Where are VASIs located on a field ?

Where are VASIs located on a field that doesn't have an ILS ? Is it a certain number of feet from end of runway ? Does it depend on runway length ? If you want to land on a short runway when is it safe to dip below VASI ? Must there be a certain number of hundreds of feet from the threshold clear of obstructions ? Clearly you don't want to cross the threshold at 50 feet if you are flying , e.g. a Mooney onto a 2300 foot field, you'll waste the first 1000 feet...

On 12/25/2012 3:26 PM, wrote:
Where are VASIs located on a field that doesn't have an ILS ? Is it a certain number of feet from end of runway ? Does it depend on runway length ? If you want to land on a short runway when is it safe to dip below VASI ? Must there be a certain number of hundreds of feet from the threshold clear of obstructions ? Clearly you don't want to cross the threshold at 50 feet if you are flying , e.g. a Mooney onto a 2300 foot field, you'll waste the first 1000 feet...


Do the math using the TCH and the angle.

On 1/12/2013 3:33 PM, Sam Spade wrote:
On 12/25/2012 3:26 PM, wrote:
Where are VASIs located on a field that doesn't have an ILS ? Is it a
certain number of feet from end of runway ? Does it depend on runway
length ? If you want to land on a short runway when is it safe to dip
below VASI ? Must there be a certain number of hundreds of feet from
the threshold clear of obstructions ? Clearly you don't want to cross
the threshold at 50 feet if you are flying , e.g. a Mooney onto a 2300
foot field, you'll waste the first 1000 feet...


Do the math using the TCH and the angle.


Here we go then: X / TCH = arc cot (glide slope angle)
X = TCH*arc cot(glide slope angle) = 50 * arc cot(3deg)
X = 50 * Arc cot (3 deg) = 922ft

He said 1000 ft. You were making which point again?

:-)

Brian W