PAPI
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PAPI
The other day, doing a visual app. , I rememberer ( hazily of course ) something about the visual approach vertical aid 3º glideslope being , not of 2 whites- two reds meaning ON G/S, but for a wide-bodied a/c , this reference being 3 WHITES - 1 RED.
Am I remembering correctly ?
( If so, I,ve been doing most of my approaches wrong for a loooong time )
Where can I check this doc. ? ( forgot most about the air law subject for ATPL )
THX .
Am I remembering correctly ?
( If so, I,ve been doing most of my approaches wrong for a loooong time )
Where can I check this doc. ? ( forgot most about the air law subject for ATPL )
THX .
Two whites and two reds is the correct "on slope" indication. What the slope is depends on the configuration of the PAPI. I know some places use an angle other than 3 degrees, while others modify the threshold crossing height of the GP, to accomodate for heavies. Check the plate of the aerodrome concerned and see what is published.
How you use the indications is up to you...
How you use the indications is up to you...
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Fair enough, NZScion.
Nevertheless, can you also recall anything like I state above on any ICAO doc.?
( Maybe my neurons are already getting stiff enough due to accu. jet-lag )
Nevertheless, can you also recall anything like I state above on any ICAO doc.?
( Maybe my neurons are already getting stiff enough due to accu. jet-lag )
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Not sure I completely understand the question, but PAPI glideslope can vary according to installation - usually 3-5 degrees but some go higher. Just check the Jeppesen cards.
Some operators recommend that if flying a widebody then fly on 3W/1R because pilot eye-height is much higher than smaller aircraft. Your wheels would land short if flying 2W/2R. Hope this helps.
Some operators recommend that if flying a widebody then fly on 3W/1R because pilot eye-height is much higher than smaller aircraft. Your wheels would land short if flying 2W/2R. Hope this helps.
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Some operators recommend that if flying a widebody then fly on 3W/1R because pilot eye-height is much higher than smaller aircraft. Your wheels would land short if flying 2W/2R. Hope this helps.
The difference between flying 3W/1R and 2W/2R is maybe 7 feet difference in wheel clearance crossing the threshold.
From Jepp:
A one degree progressive incremental spread from the outermost to the innermost light unit about the standard approach angle provides the visual guidance...
...PAPI is a point source aid. Thus a non-standard approach will not significantly alter threshold crossing height; only the approach angle will change.
The way you fix a problem of 'wheels landing short' as you put it is not to fly a steeper angle to the same aim point... you move the aim point into the runway. Such as the ozzie airservices people are doing at dunnunda international ports in preparation for the A380.
Last edited by ITCZ; 27th Feb 2008 at 09:17.
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Thx. Shore Guy.
The link makes all the difference.
According to it :
" Three-bar VASI installations provide two visual glide paths. The lower glide path is provided by the near and middle bars and is normally set at 3 degrees while the upper glide path, provided by the middle and far bars, is normally 1/4 degree higher. This higher glide path is intended for use only by high cockpit aircraft to provide a sufficient threshold crossing height. "
X
Therefore my memory wasn,t so bad.
Nevertheless...
This is stated ONLY for the VASIS,as for the PAPI I haven´t found anything about the different pilot visual reference from the 2W-2R.
Should we assume then that this is only an improving feature of the VASIS that the PAPI cannot offer ?
Because, I think I will NOT place my wheels or boogey on the same spot if I am landing on the same airport with the same PAPI with a B737, than with a B744. ( or is it ? ).
Thx Richatom for your reply too.
Couldn,t agree more.
( we´re getting somewhere here... )
The link makes all the difference.
According to it :
" Three-bar VASI installations provide two visual glide paths. The lower glide path is provided by the near and middle bars and is normally set at 3 degrees while the upper glide path, provided by the middle and far bars, is normally 1/4 degree higher. This higher glide path is intended for use only by high cockpit aircraft to provide a sufficient threshold crossing height. "
X
Therefore my memory wasn,t so bad.
Nevertheless...
This is stated ONLY for the VASIS,as for the PAPI I haven´t found anything about the different pilot visual reference from the 2W-2R.
Should we assume then that this is only an improving feature of the VASIS that the PAPI cannot offer ?
Because, I think I will NOT place my wheels or boogey on the same spot if I am landing on the same airport with the same PAPI with a B737, than with a B744. ( or is it ? ).
Thx Richatom for your reply too.
Couldn,t agree more.
( we´re getting somewhere here... )
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VASIS vs PAPI
BGS,
Check the post above your latest reply.
