely land the aircraft...;)
Click to expand...

Because they need to determine that they can land the aircraft safely and legally. Or do you consider the legal part just an option?
 
I'm drawing a blank trying to think of a time where I would be at MDA on an ILS approach, can see the runway, yet don't have the required flight visibility???
 
For 1/2 or 1/4 mile on an ILS approach - you're right, guys. And that's what the initial post was about, so I guess I'm being to picky. Could happen in theory with a non-precision approach and higher visibility required.
 
milski said:
For 1/2 or 1/4 mile on an ILS approach - you're right, guys. And that's what the initial post was about, so I guess I'm being to picky. Could happen in theory with a non-precision approach and higher visibility required.
Click to expand...

Agree with that.
 
If you're at the MAP and can see the runway environment I can't think of a scenario when you wouldn't have the required flight visibility.
 
GUNIT said:
If you're at the MAP and can see the runway environment I can't think of a scenario when you wouldn't have the required flight visibility.
Click to expand...

Only problem would be, if you're at the MAP when you see the runway, would you be in any normal position to land, since you'd be past the VDP?
 
SteveC said:
I'm drawing a blank trying to think of a time where I would be at MDA on an ILS approach, can see the runway, yet don't have the required flight visibility???
Click to expand...

My question as well. If you can see the runway, then don't you by definition have the required flight visibility?
 
Just to throw this out there:

On the ILS 34 at AVL (http://naco.faa.gov/d-tpp/0911/05061IL34.PDF), flying to the 200ft DH leaves you 2886 feet from the threshold, but almost right on top of the MALSR rabbit. At least in principle it would be possible to break out and see the lights but not have the charted min 2400 RVR visibility.

Is there something I'm missing?
 
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