Glideslope versus Papi??
Right Way Up,
Let's not get carried away. For an average jet (what part) to cross the threshold at 100ft, even it was the best case 100ft eye-height, the PAPI would have to be installed 581m past the threshold. I very much doubt that it is.
Let's face it, if a runway is suitable for Cat D ops then nobody should have any trouble landing a cat C aircraft, regardless of the glideslope indications being used.
As I said before: brief what slope indications/guidance you are going to use, then use it the whole way to the exclusion of the others. It's pretty obvious that you are going to get yourself into a tiddle if you suddenly try to jump from the ILS GS to the PAPI at 200ft where the PAPI is not aligned, so why would you do it?
Changing to a Visual AimPoint (where is that?) will unstabilise you unless the VAP is the same as the PAPI GPI or ILS GP antenna, which you had elected to use before swapping to the VAP, in which case, what's the point of using the VAP?
Leading you to cross the threshold at 100ft if you follow the PAPIs in your average jet.
Let's face it, if a runway is suitable for Cat D ops then nobody should have any trouble landing a cat C aircraft, regardless of the glideslope indications being used.
As I said before: brief what slope indications/guidance you are going to use, then use it the whole way to the exclusion of the others. It's pretty obvious that you are going to get yourself into a tiddle if you suddenly try to jump from the ILS GS to the PAPI at 200ft where the PAPI is not aligned, so why would you do it?
Changing to a Visual AimPoint (where is that?) will unstabilise you unless the VAP is the same as the PAPI GPI or ILS GP antenna, which you had elected to use before swapping to the VAP, in which case, what's the point of using the VAP?
On ILS glidepath and stable at Vref +5 kts the difference between pilot eye height and the glideslope for the following aircraft is, according to company manuals;
B767-300 4 feet
B747-400 16 feet
The B767 glideslope antennas are behind the radome and on the B747-400 there are two sets of glideslope antennas, one set behind the radome which are used when the gear is up and another set on the nosegear doors for when the gear is down. The changeover is automatic and there is no noticeable flight deck effect when it occurs.
Company manuals also state not to use VASI indications below 300' HAT although the PAPI can be used until over the threshhold.
Regards,
BH.
B767-300 4 feet
B747-400 16 feet
The B767 glideslope antennas are behind the radome and on the B747-400 there are two sets of glideslope antennas, one set behind the radome which are used when the gear is up and another set on the nosegear doors for when the gear is down. The changeover is automatic and there is no noticeable flight deck effect when it occurs.
Company manuals also state not to use VASI indications below 300' HAT although the PAPI can be used until over the threshhold.
Regards,
BH.
B747-400 16 feet
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When looking at this the first thing to look at is where the touchdown markings (aiming point) is on the runway. Annex 14 is a good reference.
The distance between the threshold and the touchdown markings is not the same everywhere. It is longer at runways available for large aircraft then runways only used by smaller aircraft.
This first fact shows that if the runway is designed for a B747 and a 3 degree approach, the touchdown markings will be such a distance past the threshold that the B747 following a 3 degree approach towards those markings will safely cross the threshold (let's say 50ft clearance).
So for the B747, the LDA is matched to the LDR and the 50ft point is at the threshold.
Now if you hop in your Citation and make the same 3 degree approach to the same touchdown markings, you will follow the same path. As you cross the threshold, you will be more than 50ft. This is not a problem since the runway is long enough for B747's but if you want to cross the threshold at 50ft then your aiming point will have to be closer to the threshold than the touchdown markings provided.
Note that I have said nothing about PAPI or ILS up to this point.
ILS CAT1 provides certified guidance down to a minimum of 200ft above the runway. Below that, obstacle clearance is not provided even if the aircraft follows the indicated glide slope.
PAPI indications provide both obstacle clearance when on slope and also ensure that the aircraft reach the threshold at the appropriate crossing height.
Refer to the above (non-PAPI) explanation for why threshold crossing heights vary.
Thre objective of PAPI is to provide obstacle clearance and safe threshold crossing height - to intentionally fly below the PAPI indication puts the aircraft at possible risk of hitting an obstacle or not crossing the threshold at the safe minimum height.
The effect of not following the PAPI is also that the approach is no longer a 3 degree approach to the published touchdown point.
Finally - why do we sometimes have PAPI on both sides of the runway?
The answer is that the extra set if there to provide some indication of lateral level in situations where this is not provided by other means. i.e. if the minima could be such that you can't use the crosbars of the approach lights for lateral level guidance. If there are two sets (one each side) then they have to provide the same indications.
So - PAPIs are there for the sole purpose of ensuring obstacle clearance and a safe threshold crossing height on the appropriate approach angle. Ignore them at your peril.
Finally - when the threshold is displaced, the PAPI may provide less than the normal threshold crossing height. However, the normal height will be provided at the start of the runway.
Regards,
DFC
The distance between the threshold and the touchdown markings is not the same everywhere. It is longer at runways available for large aircraft then runways only used by smaller aircraft.