There is a principle difference between VASIS and PAPI and that is that the VASIS glidepath is assembled from lights at two widely separated positions, whereas PAPI light are all at the same distance from threshold.
Using VASIS, your aimpoint essentially is in between the white unit and the red unit that follows the white one. Using the "upper VASIS bars" thus moves your aimpoint further down the runway than when using the "lower VASIS bars" and so increases threshold crossing height.
With PAPI, the aimpoint is right next to the PAPI unit, so using the steeper indication will only give you a very small increase in threshold height.
ICTZ stated it correctly: take out your calculator and check.
Placing PAPI 1500 ft beyond threshold, threshold crossing height of a 3 degree glidepath is 78 ft (sine of 3 degrees times 1500 ft).
There is a 1 degree difference in slope from outer to inner PAPI light, and with four lights there are three intervals, so one third degree difference from one light to the other. The next higher slope would be 3,33 degrees, giving a TCH of 87 ft.
The distance of the PAPI from threshold will be the most important factor in threshold crossing height. The nominal glideslope of the PAPI will be determined by the terrain profile, just like an ILS glideslope: normally 3 degrees, steeper if needed because of distant obstacles in the approach path.
Check the post above your latest reply.
There is a principle difference between VASIS and PAPI and that is that the VASIS glidepath is assembled from lights at two widely separated positions, whereas PAPI light are all at the same distance from threshold.
Using VASIS, your aimpoint essentially is in between the white unit and the red unit that follows the white one. Using the "upper VASIS bars" thus moves your aimpoint further down the runway than when using the "lower VASIS bars" and so increases threshold crossing height.
With PAPI, the aimpoint is right next to the PAPI unit, so using the steeper indication will only give you a very small increase in threshold height.
ICTZ stated it correctly: take out your calculator and check.
Placing PAPI 1500 ft beyond threshold, threshold crossing height of a 3 degree glidepath is 78 ft (sine of 3 degrees times 1500 ft).
There is a 1 degree difference in slope from outer to inner PAPI light, and with four lights there are three intervals, so one third degree difference from one light to the other. The next higher slope would be 3,33 degrees, giving a TCH of 87 ft.
The distance of the PAPI from threshold will be the most important factor in threshold crossing height. The nominal glideslope of the PAPI will be determined by the terrain profile, just like an ILS glideslope: normally 3 degrees, steeper if needed because of distant obstacles in the approach path.
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Hello BESTGLIDESPEED
According to ICAO Annex 14 variing pilot eye heights are an issue with VASIS but not with PAPI.
For VASIS the note after ICAO Annex 14 no 5.3.5.9 says:
hvogt
According to ICAO Annex 14 variing pilot eye heights are an issue with VASIS but not with PAPI.
For VASIS the note after ICAO Annex 14 no 5.3.5.9 says:
"If increased eye height at the threshold is required (to provide adequate wheel clearance), then the approaches may be flown with one or more fly-down lights visible."
For PAPI there is no parallel provision. In Annex 14 Figure 5-18 it just says:"Where a PAPI or APAPI is installed on a runway equipped with an ILS and/or MLS, the distance D1 [threshold to PAPI lights] shall be calculated to provide the optimum compatibility between the visual and nonvisual aids for the range of eye-to-antenna heights of the aeroplanes regularly using the runway. The distance shall be equal to that between the threshold and the effective origin of the ILS glide path or MLS minimum glide path, as appropriate, plus a correction factor for the variation of eye-to-antenna heights of the aeroplanes concerned."
I hope this will help you. Good luckhvogt
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Varying eye height may "not be an issue" with PAPI according to ICAO, but with almost 10 years flying the 747 I can tell you that 3 white and 1 red is the PAPI picture we see on a normal approach.
PAPI is a point-source. If you maintain a constant PAPI picture, you must be flying a constant descent angle. The aim point will be exactly the same regardless of whether you're flying 4 reds or 4 whites, or two reds and whites: where the PAPI globes "cross" the runway. Only the descent angle changes. For multi installations, if you hold one set constant, the others must be changing. There is no way to deliberately change the threshold crossing height unless you have a changing PAPI picture as you get closer to the runway. Not so with the T Vasi. A far better visual landing aid.
Intruder,
What are you basing your approach on? The ILS glideslope?
Intruder,
Varying eye height may "not be an issue" with PAPI according to ICAO, but with almost 10 years flying the 747 I can tell you that 3 white and 1 red is the PAPI picture we see on a normal approach.
