View Full Version : The scourge of PAPI replacing T-VASIS

23rd Jul 2005, 04:37
First of all I want to state the fact that I am not colour blind!

I was approaching Melbourne Runway 34 for the first time since the runway works had been completed and have to say that I found the new PAPI system next to useless!

We were flying in from Tasmania via HOBAY so we had the PAPI system in view for an extended period of time.

Where the old T-VASIS gave you an unambiguous indication of where you were on the visual approach path, I found the PAPI approach path information to be profoundly nebulous and quite unacceptable.

Everyone who flies in to Melbourne knows that the runway slope is quite significant on that runway. From 330 ft AMSL at the 34 threshold to 434 ft at the aerodrome reference point (which is located just 1500 metres along and 450 metres to the east of the centreline). This slope gives the illusion that you are high when on the 3 degree slope and if it wasn't for the visual slope guidance, many aircraft would approach the runway much lower than desired.

Anyway the old T-VASIS had essentially 7 separate rows of lights to indicate glide path angle (three for high and three for low). The lights were either in-view or not -in-view (which is literally as easy to interpret as black or white).

Now we have a PAPI system with just four lights in a single row which change between white and red in a progressive fashion from four red no white lights to one, two, three, and four white no red lights. The pilot is now required to perceive this difference in colour from the single light source, and also perceive a change in colour as the aircraft moves above or below the ideal glide path to the lights.

This sounds fine in theory however the reality is not quite there. Two points need to be made.

1. The white light is not white at all but rather a light shade of pink.

2. When a light is transitioning from white to red or vice versa, it does it gradually, so that the change can go unnoticed!

The other day I transitioned from 1-red 3-white, to almost 4-red 0-white without it ever really grabbing my attention. By that I mean the PAPI didn't shout out to me the changes that were happening. T-VASIS would have! It was more the fact that I realised that the picture looked normal which wasn't normal for this runway! It should have looked as though I was high. That was when I realised that the PAPI was no longer indicating 3 pink but rather 3 red lights.

Never mind the fact that the T-VASIS allows you to nominate multiple aiming points where the PAPI only allows you to nominate one. And that one point is always set up for a B747 often with an eye crossing height over the threshold of around 70 feet.

Anyway the purpose of this post is to gauge the feelings of other pilots about the apparent inevitable demise of the far-superior AUSTRALIAN T-VASIS system and wonder if there is anyway to halt and even reverse the installation of PAPI at major airports around the country.

Does anyone have information about the cost associated with installing and maintaining the two systems?

I wonder if pilots can exert any pressure on the people responsible.

Capn Bloggs
23rd Jul 2005, 05:49
They're useless. Cheap and nasty. I believe T-VASI is about 3 times as expensive (but 3 times safer!). Affordable safety, son!

I complained to the CAA when the first one went in to MA years ago. Fell on deaf ears. If ICAO approves, we've got no chance.


23rd Jul 2005, 06:42
Many years ago and with much personal T-VASIS experience, I would have agreed with you. However, in the last 20 years my experience in international operations (including all sorts of weather conditions such as LWMO, typhoons, torrential rain and black hole approaches into some dreadful destination ports), I have come to realise and appreciate the benefits of PAPI. Consider:

1. Erroneous T-VASIS indications are thought to have been the cause of some aircraft accidents. PAPIs don’t seem to have these same erroneous indications. Therefore this change may save your life sometime down the track.

2. PAPIs now appear to be the accepted International standard. There is a lot to be said for the enhancement of safety by standardisation of approach facilities. T-VASIS can now only be rarely found in some third world countries…and (including?) Australia.

If nothing else, if you are going international, you would do well to teach yourself to discriminate between shades of pink!

Mr Lucky
23rd Jul 2005, 06:45
Blip. I totally agree.
I feel that we will see this far inferior system replacing T-Vasis all over the country. The T-Vasis is unquestionably the most effective indicator of any I have seen worldwide.
The red/white vasis is also far better than PAPI.
I confess to being partially colourblind, although obviously within limits, and, particularly in bright daylight, the indication is totally useless outside about 5 miles.
I use FMS, mental arithmetic and judgement to put me on the right slope, then confirm it with the PAPI when I get close enough.
Great system.

