Glideslope versus Papi?? [Archive]

Sir George Cayley

18th Aug 2007, 17:08

Yes, good ol' CAP168. In Chapter 6 Appendix 6 is the set up procs for PAPI. But it stipulates that the origin of the slope for guidance should be co-incident with the G/S origin.

Double But, unless you are flying the exact a/c that the designers had in mind it seems unlikely you'll get an on slope indication.

Treble But, how can a set of lights positioned as required, be suitable when the electromagnetic beam is co-located but the a/c's aerial isn't dangling from the rear view mirror along with the Xmas tree air freshner and the fluffy dice?:hmm:

If during a CAT l App you become visual at 200', transfer to the PAPIs would seem the next step, but if there is no correaltaion to the G/S for non-design a/c then what's the value. If you get 4 reds do you climb? If you get 4 whites do you push?

Come CAA PAPI chappy give us a clue!

Sir George Cayley

TopBunk

18th Aug 2007, 17:35

f during a CAT l App you become visual at 200', transfer to the PAPIs would seem the next step, but if there is no correaltaion to the G/S for non-design a/c then what's the value. If you get 4 reds do you climb? If you get 4 whites do you push?

I disagree, transferring to the PAPI's is not the next step!

A good recommendation is to do nothing - the aircraft was following the loc and g/s so do nothing and give your eyes a chance to take in the picture, maintain the picture.

This 'non-design aircraft' malarky is a red herring and might account for a variation of 5 ft or so difference at touchdown - insignificant.

PAPI's are not designed to gice accurate guidance below 200ft - tha is ahy you have Cat 2/3 operations!

RAT 5

18th Aug 2007, 17:51

I had a discussion with a European National Authority inspector on this issue. His reply- paraphrased - was thus:

"ILS glideslope is primary. It is flight checked regularly to more exacting tolerances than PAPI's. The airlield has some autonomy to positon the PAPI's as seen fit for the majority and/or the most limiting of their traffic; i.e. if there are many widebody movements then the PAPI might be set to give the correct THCH for their wheels. THis will have to take account of pilot eye height. It follows that smaller a/c will, when flying 2W 2R, will touchdown slightly longer but should have no stopping problems as the RWY is long enough for their larger brethren. If a RWY is served by an ILS then the PAPI's should ideally only be switched on if the G/S is U/S."

(It used to be that with 3 bar VASIS a medium jet flew 1W 2R and the big boys flew 2W 1R, if memory serves me correctly). It would be nice to have it published that the PAPI's are set for heavies and so mediums can expect to fly 1W 3 R below 500'. I too considered that PAPI's, as VASIS, are not certified below 200'. Thus I was confused to be told by a base trainer that he wanted 2W 2R down to 50'!
Further, why do some airfileds have PAPI's left & right illuminated at the same time?

OzExpat

19th Aug 2007, 11:48

Further, why do some airfileds have PAPI's left & right illuminated at the same time?
They're called Double PAPI and I feel sure that your company's Route Guide will tell you about such things.

RAT 5

19th Aug 2007, 12:23

Loopdeloop

19th Aug 2007, 13:06

TopBunk - Advice to do nothing is good but non-type/red herring comment is incorrect. I would contend that the eye height between say a CRJ and a 747 is both significant and more than 5 feet.
In fact when converting to the 747, my BTC advised to look for 3 whites one red to maintain the path for most runways.

angelorange

19th Aug 2007, 13:20

PAPIS are flight checked along with all runway lighting every 6 months. This includes alignment c.f. radiating glideslope where applicable. Intensity, transistions and angles are tested. The quality of lighting units, obstacles or even long grass etc can affect results.

Military fields tend to have PAPIS set at 2.5 deg not 3 deg.

