The scourge of PAPI replacing T-VASIS
Thread Starter
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.
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.
d) Main gear touchdown will therefore be around 450-600 metres beyond the threshold.
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.
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.
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.
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
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
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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....
Carefull out there because we have statistics....
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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.
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.
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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!!)
out.
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!!)
out.
PPRuNeaholic
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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.
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.