23rd Jul 2005, 08:10
FlexibleResponce they're fair points you raise.

I did my time, flying international operations for a little over five years. For me, flying overseas now must involve a glass of wine in hand and a good movie.

And before anyone says it, yes I have seen the T-VASIS indicate two dots fly up and two dots fly down simultaniously, and is susceptible to refraction through fog/mist etc. So I acknowledge that it is not a perfect system as it is but at least you know when it is giving you eroneous information.

May I suggest to the powers that be that the PAPI use Green and Red lights rather than White (Pink) and Red!

23rd Jul 2005, 08:23
I grew up with VASIS but havent seen any for years. Not sure I could interpret them anymore!!!

Papi are better, I feel, for Instrument approaches, whereas VASI is far superior for visuals.

PAPIs also need some warm up time before use. If they have just been switched on for you, you can see 4 pinks no matter where on the slope you are.

I guess its an indication that the world is expecting everyone to do an instrument approach!

Jenna Talia
23rd Jul 2005, 09:15
I confess to being partially colourblind, although obviously within limits, and, particularly in bright daylight, the indication is totally useless outside about 5 miles.

Well, I can tell you that I am not the least bit colour blind and still find the indication useless outside of 5 miles!

In poor viz, you may as well not have them. T-Vasis is far more superior, but realistically due to cost considerations we are stuck with it.

Non Normal
23rd Jul 2005, 09:57
I much prefer T-VASIs to PAPIs, and I am not the slightest bit colour-blind.

For one thing, T-VASIs are pretty fool-proof and it's so bleeding obvious what they're getting at that. PAPIs, on the other hand, can be a bit hard to spot in terms of the colour changes (especially some of the cheapo dodgy installations that seem entirely consisting of suble pink than red or white, no matter whether you are high or low or on the glideslope).

There is also a danger in transitioning from T-VASI to PAPI unless the change is clearly brought to the pilot's attention (I know we should check, but still, anyway, there are those who don't, or plain forget!). "It's a T-VASI, so I'm on the right track. Oh DAMN! It's a PAPI and now I'm hopelessly high!!" can happen.

Anyway... I think PAPI is a backward step.

From the human factors perspective, T-VASI is far superior IMO.

...still single
23rd Jul 2005, 12:18
Bloody pilots!
Who the hell do you think you are?!? PAPI is much superior because everyone else has it. If ICAO says it's good, then it must be good. I suggest that everyone here repeat that ten times... "If ICAO says it's good, then it must be good"
And if the government decides it's a good idea to spend a big chunk of money on ripping out perfectly good T-VASAI (plural of T-VASI), then it must be a good idea because the government knows....no, hang on, let me get back to you on that one....

23rd Jul 2005, 12:29
Both systems are VISUAL approach systems and it doesn't matter whether you fly an ILS in cloud to say 3 miles and become fully visual either on a T-VASIS or a PAPI the resulting visual angle of approach is the same. So it has nothing to do with coming into the view of the VASIS from an instrument approach or not.

When PAPI was first mooted many years ago, it was argued correctly that PAPI indications were colour dependant and thus wide open to the pink or vague colour difference under certain atmospheric conditions that was mentioned in the early posts. In fact the PAPI is still a very accurate visual aid, providing that it is serviced correctly - and that is the problem.

Like all VASIS types around Australia, once the initial installation is completed and a commissioning flight test by a dedicated aircraft is completed, there are no more scheduled flight tests unless pilots submit a formal complaint with full details of what they saw.

Even then, although airport Maintenance staff may go out to the VASIS and have a look for crook lamps, snakes, long grass or earth movement etc, there will not necessarily be a flight test arranged due to the cost of flying the dedicated navaid test aircraft to wherever.

In the old days when the Department of Civil Aviation Flying Unit F28, F27 or DC3 were on tap, a crew would be despatched to re-test the VASIS at tax payer's expense. VASIS was also subject to routine annual flight tests. Now that a private operator has the contract for navaid calibration work, the tendency is to cut costs to an absolute minimum and therefore the services for a dedicated VASIS flight test by the current contractor is seldom called for.

