PAPI guidance below 300 ft
 

During flight calibration testing of visual approach slope systems, the relevant technical manual used by technical staff when these systems first were introduced, stated that these systems were not intended for use below 200 ft. The reason given was the aircraft should have been stabilised on a visual approach well before reaching 300 feet and that it was not possible to ensure the light signals gave accurate readings below that height. This was due to siting of the light boxes to one side of the runway giving rise to a lateral error.

It is common to see pilots using these systems for guidance well below 200 feet. Not only that, but pilots but still calling if the signals show below or above on slope when below 200 ft resulting in superfluous "support" calls that are both annoying and distracting.

There must be a cut-off height on short final where visual signals become invalid. Can anyone quote that height from an official document?

Further to that. Most international runways (in Australia, anyway) served by PAPI, have a published mean eye height over the threshold (MEHT) eye height over the threshold for long bodied aircraft types. Typically 74 feet. This invariably means a smaller type (737, A320 et al) using the ILS electronic glide slope indication will see three or sometimes four reds on a PAPI that is calibrated for long body types (B777 and similar length). If a smaller type is now using PAPI guidance solely, (ILS inoperative or not installed) does this mean that using the normal two reds and two whites will of necessity place that type higher over the threshold than desirable?

If that statement is true, then what combination of red/white visual signals should be tracked in order to produce the normal 50 feet wheel height over the threshold for (say) 737/A320 types. Appreciate quotes from relevant official documents.

superfluous

I like the idea that there is a great deal of information coming out of the PNF.

Certainly things like: you are ugly and you smell funny is truly in the world of superfluous, but high or low, fast or slow ain't too bad.

Don't confuse PAPI with VASI

I cannot produce direct quotes from any documents, but I have read that PAPI was produced for low vis ops. My last employer discouraged its use below 3-400 feet saying aiming point was the way to go, however when I was employed in the UK we used it and I continued to do so with anything else that was available.

Yes if you consider touching down a little longer is not desirable, which would be the case on a short runway but not necessarily so on a long one.

Look into MEHT ie on a 767 with a MEHT of 53ft you would expect accurate signals all the way down however if the MEHT is something like 73ft you would expect the PAPI to give three red in the last 200-300ft as you drive to your aiming point

A37575

The closest I can cite is what is contained in ICAO Aerodrome Standards:

5.3.5.37 The angle of elevation settings of the light units in a PAPI wing bar shall be such that, during an approach, the pilot of an aeroplane observing a signal of one white and three reds will clear all objects in the approach area by a safe margin.

The only time a PAPI will have an MEHT of over 50ft will be on a runway that is served by long-bodies, which in turn means the runway itself is quite long. A smaller type will obviously cross the fence at greater than 50ft but will have more than ample runway to pull up on because the runway can take long-bodies.

The design guidance can be helpful for the discussion...
http://i62.tinypic.com/2djyq79.jpg

This discussion was thrashed to death a couple of years ago. The general consensus is that at 200' on a stable approach on glide path you should be concentrating on the touchdown point not some fairy lights.

True, but you need to be mindful of runways that are shortened for works but still have the 74' MEHT.

Thanks for the instructive replies. :ok:

RAT is right!

PAPI Origins
 

You might be interested to know how PAPIs became a replacement for VASIs.

In the mid 1970s PAPIs were used as a visual aid for use by (principally) aeroplanes and a helicopter (HS748, BAC 1-11 and Wessex 2) operated by the Blind Landing Experimental Unit (BLEU) at RAE Bedford to assist pilots flying normal (3 degree), steep and two-segment approaches. Thanks to an initiative shown by the two airfield lighting boffins, JJ and TS, ICAO agreed that PAPIs might be employed as an alternative to VASIs on civilian aerodromes.

As one of the BLEU pilots (the clue is in my PPrune name), I used them on many occasions, with a chap on the ground adjusting them to a range of different approach slopes in the time it took us to fly a circuit. One trial we conducted on a clear day with our flight being monitored by highly accurate kine-theodolites involved each of three pilots flying three approaches to Bedford's long runway: one with PAPIs, one with VASIs and one with no visual light aids. The most accurate approach was that flown using PAPIs and the next most accurate was that using neither PAPIs nor VASIs. With VASIs it was all too possible to 'bounce' in and out of the relatively wide approach slope corridor.