This first fact shows that if the runway is designed for a B747 and a 3 degree approach, the touchdown markings will be such a distance past the threshold that the B747 following a 3 degree approach towards those markings will safely cross the threshold (let's say 50ft clearance).
So for the B747, the LDA is matched to the LDR and the 50ft point is at the threshold.
Now if you hop in your Citation and make the same 3 degree approach to the same touchdown markings, you will follow the same path. As you cross the threshold, you will be more than 50ft. This is not a problem since the runway is long enough for B747's but if you want to cross the threshold at 50ft then your aiming point will have to be closer to the threshold than the touchdown markings provided.
Note that I have said nothing about PAPI or ILS up to this point.
ILS CAT1 provides certified guidance down to a minimum of 200ft above the runway. Below that, obstacle clearance is not provided even if the aircraft follows the indicated glide slope.
PAPI indications provide both obstacle clearance when on slope and also ensure that the aircraft reach the threshold at the appropriate crossing height.
Refer to the above (non-PAPI) explanation for why threshold crossing heights vary.
Thre objective of PAPI is to provide obstacle clearance and safe threshold crossing height - to intentionally fly below the PAPI indication puts the aircraft at possible risk of hitting an obstacle or not crossing the threshold at the safe minimum height.
The effect of not following the PAPI is also that the approach is no longer a 3 degree approach to the published touchdown point.
Finally - why do we sometimes have PAPI on both sides of the runway?
The answer is that the extra set if there to provide some indication of lateral level in situations where this is not provided by other means. i.e. if the minima could be such that you can't use the crosbars of the approach lights for lateral level guidance. If there are two sets (one each side) then they have to provide the same indications.
So - PAPIs are there for the sole purpose of ensuring obstacle clearance and a safe threshold crossing height on the appropriate approach angle. Ignore them at your peril.
Finally - when the threshold is displaced, the PAPI may provide less than the normal threshold crossing height. However, the normal height will be provided at the start of the runway.
Regards,
DFC
Capn Bloggs,
Not getting carried away thanks. If you fly the NICE 04L approach following the PAPIs you will cross the threshold at 100ft. Partly down to it being set to Cat D aircraft & possibly misalignment.
Not getting carried away thanks. If you fly the NICE 04L approach following the PAPIs you will cross the threshold at 100ft. Partly down to it being set to Cat D aircraft & possibly misalignment.
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1. Trying to keep ife simple: if you are on a Cat 2/3 approved rwy for autolands the a/c will follow the ILS G/S to touchdown; so why not do the same on a visual day and manual landing if there is a difference between it and PAPI.
2. In the old days of VASIS 2 & 3 bar we flew 2 red 1 white on 3 bar systems in a medium a/c. I always wondered why not the same on PAPI; 3 red 1 white.
3. I was told by a CAA inspector that an airfield operator had discretion how they set up the PAPI. The angle was published but not the touchdown point. This could be set by the operator for the most critical type, or most common type, of a/c they expected so as to give a safe THR crossing HT. This touchdown point is not published, but by nature if it is safe for a BIG a/c it is safe for a smaller one. However, the ILS G/S remained the primary GP guidance aid for all a/c, and it was this which was flight checked to the more critical tolerances.
Having said that, a final visual segment is pilot controlled. Mostly I have found that, if there is a difference, it will bring me high on PAPIs not low. Diving at the rwy from 200' when in trim on G/S does not seem the best idea. Does anyone have experience of the ILS G/S bringing you low on PAPIs? And if so is it worse than 3 reds? I know there are wavy G/S's, but these do not count. This is where the is quite a difference passing 500', but they recover to be the same at DA.
2. In the old days of VASIS 2 & 3 bar we flew 2 red 1 white on 3 bar systems in a medium a/c. I always wondered why not the same on PAPI; 3 red 1 white.
3. I was told by a CAA inspector that an airfield operator had discretion how they set up the PAPI. The angle was published but not the touchdown point. This could be set by the operator for the most critical type, or most common type, of a/c they expected so as to give a safe THR crossing HT. This touchdown point is not published, but by nature if it is safe for a BIG a/c it is safe for a smaller one. However, the ILS G/S remained the primary GP guidance aid for all a/c, and it was this which was flight checked to the more critical tolerances.
Having said that, a final visual segment is pilot controlled. Mostly I have found that, if there is a difference, it will bring me high on PAPIs not low. Diving at the rwy from 200' when in trim on G/S does not seem the best idea. Does anyone have experience of the ILS G/S bringing you low on PAPIs? And if so is it worse than 3 reds? I know there are wavy G/S's, but these do not count. This is where the is quite a difference passing 500', but they recover to be the same at DA.
Does anyone have experience of the ILS G/S bringing you low on PAPIs? And if so is it worse than 3 reds?
Practically speaking, the PAPI visuals are so nebulous that only in the last couple of hundred feet can we notice a low PAPI indication, and that is with a ILS TCH of 50ft and a PAPI MEHt of 70-odd feet.
