VASI/PAPI Lights Inconsistent

I have noticed that the VASI/PAPI lights can be very inconsistent, to the point that I can't rely on them. On numerous occasions when using the visual glide slope, which I assume is accurate, they often say I'm too high or too low. The other day I was in Instant Replay of a landing doing some screen shots and I noticed that when I moved the spot plane view down lower the PAPI lights suddenly went from pink to white. Does anyone know what's happening there? Has anyone else found these lights to be unreliable?

 

I'm getting better at recognizing the proper glide slope using runway perspective and am making decent landings, but it would be nice if these lights could be made to work properly.

 

 

Thanks,

Clayton

Through all the flying I've done since FS4, and me being a heavy user of VASI/PAPI lights, I have to note I have never encountered them being inconsistent. In fact they are the one dependable source for making sure I don't mess up a landing. I can not think of an explanation for the light turning while in the replay. If they often say you are too high or too low, fly to where they are red over white=you're all right. White over white=you're too high, red over red=you're dead.

Clayton, I too have noticed an inconsistency, but ONLY on the aircraft carrier. Mind you, that has the runway 55 feet above a water level (ie, not "solid earth") that is modified by exclude_files. And if you remove the exclude files the water has huge "mountains" in it. So I am not surprised that the definition of where the "ground" is, and thus where the slope is calculated from, is a bit "rubbery".

 

The other thing is, programs like ADE and AFCAD allow you to have the lights a fair way "up" or "down" the runway (what I mean is that the distance between the touchdown point and the lights can be varied enormously). Maybe if you experiment with this, you might hit on the "right" location for the PAPI lights?

I have never noticed them to be "very inconsistent" .... or even a little so. Very helpful in landing under all conditions.

This was discussed in another thread. I think it was mentioned that there may be some files corrupted that is causing that. Do a search and dig it up.

Remaking my second point, and please indulge my ASCII drawings of aircraft and runways and VASIs ...

 

 

 

If you have a VASI on a runway like this:

 

\\................|...........................

>==- -::===================================================::-

//................|...........................

 

 

 

Then obviously that will give you a different touchdown point than if you have the same VASI on the same runway but like this instead:

 

 

\\.........................|...................

>==- -::===================================================::-

//.........................|...................

 

 

Now nominally, of course, both of those will give you the same slope, but with a touchdown point on a different part of the runway. But ... if you are conscious of landing on a short runway, where you want to land as close to the beginning of the runway as possible, you are going to "see" that as a different slope to the end of the runway. Even though it actually isn't.

 

This is moderately common with both default and add-on airports, where if you follow the VASI exactly, your landing point can be as far as a third of the way along the runway.

 

Clayton, I wonder if this is relevant to your original post? Is this a part of the "inconsistencies" that you are seeing?

Steve .... admire your art work .... you must have been a genius on a dot matrix printer!

 

Good luck with the move.

Actually, I was. I was doing pixel addressing on an Okidata Microline 84 dot matrix printer using my own programs about 5 years before Microsoft discovered it. Been a geek for >40 years now and still proud of it. Thank you for the compliment.

Remaking my second point, and please indulge my ASCII drawings of aircraft and runways and VASIs ...

 

Now nominally, of course, both of those will give you the same slope, but with a touchdown point on a different part of the runway. But ... if you are conscious of landing on a short runway, where you want to land as close to the beginning of the runway as possible, you are going to "see" that as a different slope to the end of the runway. Even though it actually isn't.

 

This is moderately common with both default and add-on airports, where if you follow the VASI exactly, your landing point can be as far as a third of the way along the runway.

 

Clayton, I wonder if this is relevant to your original post? Is this a part of the "inconsistencies" that you are seeing?

 

Hi Steve,

Sorry for my late reply, was out of the loop for a few days. Yes, I think you're on to something as I remember noticing that the lights are at different locations. All the runways I land at aren't short but I do land at a lot of small fields and tend to want to land close to the beginning. I will play close attention to this in the future.