We also conducted trials of the first (and only) British-designed GPWS, and when demonstrating its operation at Bedford, i.e. diving towards the runway, on a day when the visibility was not especially good, I used guidance from PAPIs to help me demonstrate to the aviation Press standing behind me how the GPWS functioned 'in a timely manner' whilst ensuring that we remained over the aerodrome. Interestingly, the Press were more fascinated by the PAPIs than by the GPWS!

Although ordinarily you would not expect to expect to use PAPIs below 200ft above touchdown elevation since by that time on a manually-flown approach you should have acquired sufficient visual cues to have confidence that you could follow-through to a safe touch-down, we noticed - as you might expect - that they still provided a measure of guidance below that height. This, however, was not and should not be relied upon as primary guidance for reasons already stated by other respondents.

After leaving Bedford I enjoyed (!) a spell in the MOD where, when a general question was asked if anyone had any ideas as to how finance that had been arranged for the introduction of Tornado but not spent due to delays might be used, I proposed and had accepted a suggestion that industry might be persuaded to invest in produced a few sets of PAPIs for use at Northolt, to facilitate accurate approaches over built-up areas, and at a Lightning station to reduce the risk of tail-strikes, again by helping to promote stable approaches.

After that, the idea caught on and now PAPIs are used across the globe. Incidentally, our proposal was that a set should comprise eight boxes with four on either side of the runway co-located with the glide slope origin. If you've flown an approach with this arrangement you will have observed that the gap between each group of four helps define that origin, and of course for the occupant of the right-hand seat the right-hand group is more in line with his/her view of the runway.

And this all began 40 years ago!

OTHERS REFERENCES
 

Once on a PAPI, TWO REDS/TWO WHITES then below 2-300 feet its more important to keep a constant VERTICAL SPEED, typically around 700 fpm coupled with the aiming point AT A CONSTANT POSITION ON YOUR VIEW OUT THE WINDOW rather than chasing the PAPI.This is my instructional method, has worked fine over the last 26 years.

PAPI considered not useable below 200ft

Yet I heard of one 'superior' operator who taught base training so as to maintain PAPI to 100'. Dubious technique?

DUBIOUS
 

Following a PAPI below 300 feet from the threshold elevation may or may not be dubious to some, however the really important information to the pilot is the IVSI rate of descent which can vary depending upon actual groundspeed on the day but is TYPICALLY about 700 fpm for most jets.If this is monitored and adhered to it is very likely that you will arrive just above the correct touchdown point in the "zone" so to speak and what happens next is dependent upon your flare technique, another issue altogether.Chasing the PAPI below 2-300 agl is not a good idea in most cases.I have conducted 100s of hours of base training in the real jet airplane and this mirrors what we have previously practiced in the SIM and it seems to work quite nicely in general..........

Because PAPI is a system with a focused, projected, and ‘sharp transition’ beam, the limitations of its use depend more on the airfield installation, aircraft type, and its purpose.
Theoretically it can be used as low as it is possible to see the lights, depending on weather and task. Thus for a visual / night approach in a helicopter, PAPI could provide guidance all the way down to the pad (the PAPI boxes could be laterally angled towards the centreline).
In practical terms the height bands defined by the vertical angular difference in the colour changeover, which change with altitude – tightening as altitude reduces, dictate usability together with the aircraft speed and control response.

Airfield (runway) use depends to some extent on the range of tasks.
The discussion of MEHT relates to the centre of the beam, but might overlook a small range in height depending on the angular difference in the point of colour changeover. Adjusting these settings (within limits) could provide acceptable accuracy for a greater range of aircraft types. There is of course a point where larger aircraft would not meet the safety requirements and an alternative PAPI set would be required.
There is also some variability in an installation’s lateral displacement, angular setting, and a particular design's angular beam spread.

These aspects focus predominantly on the safety clearances at the threshold, but in low vis the system is used more a (spot) check of the primary guidance, opposed to a full guidance system. These checks (a quick glance) can be as low as it is practical to take time to look and the range of visibilities, e.g. one or two spot checks after Cat 2 visual contact.
For non-precision low vis approaches, the PAPI could become the primary guidance system after visual contact, and the system could again be used as low as practical. However, there should be a gradual transition from using PAPI for guidance to that of a spot check of the final visual approach and landing.

Changing the glideslope angle also affects the range of height between colour changeovers, thus a steep approach using standard changeover settings might initially appear easier to fly, but at lower altitudes it provides more viable – flyable guidance.