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if you are on a Cat 2/3 approved rwy for autolands the a/c will follow the ILS G/S to touchdown; so why not do the same on a visual day and manual landing if there is a difference between it and PAPI.
In the old days of VASIS 2 & 3 bar we flew 2 red 1 white on 3 bar systems in a medium a/c. I always wondered why not the same on PAPI; 3 red 1 white.
VASI was a multiple plane system and each unit was set to say 3 degrees. What you did with VASI was to put yourself above a 3 degree slope towards the near unit (white) and below a 3 degree slope to the far unit (red) thus you made an approach between the two 3 degree sloped planes indicated by the units.
When flying a large aircraft, you placed your eyes between the 3 degree planes of the two furthest units (ignored the nearest one) and thereby increased your threshold crossing height but also moved your visual aiming point further down the runway.
This touchdown point is not published, but by nature if it is safe for a BIG a/c it is safe for a smaller one.
The ILS GS and PAPI should always tell you the same (when flying above the certified minima for the ILS GS) ICAO Annex 14 makes provision for widening the PAPI on-slope indications to allow for differences in PAPI and ILS GS set-up.
The problem with using the GS below 200ft in a CAT 1 system is that the GS may not always be at 3 degrees and there can be reflections etc etc
However, the PAPI guarantees you obstacle protection until you cross the threshold.
Simce EBCI was used as an example earlier, have a look at the AIP charts. You can see that the touchdown markings are more than 300m beyond the threshold and this will give a high threshold crossing height for small aircraft. You can also see from the chart where the PAPI and GS antenna are located.
Regards,
DFC
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duck down
So is there an article in the Annex that specifically states not to fly below glide slope in a turbojet a/c, otherwise you are in violation. This to avoid the dive and duck down when breaking out and going below the GS, and if so which one is it. Similar to the FAR's ?
Tx
Tx
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In my neck of the woods both the G/S and papi are the nominal 3deg slope however the G/P will be set at 1,000' (+/- maybe 50') and the papi 1400' (also +/- 50' give or take), the papi being set for heavy aircraft.
Flying the 73NG Boeing only privide tech info for a 1000' aim point (ie the G/S) being a narrowbody medium aircraft.
IF, and only IF, you accept that a medium aircraft with tech figures only for a 1000' aim point should always use a 1000' aim point (you really want to run off the end of a runway because you used a non standard boeing aiming point with no available data for such an aiming point?? As an expat that will probably see you go straight to gaol, lets discuss it all at a FAR later date!) you follow the G/P to the deck or you understand, and adapt, the papi to what YOU require in your narrow body aircraft.
Generally G/S and papi will be same to 200', below 200' you 'slide' onto 3 red/1 white and at around 100' you'll be 4 red; total vindication will be when you hear the "50" call as you pass the threshold.
Well done, come back and play again tomorrow!
Cheers
galdian
Flying the 73NG Boeing only privide tech info for a 1000' aim point (ie the G/S) being a narrowbody medium aircraft.
IF, and only IF, you accept that a medium aircraft with tech figures only for a 1000' aim point should always use a 1000' aim point (you really want to run off the end of a runway because you used a non standard boeing aiming point with no available data for such an aiming point?? As an expat that will probably see you go straight to gaol, lets discuss it all at a FAR later date!) you follow the G/P to the deck or you understand, and adapt, the papi to what YOU require in your narrow body aircraft.
Generally G/S and papi will be same to 200', below 200' you 'slide' onto 3 red/1 white and at around 100' you'll be 4 red; total vindication will be when you hear the "50" call as you pass the threshold.
Well done, come back and play again tomorrow!
Cheers
galdian
DFC,
That's not the case here. Runway markings are in standard positions on all runways ie 150m, 300m and 450m, regardless of the PAPI location. The MEHT (min eye height over threshold) for all PAPIs in Oz is published on the Jepp aerodrome chart in the lighting section. Some are as high as 72ft. They are not located relative to the runway markings but rather to achieve a particular MEHT.
Galdian,
Fair enough when the GS is available. On those runways where the PAPI GPI is 1300ft or so and the GS is off, you will find that you have at least one thousand metres of extra bitumen over the requirements upon which to land your -800 because the runway/PAPI, as you point out, is set up for big jets. Besides, if you don't follow the PAPI to the 1300' point, how are you going to stabilise your approach slope? VNAV in my machine is very good but not that good. Following the PAPI down until a couple of hundred feet and then stuffing the nose down to land on the 300m markers is not conducive to a good or safe landing.
The touchdown point is certainly published. It is very obvious and is very well marked on the runway. The PAPI are required to take you towards the touchdown point.
Galdian,
IF, and only IF, you accept that a medium aircraft with tech figures only for a 1000' aim point should always use a 1000' aim point (you really want to run off the end of a runway because you used a non standard boeing aiming point with no available data for such an aiming point?? As an expat that will probably see you go straight to gaol, lets discuss it all at a FAR later date!) you follow the G/P to the deck or you understand, and adapt, the papi to what YOU require in your narrow body aircraft.