The upshot of all this is that it is left to pilots to officially notify ATC or the appropriate authority that runs the airport if they perceive a problem. A certain degree of colour blindness is allowed for pilots for purposes of holding an ATPL, but the downside of that is some pilots may experience occasional difficulty in interpreting PAPI signals. It was no problem with T-VASIS unless you were in a gross 1.9 degree undershoot in the red, but then the three fly up lights had already given you advance warning of an impending undershoot.

While I personally have always liked T-VASIS and prefer it to PAPI for several reasons, the fact remains that it is more expensive to maintain. The atmospheric conditions that can give rise to erroneous VASIS light signals also can affect PAPI. Vague pinkish colours rather than bright red lights can cause confusion.

Kaptin M
23rd Jul 2005, 13:17
IMO - the Australian T-Vasis provides the pilot with information that is calibrated more accurately than PAPI - but do we REALLY need this info?
PAPI is the worldwide standard now - as a matter of fact, the majority of non-Australian, international pilots flying into OZ probably have NO IDEA how to interpret the T-Vasis.
And so, Australia is merely adjusting to conform to the majority consensus..PAPI.

Yes, T-Vasis was great while we had it - it also had it flaws though...I've seen full fly up/fly down indications in ground fog conditions (in Hobart)...but the majority opinion - be it for $$$'s, or simply non-exposure to the Australian T-Vasis - is for PAPI.

(Besides, how could you expect Septics to count any more than the number of digits on 1 hand for ANYTHING??!!!)

23rd Jul 2005, 21:25
I cut my Ops teeth out on the airfield at Heathrow, over 25 years ago. At that time, we had VASIS installed on 5 out of 6 approaches. We had a weekly routine with the engineers, calibrating each box of each set. This took a crew of 5 or 6 people a complete morning. The results were less than satisfactory from an accuracy point of view; the first 747 movement would blast the boxes and we'd have to go and check them again, if anyone complained. Far from satisfactory! In the early eighties, a PAPI replacement programme was started. The units are much more blast-proof and stay in calibration very well. We also had mega problems with pink emissions from the units and went to 30 min warm-up periods then eventually permanent heaters being fitted to alleviate this problem. The units now are very reliable and accurate and I for one wouldn't DREAM of going back to VASIS.
You pilots want us Ops types to give you the best, most reliable, fail-safe aids that we can. It isn't just a money thing- from my point of view anyway.
The only downside for me with PAPI is the aforementioned business with B747 eye-height; it does mean that everyone else touches further down the runway than necessary. I've advocated a 5-light setup in the past, so you can choose a nearer or further aiming point, but someone's bound to choose the wrong one!
Incidentally, each 'light' consists of several lamps so that some lamp failures can occur but the system remains usable - not always the case with VASI.

Stick with it - it's worth the hassle!

The Odd One

John Citizen
23rd Jul 2005, 21:36
Repeat this to yourself 10 times :
1 - "most pilots on pprune think VASIS is better"
2- "PAPI is cheaper than VASIS"

I am happy to repeat your statement :
"If ICAO says it's good, then it must be good". Sure PAPI might be "good enough" for ICAO but still not be better than VASIS (as most pilots agree). PAPI is also cheaper to install, so this might be part of the reason ICAO choose PAPI.

PAPI might be more "cost effective", but not the best means.

24th Jul 2005, 01:25
Sort of makes you wonder why they dont actually put in an ILS for MEL Rwy 34.

Any reasons apart from the obvious one being cost??

24th Jul 2005, 04:36
Please re-read your instruction manuals before addressing a thread dealing with T-VASIS on the basis of your experience with VASIS. Birds of quite different feather. Speaking as a sometime calibrator, T-VASIS, whether in a military or civvy environment, rarely needed much adjustment at the six-monthly.

24th Jul 2005, 06:12
Well, I'm staggered that we're even having this discussion!

T-Vasis versus Papi, it must be obvious to any practising pilot who's been around for 20 or 30 yrs, and has used both, which is the best system! ( Clue: it starts with T )

By the way, I think the New Zealanders actually invented it , didn't they? :sad:

24th Jul 2005, 06:13
Doesn't TVASI operate in the reverse sense to the ILS? You fly towards the needle, and then away from the lights.

Pimp Daddy
24th Jul 2005, 06:35
Sort of makes you wonder why they dont actually put in an ILS for MEL Rwy 34.

Any reasons apart from the obvious one being cost??