PAPI provides a highly accurate beam defining the glidepath, with low ambiguity in deviation relative to the beam centre than the older systems (VASI). It is important to consider how the system should be used, in what situations, and aircraft type. It is not necessary to have a hard cut-off / min-use height, but crews should have knowledge of how the system works and the difference between a guidance system and an aid to check / monitor the late stages of the approach.

JESUS
 

Holy moly, that is a long winded way of saying...........actually im not sure what your point is.Whats wrong with looking out of the window at your AIMING POINT and keeping it in the same position in the window view coupled with the odd look inside to check AIRSPEED and SINK RATE?........whatever happened to basic flying skills.....JESUS

PAPIs
 

There are some good replies here. Below your DA/MDA the approach should be visual using the correct RoD and visual aspect of the runway, not using the PAPIs.

Because of the way the PAPIs are set up a pilot who flies the PAPI to touch down will end up with a flat long approach from DA with power on to hold the speed. All of which will make for a long landing with too much power.

It is perfectly normal and correct for smaller commuter aircraft to be in 3 reds and one white below DA/MDA on a correct visual approach. It can be seen from the helpful diagram posted above that it is perfectly safe and clear of obstacles. There used to be very helpful diagrams in an older version of the UK CAP168 which are unfortunately not there in the current edition.

Some charts publish LDA for a particular runway and with very good reason also state a reduced LDA if landing beyond the PAPI.

In short I agree with the advice above.

Next thing will be to follow the glide slope till touchdown. I agree with Piratepete here.

When I did base training on B732 it was a company or UKCAA requirement to achieve an acceptable approach and landing with VASI off. The technique was similar to that taught at flying school. Now there's a coincidence????
Later I flew the line and indeed there were some minor Greek islands where there were no lights, and even if there were VASI's the sun obliterated them anyway.
Later I flew for an operator that forbid approaches with no glide slope guidance. This became a problem to an airport with an NPA and PAPI's on maintenance. Then it became a captain's day only landing with full VNAV FMC guidance. It was still the case night landings with no glide slope guidance we're forbidden.
If the company considers its pilots to be so incompetent and incapable I wonder what other skills are lacking.
How can this most basic of manoeuvres be considered so difficult? All this talk of PAPI's below 300' etc. You shouldn't need the things below 500' on a visual approach if you're capable. OK if you pop out from an NPA at 600' it is comforting to have PAPI's; even more if they are 2W2R. I get students wanting to G/A with 3 reds at 200'. Guess what; as you go around they become 2W2R for a split second, but then it's too late.

I agree. My company's guidance and the one we trainers push is ignore PAPI and/or ILS G/S below 200ft. The landing is a visual manoeuvre based on runway aspect. Besides, at major airports frequented by heavies the PAPI are set for the greater eye-height so in a 737/320 you will see 3 reds anyway below 300ft when on the correct flight path to the TDZ aiming point. Furthermore chasing the fairy lights below 200ft risks de-stabilising the approach and increases the chance of a firm arrival or a long landing beyond the TDZ. The latter is undesirable on a short runway with obvious risks. Piratepete talks of maintaining v/s of 700ft/min. That is incidental and we certainly do not tell trainees to chase the v/s. Just look at the TDZ aiming point, keep it 1/3rd of the way up the windscreen, be at the right attitude and speed and you will be on a 3 degree slope. In my aircraft (320 series) when the FDs are deselected the FPV serves as an accurate flight path indicator and it's use is strongly pushed. As far as the ILS G/S is concerned, if it's not a CAT3 installation with the LVO protections in place you should not be referring to it below CAT1 DA.

For the airbuses it's a clear cut deal as per FCOM:
Do not follow PAPI or TVASI guidance below 200 ft if the published MEHT is
below the recommended PAPI or TVASI MEHT. Then there's table
A332 - 52 ft
A333 and A343 - MEHT 51 ft
A 345 - 55 ft
A346 - 53 ft.