 

From your remarks I am assuming that the "sensor", whatever it is that decides what lights to show, is near the lights, yes? Do you know what the sensor is and how it works? I can see the real PAPI lights at runway 32 here at PBI as I drive past on the highway. I should try to find a place to park and watch them as planes land...might see something interesting.

 

Speaking of lights, one of my ongoing flights is a tour of Italy, beginning in Sicily at the bottom, with an Aero Commander 680 which has excellent STOL capabilities. My last flight was to a small field on the SW coast and had to fly over some mountains from the east and then make a rapid descent. It was at dusk and I expected not only a VASI but at least minimal runway lights as well. I was surprised, coming over the mountain ridge, to see NO electric lights of any sort and just enough natural light to see the runway. So it was a purely eyeball approach and a pretty good landing. Good thing I didn't try a night flight :)

 

Thanks for your help,

Clayton

...I am assuming that the "sensor", whatever it is that decides what lights to show, is near the lights, yes? Do you know what the sensor is and how it works?

 

There is no sensor, the lights are static, not dynamic.

 

Sort of like traffic lights that have shields around them so you cannot see them from the other lane.

 

Have a look at this- http://aviation.stackexchange.com/questions/5170/how-do-papi-lights-work

 

peace,

the Bean

There is no sensor, the lights are static, not dynamic.

 

Sort of like traffic lights that have shields around them so you cannot see them from the other lane.

 

Have a look at this- http://aviation.stackexchange.com/questions/5170/how-do-papi-lights-work

 

peace,

the Bean

 

Fascinating, how they work. And a very interesting web site.

 

Thank you,

Clayton

Clayton, one thing you can do.... If you have AFCAD or ADE you can look at the various airport.bgl files and see whether the PAPI lights are all set at the same angle. Or not. Dunno whether NASA or NTSB or FAA or whoever has a standard ?????? Here in Oz most airports use the T-VASI system (invented here in Oz ...), and it is usually set at three degrees, which is a 1:19 glideslope, which equates to a final approach from 5500 foot altitude at 20 miles out.

 

Maybe PBI does airside tours? Worth asking. They might be able to tell you a bit more about the PAPI lights there. Sydney airport certainly does those tours - my son used to work there.

I may have read the OP wrong and maybe I am misunderstanding this but as I see it you were watching a replay and changing views and panning around the plane. Since the lights work based on where your eyes ( and airplane ) are in relation to the runway wouldn't panning and changing views be moving your viewpoint (and as far as the lights are concerned, the airplane) to different locations, causing the lights to change? I have been on approach with 2 red and 2 white when viewed from the flight deck, but change the view to spot and even when looking straight from behind and above the lights are now 3 white and 1 red. The viewpoint moved higher than before and the lights reflect it.

I may have read the OP wrong and maybe I am misunderstanding this but as I see it you were watching a replay and changing views and panning around the plane. Since the lights work based on where your eyes ( and airplane ) are in relation to the runway wouldn't panning and changing views be moving your viewpoint (and as far as the lights are concerned, the airplane) to different locations, causing the lights to change? I have been on approach with 2 red and 2 white when viewed from the flight deck, but change the view to spot and even when looking straight from behind and above the lights are now 3 white and 1 red. The viewpoint moved higher than before and the lights reflect it.

 

Yes I think you are right on target with this. Combined with what the others have said, it explains everything I was experiencing. I've really learned a lot from this thread and it makes me appreciate these forums even more.

 

Thanks very much,

Clayton

Clayton, one thing you can do.... If you have AFCAD or ADE you can look at the various airport.bgl files and see whether the PAPI lights are all set at the same angle. Or not. Dunno whether NASA or NTSB or FAA or whoever has a standard ?????? Here in Oz most airports use the T-VASI system (invented here in Oz ...), and it is usually set at three degrees, which is a 1:19 glideslope, which equates to a final approach from 5500 foot altitude at 20 miles out.