How often do you really get gooey weather with a northerly in Melbourne?

Normally just blows 40 [email protected] and thats it.

24th Jul 2005, 07:34
Perhaps the T vasis are being ditched cos you cant get the spares anymore.After all who else uses the things. I can also say that 90% of international pilots will interperet the things the wrong way,so they cant be that clever!

24th Jul 2005, 07:51
Outofsynch. If the PAPI needs a warm up period before giving reliable signals, you would think that Air Services would warn of this via AIP. It it was a significant problem then surely PAL actuation would prove insufficient time for the lamps to warm up in order to prevent pink rather than red lights.

Occasional single or two lamp failure on a VASIS box makes almost no difference to the integrity. The light source appears a little dimmer, that's all. However if one complete box goes out of action due a major electrical problem, then that can quite misleading. Of course one box u/s on a PAPI would be misleading, too.

24th Jul 2005, 10:53
Very good point Pimp Daddy, but recently I had to do a full blown Rwy 34 VOR/DME down to the minima due to low cloud and haze etc one evening.

Yep, its great fun doing the normal visual approach overhead YMEN for Rwy 34 MEL, but at the same time you do get sick and tired of occasionally landing MEL Rwy 16 right down to minima with something like a 9 or 10 kt tailwind.

We dont often have to do an ILS in anger onto SYD Rwy 25 either, but there is an ILS available.

Just makes you wonder really whether noise sensitive areas may come into it for being an excuse.

They are installing a CAT II or CAT III ILS onto 16 in YMML which is a great start and hopefully the others will follow suit where they are needed.

Bill Smith
24th Jul 2005, 12:11

Out of Jepps AU-321

Condensation on PAPI lenses is known to be a cause of color distortion. therefore, PAPI system should be activated at least 10 minutes prior to use so that any condensation that may have formed on the lenses is evaporated before use.

We all learn something everyday !

24th Jul 2005, 21:58
This thread really only serves to highlight how antiquated Australian aviation really is. It is the thought process that I see on these pages that explains why Australia remains a decade or two behind the rest of the world in operational technology. When are we going to wake up and realise that we are a minority in global aviation, we really arent any better (as our supposed good accident statistics really only reflect a flat country with benign weather), open our eyes and join the 21st century.
PAPI is everywhere and is working fine.

25th Jul 2005, 01:19
Pharknose. Your cynical and quite unamusing diatrabe missed out on the most important reason for the excellent safety record of Australian airlines, and that is the absence of the "saving face" curse that permeates through many cultures. The same dangerous culture that says real men don't go around.

There is also a flight deck atmosphere in Australian cockpits (most of the time, anyway) that discourages the master and the boy attitude. The first officer is not just a bum in seat. He is second in command and in general (there are always the odd exception) his opinion is respected by the captain. Not so in other less democratic cultures where God Almighty (or any equivalent deity) is in the left hand seat and the first officer is just the bum that pulls up the gear when ordered and shuts up until spoken to.

25th Jul 2005, 01:39
Who-knose. Your wind-up doesn't even make sense. But I will shoot it down anyway.

Regarding technology I come across when I turn up for work each day. Hmmm lets see. There's

Enhanced GPWS
Double GPS used for FMC position updating.

RNAV (GNSS) approaches
RVSM airspace.
I read in the notams about the ADS-B trial in Queensland.

What century is this again?

I wish I had more time but must go to work now. Geez I hate my job!

Angle of Attack
25th Jul 2005, 09:01
All have valid points and I believe both systems to the pilot are as accurate as each other, although T-VASIS will indicate more subtle changes quicker than PAPI. Although you dont need a visual slope system at 5 or further miles, it comes into its own breaking out visual up to around 1000ft in low viz and thats where its critical. In my opinion PAPI is superior and easier to interpret in the heat of the moment (unless your colour blind of course!) But I can appreciate some find VASIS easier to perceive. Its much like whether you like a Ford or a Holden right? haha! The day of cost is here and PAPI will prevail whether its good or not.

25th Jul 2005, 10:58
Hello gentlemen

Speaking from the point of view of a 744 driver I would have to applaud and welcome the arrival of a standard Papi system to Australia.
In a classic nut shell the T. vasis system is next to useless, in anything where the flight deck is more than 20ft from your bogeys.