RAT 5

19th Aug 2007, 19:34

loopyloo:

Please read previous note. How did your BTC know what touchdown point the PAPI's were set up for? If there is an ILS, then the G/S is primary. If nothing, then Mark 1 eyeball is required. Using either PAPI or G/S Mark 1 eye ball is always the final arbitrater, but the G/S should be accurate. Airmanship at all times.
Flying something so vast as a B747 it would seem a touch presumptious to say 3W 1 R, if on a limiting RWY. Sounds like a guess to me, rather than an exact science.

cossack

19th Aug 2007, 21:13

FWIW in Canada the PAPI will be switched off when the ceiling is below 500ft I assume to avoid this "hunt the correct glideslope syndrome" at low altitude on a poor viz approach. This certainly wasn't the case when I worked in the UK.

relax.jet

19th Aug 2007, 23:07

PAPI should be set for a critical type of the airplane for one particular RWY, that’s why! :ok:

safetypee

20th Aug 2007, 00:49

PAPI is an extremely accurate angular approach path indicator. Where it is installed with a precision electronic GS, PAPI should match that GS or publish a deviation.

A discrepancy between the visual and electronic GS may result from the aircraft eye/GS aerial distance being different to that assumed by the PAPI installation. Allowances for eye/wheel height are made as above, and in extreme circumstances a second ‘long body’ set of PAPIs can be installed further from the threshold for large aircraft e.g 747 – double PAPI. Both sets of PAPI’s should never be displayed at the same time.
An alternative for any discrepancy is that at very low altitude (normally below 100ft) the ILS GS is beginning to flatten out (reducing angle) due to the parabolic effect of the aerial location and transmission method (reflection) – GS above the aircraft, PAPI shows low; or possibly that the aircraft autoland system is raising the nose and flattening the approach angle with respect to the PAPI GS, PAPI shows high.

There is a long standing myth about PAPI accuracy, possibly due to the bad reputation of VASI, which was inaccurate below 200ft, and also that this fact was perpetuated by some PAPI installations being called PAPI/VASIs.
PAPI has been demonstrated in land-based ‘carrier’ type approaches and a wide range of specialist military applications – multiangle, two segment (civil and space shuttle), and autonomous resupply - all high accuracy systems at low altitude.

Normally a PAPI installation will attempt to match a one light change over (RR/WW to RRR/W) to the ILS deviation scale i.e. 1 light per dot. This is not always possible and some installations have a ‘tight’ or ‘slack’ beam where the transition angles are closer or wider than normal. Steep approaches usually have a tighter beam to compensate for the change in GS geometry.

The Canadian action is interesting – is this due to myth, or due to the potential to chase the very accurate beam (or overly ‘tight’ beam) at low altitude?

Only Cat 2 / 3 ILS beams are monitored; some Cat 1 beams are decidedly inaccurate below 200ft.
PAPI should be used with the ILS; the ‘sharp-transition’ light change-over enables any sudden sink to be identified quicker than with ILS – and it’s a head up display!
PAPI can ‘go out of alignment’ due to several reasons, most of which are checked by ATC e.g. first switch-on on a frosty morning, ice or frost may distort the beam, or a unit has been hit by a grass cutter!

OzExpat

21st Aug 2007, 12:26

PAPI can ‘go out of alignment’ due to several reasons, most of which are checked by ATC e.g. first switch-on on a frosty morning, ice or frost may distort the beam, or a unit has been hit by a grass cutter!

Each PAPI light is mounted on a single pole - any one of these poles can sink, or rise, due to earth tremour. A pole can also sink after heavy rain that locally water-logs the soil. I've seen all sorts of problems like that, over the years since PAPI was introduced here.

fireflybob

22nd Aug 2007, 08:51

So if that is true why on earth would folks fly a PAPI showing 3 reds and one white? Wouldn't it mean your aiming point is the same as an on slope indication but you fly a shallower angle to get to it?
Thoughts??

Yes I would agree!

OzExpat

24th Aug 2007, 12:12

Ozexpat: Please expand. No our route guide does not mention them. I'm still curious as to their worth, especially as the ones I've seen are on an ILS RWY, illuminating at the same time as the G/S. Seems like a waste of amps/volts to me.
Sorry that I missed this RAT 5, but the only reasons I've ever heard for having a double PAPI are :-

1. Redundancy; and
2. The previous installation was a T-VASIS.

I favour the redundancy argument, especially at international aerodromes, but this benefit is sometimes negated because both PAPI systems are left on when a faulty one should be turned off. Of course, this makes it a tad difficult for us to figure out which one is giving the right information. :}

safetypee

24th Aug 2007, 20:18

T-VASI has some advantages, see previous thread discussions.
At major commercial airports which operate long body aircraft, the double PAPI installation provides suitable flexibility for a range aircraft types; all in proportion to the runway length etc.
PAPI has an advantage over other systems in that it uses a projected beam of light – a lens / filter system like some old film/slide projectors. This provides a narrower and more powerful beam of light which usually enables an earlier point of contact both in good and poor visibility.