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Thx EMIT for the link.
Thx hvogt too for the answer.
Am I understanding right ?
Putting it simple :
VASIS will get the wheels of my a/c at the same dist. from GND as for a shorter a/c due to the different pos of the lights ALONG the long. axis of the RWY ( this is, creating PARALLEL glideslopes ). therefore, one g/s for the cockpit, and one for the wheels. Bringing them right on 50´HAT, just like a shorter fuselage would follow.
Whereas PAPI, due to its ACROSS pos. to the RWY´s long. axis, creates CONVERGENT, i.e., DIFFERENT DEGREEE G/S´ . Therefore, following 3W´s - 1 R will only bring the a/c in a steeper desc. but the wheels to a height equal to the lower g/s on the VASIS if followed.
Shouldn´t I be intersecting the whites and reds in my way down in order to follow the ILS down to 200´ ?
( And I thought this was gonna be quickly sorted out..... )
Thx you all for the patience.
Rgrds.
Thx hvogt too for the answer.
Am I understanding right ?
Putting it simple :
VASIS will get the wheels of my a/c at the same dist. from GND as for a shorter a/c due to the different pos of the lights ALONG the long. axis of the RWY ( this is, creating PARALLEL glideslopes ). therefore, one g/s for the cockpit, and one for the wheels. Bringing them right on 50´HAT, just like a shorter fuselage would follow.
Whereas PAPI, due to its ACROSS pos. to the RWY´s long. axis, creates CONVERGENT, i.e., DIFFERENT DEGREEE G/S´ . Therefore, following 3W´s - 1 R will only bring the a/c in a steeper desc. but the wheels to a height equal to the lower g/s on the VASIS if followed.
Shouldn´t I be intersecting the whites and reds in my way down in order to follow the ILS down to 200´ ?
( And I thought this was gonna be quickly sorted out..... )
Thx you all for the patience.
Rgrds.
Whereas PAPI, due to its ACROSS pos. to the RWY´s long. axis, creates CONVERGENT, i.e., DIFFERENT DEGREEE G/S´ . Therefore, following 3W´s - 1 R will only bring the a/c in a steeper desc. but the wheels to a height equal to the lower g/s on the VASIS if followed.
Shouldn´t I be intersecting the whites and reds in my way down in order to follow the ILS down to 200´ ?
In New Zealand, the PAPIs are set up to accomodate the largest aircraft using the runway. The exact specifcations are prescribed in NZCAA AC 139 beginning on page 97. (Link to document)
For this reason, NZAA and NZCH (which handle nearly all of the heavies operating into or out of the country) are positioned to have a TCH of 73ft, which offers the heavies sufficient clearance from the fence and all other obstacles if they were to be flown with 2 red 2 white from the pilots perspective. These airports regularly handle aircraft of B747/A340 size.
Smaller airports have different TCHs. For example, NZDN, which normally handles aircraft up to B737/A320 size has the TCH set to 58 ft, while NZNP, which only normally has up to DH8C (and maybe AT72?) has the TCH set to 47 ft.
For this reason, NZAA and NZCH (which handle nearly all of the heavies operating into or out of the country) are positioned to have a TCH of 73ft, which offers the heavies sufficient clearance from the fence and all other obstacles if they were to be flown with 2 red 2 white from the pilots perspective. These airports regularly handle aircraft of B747/A340 size.
Smaller airports have different TCHs. For example, NZDN, which normally handles aircraft up to B737/A320 size has the TCH set to 58 ft, while NZNP, which only normally has up to DH8C (and maybe AT72?) has the TCH set to 47 ft.
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I think I got a "preliminary conclusion " ( susceptible of debating, of course ) :
Thank you NZScion for the link. It confirms the one sent by ShoreGuy ( I guess it is all ICAO´s )
For as to VASIS, it is clear that it DOES contemplate a solution for the higher-lower cockpits ref. pt. of view, and the theory of the PARALLEL glideslopes I was talking about before seems to be demonstrated in fig. 5-12 of such doc.
As for our topic, the PAPI, ( according to the same doc. ) it DOES seem to work ONLY for the type of aircrafts the aerodrome has decided is going to operate with.
The recommendation is to place the lights at a DISTANCE where the wheel clearance over the threshold of THE MOST DEMANDING A/C and MOST REGULARLY using the RWY is ensured.
Nevertheless, when this height is not met, then a "reduced wheel clearance is accepted".( table 5-2 on pg. 100 ).