Agree with the old and proven strategy, simply look outta window and fly. :ok:

It's a very interesting discussion, and leads to a broader one, about the meaning of stabilised approaches.
Wingswinger, above, mentions de-stabilising the approach by chasing the lights or the v/s in the late stage. Newer pilots will probably only know about "stabilisation criteria" being a set of numbers and conditions which are to be met, and maintained.
20 years ago an approach which was steadily and consistently 30 feet low, would not have been seen as unstable (although during base training on the 732, I was criticised for allowing 3 reds at <200 to become 4 reds at<100. Well if you maintain the correct approach angle that is what will happen. I didn't argue).
From 300 feet, even with 3 reds, you are going to hit the tarmac. 30 feet vertical error is about 700 feet of runway.
From the trainer's perspective, or even the normal line captain who has to sign in what's left of the aircraft, I'd much rather see no correction to a slightly low late final than yank-and-float. 4 whites might be a different matter, but it's too late to save it with a stuka dive by then.
Local effects also come into play, eg at Corfu, where a 3.5 slope on the NPA meets 3.1 PAPI. And less objectively at a runway where you "know" that the house thermal over the car park will punt you 50 feet up.
That, I suppose, is when you have to do some of that old fashioned "pilot s**t".

I also find that pilots who pay too much attention to VSI displays, fairy lights and attitude displays at low level do not pay enough attention to what their backside is telling them. You correct for x-winds by instinct and feel, often making the correction before the effect has taken effect: if you know what I mean. The same is true for the vertical bumps & humps that mother nature puts in our paths.
Glad the hear someone talk of 'house thermals'. I briefed an arrival, with ILS, on a hot hot day into a dusty area, reasonable headwind, with slightly rising ground inside the OM. I suggested the PF take gear a little earlier to avoid the a/c accelerating as he pushed down to maintain the glide slope with the balloting a/c. The ah ha moment was a joy as he told the story of exactly this happening the week before when taking gear at the usual close in point aiming for a 500 stable point. The bucking bronco was a handful. Much cursing & swearing. It was only JUST achieved with frisky neck hairs.
The house thermals this week over Montmin & Annecy were a joy: if you know what I mean.

I always found the motorway on final to CIA 15 a particular joy in August for the same reason. Massive lift, power off, nose down, then at around 100ft the lift fairies occasionally just disappear requiring a handful of power and a firm yank. Keeps you on your toes :eek:

Indeed, especially as the PAPI's bring you over the threshold at 80'. It's bizarre; on glide all the way down; looking good, and the last 300' go haywire as you see the touchdown point migrate too far into the RWY. This really is one where you need to keep the crash point fixed in the screen.

RE-INVENTION
 

Not because im any sort of expert but because in xxxxxxxxxx im required to train very low hours young pilots to heavy jet type rating first in the SIM followed by base training PPCs (yes a full PPC in a real a/c to obtain the initial type rating) ive had to re-invent myself as an instructor and first deconstruct in my head how to fly visual one engine and two circuits, touch and goes, and go-arounds etc IN AN EFFECTIVE MANNER.Focusing on a steady V/S coupled with keeping the aim point in the correct position works very well for landings in the SIM but things are much harder in the real world with all the thermals, wind effects etc.Bottom line- keep it simple, and dont over-analyse. Its a visual exercise FFS.

Improper Use of Aids?
 

What am I missing? I've read the inquiry several times and it simply does not compute. Here's why: For non-ILS approaches, the properly aligned PAPI is a great aid. However, it seems to me that at levels as low as 200' agl, the pilot should be looking at the rwy, not the PAPI. If, by the time s/he reaches about 200' - 300' agl, but cannot clearly see the rwy, the Go Around procedure should already be in process. I do not know the lowest effective height agl for PAPI, but by 200' the touchdown spot should be the only focal point or, again, the Go Around already in progress.
Go, what am I missing? A lower agl threshold certainly may be appropriate for a low/slow airplane like a C172, with a landing/stall speed of well <<100Kts. But, for a large transport, landing and well >>100kts, it is simply too late for the PAPI to be on any real value. Straighten me out guys! Thanks.:confused:

NFZ: You are straight. Stay cool.

re: What am I missing?
 

I certainly agree that not only below 200ft, but by the time you pass MDA/DA/DH you should be visual and looking for the runway (with approach lights in view) or looking at the runway itself, ideally the actual touchdown zone. If the touchdown zone is in view, the PAPI will be too, since it is longitudinally abeam the touchdown zone. The PAPI should be good reference while visual in extremely windy and limited visibility conditions. It was put there for a reason and designed for this very purpose.

We assume that trained and qualified pilots, ATPs especially, should be able to visually assess the aircraft's position for landing and complete the visual segment to a safe touchdown - or go around. Something in this particular approach event defeated that and the airplane touched down short of the runway.