I won’t go into the mathematics of it all, but the major difference between the Papi and the vasis setup is the T vasis system guides the pilot to a set height above the threshold not taking into account what type of aircraft you are operating.
While the Papi system guides the pilot to a touch down point.
Thus ensuring all crossing heights of all aircraft.

We should have changed years ago, but alas Casa have a certain misunderstanding they know better than the rest of the world syndrome.

But the main reason this change should be employed and applauded is the simple fact that it standardizes Australia with the rest of the world.
I know if you are only flying domestically you may see this as an unnecessary change for slow old 744 pilots but I am sure if you give it a chance you will forget everything about the T vasis as quick as we all forgot about Australian domestic DMEs
Have a great day

25th Jul 2005, 14:01
When the windscreen wipers are going eewacka eewacka eewacka at a zillion beats a minute. When the rain is crashing on the windshield in a bleary inch of water depth and the FO is pumping rain repellant like he has just found religion. You are close to minima but your outside world has now become two-dimensional and you have no depth perception as you peer into a grey wall of obscurity. Just then first barbettes of the approach lighting system dimly appear in the lower extremities of the windscreen and disappear as quickly under the nose. But you resist the temptation to push over in the classic duckunder land short of the runway scenario and instead use these lights for lateral lineup only. Then the PAPIs mercifully emerge on the left side and voila, you have accurate vertical guidance to follow to a safe touchdown. Under these conditions you will understand the benefits of PAPIs and realise on the other hand that T-VASIS are of very limited value.

Who really cares how good T-VASIS/PAPIs are in fine and beaut visual conditions especially at ranges in excess of 5nm? Any pilot worth his salt can cope in visual conditions with or without visual glideslope aids. It’s the performance capability of these aids, which includes reliable and accurate indications (read non-erroneous trying to kill you and your passengers) in difficult and extreme conditions that cuts the mustard.

For the benefit of the newbie’s its worth repeating, T-VASIS have been implicated in fatal aircraft accidents. In simple words, T-VASIS will kill you under certain conditions. You owe it to your family and passengers to do the research to understand the limitations of T-VASIS. If you can’t accept the lessons of previous accidents you too may well be doomed to repeat history. This will look very tacky on your CV.

25th Jul 2005, 22:20
Blip when I said Operational Technology I was referring to what you do rather than the machinery. Take a look at the published variations to ICAO that Australia has and ask the question are we such a bunch of experts here and know better (bear in mind that the majority of aviation happens in the northern hemisphere) or have we got a way to go. It wasn't that long ago when Ansett were fitting FE panels to 767's while the rest of the world were doing just fine leaving the FE panels in the era of the 727. Here we are referring to PAPI as a scourge when it has been working just fine in parts of the world where a lot more flying happens often around mountains and in severe weather conditions (that domestic aussies have never seen) on any day, all day. And heaven forbid we no longer need ATC to tell us how much fuel to carry. Centaurus in comparison to the Asian cultures you are correct but in the western world we are still bogged down in the "word game" that means the aircraft can only fly because we talk to it and CPM's NPM's ('Check' per minute & 'Noted' per minute) are often considered a measure of your worth. There is also academic info out there that indicates that we are still a little too hierarchal in our cockpits and that some of the skills of CRM are yet to sink in and be reflected in our operational philosophy.
While you are furiously machine gunning this post take time to think about the 35 day currency thing on the ILS and why it is there whereas the NDB is 90 days. The statistics out there well establish that it is the NPA that you are more likely to become unstuck on than the ILS and aircraft systems reflect so. Here in Australia, at difference to our northern colleauges who also operate to Cat III, we have to be super current on an ILS and yet the NDB only gets a 90 day look in. Is this because we know better or is it a hang over from days gone by when the ILS was the newbie on the block and rare thus treated with the same inertia as we are seeing here with the PAPI?

26th Jul 2005, 00:05

means the aircraft can only fly because we talk to it and CPM's NPM's ('Check' per minute & 'Noted' per minute) are often considered a measure of your worth


I will have to use your TLA's in my next "discussion" about our operating procedures. Less is most times better :rolleyes:


26th Jul 2005, 00:18
IN respect of pondoklabu comments, as a pilot of a longbody aircraft I'd much rather fly a PAPI than a VASI or T-VASIS any day.