Looking out for my A/C´s eye-to-wheel dist. ( 34´), I come up suddenly with another info I wasn´t looking for : I have a Minimum wheel clearance at the threshold!! and Guess what. It´s 20´ !!!
20´= 6 m.
Now take a look to the 5-2 table again, and there you got it; I find myself in the reduced wheel clr. height column 3 !
Therefore, airports who don´t consider a widebody as a regular traffic MAY NOT have placed the PAPI lights where they need it to ovfly the threshold at 50´, but, I guess we oughta think they have ALWAYS placed them in such position that AT LEAST the min. WCH is ensured.
CONCLUDING :
On a PAPI,
FLY THE 2W-2R glideslope no matter what a/c you´re coming in with, You have minnimum ( although sometimes reduced ) wheel clearance with a widebody.
Any rebates ?....
( Man, come to think all these years I have been flying close to 50' HAT, and have thought all the calc´s. were done taking that into account, and I realize now that every time I make a visual, I might be crossing the thr. below half the dist. I thought I was at some smaller airports ).
Thanx all of you for the valuable help.
Thank you NZScion for the link. It confirms the one sent by ShoreGuy ( I guess it is all ICAO´s )
For as to VASIS, it is clear that it DOES contemplate a solution for the higher-lower cockpits ref. pt. of view, and the theory of the PARALLEL glideslopes I was talking about before seems to be demonstrated in fig. 5-12 of such doc.
As for our topic, the PAPI, ( according to the same doc. ) it DOES seem to work ONLY for the type of aircrafts the aerodrome has decided is going to operate with.
The recommendation is to place the lights at a DISTANCE where the wheel clearance over the threshold of THE MOST DEMANDING A/C and MOST REGULARLY using the RWY is ensured.
Nevertheless, when this height is not met, then a "reduced wheel clearance is accepted".( table 5-2 on pg. 100 ).
Looking out for my A/C´s eye-to-wheel dist. ( 34´), I come up suddenly with another info I wasn´t looking for : I have a Minimum wheel clearance at the threshold!! and Guess what. It´s 20´ !!!
20´= 6 m.
Now take a look to the 5-2 table again, and there you got it; I find myself in the reduced wheel clr. height column 3 !
Therefore, airports who don´t consider a widebody as a regular traffic MAY NOT have placed the PAPI lights where they need it to ovfly the threshold at 50´, but, I guess we oughta think they have ALWAYS placed them in such position that AT LEAST the min. WCH is ensured.
CONCLUDING :
On a PAPI,
FLY THE 2W-2R glideslope no matter what a/c you´re coming in with, You have minnimum ( although sometimes reduced ) wheel clearance with a widebody.
Any rebates ?....
( Man, come to think all these years I have been flying close to 50' HAT, and have thought all the calc´s. were done taking that into account, and I realize now that every time I make a visual, I might be crossing the thr. below half the dist. I thought I was at some smaller airports ).
Thanx all of you for the valuable help.
Man, come to think all these years I have been flying close to 50' HAT, and have thought all the calc´s. were done taking that into account, and I realize now that every time I make a visual, I might be crossing the thr. below half the dist. I thought I was at some smaller airports
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Hi,
Thank's for all and you Bestglidespeed...interesting debate and a real good occasion to review some basic...
In addition to all doc's already proposed I'd like to submit this one..which I consider really well made by the French authorities..
Ill try to find it in english..but no success..anyway the pictures are talking by themselves..
http://www.sia.aviation-civile.gouv...._CHAP02_V3.pdf
Don't hesitate for any translation required..
rgds
Thank's for all and you Bestglidespeed...interesting debate and a real good occasion to review some basic...
In addition to all doc's already proposed I'd like to submit this one..which I consider really well made by the French authorities..
Ill try to find it in english..but no success..anyway the pictures are talking by themselves..
http://www.sia.aviation-civile.gouv...._CHAP02_V3.pdf
Don't hesitate for any translation required..
rgds
PAPI is a highly reliable and accurate aid below 200 ft. At lower altitudes you may not wish to use PAPI to establish the visual glidepath (long body aircraft, GS Ax position, or PAPI location), but it remains a useful aid for assessing the trend of the approach and detecting sudden changes in vertical position, i.e. windshear.
For general info and description, see pages 194/5, and 253-> in CAP 168.
Also pages 9 – 12 etc in CAP 637 Visual Aids Handbook.
For general info and description, see pages 194/5, and 253-> in CAP 168.
Also pages 9 – 12 etc in CAP 637 Visual Aids Handbook.