VASI Distance - SM or NM

[FlyLawyer]

Most VASI systems provide coverage of up to 20 miles at night and 5 - 10 miles during the day according to the AIM. However, it doesn't specifically state whether this range is Statute Miles or Nautical Miles. I am sure there is some obscure source that states specifically, but I just haven't found it. Anybody know for certain let me know with a reference.

Personally, I really don't care, but this question will be asked at an upcoming interview - so I need to know.

Thanks for the help.

 

[avbug]

The VASI provides coverage up to five to ten miles in the day and up to 20 miles at night. This is general. It's not gauranteed, or a criteria for establishing a VASI. How far depends on the visibility. There is no set distance.

The safe obstruction clearance plan, generally, extends 4 nautical miles from the runway threshold.

 

[A Squared]

When the AIM refuses to state the range any more precisely than plus/minus 50% of the total value, it is utterly absurd to debate whether the units are NM or statute miles, a differnce of 15%.

Think about it, you don't know to within 5 mileswhat the effective distance is, why argue whether it is 5-10 miles or 5.8-11.5 miles. It's just completely nonsensical.

regards

 

[Singlecoil]

The VASI provides coverage up to five to ten miles in the day and up to 20 miles at night. This is general. It's not gauranteed, or a criteria for establishing a VASI. How far depends on the visibility. There is no set distance.

The safe obstruction clearance plan, generally, extends 4 nautical miles from the runway threshold.

In addition to what avbug correctly stated above, it is best to check the AFD for the airport you are going to. If it is non-standard, the AFD will note that.

For instance:

Nome, Alaska.

"VASI RWY 20 unusable beyond 2.5 NM"

That's because there is a mountain beyond that. If you get on the VASI ten miles out, you will soon feel a puckering sensation when the airport lights disappear. Don't ask me how I know.

 

[ERJdca]

If your looking for the technical answer, that VASI GUARENTEEs obstacle clearance within 10degrees and 4NM of the runway. It can be VISIBLE up to 10 miles during the day, and VISIBLE up to 20 miles at night. It is in the AIM

 

[FlyLawyer]

If your looking for the technical answer, that VASI GUARENTEEs obstacle clearance within 10degrees and 4NM of the runway. It can be VISIBLE up to 10 miles during the day, and VISIBLE up to 20 miles at night. It is in the AIM

Gee, thanks for the technical epiphany. I never would have considered reading the AIM - even though I conspicuously referred to it in the original post. But thanks anyway, for I have a short memory.

"Think about it...It's just completely nonsensical."

Yeah, I agree, and I stated earlier that I really didn't care either - but the Captain that conducts the interviews and doles out the class dates seems to think that this technical trivia is important.

Nonetheless, I researched this issue and spoke with an FAA facility installation technician in DC. The mileage requirements referred to, according to installation regulations promulgated by the FAA, are in Nautical Miles.

 

[ERJdca]

"day according to the AIM. However, it doesn't specifically state whether this range is Statute Miles or Nautical Miles.


i answered that, and said it was in the aim, whats the problem? Is that not what you were asking? I clearly see you read the aim but didn't see this. PILOTS!! ugh!

 

[A Squared]

Yeah, I agree, and I stated earlier that I really didn't care either - but the Captain that conducts the interviews and doles out the class dates seems to think that this technical trivia is important.

Yeah, I understood that *you* didn't care, just that you expected to be asked this. I was marvelling at the stupidity of an interviewer who would ask a meaningless question such as this, maybe I should have made this clearer.


regards

 

[80/20]

VASI range in NM or SM?
From AC 61-23C Pilot's Handbook of Aeronautical Knowledge: "The VASI provides ……. to 4 nautical miles (NM) ….."

How far? Various VASI systems provides different ranges from 3 to 6 miles (daytime). Not that I think one needs to memorize it but VASI-2 and VASI-6 gives 3 miles, VASI-4 gives 4 miles, VASI-8 and VASI-12 gives 5 miles. FAA Order 8200 - Flight Inspection and Procedures and FAA Order 6850.2, Visual Guidance Lighting Systems have more details.

 

[avbug]

The only issue with VASI is the distance for obstacle protection, and that term needs to be used very loosely.

Distance that the VASI can be seen is entirely dependent on the prevailing visibility on any given day.

Obstacle distances are given in nautical miles.