26th Jul 2005, 00:23
For info about the history of T-VASIS have a look at www.airwaysmuseum.com (http://www.airwaysmuseum.com) - go to 'History', then 'Navigation and Communications', then follow your nose.

26th Jul 2005, 04:19
There's enough evidence here on VASI and PAPI to show they both have limitations. However, it is even more revealing of the "narrow" operating environment of the domestic Australian airline pilot. If you are so dependent on having either VASI or PAPI, (and thus debating so), for landing on any runway, then your pilot judgement appears to be too dependent on this source. If you can't be sure of your relationship to the landing runway, then go somewhere else or try again. Mr. Lucky's reply is the one I like. "I use FMS, mental arithmetic, and judgement to put me on the right slope, then confirm it with the PAPI, when I get close enough." To go from "1-red 3-white to almost 4-red 0-white", without first noticing the runway "picture"/aiming point was changing before then is not something I'd like to hear. Blip, you said you know what the right "picture" is suppose to be for Mel 34. Suggest you change to Mr. Lucky's process which is the reverse of yours as described. You should consider going to the P.N.G. highlands for some training on up to 14% gradient airstrip slopes with morning fog burning off or with afternoon upslope tail winds for landing. Assuming you are an airline pilot (and P.N.G. is not possible), then regularly ask your simulator instructors to give you visual landings with PAPI turned off and a wind change at the various airports you land at (Mel 34).

Direct to
26th Jul 2005, 06:10
Two great contributions. Good on you "Pharknose" and "pondoklabu" at least with your sensible and constructive comments the rest of the Australian pilots can have a balanced arguement.

You never know the rest of the World may be right!

We Aussies just have to think out of our own backwater. ( Did i say that? I ment backyard!) :ok:

29th Jul 2005, 10:44
Oh Dear!...what a bunch of uneducated,untrained,immature pilots you all are in supporting Papi over T-Vasis...

I really do wonder what planet you all come from!

Thank goodness I drive these days!!

Capn Bloggs
29th Jul 2005, 11:24
I won’t go into the mathematics of it all, but the major difference between the Papi and the vasis setup is the T vasis system guides the pilot to a set height above the threshold not taking into account what type of aircraft you are operating.
While the Papi system guides the pilot to a touch down point.
Thus ensuring all crossing heights of all aircraft.


29th Jul 2005, 14:38
Thanks for all the thoughts. It's interesting to see who believes what and why.

I've done some reading since begining this thread and can recommend them to others.

Firstly thanks to Philthy for that link! Excellent information about the T-VASIS. And there's a great photo of Alice Springs RWY 12 with what must be a brand new lighting system. I just saw that photo and could tell instantly that from the aircraft's present position a 3 degree descent path would take it towards the 150 metre markers. In other words it was about 25 feet low. Too easy! :)

The other good (informative) read was an FAA Advisory Circular on the subject of PAPI systems. Found here:


Some points I gleened from the AC...

"The minimum allowable TCH varies according to the height group of aircraft that uses the runway, and is shown in table 1. The PAPI approach path
must provide the proper TCH for the most demanding height group that uses the runway."

And for "Height Group 4" aircraft such as the B747, L-1011, DC-10 etc the Threshold Crossing Height is 75 ft (+5 ft, -15 ft).

So here is some things worth noting.

a) PAPI has only one aiming point.

b) From 75 ft at the threshold, a 3 degree descent path intersects the runway at 450 metres beyond the threshold. So this is where the PAPI is installed (more or less).

c) The B737 pilot eye height over the threshold should be only 50 ft, with a main gear height of 33 ft. Therefore if the B737 pilot is to make proper use of the PAPI system, s/he must accept an aiming point 150 metres further down the runway than normal.

d) Main gear touchdown will therefore be around 450-600 metres beyond the threshold.

e) At 135 kts the aircraft is passing over the runway at 70 metres per second. That doesn't leave much room for error in the flare! because...

f) Our company considers any touchdown beyond 600 metres to be a long landing and is noted by the QAR!

