What is a VGSI?
 

Prompted by the SFO thread, I need to ask whether the VGSI is just another (US) name for PAPI or whether in fact the two pieces of equipment are different in usage?

Hi BOAC

I believe VGSI is the collective term for approach angle indicators and is not a synonym for PAPI/ VASI or any other type of individual indicator, but I stand by to be corrected.

What is a VGSI?
 

From Wikipedia, i hope this might help:
Visual Glide Slope Indicator or Visual Glideslope Indicator (VGSI) is a ground device that uses lights to assist a pilot in landing an airplane at an airport. The lights define a vertical approach path during the final approach to a runway and can help the pilot determine if the airplane is too high or too low for an optimum landing.

There are several different types of VGSI's:

Visual Approach Slope Indicator (VASI)
Precision Approach Path Indicator (PAPI)
Pulsating Visual Approach Slope Indicator (PVASI)
Three-color Visual Approach Slope Indicator (T-VASI)
Helicopter Approach Path Indicator (HAPI)

Three-color Visual Approach Slope Indicator apparently is a local Eastern Bloc device .. things one learns on the net.

Generally, when one refers to T-VASIS, one is probably referring a T-system such as is described here.

Perhaps that explains the angle of 2°51’ at SFO?

VGSI Deviation
 

Can you guys help me with this question?

While on a visual approach with a 3.2 PAPI, At what altitude will I cross the path at 1 mile, 2 miles and 3 miles if I stay on 2 reds/2white?

If I fly a bit lower, say 3 red/1 white? same question...

Any practical formula?

Thanks for your expertise!!

Greatly appreciated

Don't forget the alignment of elements non-lighting system. Have never actually encountered one yet.

https://books.google.ca/books?id=B3a...rcraft&f=false

And maybe even the paddles guy on an aircraft carrier.

Landing Signal Officer - Wikipedia, the free encyclopedia

the formula for a 3 degree glideslope is 300' per one nautical mile

3 miles, 900feet

it is actually closer to 316 feet per nautical mile.

steeper than 3 degrees would be a little more.

gouge, or little rules of thumb, would get too complicated for a pilot to quickly ,mentally calculate to the Nth degree. But I imagine you can. At TOO great a distance, earth curvature comes into play.

But 300' per nautical mile is close enough. That Asiana Air at KSFO could have used that formula. Or just looking at the visual approach plate you would see that you should be 1900' to 2000' over a convenient landmark


another convenient formula iis to multiply your groundspeed (or airspeed if you have nothing else) by 5 to determine the rate of descent to make good a 3 degree glideslope.

150 knots, your rate of descent should be 750 fpm

get it?

HazelNuts:

All the PAPIs at SFO are 3.0 degrees:

http://aeronav.faa.gov/afd/30apr2015..._30APR2015.pdf

Asiana just needed to recognize the autothrottle was not engaged. 5 x ground speed for rate of descent? Close, but you need to add a bit. If you use 750 rpm for 150 knots GS you will end up high on profile.