There are many dangers in deliberately flying low (RRR/W). The approach path will be a closer to obstacles or the ground, particularly on short final; the reduced altitude clearance decreases the safety margin in the event of windshear or wake turbulence and will result in a low threshold crossing height with a danger of early touchdown – even in the undershoot. Conversely, flying a shallow slope and then converting to a ‘normal’ threshold crossing height can extend the flare and landing touchdown point with all of the dangers of an overrun particularly on a down-sloping runway where the effects are magnified.

A significant point from the original question is the altitude that any disparity between PAPI and ILS is noticed. In my experience there are few if any mismatches above 100ft; thus a mismatch at 200ft might suggest a PAPI alignment error, an ILS GS transmission error, or that your aircraft has an exceptional eye/ILS aerial height.

oldebloke

25th Aug 2007, 22:54

Canada AIM 7.6.3
Where Vasi is provided on a prec approach it will be turned off,unless requested,when wx below 500',to avoid contradition between the precision approach and Vasis glidepaths:ok:

yyz340c

26th Aug 2007, 20:00

You may find some of the additional detail at this site interesting:

http://www.tc.gc.ca/CivilAviation/publications/tp312/Chapter5/5-3.htm#5.3.6

Pardon me if I missed mention of this in a previous reply, but the PAPI and glideslope indications below 200' will only coincide if the aircraft's glideslope antenna and the pilot's line of sight are also aligned when in the normal approach attitude, and then only if the PAPI and glideslope angles and placement are both exactly the same. Given these variables, it is difficult to provide a generic answer for every glideslope / PAPI / aircraft combination. The technical specifications available at the above website will give you an idea of some of the design and installation criteria, if you have the time and inclination to read through them.

Fly safely ...

stator vane

27th Aug 2007, 13:24

i was undergoing an evaluation into LFMH (EBU) ILS 18--close in final and the checker in the right seat said, "YOU"RE BELOW THE PAPI!!!!" like all were going to die----

i said, "i'm on the glideslope."

"YOU'RE BELOW THE PAPI!!!!!" even closer to death!!!!

"i'm following the glideslope!" at that point thinking......(can't put it here)---

"YOU'RE BELOW THE PAPI!!!!!" sounding as if his life was passing before him

we somehow made it without any grass stains on the tyres---

so it all depends on what the checker thinks on the day!!

his evaluation of my flying was below par--

safetypee

27th Aug 2007, 18:19

yyz340c re: eye / GS aerial height. I recall that there are design recommendations which indicate acceptable values for aircraft installations, thus limiting the extent of this error – possible the value was 5 ft in the approach configuration and at the approach speed.

PAPI has a relatively narrow beam as shown in the Canadian diagram; if you wish you can calculate the height difference between the WW/RR changeover points (angular difference and slant range), thus bound the aircraft altitude where the PAPI and GS should (could) agree. However, the most significant difference is that PAPI quickly ‘switches’ between W/R due to its design characteristic (sharp transition), whereas VASI suffers from a large ambiguous zone of ‘pink’; thus the advice to be cautious of VASI.
It is unfortunate that the Canadian section is titled visual approach slope indicator 'VASI' where they are discussing PAPI (APAPI), which is to be their standard.

InSoMnIaC

28th Aug 2007, 21:36

unless low visibility procedures are in progress and the ILS sensitive area is clear How can you be so sure that the GS is all that accurate from 200' to the ground?

if the viz is good use the papi as a guide but don't just blindly follow it or the GS for that matter.

Airportdata

19th Jun 2009, 17:58

PAPI and Localizer Glideslope are not designed to coincide or give the same information. It is rarely possible to compare the visual indication with the Glaidepath when you are established on Glidepath. Even at higher altitudes there are discrepencies. As you descend on the glidepath with the autopilot on you may get a chance to compare the two.