Now regarding the point made by some that Australia needs to get in line with the rest of the world. All I can say is that it reminds me of the manta made by some regarding Class E airspace and RPT jet operations a couple of years ago. Remember? Worlds best practice... Europe and America do it so it must be good, bla bla bla...:rolleyes:

Capn Bloggs
29th Jul 2005, 23:33
Spot on. It reminds me of a high-ranking Virgin "Flight Manager" (or something like that) who protested violently at a suggestion for Perth that the 03 ILS be raised to 3.3 deg, quoting landing performance dramas. I bet he did not take into account the 450m-odd PAPI GPI! (Quite apart from the fact that the runway is only 3500m-odd long anyway...).

30th Jul 2005, 01:03
Our company considers any touchdown beyond 600 metres to be a long landing and is noted by the QAR!

How does the QAR calculate touchdown position? If, as I think but I'm willing to be corrected, it uses glideslope information they can't determine touchdown point on a non-ILS equipped runway and, if it is an ILS runway, I'd much rather be using the glideslope anyway!

It's interesting to note that my company puts a disclaimer on the use of all visual approach aids stating that they're a guide only and not to be used below 300' where the primary visual reference should be the aimpoint and runway perspective.

Capn Bloggs
30th Jul 2005, 01:12
my company puts a disclaimer on the use of all visual approach aids stating that they're a guide only and not to be used below 300' where the primary visual reference should be the aimpoint and runway perspective.
DA, is your outfit suggesting that, at 300ft, you ingnore where you were going (stablised on the ILS/PAPI/TVASIS glidepath) and suddenly dive at the "proper" visual aim point (wherever that may be)?

30th Jul 2005, 01:35
Amos 2 , have you ever flown away from your godzone country.Try it one day and you may be confused as there wont be many T vasis to stare at!

30th Jul 2005, 02:01
DirectAnywhere. Yes I was wondering the same thing as I was writing. It probably has something to do with GlideSlope and/or Ground Speed vs time spent below a certain radio altimeter value before touchdown.

So if you aim for 1000 metres down a non-ILS runway and then flare and land normally, will it take note? I cannot answer that question. But I suspect not.

Anyway the point is that for the vast majority of aircraft PAPI sets them up for a long landing. Our company consider this a parameter worth monitoring and will make it known if an undesirable trend appears, especially if involves a particular aircraft type and/or runway.

30th Jul 2005, 02:14
d) Main gear touchdown will therefore be around 450-600 metres beyond the threshold.
I think that this is an incorrect statement leading from incorrect interpretation of the document.

Blip forgot to mention that PAPIs will be aligned with the ILS glide slope for those runways that have an ILS. Therefore the touchdown point for PAPI or ILS approach will be identical.

Major airport ILS glide slope and PAPI glide slope ground intercept/visual aim points have to accommodate the largest jet using the facility and from observation generally fall into the range of 1100’ to 1300’ from the threshold. Typically the threshold crossing heights seem to fall in the 62’ to 68’ range. Consult your Jeppeson runway plate for each specific runway. These runways by definition are long enough to accommodate the largest jet that is allowed to operate on them.

Smaller runway jet operation can install the ILS/PAPI ground intercept/visual aim point closer to threshold to accommodate the smaller jets.

On Table 1 of Blip’s reference one can see for “Height Group 4” that there is a very large difference between the cockpit eye height and the wheel height, which exceeds 25’. Some people may not have considered that this means that the threshold crossing pilot’s eye height is very different to the threshold crossing wheel height of the MLG. This in turn means that the aircraft MLG touchdown actually occurs when the pilot is still greater than 25’ above the runway. This also means that if the pilot flew the visual glide path without flaring, touchdown would occur some hundreds of feet before the PAPI installation. There is also the consideration of the distance between the MLG and the pilot, which is around 80’ on some of these large aircraft. This means that MLG touchdown actually occurs an additional 80’ behind where the pilot is along the runway.

My airline only flies “Height Group 4” aircraft and our touchdown point must fall between 1000’ and 2000’ from the threshold. This is very similar to the max distance of 600m that Blip quotes for his “Height Group 2” 737. We seem to achieve these requirements just fine using PAPIs at international ports all over the world.

I also agree that sometimes we do get caught up in the mantra claptrap that tends to cloud our vision and judgment. I think in this case we need to keep our minds open and to analyze the facts while leaving the emotional NIH/NIMBY baggage at home.

30th Jul 2005, 10:23
Capn Bloggs,

Should have highlighted this is for visual approaches, but essentially yes.

