Starting, completing approaches: ceil<DH

[GravityHater]

2 days ago a pilot friend was going into an airport that was reporting for at least 1 hour on the AWOS 100' OVC 1&1/2BR -RW. I said, 'Wow, below minimums'. He said everyone was getting in on the ILS, including pt 91, 135,121. He also said he didn't see anything on the ground until 100'agl. He is not a story-teller type. Few of these a/c or pilots would have been equipped/certified for anything other than cat 1.
Is this legal?

 

[Weasil]

what was the visibility? Ceiling has nothing to do with it.

 

[snoopy_1]

1&1/2 is well above mins for most ILS approaches. At DH you have to see lights to make it legal though, not at 100'.

 

[EagleRJ]

The visibility is what is controlling for all aircraft- 91, 135, and 121. The reported ceiling only helps IFR aircraft tell when they will break out of the clouds.

Normally the ceiling and visibility are fairly proportional- in other words when it's 100 overcast, the visibility will be 1/4-3/4 mile. It's a little unusual to have a reported ceiling of 100' with visibility of 1 1/2 mi. Of course, it's an AWOS, and you know to take those reports with a grain of salt.

For all aircraft, you are not permitted to land unless your flight visibility is equal or better to the published visibility minimums. Determining that is up to the Pilot in Command, since there may be a patch of fog over the AWOS or ATIS transmissometer while the runway threshold is clear.

Normally, when flying an ILS "to minimums", the first thing you see is the end of the approach light array. Part 91 then lets you leave DH at that point and continue down to 100' above the threshold, where you should pick up the runway. Most airlines have callouts for the non-flying pilot like "Approach lights in sight- continue" to cue the flying pilot that they may continue to 100' HAT before looking up.
At 100', you should be able to see the 'runway environment', so you can land. If you still can't see anything, you must go missed approach. At that point, you don't have the required visibility anyway.

Here is the pertinent language from 91.175. Emphasis mine.

(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—

(1) The aircraft is continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers, and for operations conducted under part 121 or part 135 unless that descent rate will allow touchdown to occur within the touchdown zone of the runway of intended landing;

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

(3) Except for a Category II or Category III approach where any necessary visual reference requirements are specified by the Administrator, at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:

(i) The approach light system, except that the pilot may not descend below 100 feet above the touchdown zone elevation using the approach lights as a reference unless the red terminating bars or the red side row bars are also distinctly visible and identifiable.

This is a frequently misunderstood line of the FARs. Those red bars they are talking about are the red lights at the end of ALSF-1 and ALSF-2 approach lights. If you can see those lights, you may continue below 100' HAT, however if you can't see the runway by that point, you probably don't have the required flight visibility!
The rest of the visual cues constituting the 'runway environment' that will allow you to continue below 100' HAT are:

(ii) The threshold.

(iii) The threshold markings.

(iv) The threshold lights.

(v) The runway end identifier lights.

(vi) The visual approach slope indicator.

(vii) The touchdown zone or touchdown zone markings.

(viii) The touchdown zone lights.

(ix) The runway or runway markings.

(x) The runway lights.