In most cases The PAPI instalation is installed on a Non Precision approach runway for descent information below MDA. In other words it is for a visual approach.

Some airports have PAPI which also coincide with the Precision Runway. This is rare in Canada. You will find PAPI on all Instrument runways in St. John's Itl - CYYT. This is due to moderate to severe turbulence, and windhshear.

The reason they do not comapare is that they are located at a different location. The planned touchdown point is often set up at a different location. They were never intended to be the same.

At lower altitudes the visual (PAPI) and instrument signal (Glidepath) often cross each other.

Check Mags On

19th Jun 2009, 18:54

Aéroport de Nice Cote d'Azur - FAQ, Saleya, PAPI (http://www.niceairport.com/eng/page_faq_papi_quest1.htm)

Nice in south of France is a good example, the Jeppesen plates state the papi is for a cat d aircraft.

Phantom Driver

19th Jun 2009, 19:25

The more enlightened aerodromes put a little note on the Jepps ;words to the effect of -"PAPI indications not useable below 200 feet". Valid on a stabilised approach.

However, on the 744, ground effect at (Cat 1- manual flown) minimums tends to reduce the descent rate and drive you a little high on the slope. Doesn't take much to change from 2W/2Reds to 3W/1Red; not a particular problem, as this is what you expect to see at 50 ft RA as you cross the threshold (on the 74).

Trouble is, pushing the nose down at that height at high landing weights (higher RoD's) to get back on the slope (not!) could possibly generate a "sink rate" warning due to the narrow margins, and (in my outfit at least) a little e-mail from the FDAP monitoring department. On the other hand, watch the PAPI's when the Autoland is at work. Always interesting, because it can be surprising sometimes, depending on individual runway settings, or for whatever other reason. Good old autopilot doesn't care, just sticks to it's job, which is invariably done well and usually far better than Yours Truly.

When manual flying, I like to listen to what the Auto Callout has to say as the threshold passes beneath. "50 feet" suggests all is well.

G-DAVE

20th Jun 2009, 00:09

Follow the ILS or VOR,DME,NDB to MDH (MDA) as applicapple. When visual, use the PAPI's as a guide, but remember back to your first lesson as a pilot. If the 'picture' looks right, then it is right, and land. If not, go around.

No need to discuss various glide angles, PAPI 'eye hieghts', aerodromes set for certain aircraft types etc etc.

We are trained to land our aircraft as hands on, eyes out, capable people.

Fly the aircraft, hands on, eyes out, isn't that whats it's all about?

OPEN DES

20th Jun 2009, 02:37

I just 'eye ball' the last 200ft. I will primarily look at and follow the G/S and also use the PAPi for a 'gross error' check, 3 white or 3 red is fine.

muduckace

20th Jun 2009, 04:43

I am sure there are several similar approaches but Quito is a fine one. The G/S is set at at about 6 deg as you fly down a mountain and the PAPI is to be flown after safe ground clearance is obtained. Have landed here a few times on a G/S approach, the aircraft we were operating were not designed for carrier landings.

muduckace

20th Jun 2009, 04:54

EBCI is probably setup for the millitary fast jets there. It's the same in Eindhoven (EHEH) it's stipulated on the Jeppesens.

Below 200 feet you'll hear people say the PAPI are useless. Only way around it is to fly the aircraft visually and down onto the markers.

I have also experienced a fine example when this mindset failed. I believe the identifier to be MROC (costa rica). The landing pilot was fixed on the threshoald, below G/S. The surrounding terrain gave an impression of the the threshold being lower than it was, the understanding of this was late and the landing pilot flared in an attempt to arrest our rate of decent only to drive the mains harder down, it was the only time I heard 30 call out on the R/A 2 times. The bounce was not all that bad but the landing rattled my fillings as we were in a stall.

20th Jun 2009, 05:46

PAPI and Localizer Glideslope are not designed to coincide or give the same information.

5.3.5.36 When the runway is equipped with an ILS and/or
MLS, the siting and the angle of elevation of the light units
shall be such that the visual approach slope conforms as
closely as possible with the glide path of the ILS and/or the
minimum glide path of the MLS, as appropriate.

This is flight checked, by the way.

In addition, localizers do not have glide slopes. ILS systems do.

