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Blip
6th May 2009, 03:56
I have no idea how to go about this and therefore seek advice from people who have dealt with aviation authorities such as ICAO, FAA, CASA (UK, AUS), etc.

The problem as I see it...

The white light of a white/red PAPI system is too close to the colour yellow/orange and this results in inadequate contrast with the red lights.

You know what I mean! If you are on the correct descent path with the PAPI indicating two reds and two whites, and then start descending below the correct path, the transition from two reds to three reds is very gradual and nebulous. It certainly does not attract your immediate attention!

Even if you are on the correct descent path with solid red and "white" light indications I often find due to particulate air polution such as smoke, smog, or dust, the white light isn't really white, but rather an orange hue.

I believe the problem lies in the fact that the PAPI specifications standards of ICAO, FAA, etc. allow the manufacturers to use halogen bulbs for the white lights. The problem with these lights is that they are not hot enough.

White light emitted by light bulbs can be defined in terms of temperature. The hotter the temperature the whiter the light (because as the temperature increases it includes more of the green, blue, and violet light spectrum (higher frequencies).

Apparently Halogen light is at 3200K whereas sunlight is 5250K.
(Kelvin (K) is a scale used to measures absolute temperature).

These days we can do much better than Halogen light bulbs and that is to use Xenon light bulbs.

Xenon light bulbs emit light at a much higher temperature (around 5000K) and therefore are much further away from the red/orange light and closer to pure white.

We've all seen Xenon headlights on cars. They look positively blue in comparison to the normal halogen headlights.

Another example of the hotter blue light is the (ironically) "cool white" compact fluorescent light bulbs as compared to the "warm white" variety. If you look at the box you will see that the "warm white" bulbs are described as emitting 3000K white light and the "cool white" bulbs are described as emitting 5000K white light.

Here is a web site that describes the contrast between Halogen and Xenon well.

Advantages of Xenon headlights (http://www.white-light.net/WhyXenon.aspx)

The blue Xenon light (by comparison to the halogen light) presents a much starker contrast to the red filtered lights used in the PAPI system. It would make the PAPI system a much more effective tool against the risk of inadvertently flying too low and short of the runway especially during visual/circling approaches.

So my question is, how do I go about putting this argument to the various authorities to the view of initiating the required changes?

Can someone describe the processes involved and how to get them started?

And yes I'm serious!! :)

Bullethead
6th May 2009, 05:09
G'day Blip,

I fully agree with you and think that the T VASIS system was vastly superior to the PAPI sytem which replaced it and I wonder why the T VASIS system ever went out of favour.

Regards,
BH.

mustafagander
6th May 2009, 06:34
Bullethead, ever hear of the "not invented here" syndrome?

I agree with you 100%, T vasis is much better in dodgy conditions when there is fog etc. It is also a direct indication, ie you will land in the area of the r/w to which it points, hence very little thinking/interpretation required.

411A
6th May 2009, 06:57
Gosh, T vasi, had almost forgotten about those.
First one I used was at Perth Australia circa 1978, in a 707.
Quite nifty, very accurate.
So, if they have been withdrawn...why?
Always enjoyed PER...really nice folks there.

Rainboe
6th May 2009, 07:47
...................

16down2togo
6th May 2009, 08:10
Have to agree with Rainboe,
once you got to OZ after not beeing there for a while one had to really think about the indication, PAPI is for the stupid like me and if it is a bit orange there is still a difference between orange and red.
Maybe we could use whiter bulbs as they are available those days but please no unecessary complicated indication.
16

Nightrider
6th May 2009, 08:41
There is a reason they have taken over- it's because they are better. I certainly agree!

A few days back, during a night approach on a non-standard 3.9° ILS in montainous terrain the lighting system was very much dimmed. The papi was dimmed that much that all four lights appeared to show red.

The problem as I see it...

The white light of a white/red PAPI system is too close to the colour yellow/orange and this results in inadequate contrast with the red lights.

The problem with the dimming of the "standard" bulbs is the heat produced with the power available. These bulbs generate only the correct and designed light (colour) when operated at the nominal power.

A quick call to ATC to increase intensity will solve most, if not all, of the issues mentioned.

The problem is that a light pointed at you at high intensity, giving the correct and expected colour spectrum, may disturb you during the approach; a dimmed lighting, as perhaps requested by a previous aircraft, may give you the expected 2 white / 2 red only on short final.

Centaurus
6th May 2009, 14:08
and I wonder why the T VASIS system ever went out of favour.



While T-VASIS is considered by many as far superior to PAPI because it does not rely on colour discrimination (the advantage being to pilots who may be mildly colour blind will have no problems interpreting T-VASIS light sources), nevertheless T-VASIS has more lamps and boxes and more expensive to maintain.

Both T-VASIS and PAPI are subject to certain limitations (erroneous indications) in misty weather, one of the important safety aspects of T-VASIS is that in a gross undershoot situation at 1.9 degrees the lights go red.

With PAPI, the presence of all red lights means you could be slightly under the ideal glide path to where all lights go red but that proceeding lower still below the glide path the red lights stay as is - in other words no graduated below all reds slope. Put another way, with T-VASIS all lights red means you are in a dangerous undershooting situation. Papi all red could mean anywhere between a mild undershoot to scraping the terrain.

Capn Bloggs
7th May 2009, 04:02
There is a reason they have taken over- it's because they are better.
No they are not. Rainboe and I must agree to disagree. :} Like a lot of Australian aviation: dumbing down to the lowest common denominator - the rest of the world! Hard to soar like an eagle when you're surrounded by turkeys...

