Visibility to land on Pt 121?

[BoeingBoy]

It really comes down to one question. Do you have the flight visibility required by the approach chart?

If the answer is yes you can land, if not, you must go around.

The FAA says that even though transmissometers measure vis down the runway (not flight vis--duh), if they are reporting less than mins and you have an incident (blown tire, veer off runway) they will absolutely violate you. The thinking is that flight vis at 1 foot above the runway = RVR. You get paid for flight time, go around and think about it...maybe your wake turbulence will clear the fog for the next pass.

Prevailing visibility is another thing altogether...the tower can frequently be calling less than 1/2 mile while your runway has better than 6000 vis.

Be conservative, if your runway's RVR is less than that required for the approach, go around early and make it easy on yourself. If you're out of gas and on fire it doesn't matter what the vis is...you're exercising PIC emergency authority....land.

 

[typhoonpilot]

This is an age old debate and I tend to agree with Rally and minitour here. The FARs are quite explicit when they say, " the flight visibility is not less than the visibility prescribed in the standard instrument approach being used ". One must be careful to listen to the question very clearly though. I would not try to land if the RVR was below minimums because they are telling you the condition on the runway. However, if the tower reported visibility was below the charted visibility minimums you could have a good argument to use flight visibility. Who knows how far away the tower is from the threshold and how different the wx conditions are ? In an interview you might want to look for ways to make it work and not be too rigid in your stance, but always have a bottom line that you will not cross for safety.

Another point slightly off topic on how to make it work is to ask the tower for the visibility or RVR again. It used to be some places would make it work for you. Arcata/Eureka was a prime example of that.

Typhoonpilot

 

[minitour]

Holiday Inn Express !!!

Nah...I sleep at the mainline locatioins...

 

[Singlecoil]

This does have the odor of a CRM question. He's giving you the scenario of a Captain insisting its OK to land and he wants to see how you'll react. He should be more up front with you that it is a hypothetical situation in my opinion. Personally I think going up against RVR is not wise. Anybody who has ever flow in blowing snow knows what I mean. You can see the runway just fine until you start your flare, then you can't see a bloody thing. Flight vis was 10 miles, but RVR was 1000 for a reason.

 

[A Squared]

Posted by mmmm donut:

>>>>"The GP length is more than 1000' "

Yeah, you're right, for 1000' horizontally the glidepath distance is longer. More specifically for a 3 degree glidepath the distance is 1001.37 feet. What was your point again? That the extra 18 inches is going to make the difference when your required RVR is 1800 ????

 

[mmmdonut]

Good math, but you measured from the wrong point.


TDZ to start of runway : 1000'

Rope extended from end of aimpoint markings to point in space along glide slope at DA (200') : way more than 1000'

I think you measured to TCH. (approx 50')

keep workin on it though.

 

[Andy Neill]

So if you saw the fixed distance markers (1000' down the runway) at a DH of 200 above touchdown, then the run to the asphalt would be 200/sin(3 degrees) = 3821' (3827' flight vis). If you had descended to 100 above touchdown before seeing the fixed distance markers then the run to the asphalt would be 1911' (1913' flight vis). I don't see what either one of those calculations has to do with the point at hand, however.

If I were wearing the 4 stripes, and I saw the required amount of visibility from my nose to the ashphalt, I would land regardless of what the RVR or prevailing visilbility was being reported. If I couldn't see that far down the runway, I wouldn't even if the RVR was reporting above mins.

 

[A Squared]

Good math, but you measured from the wrong point.


TDZ to start of runway : 1000'

Rope extended from end of aimpoint markings to point in space along glide slope at DA (200') : way more than 1000'

I think you measured to TCH. (approx 50')

keep workin on it though.

Ahhh, OK, I misunderstood you the first time around, I thought that you were trying to say that the flight visibility was more than the ground visibility because it was measured along the glidepath (sloping) rather than horiozontally.

 

[mmmdonut]

Ahhh, OK, I misunderstood you the first time around, I thought that you were trying to say that the flight visibility was more than the ground visibility because it was measured along the glidepath (sloping) rather than horiozontally.

Naw... skeezer was right.. this is just a commonly miscommunicated subject. I'm confused!!

 

[atldc9]

On another note, for Cat II or III ops, if you receive a report of required RVR being less then required for the approach at any point prior to touchdown, you must execute a missed approach. The old rule of once inside the FAF does not apply to CAT II and III ops.