Operation Below DH

[MrBojangle]

When making the decision to proceed below the DH, I understand the lighting/visual requirements and the "continuously in a position to land." But could someone explain what "the flight visibility must not be less than the prescribed visibility in the standard IAP" means.
Also, lets assume you're part 91 and have started the approach with visibility less than prescribed, but you see the runway environment at the DH. Can you legally descend anyway??
Thanks.

 

[flyer172r]

Flight visibility means the average forward horizontal distance, from the cockpit of an aircraft in flight, at which prominent unlighted objects may be seen and identified by day and prominent lighted objects may be seen and identified by night.

That's taken from the FARs. So basically, if the approach requires 1/2 sm. visibility, then when you get to DH you have to be able to see 1/2 sm. in front of you in order to land. Technically, if you get to DH and don't have the required flight visibility, you can't land even if you see the runway. However, guess who determines what the flight visibility is: the PIC.

 

[Donsa320]

When making the decision to proceed below the DH, I understand the lighting/visual requirements and the "continuously in a position to land." But could someone explain what "the flight visibility must not be less than the prescribed visibility in the standard IAP" means.
Also, lets assume you're part 91 and have started the approach with visibility less than prescribed, but you see the runway environment at the DH. Can you legally descend anyway??
Thanks.

I can't resist this. If you are not prepared to make that call at the DH, why would you fly the approach in the first place?

DC

 

[Doc Holiday]

Most ILS approaches bring you down to 200' AGL and 1/2 SM. At some locations the DH and/or visibility requirement are greater. For example, let's say an ILS has a DH of 300' and visibility requirement of 1 1/2 SM. You are Part 91 and start the approach even though reported visibility is 3/4 SM. When you arrive at DH, you see just the REILs and nothing beyond. (At 300' on a 3 degree glideslope you would be approximately 1 mile from the threshold) So now you have 1 mile flight visibility, which is less than the 1 1/2 SM required. Therefore you would be unable to descend below DH and land legally. This was just a quick example, reference 91.175.

 

[MrBojangle]

Let me rephrase myself. I know most ALS extend to around 3000 ft on a precision approach, and the MM is located approximately 3500 ft (so approximately at the DH). So here we have about 500 ft (1/12 mi) from over the MM to the beginning of the ALS. Assuming standard minimums, if all you saw was the beginning couple of lights at the DH how many people would elect to continue and why?

 

[avbug]

Donsa asked the more relevant question. Why, if the approach is below minimums, would you initiate the approach to begin with? We enter into the miraculous to merely fly an instrument approach proceedure...we fly blind to a spot near the ground, and then land. But why would you elect to do so knowing that the minimums did not exist...why would you choose to fly to a spot near the ground, unable to see, when the very minimal visibility required for this great feat is known to not be available? Seems to me a lot like running onto a highway blindfolded, knowing there's traffic, in the hopes that it will be gone when you arrive.

Having so said...you ask if upon arriving at DA we find the approach lighting visible...do we continue? In accordance with 14 CFR 91.175(c)(3)(i), descent to 100' above TDZE is permissible with nothing but the ALS. As you're at DA/DH with the ALS in sight, is there a reason you won't be continuing?

This is up to you. If you're continuing and the visibility is indeed below minimums, you're setting yourself up for a hazard, as well as a potential violation on several counts. You can always say that flight visibility was adequate, but with the availability of official weather, in the event you cause an incident or accident, you stack the deck against yourself.

There are legitimate times when one might consider an approach under Part 91 when weather is reported below minimums...the most obvious to me is a time when it's clear and a million, you can see it, and know that the transmissiometer is frosted over or a reporting error exists. Other times with changing conditions, one might expect it to improve...it may have dipped below just as you began the approach, for the fifth time in the last twenty minutes. But generally, if it's that low, you probably shouldn't be wasting your fuel when you could divert to a place that is above minimums.

If under Part 91 you're carring enough fuel to blast away all day at that approach with abandon, then have a ball.

 

[BushwickBill]

When making the decision to proceed below the DH, I understand the lighting/visual requirements and the "continuously in a position to land." But could someone explain what "the flight visibility must not be less than the prescribed visibility in the standard IAP" means.
Also, lets assume you're part 91 and have started the approach with visibility less than prescribed, but you see the runway environment at the DH. Can you legally descend anyway??
Thanks.

Yes Part 91 you can. You may as well "take a look" there is nothing wrong with it. You should prepare to go missed. Lots of automated weather stations are positioned on parts of the airport that may have worse weather than the approach end. Some automated weather stations take a while to update as well. STS is a perfect example.

 

[FastestPA31Ever]

A related question for cargo pilots that I always pondered...does seeing the ambient strobing from the rabbit in the fog count as seeing the approach lights?

Partially kidding. I agree with the guy who said bring lots of fuel. Keep those options open!

 

[Tug Driver]

My policy is that if I think Im going to have to go missed...I just head for my alternate.

I rarely start an approach when its iffy for a landing. No "look-sees"

 

[mar]

Boooorrrrrriiiiiinnnnnngggggg

My policy is that if I think Im going to have to go missed...I just head for my alternate.

I rarely start an approach when its iffy for a landing. No "look-sees"

Why take the fun out of it?

I bet you drink non-alcoholic beer?

Geeze, when I flew 135 freight I had a "three strikes and I'm out" policy--and that was VFR!!!

C'mon, have some fun!