Where are VASIs located on a field ?

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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...

[Sam Spade]

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.

[Brian Whatcott]

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