Without placing blame on anyone, what is it in our system that we see such events? Was the airplane suitably stabilized on the approach? Was there sufficient visibility to conduct the localizer only approach and landing? Was something missing or optically illusional in the visual cues? Is more training and proficiency needed to actually fly the visual segment, and make the correct decision about landing or go-around?

If we cannot count on pilots to skillfully perform the visual segment - visually - then the safety basis for all but Cat III instrument approaches is faulty.

Got cleared for a visual approach in really bright sunlight and flew a curved constant aspect approach rolling out onto final at about 800' AGL with the aiming point in the right place and stable, on speed, very pleased with myself, and got a very agitated pilot in the other seat tell me I was high when the four whites became just about visible at about 400' (you couldn't see the lights before that because of the sun). They fairly quickly went one white, three reds, two reds two whites, one white three reds and then we landed in the right place at the right speed. I often fly with a logger and we analysed the points afterwards and I had flown a reasonably accurate 3.5 degree glide path with no change in power setting at all from 3500' until I closed the throttles at about 40'. My aeroplane will comfortably fly an approach up to about a 4 degree glide and there are procedures which allow an approach path up to 4.5 degrees. In my opinion, picking up and adjusting to the lights at approximately 400 feet would have destabilised the approach or at least risked that but flying a clearly stable visual approach (exactly as if there were no lights at all or they were out of service) was fine. To answer the original posters question, surely you can't simply fly three whites and a red or three reds and a white to fly a three degree approach in an aircraft thats got a different eye height to what the lights are set for. If you fly 2R2W you are on the path the lights are set for and if the eye height is different you will touch down deep or short (probably deep as they should be set for the largest type). If you fly a different combination, youre on a different path. Isnt it as simple as that?

No, because regardless of what light combination you use/fly, your eyes will always hit the ground in exactly the same place: abeam the PAPI boxes. Flying 3 whites will result in exactly the same touchdown point (length of aeroplane/deck angle/cockpit-wheel height difference notwithstanding) as flying 3 reds. 3 whites is higher than 3°, 3 reds is lower, but you will always end up at the same place on the runway.

Just fly 2w/2r. If you are in a long-body, the PAPI MEHT will/should be set further in so you don't tocuhdown short. If you're in a little tiddler (737, 320) then you will touch down longer than normal (if you haven't changed the aim point to the 300m markers) but who cares, the runway will be more than long enough, unless Aeroscat is doing WIP on the far end! :)

Yes. That's why I said "surely you can't"......
And the point is if you can't see the lights you fly an approach based on experience. If you see PAPIs at 400 feet that don't agree, who cares! If the approach is right, carry on. I wouldn't change an approach path on breakout at 200 or 100 based on the PAPIs following a perfectly stable approach. I'd keep the descent rate the same, the aiming point steady in the windscreen, and mentally revise what I'm going to do if I baulk. Sod the PAPIs! Irrelevant at that point.

Bit of a bugger if the PAPIs are correct and you're suffering from some kind of black hole illusion or similar.

Fairly unusual to get a black hole illusion when flying a visual approach in extremely bright sunshine which is what caused the PAPIs to be invisible..

Just to be clear, what do you do when you break out at 200 feet from an ILS and see three reds or three whites? Keep the stable approach going or fanny about with pitch and power to get 2 reds and 2 whites? PAPIs becoming observable late on a visual approach is the same. Do you divert if they are unservicable?

I care. If I pop out off an NPA at 400ft 4 reds or whites, a go-around it is. You'd be an idiot to try to salvage a landing from and obviously unstable approach, in the true sense of the word. ILS...different story. See next:

Hang on. The only approach you'd be breaking out at "200 or 100" would be an ILS. Continue to use the GS. Unless the MEHT matches the TCH, then the PAPI will be "off".

If you've done a hero visual approach and suddenly find you have 4 whites or reds above 200ft then continue for landing at your peril. The PAPIs are installed for a reason.

As for diverting, here, we are permitted to operate without slope guidance for only 7 days. And in that 7 days, you must be qualified for no-slope landings.

Er....

What's different there from what I originally said?

Your mindset of someone needing to be a hero to fly a visual approach is exactly what's wrong with today's fly by numbers magenta line environment.

It's not heroic of a pilot to make a visual approach. It's utterly dismal if they can't! Are you telling me that you can't accurately land your aircraft visually without glide slope information? Astonishing...