Still, PAPI makes stabilising our approaches much easier now: "hey Bloggs, you're going a bit low!" "ya reckon? They look mostly white, well pink, err orange to me!". "Yeh OK, press on!".

Useless system that works only at 300ft and below - too late to be of any value then.

You get what you pay for: cheap and nasty.

Changing the globes for better technology sounds like a great idea to me. I'm not sure CASA would get involved, depending on how tightly they define the system specs. How about approaching the Airports Association (http://www.aaal.com.au/); the airport owners/operators make the decisions about what gear they use.

Clandestino
7th May 2009, 07:42
The white light of a white/red PAPI system is too close to the colour yellow/orange

...depending on the installation and brightness setting. Some PAPIs are very distinctly white/red, some are closer to yellow/orange. Perhaps we should convince every airport to put proper lightbulbs into their PAPi projectors and change them regularly.

VIE used to have T-vasis on 16/34. Fun part was that its crossbar was made of four lights. "Your PAPI is not working, it shows four whites on the glide" calls on gnd frequency vere pretty regular.

AerocatS2A
7th May 2009, 07:59
I've seen someone fly what they thought was an on-slope approach on T-VASIs, it was then pointed out to them that they were actually high on PAPIs. The lesson learned, brief the bloody lighting system!

Blip
7th May 2009, 12:42
OK OK thanks for the inputs so far everyone.

I didn't want this thread to turn in to a PAPI vs T-VASIS debate but there you go it's happened.

For what it's worth I personally believe that the T-VASIS is superior to the PAPI because as has already been pointed out there is no colour perception required (which also eliminates the problem when the lights are dimmed for night operations), there can be multiple aiming points so that each set up can accommodate many different types of aircraft, and if you do see red lights? for goodness sake hit the TO/GA switch because you are about to hit mother earth!

For those of you who don't understand how T-VASIS works you can think of it this way (although it is not strictly correct but the concept works very well). Think of the four horizontal lights as the centre (and most commonly used) aiming point which is usually at the 1000' markers at an angle of 3 degrees.

If you see a lights sticking out closer or further down the runway than those four horizontal white lights (that appear from your perspective to be below or above the four horizontal lights), that simply means that if you were to fly a 3 degree path from your current position to the runway, your eyes will meet the runway abeam that light which sticks out the most. So if the dots appear to make a T, a three degree path from your present position will have you arriving abeam the bottom of the T. The longer the T is (one, two, or three lights), the further short of the 1000' aiming point you will land. If you see an inverted T, a 3 degree path from your present position will have you landing beyond the 1000' aiming point abeam the top of the inverted T. No thinking required.

But any way I am resigned to the fact that PAPI seem to be cheaper to own and operate and that they comply with the minimum specifications required. I just think that they can (and should) be improved with the use of xenon bulbs.

So I've gota ask, how many pilots does it take to change a light bulb? :}

AerocatS2A
7th May 2009, 13:07
So I've gota ask, how many pilots does it take to change a light bulb?At least three. The light bulb actually gets changed by a machine, but you need one pilot to program the light bulb changing machine. You then need a second pilot to monitor the first pilot as he programs the machine. If it's going to take longer than 12 hours to program the machine, then you need a third pilot who can relieve one of the other pilots part way through the machine programming process.

The pilots will make use of a union to negotiate how much they get paid for programming the machine. The bigger the light bulb is, the easier the machine will be to program and, perversely, the more the pilots will get paid. The oldest pilot will look back fondly on the days when he used to change smaller light bulbs by hand with out the aid of any machines at all and may occasionally touch the light bulb himself just to "keep his hand in".

Every now and then the system of machine plus three pilots will fail completely and a light bulb will get broken. Posters on a light bulb changing internet forum will then discuss in great detail why the bulb got broken. At some stage it will be suggested that it was because the pilots don't get paid enough and are forced to change too many light bulbs each month.

bfisk
7th May 2009, 17:21
While we're at it: anyone else used to fly on PLASI? I did my flight training in the US on PAPIs and VASIs, but to my surprise, most of the regional airports in Norway use PLASIs for visual vertical guidance. What's up with that? IMHO they are far inferior to the other systems, and if it's one place you could use a proper system, it's there :confused:

boofhead
7th May 2009, 19:34
PLASI is really great. No interpretation and very accurate. I don't think it covers the quoted range though. I use one at Merrill Field in Anchorage. Even my students get it first time.

Nightrider
8th May 2009, 09:42
Did PLASI ever receive certification for fixed wing aircraft or is it still certified at certain places for rotary wing only?

FlyingTinCans
8th May 2009, 12:42
:D AerocatS2A, nice to see humour is still around on Pprune! :ok:

capt_akun
9th May 2009, 03:31
So I've gota ask, how many pilots does it take to change a light bulb?

None..

Call the engineers.

Blip
10th May 2009, 01:51
None..

Call the engineers.

If only it was that simple! :{

muduckace
11th May 2009, 06:38
When did you guys quit looking at the runway? Granted a valid point to promote a comfortable safe landing but this mindset as I see (and may be wrong) directs too much attention away from basic approach/landing skills.

One exemption I have experienced when the landing pilot was focused on the runway and the environment created an illusion MROC at night given it's situation in hills and runway height variance.

bfisk
11th May 2009, 10:56
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.

Blueskyrich
11th May 2009, 21:46
So I've gota ask, how many pilots does it take to change a light bulb?

Ah that's easy - two. One to hold the bulb in whilst the other spins the earth around him ;) :ok:

DeathStar-Alpha
11th May 2009, 23:54
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 :ok:

Blip
12th May 2009, 01:17
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. :rolleyes:

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.

ft
24th May 2009, 08:26
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.

blackburn
24th May 2009, 09:27
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