In most cases The PAPI instalation is installed on a Non Precision approach runway for descent information below MDA. In other words it is for a visual approach.

5.3.5.1 A visual approach slope indicator system shall be
provided to serve the approach to a runway whether or not the
runway is served by other visual approach aids or by nonvisual
aids, where one or more of the following conditions
exist:
a) the runway is used by turbojet or other aeroplanes with
similar approach guidance requirements;
b) the pilot of any type of aeroplane may have difficulty in
judging the approach due to:
1) inadequate visual guidance such as

...

Capn Bloggs

20th Jun 2009, 13:35

In Oz, most of the PAPIs at the major airports have been set with an eye-height of around 60-70 ft, whereas the ILS has stayed at a Threshold crossing height of 50ft (or thereabouts). The reason I've heard bandied around is to make the PAPI look normal ie 2R/2W when the ILS is flown by a wide/long body (I assume brought about by the intro of the A380). This makes sense, as the eyes in the cockpit and the GS antenna would be more vertically-spaced than for a smaller aircraft.

We brief what we'll see on each approach ie a flyup indication on the PAPI down low (we are required to follow the GS to touchdown if it is available: also stops FOQA events).

displaced gangster

20th Jun 2009, 22:35

At YPPH RW03 the MEHT (pilots eye height) over the threshold is 71ft,the TCH (G/S height) is 50ft.

If the difference between the eyeheight and the G/S aerial on your particular aircraft is 21ft,and assuming a precise coupled approach is flown,both the PAPI and GS indicator will indicate on slope.

I would be interested in seeing the MEHT/GS difference for several Cat C & D aircraft.:eek:

Right Way Up

20th Jun 2009, 23:26

Nice in south of France is a good example, the Jeppesen plates state the papi is for a cat d aircraft.

Leading you to cross the threshold at 100ft if you follow the PAPIs in your average jet.

Its about time that airlines taught visual aiming point as the important criteria below 200 ft as 3 whites/ 1/2 dot high at 200 ft is a small error at this point. I have seen guys completely destabilising approaches at this point for no good reason.

STS-3

21st Jun 2009, 00:59

B717-200-Height difference between Pilot eye height and glide slope antenna is published as 6 ft.

Capn Bloggs

21st Jun 2009, 01:46

Right Way Up,
Leading you to cross the threshold at 100ft if you follow the PAPIs in your average jet.

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?

Bullethead

21st Jun 2009, 04:03

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.

Capn Bloggs

21st Jun 2009, 05:36

B747-400 16 feet
By my calculations, that's equivalent to 93m of horizontal disance at 3°. So for the pilots to see 2W/2R on the PAPI all the way down to the flare if the aircraft was following the ILS GS, the PAPI would have to be located 93m further down the runway than the ILS GS ground antenna.

DFC

21st Jun 2009, 18:02

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

Right Way Up

22nd Jun 2009, 12:31

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.

RAT 5

22nd Jun 2009, 20:29

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.

Capn Bloggs

23rd Jun 2009, 01:35

Does anyone have experience of the ILS G/S bringing you low on PAPIs? And if so is it worse than 3 reds?
It is a shame that other countries do not publish the minimum eye height of the PAPI, for example, Nice. Then you could determine why you cross the threshold at 100ft. In Australia the PAPI angle and the Minimum Eye Height is published, so one can immediately determine whether the PAPI will indicate low if you are on the ILS GS (since the ILS GP generally has a TCH of 50ft, equating to a GPI of 290m along the runway).

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.

DFC

23rd Jun 2009, 09:34

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.

The GS will only be working correctly when the GS sensitive area is clear of aircraft and vehicles. If you have a CAT3 system and want to use the GS below 200ft then you have to ensure that the protections are in place on the ground. Can't put my finger on the piece of paper but we hab a remider about practice autolands some time back that cautioned about doing them without the normal protections in place on the ground.

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.

PAPI system is angular and radiates from a point - just like your ILS. If you fly a constant 3 white and 1 red you are flying a steeper approach angle.

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 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.

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

ericthepilot

2nd Nov 2009, 01:02

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

galdian

2nd Nov 2009, 07:21

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

Capn Bloggs

2nd Nov 2009, 07:41

DFC,
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.
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,
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.

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.