Vis or RVR? What's legal in this case?

kicktireslightfires

kicktireslightfires

Pre-takeoff checklist
Joined
Jun 11, 2020
Messages
354
Display Name
Display name:
kicktireslightfires
Sorry in advance if this is a stupid question, but I noticed MIA was recently reporting ¼ vis but with 3,000 RVR. So if the minimums are 1/2 sm visibility, is this legal or not? 3000 RVR converts to 5/8 vis so does a part 91 piston pilot use the ¼ vis or the RVR conversion? I'm guessing the part 91 pilot could not shoot the approach in these conditions because I think I remember reading that RVR only applies to airliners? But airliners use RVR and therefore the vis would be just above minimums for them as for airliners only the RVR supersedes the visibility number?

Thanks in advance!

https://i.ibb.co/RCcpQzq/IMG-2495.jpg

IMG-2495.jpg
 
You could shoot the approach but may not be able to land. The vis is in flight vis. If the in flight vis is 1/2, you can land. That being said, in practice I would lean towards the most limiting number. Even though one is legal and the other not, they are both pretty close together.
 
for part 91 ops, none are controlling. a part 91 aircraft may start the approach if visibility is below mins, if at DH or MDA you have legal visibility you can land.
 
Unless things have changed since my part 91 days it is legal to shoot the approach under part 91 since minimums don't apply to that decision. Part 135 and 121 are a different story altogether (everyone chime in here and repeat "a different story"). As I understand it an approach to rwy 9 would be legal since RVR is considered superior to the reported 1/4 sm visibility. It is possible to have other legal minimums available under part 135 or 121 which would make the decision a total yawn.
 
kicktireslightfires said:
Sorry in advance if this is a stupid question, but I noticed MIA was recently reporting ¼ vis but with 3,000 RVR. So if the minimums are 1/2 sm visibility, is this legal or not? 3000 RVR converts to 5/8 vis so does a part 91 piston pilot use the ¼ vis or the RVR conversion? I'm guessing the part 91 pilot could not shoot the approach in these conditions because I think I remember reading that RVR only applies to airliners? But airliners use RVR and therefore the vis would be just above minimums for them as for airliners only the RVR supersedes the visibility number?

Thanks in advance!

https://i.ibb.co/RCcpQzq/IMG-2495.jpg

IMG-2495.jpg
Click to expand...

twice you said ¼ vis. We’re those typo’s
 
Reported visibility for an airport may differ substantially from RVR for a runway (or a portion thereof).
Minimums on the approach chart say [RVR] or [vis], not [RVR] and [vis]. Vis only becomes controlling if RVR is inop.
If you have to have weather above minimums to initiate an approach (Part 121, 135, etc.), it will generally be the touchdown zone RVR for the runway. As others have indicated, Part 91 doesn’t require the weather to be above minimums to fly the approach.
 
Last edited:
Part 91. Do whatever you want just don’t crash and have adequate visual reference to continue at minimums. Part 121 and 135 rvr is controlling.
 
kicktireslightfires said:
Sorry in advance if this is a stupid question, but I noticed MIA was recently reporting ¼ vis but with 3,000 RVR. So if the minimums are 1/2 sm visibility, is this legal or not? 3000 RVR converts to 5/8 vis so does a part 91 piston pilot use the ¼ vis or the RVR conversion? I'm guessing the part 91 pilot could not shoot the approach in these conditions because I think I remember reading that RVR only applies to airliners? But airliners use RVR and therefore the vis would be just above minimums for them as for airliners only the RVR supersedes the visibility number?

Thanks in advance!
Click to expand...
Check the FAA approach charts. On an RVR runway the RVR controls. It's only when the RVR is inoperative that you use the RVR-to-feet table.

IMG-2495.jpg
 
Understand that vis is what the weather observer sees. "I can see X thing, so the vis is Y."

RVR is what the measuring system at approach and landing area of the runway sees.
 
Tarheelpilot said:
Part 91. Do whatever you want just don’t crash and have adequate visual reference to continue at minimums. Part 121 and 135 rvr is controlling.
Click to expand...

I'm guessing @Tarheelpilot used the word adequate as a shorthand. Adequate is not a legal term nor a term of art. Operations below DA/MDA require that specific conditions are met. See 91.175(c)(3).
 
Pinecone said:
Understand that vis is what the weather observer sees. "I can see X thing, so the vis is Y."

RVR is what the measuring system at approach and landing area of the runway sees.
Click to expand...
RVR is not visibility. It is seeing conditions: How many HIRLs you will see as you touchdown.
 
Pinecone said:
Understand that vis is what the weather observer sees. "I can see X thing, so the vis is Y."

