121 Approaches and Weather

[BobDDuck]

So we all know that you can't shoot an approach if you don't have the required visibility outside the final approach fix. 121.651 says

(b) Except as provided in paragraph (d) of this section, no pilot may continue an approach past the final approach fix...

However, it doesn't say you can't start an approach knowing the weather is below mins with the intent to break off the approach UNLESS you get better weather from some controlling authority before you hit the final approach fix.

Right?

Scenario:

(completely hypothetical of course)

Flying into an airport with two approaches. An RNAV which requires 1 3/4 miles and an ILS which requires 3/4 miles. The weather comes via an ASOS that updates about every 6 minutes. There is an operating FAA control tower on the field but they have no radar. The airspace around the field is controlled by a nearby Navy Approach facility.

After getting vectors to join the ILS which kind of sucked (ended up AT the final approach fix going through the localizer 600 feet above the glideslope) do a go around and get put back on a downwind to try again. Check the weather and the ASOS is now reporting 1/2 mile however it is from 3 minutes ago.

I interpret 121.651 that I can get vectors back around and join the approach but can not go past the final approach fix unless the ASOS updates and says > 3/4 miles or tower gives me an updated visibility that is better than 3/4 miles.

Am I right in thinking that?

 

[jtrain609]

That is how I understand the regulation also.

The real problem is the 1 minute weather; in order to be legal, you'd need to have the weather dialed up as you cross the FAF, and you'd need to make sure that within the minute you cross the FAF, you have the required weather to shoot the approach.

Now have I ever done this? Of course, every time!!! But is that how it always happens for most crews? I'd suspect not. I'd imagine most guys check it at some arbitrary point and then shoot the approach.

You could also always ask the tower what the visibility is.

 

[BobDDuck]

You could also always ask the tower what the visibility is.

In the hypothetical story that's what we did (about .6 DME from the FAF) and he said "well, the last plane said they broke out right at mins and they landed a minute ago".

Like that's really helpful.

He did eventually say that it was 3/4 a mile (about .1 DME from the FAF) so we were (hypothetically) good to go.

 

[jtrain609]

The tower controller obviously wasn't with it. When you ask for the visibility, the only thing the tower should say is, "What do you need? 3/4? New weather just came out, looks like 3/4 of a mile, cleared to land."

 

[BobDDuck]

WAY ahead of you.

Hypothetical radio conversation:

FO: XXXX Tower, XXX 345 ILS 4. Your ASOS is reporting 1/2 mile. We need 3/4. What's the visibility now?

 

[seagull]

The real problem is the 1 minute weather; in order to be legal, you'd need to have the weather dialed up as you cross the FAF, and you'd need to make sure that within the minute you cross the FAF, you have the required weather to shoot the approach.

Is there a letter of interp that supports this? Does the added workload of trying to obtain that next observation when you are in an usually critical phase of flight increase or decrease the risk of the operation?

 

[jtrain609]

Is there a letter of interp that supports this? Does the added workload of trying to obtain that next observation when you are in an usually critical phase of flight increase or decrease the risk of the operation?

It's what I was taught in school at an air carrier, but I don't have a letter of interp.

I think that the added workload decreases safety.

I still think it's the only way to be 100% legal unless you've got something different in your ops manual that the FAA has signed off on.

 

[FOD]

Why would you even put youself in such a situation? If its under the required mins when you arrive, then you hold till you hit your bingo fuel, if it hasn't increased by then, you divert to your diversion airport. I can't imagine trying to explain that one to the chief pilot or fed, that you where going to shoot the approach (and monitor ASOS) until the FAF, with a plan of going missed if the Vis hasn't come up. Plus, if its an airport with no radar an ASOS, chances are its not a simple missed, don't mess around with that while flying 121.