First "real" hold (long)

"Barry" wrote
But as I replied to Dan Luke, neither the visibility at 100' nor the ground
visibility can replace the requirement for flight visibility to continue the
approach below DH.

But there is no flight visibility requirement for the ILS at PNS for
civil aircraft unless RVR is not reported. (Note that military
minimums DO specify flight visibility, but military aircraft are
excluded from the requirements of 91.175(c)) The minimums for the
approach are 321 MSL (DH) and 2400ft RVR. RVR is not the same thing
as flight visibility, and in fact every book of approach plates gives
a table for conversion from RVR minima to meteorological visibility,
to be used when RVR is not reported.

I've always interpreted 91.175(c)(2) to mean that you must
have the required visibility at all times below DH. Is there a
reference that contradicts this?

First, I'm not convinced this interpretation is correct. I'm aware of
no reference that contradicts OR supports it, but it is certainly not
in line with normal operating practice, even at the prefessional level
where scrutiny is high.

Second, even if it is correct, it would certainly apply only to those
approaches where minimum visibility, rather than minimum RVR, is
given. The fact that a conversion table is given (and the fact that
the numbers DO NOT convert directly - 2400 ft RVR becomes 1/2 sm
visibility, which is 2640 ft) certainly indicates that the terms are
not interchangeable.

Michael

"Barry"wrote:
A lot of pilots don't understand that the rule about going
down to 100' on the approach lights doesn't remove the
visibility requirement. If you see only a few approach
lights at DH, you almost certainly do not have the required
visibility, and should go missed.

Well, maybe you don't have it at 200', but you might at
100'. In my experience, horizontal visibility can vary a
great deal with the last couple hundred feet of altitude.
That certainly is true when a ground fog is lifting, as
was the case at PNS last Sunday.

OK, but 91.175(c)(2) says you must have the required
flight (horizontal) visibility to coninue the approach below
DH, not just at 100' or at landing.

Yes, but who says what the flight visibility is? I do, that's who, and if I
see the threshold lights when I reach DH, it's a pretty good bet I have a
half mile of flight vis. That gives me 100 more feet to get down and see the
actual runway and land.

I don't know why the RVR was reporting so low, but the vis. was certainly
good enough for me (and probably the 208 ahead of me) to complete the
approach without fudging.
--
Dan
C-172RG at BFM

"Dan Luke" wrote in message
...
Yes, but who says what the flight visibility is? I do, that's who, and if
I
see the threshold lights when I reach DH, it's a pretty good bet I have a
half mile of flight vis. That gives me 100 more feet to get down and see
the
actual runway and land.

If you see the threshold lights, you can descend below 100' AGL on that
basis alone. There's no requirement to see the actual runway.

--Gary

"Gary Drescher" wrote:
Yes, but who says what the flight visibility is? I do, that's who, and
if
I see the threshold lights when I reach DH, it's a pretty good bet I
have a
half mile of flight vis. That gives me 100 more feet to get down and see
the actual runway and land.

If you see the threshold lights, you can descend below 100' AGL on that
basis alone.

That's not the way I read the reg.: see below.

There's no requirement to see the actual runway.

Didn't mean to say there was - but Barry's question is one of having the
required *flight* visibility to go below DH. According to the reg. cited,
just seeing the lights is not sufficient to allow that extra 100'; you must
also have the flight vis. required on the plate.

From 91.175:
(c) Operation below DH or MDA. Except as provided in paragraph (l) of this
section, where a DH or MDA is applicable, no pilot may operate an aircraft,
except a military aircraft of the United States, at any airport below the
authorized MDA or continue an approach below the authorized DH unless-

[snip]

(2) The flight visibility is not less than the visibility prescribed in the
standard instrument approach being used; **and**

[snip]

The RVR-to-vis. chart notwithstanding, the pilot is the judge of flight
visibility, but it's still a *requirement* in addition to seeing the lights.

--
Dan
C-172RG at BFM

"Dan Luke" wrote in message
...

"Gary Drescher" wrote:
Yes, but who says what the flight visibility is? I do, that's who, and
if
I see the threshold lights when I reach DH, it's a pretty good bet I
have a
half mile of flight vis. That gives me 100 more feet to get down and
see
the actual runway and land.

If you see the threshold lights, you can descend below 100' AGL on that
basis alone.

[snip]
The RVR-to-vis. chart notwithstanding, the pilot is the judge of flight
visibility, but it's still a *requirement* in addition to seeing the
lights.

Sorry, I was unclear. I agree that there's still a flight-visibility
requirement. My point was just that there's no specific requirement to see
the runway at 100' AGL. In practice, though, if you don't see the runway at
100', you probably don't have the required visibility. So we're in
agreement.

--Gary