Starting a campaign to improve PAPI
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Surely, going into a big runway during daylight, good vis, relatively flat area, no slopes, etc etc, it's no problem. It's when it's pitch black below an overcast layer at night and you're going into a 800m runway with only edge lights and approach lights, no electronic glideslope, perhaps reduced visibility, tight circling, drifting snow across the runway etc etc... That's a whole other ballgame. Absolute no-go in case of malfunctioning VASI/PAPI/PLASI as far as I'm concerned.
Join Date: May 2009
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Why not integrate both systems???
On the T-VASI instead of 4 whites why not make it a normal PAPI, it would be an easy upgrade compared to changing to a whole new system, and you've got the best of both worlds. If you're slightly below appch path you'll get the usual 1 white 3 red aswell as the the white light below on the T-VASI...
in all situations a) you know you're below/or high, and b) you know how low/high, and where your predicted to land
Just a thought
On the T-VASI instead of 4 whites why not make it a normal PAPI, it would be an easy upgrade compared to changing to a whole new system, and you've got the best of both worlds. If you're slightly below appch path you'll get the usual 1 white 3 red aswell as the the white light below on the T-VASI...
in all situations a) you know you're below/or high, and b) you know how low/high, and where your predicted to land
Just a thought
Thread Starter
I like the idea STA except that you are now doubling the maintenance cost of a single installation. Apparently that is what is killing the T-VASIS in the first place. It all comes down to money it seems.
Another idea might be to have one side of the runway PAPI, and the other side T-VASIS. Then we'd all be happy (half joking). Also a prohibitively expensive system.
Another variation would be to get rid of the white lights altogether and have only red lights with perhaps a couple of marker lights to the side of the red lights to indicate where the red lights would be if you can't see any (because you are too high and would have four whites in the current PAPI design. eg.
O is a white light (xenon white!)
o is a red light.
/ \ is the runway.
OO / \ = very steep
OO o / \
OO oo / \ = on slope
OO ooo / \
OO oooo / \ = very shallow
The point here is that you don't have to differentiate between red and a soft orangey white. The red light is either on or off (or transiting between the two which is also obvious and useful) unlike the nebulous white to red transition.
Put it another way, if a pilot is making a circling approach and is rolling out on to final, or making a blackhole runway-aligned approach, and that pilot looks up to see how the picture is looking outside, how much quicker would counting the red lights be done rather than looking at them for a period of time to allow your eyes and brain to see then differentiate the colour appearance of the four individual white/red lights?
I think I might be on to something here!
PS My diagrams aren't being spaced properly. When I use more than one space between characters, this BB reduces the space back to one. But I think you get the idea.
Another idea might be to have one side of the runway PAPI, and the other side T-VASIS. Then we'd all be happy (half joking). Also a prohibitively expensive system.
Another variation would be to get rid of the white lights altogether and have only red lights with perhaps a couple of marker lights to the side of the red lights to indicate where the red lights would be if you can't see any (because you are too high and would have four whites in the current PAPI design. eg.
O is a white light (xenon white!)
o is a red light.
/ \ is the runway.
OO / \ = very steep
OO o / \
OO oo / \ = on slope
OO ooo / \
OO oooo / \ = very shallow
The point here is that you don't have to differentiate between red and a soft orangey white. The red light is either on or off (or transiting between the two which is also obvious and useful) unlike the nebulous white to red transition.
Put it another way, if a pilot is making a circling approach and is rolling out on to final, or making a blackhole runway-aligned approach, and that pilot looks up to see how the picture is looking outside, how much quicker would counting the red lights be done rather than looking at them for a period of time to allow your eyes and brain to see then differentiate the colour appearance of the four individual white/red lights?
I think I might be on to something here!
PS My diagrams aren't being spaced properly. When I use more than one space between characters, this BB reduces the space back to one. But I think you get the idea.
Last edited by Blip; 12th May 2009 at 03:57.
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In most PAPIs (i e all I've seen, and that's a fair amount) there is no 'red bulb' and 'white bulb'. You have one projector light in front of which sits a red filter, essentially a red glass pane. Change the colour temperature of the bulb and the colour of both red and white will change.
A good PAPI unit will have a transition zone of less than 0.05 degrees between fully red and fully white. Poorly maintained PAPI units will quickly go well above this, and you may end up with transition zones bordering on 0.20 degrees. With 0.17 degrees being the nominal difference between on glide path and a unit changing colour for a stand-alone PAPI, that's a lot.
Wide transition zones are usually caused by dirty lenses, dirty or worn glass panes in the units, improperly levelled units, improperly installed or seated filters or condensation which has not yet evaporated in a newly turned on PAPI box.
A good PAPI unit will have a transition zone of less than 0.05 degrees between fully red and fully white. Poorly maintained PAPI units will quickly go well above this, and you may end up with transition zones bordering on 0.20 degrees. With 0.17 degrees being the nominal difference between on glide path and a unit changing colour for a stand-alone PAPI, that's a lot.
Wide transition zones are usually caused by dirty lenses, dirty or worn glass panes in the units, improperly levelled units, improperly installed or seated filters or condensation which has not yet evaporated in a newly turned on PAPI box.
As Centaurus has said, T-VASIS are more expensive to maintain. Additionally, I am told that spare parts are no longer available. And if you were to install a new T-VASIS, there are ten boxes per side against the PAPI with four per side and hence considererably more expensive to install and calibrate. Flight checking both aids is almost the same procedure. Note that in Australia a number of PAPI's have never been flight checked.
So essentially the cheaper item now rules the market place!!
This is an interesting thread - I hope to see some positive outcomes from the ideas being put forward.
Blackburn
So essentially the cheaper item now rules the market place!!
This is an interesting thread - I hope to see some positive outcomes from the ideas being put forward.
Blackburn