RVR is what the measuring system at approach and landing area of the runway sees.
Click to expand...
The “weather observer” today is more than likely an AWOS or ASOS, which like a live weather observer, has a specific location that is NOT at the runway. Not the most accurate means of determining visibility at the runway. Hence the reason RVR exists and is controlling.
 
aterpster said:
RVR is not visibility. It is seeing conditions: How many HIRLs you will see as you touchdown.
Click to expand...
In fact, EASA low vis departures require that the pilot count and confirm the number of lights they can see before they can begin the takeoff roll.
 
Arnold said:
In fact, EASA low vis departures require that the pilot count and confirm the number of lights they can see before they can begin the takeoff roll.
Click to expand...
I’m genuinely curious if you have a reference for that. I flew a long time in EASA land, and never heard of that. Of course, I was flying for a US carrier, so me not hearing that may not mean much. In a very cursory look at the EASA documents, I didn’t see anything like that. Just wondering.
 
Arnold said:
In fact, EASA low vis departures require that the pilot count and confirm the number of lights they can see before they can begin the takeoff roll.
Click to expand...

Thankfully I don’t fly in Europe.
 
aterpster said:
RVR is not visibility. It is seeing conditions: How many HIRLs you will see as you touchdown.
Click to expand...

It is seeing conditions ALONG the runway.

Visibility is seeing conditions in various directions for a location that is not necessarily right by the runway.

And vis during daylight is seeing unlighted objects, but RVR is done with lights.
 
Sluggo63 said:
I’m genuinely curious if you have a reference for that. I flew a long time in EASA land, and never heard of that. Of course, I was flying for a US carrier, so me not hearing that may not mean much. In a very cursory look at the EASA documents, I didn’t see anything like that. Just wondering.
Click to expand...

I will look into that. It is what I was taught when training to be an EASA instructor but I never actually verified the info. Good question.
 
Arnold said:
I will look into that. It is what I was taught when training to be an EASA instructor but I never actually verified the info. Good question.
Click to expand...

Ah, it was not as hard to find s I thought it would be. See: https://www.easa.europa.eu/sites/de...ex V (Part-SPA) (corrected on 29.08.2018).pdf Page 18.

page 18. The requirement is for

(b) for an LVTO with an RVR below 150 m but not less than 125 m: (1) high intensity runway centre line lights spaced 15 m or less apart and high intensity edge lights spaced 60 m or less apart that are in operation; (2) a 90 m visual segment that is available from the flight crew compartment at the start of the take-off run; and (3) the required RVR value is achieved for all of the relevant RVR reporting points;

to comply with subsection 2 using a runway with centerline lights spaced 15 meters apart the confirmation from the flight crew compartment is achieved by counting six centerline lights.
 
Pinecone said:
It is seeing conditions ALONG the runway.

Visibility is seeing conditions in various directions for a location that is not necessarily right by the runway.

And vis during daylight is seeing unlighted objects, but RVR is done with lights.
Click to expand...
Aren't HIRLs along the runway?
 
unsafervguy said:
for part 91 ops, none are controlling. a part 91 aircraft may start the approach if visibility is below mins, if at DH or MDA you have legal visibility you can land.
Click to expand...
And to make it clear, for a part 91 guy, legal visibility means FLIGHT VISIBILITY, i.e., what you determine it to be, not what the ground observer/AWOS is reporting. You need to be able to make out stuff 1/4 mile (or whatever the vis mininum is) away as well as having one of the required runway environment items in sight (often not quite coincidentally about the same distance).
 
When they started adding RVR at the major airports, I didn't have to miss so many nice layover bars. It's nice to stay routine.
 
Arnold said:
Ah, it was not as hard to find s I thought it would be. See: https://www.easa.europa.eu/sites/default/files/dfu/Annex to Decision 2012-019-R - AMC-GM to Annex V (Part-SPA) (corrected on 29.08.2018).pdf Page 18.

page 18. The requirement is for

(b) for an LVTO with an RVR below 150 m but not less than 125 m: (1) high intensity runway centre line lights spaced 15 m or less apart and high intensity edge lights spaced 60 m or less apart that are in operation; (2) a 90 m visual segment that is available from the flight crew compartment at the start of the take-off run; and (3) the required RVR value is achieved for all of the relevant RVR reporting points;

to comply with subsection 2 using a runway with centerline lights spaced 15 meters apart the confirmation from the flight crew compartment is achieved by counting six centerline lights.
Click to expand...
Interesting. Thanks for the reference. My question then becomes, how do you know how far the runway lights are spaced? That section says “15 meters or less.” What if the lights are spaced 12 meters apart? You count 6 and are actually seeing 72 meters versus 90 meters. I don’t know if host country pubs will tell you that.

Thanks for the education.
 
You must log in or register to reply here.
Back
Top