Prescribed Visibility-Landing IFR

[Sidious]

§ 91.175 Takeoff and landing under IFR.

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


So... One thing that has confused me is that during my CFII training, my instructor harped on the difference between RVR and SM.

Something along the lines of "If the approach procedure says you need 2400 RVR but the ATIS says its 1/4 vis then you can still land"

Then just the opposite of "If it says you need 1/2 SM vis and they report 1800 RVR then you cant land"

I've researched it in the IFH and AIM but have come up dry... Its been a year since I did my CFII and am just now using it so forgive my being rusty.

Part 91, we can attempt to do the approach even if they are reporting lower vis then the plate allows. How would you explain that to the FAA if you land and they are waiting for you? Just that the "Flight" vis was better then the reported vis on the ground?

Let me know if that question isn't clear.

Thanks!

 

[400A]

There are tables in the AIM to convert RVR to SM. Basically, if the plate shows an RVR requirement and the RVR is reported, RVR is controlling regardless of what tower vis, is.

For RVR 1800 ILS you need to be trained for that (part 135/121) as 1800 and 2400 are 1/2 mile.

To be honest I can't recall ever hearing the RVR reports on the ATIS, but I do remember getting them from approach and tower, but I am getting old.

 

[Sidious]

There are tables in the AIM to convert RVR to SM. Basically, if the plate shows an RVR requirement and the RVR is reported, RVR is controlling regardless of what tower vis, is.

For RVR 1800 ILS you need to be trained for that (part 135/121) as 1800 and 2400 are 1/2 mile.

To be honest I can't recall ever hearing the RVR reports on the ATIS, but I do remember getting them from approach and tower, but I am getting old.

Ok, so if on the approach you hear an RVR report that is lower then required but you end up seeing the runway in sight and land, do you think the FAA would give you a hard time about that?

 

[drunkenbeagle]

Ok, so if on the approach you hear an RVR report that is lower then required but you end up seeing the runway in sight and land, do you think the FAA would give you a hard time about that?

If you have the runway in sight, further away than the minimum visibility, then by definition - you had the required flight visibility.

Assume a 600' MDA 1/2 mile minimum:

Scenario A: Reported is 1/4 mile visibility. You are 3/4 miles from the field and have it in sight. You are fine.

Scenario B: Reported is 2 mile visibility. You are a 1/2 mile and don't see the field, and aren't in a cloud. You should in theory go missed. Even if you continue on and do see the field before going below the MDA, you technically didn't have the required flight visibility.

The sensors that determine RVR are far from perfect. Smoke, low fog, etc can make them lie. Which is why flight visibility is the rule, not reported ground visibility.

The FAA won't go after you. They weren't in the cockpit, and have no idea what you could see and what you couldn't.

 

[mshunter]

Just be sure if the feds are there, you can explain by some landmark (i.e. the rabbit length or some other visual landmark) that you had the vis.

 

[ppragman]

How would you explain that to the FAA if you land and they are waiting for you?

"I hit minimums, there was a hole/break in the clouds/slight increase in the ambient visibility/the fog parted/etc., and the flight visibility increased to that which was required to successfully execute the approach."

Don't bust mins, but it is possible to safely complete approaches occasionally when the wx is reported below minimums. There are many times when the wx at the AWOS/ASOS is much much lower than at the touchdown zone.

I've seen airports where the weather station sits in a depression and the fog will fill it in, showing something like 1/4mile and fog and the field is wide (really really wide ) open.

 

[Maurus]

:yeahthat:

I had something like that happen to me one night coming home from an IFR X-country. It wasn't an issue since it still was above mins, but it forecast CLR with 1 1/4 mi vis. Got down on the ground and vis was unrestricted. Had no idea what happened there.

 

[subpilot]

Ok, so if on the approach you hear an RVR report that is lower then required but you end up seeing the runway in sight and land, do you think the FAA would give you a hard time about that?

For 121, you can't continue beyond the FAF if the visibility is below minimums. Once you do continue beyond the FAF, even if the visibility goes below minimums you can still go all the way to DH and if you get runway in sight then you are good to go.

 

[N18040]

I have heard that all you have to do is make a PIREP stating that the visibility is the minimum required, then whatever you reported will be official and you are good regardless of what anyone else sees.