 

Maybe PBI does airside tours? Worth asking. They might be able to tell you a bit more about the PAPI lights there. Sydney airport certainly does those tours - my son used to work there.

 

I don't have either of those programs but one of the nice things about the website that Bean posted is a series of other questions in the lower right hand margin, one of which was asking how the PAPI lights are calculated. One of the things it said was that they were done for each airport and took into consideration local obstacles and restrictions. I remember reading somewhere that 3 degrees is the standard glide slope, but apparently it can vary for a particular airport.

 

Clayton

...it is usually set at three degrees, which is a 1:19 glideslope, which equates to a final approach from 5500 foot altitude at 20 miles out.

 

Your math is off a bit.

 

A 3% slope equals 318ft/nm whereas 5500 ft/ 20 miles = 275 ft/mile which is more like 2.6 degrees.

 

And obviously when you said "a final approach from 5500 foot altitude at 20 miles" you meant 5500 feet above TDZ, not altitude, 'cause starting an approach into Telluride at 5500 ft ASL is not gonna work.

 

peace,

the Bean

I got the 5500/20 miles comment from a Qantas A380 pilot in a casual conversation. There may have been some more context around it. Don't remember. It seems to work ok for me.

 

All of my airports are at sea level or nearly so. Not too many carriers have a flight deck at 5500 feet. No idea where Telluride is, and have no interest in or intention of finding out.

[quote=old_wombat;1965665

All of my airports are at sea level or nearly so. Not too many carriers have a flight deck at 5500 feet. No idea where Telluride is, and have no interest in or intention of finding out.

 

Steve, you've got to "get out" more! Most join the navy to "see the world". Please take shore leave and enjoy. There's more to the world than "flat".

"Get out more"???? I've been around the world twice. Been to nearly half the US states, including Alaska. Lived in South Carolina, Papua New Guinea, Australia, England, Canada. Been to every continent including mainland Antarctica. Went parachuting when younger. Rode in a helicopter. Been underwater in a submarine. Is that enough "getting out"? Now I'm 60, got one artificial hip, had my second lot of cancer surgery, and look after my wife who is in constant pain. So I go birdwatching, do some woodworking, and build FS scenery. Looking forward to moving house to a clime where there is no winter. I have no regrets about missed opportunities.

No idea where Telluride is!

 

You've got to get out more, join the Girl Scouts....see the world! You've never hear of Telluride:eek: Colorado at about 9200 feet airport elevation.

It's a great approach. Every pilot should try it.

It's a great approach. Every pilot should try it.

 

 

Ahhh... 3.62° Glide Slope for the ILS/DME for RWY 9 @ KTEX is mere child's play!

 

How about an Approach @ 8° Glide Slope, starting @ 15,000'? Try the Avon STOLPort:

 

http://www.airfields-freeman.com/CO/Airfields_CO_NW.htm

 

This place actually existed, and the Airline that flew there (Rocky Mountain Airways) was the Worldwide Launch Customer for the deHavilland Dash 7.

 

Shoot... you can even fly this Approach in FS9! The Filename is kwhr.zip

 

https://www.flightsim.com/vbfs/fslib.php?do=copyright&fid=101463

 

 

Alan :pilot:

"Get out more"???? I've been around the world twice. Been to nearly half the US states, including Alaska. Lived in South Carolina, Papua New Guinea, Australia, England, Canada. Been to every continent including mainland Antarctica. Went parachuting when younger. Rode in a helicopter. Been underwater in a submarine. Is that enough "getting out"? Now I'm 60, got one artificial hip, had my second lot of cancer surgery, and look after my wife who is in constant pain. So I go birdwatching, do some woodworking, and build FS scenery. Looking forward to moving house to a clime where there is no winter. I have no regrets about missed opportunities.

 

Ahhh.... it was a funny regarding your comment about aircraft carriers, sea level ..... ahhh forget it. I'll let Zippo take the heat next.