Two/three bar VASI are largely useless below 300' for long-body aircraft.

T-VASIS provide an unacceptably large range of main wheel crossing heights for a given indication. For example, two dots fly down - recommended for a jumbo - will provide main wheel crossing heights from 29-48' a range of nearly 20' giving a difference in touchdown points of nearly 400'.

PAPI is far more useful for long body aircraft and allows better co-ordination with an ILS glidepath.

PAPI or an ILS glidepath should essentially co-incide with the required 1500' visual aiming point. Reference to the required aimpoint should obviously be made prior to 300' but below 300' primary reference for a visual approach should be to the aimpoint with reference to other approach aids.

31st Jul 2005, 07:23
Hello again gentlemen.
Dear Amos2 and Capt Bloggs, I am sorry you don’t agree with me on the virtues of the Papi system over the incumbent T vasis system but I will however show you both the respect that you both failed to show to all the people who had a different view to yourselves.

The Papi system is aligned when possible to the ILS system, and like the ILS they both don’t care about crossing heights they are calibrated on touched down area, and yes they both do allow for the largest aircraft in respect of TCH. But it doesn’t matter if you are flying a Cessna 152 or a 744 if you are on the ILs and following the glide path and you happen to glance left you will observe the Papi giving you the same indications as the ILS irrespective of aircraft type. However if following the same ILS you glace to notice a T vasis the indications you get will differ depending what aircraft you are flying to the point in a 744 you must fly 2 dots fly down to remain in the 3' slope. In fact if you fly a on slope indication on the T vasis your wheels in a 744 crossing the threshold will between 4 to 12 ft a tad low you may say.

So in essence why would you want a system that is suppose to assist your approach path but is useless below 300' and gives you information that works for 1 aircraft type but not another.

Have a great day

TAY 611
31st Jul 2005, 22:00
Taking a look at Jeppview I notice that London Heathrow has Papi. Be carefull there guys it has to be way below Australian standards as it also gets its share of bad weather and traffic. KLAX also doesn't have a T-Vasi and it also doesn't have a PAPI or any sort of visual guidance (only electronic). Watch yer step there guys as all that traffic flowing through there has gotta be way below Australian standard and according to this topic must be just an accident waiting to happpen. I was also taught, and checked to fly without any sort of slope guidance and normally find that between the Electronic slope, The Visual slope and an assesment of my aiming point (thats me looking out the window) I can generally fly a stable approach to touch down in the appropriate area. Must admit the longest body I have flown is a 737 though it is by far not the highest performer Ive flown. I have more things to focus my attention in this game than just the virtues of Papi vs T-Vasis.
Carefull out there because we have statistics....

31st Jul 2005, 22:43
TAY 611

Don't you know that in Australia we invent things that are soooo much better than the rest of the world's inventions.

Get a life guys, Vasi Tvasi and papi are all fine............but they are only part of the big picture.

1st Aug 2005, 06:35
Well said fella's cheers

Captain Can't
1st Aug 2005, 07:01
Surely there's some qf 737 guys who have sat through the DJ flare's rant on T-VASIS vs PAPIs!
I'm actually starting to lean towards the papi for it's simplicity (in assisting)... sure, you may have trouble spotting it from 5nm +, but I thought it was more for the last 5nms? You'll struggle to see most T-VASIS at that distance (i have found)
but what the other guys have said also, they obviously aren't necessary, but are nice to have. (cause we are all good enuff to do without i'm sure ;) )
the only thing that bugs me is that they are too far in for my type! (damn the big jets!!)

1st Aug 2005, 07:34
How come folks are talking about trying to use T-VASIS or PAPI beyond 5 NM? The old certification standard for T-VASIS was a maximum range of 5 NM, nothing more. The current certification standard for PAPI is a range of 4 NM.

Some systems will perform better than that, but it really depends on the intensity setting and the environmental conditions. I've seen systems that struggle to be seen at 4 NM, even under ideal conditions.

In any event, what's wrong with flying a standard profile and using the mark-one eyeball? Whether the system is a VASI, T-VASIS or PAPI, it's just a helpful tool when it works as advertised.

2nd Aug 2005, 01:34
Used the papis for 34 mel the other day,what a relief!