PAPI/ VASI question

[Triguy7]

To what level (altitude) on approach to a runway are the PAPI or VASI useable? Will they show proper glide path at 50 feet? 30 feet?

Thank you in advance.

[esreverlluf]

Our (company specific) books say VASI should not be used below 300'. PAPI, on the other hand, becomes more accurate as you get closer to it. Be aware though, that the PAPI installation (distance from approach end of runway) may not be appropriate to your aircraft type.

In any case, for the last few hundred feet I would suggest you should be focussing on the aiming point anyway.

[TCAS FAN]

Why the question? You would have a serious problem if you are still looking at the VASI/PAPI rather than concentrating on flaring.

[B737900er]

I was told from a TRE that PAPI are only good to 200' because after that your meant to fly visually. There is also the dilemma of the PAPI's being positioned to cater fro larger aircraft.

[Pull what]

European Regulations

AMC1 to IR-OPS CAT.OP.MPA.305(e) and Appendix 1 to EU-OPS 1.430 define the required visual references for continuion of a precision approach or a non-precision approach as follows:

[B]Non-Precision Approach A pilot may not continue an approach below MDA/H unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:[/B]
(i) Elements of the approach light system;
(ii) The threshold;
(iii) The threshold markings;
(iv) The threshold lights;
(v) The threshold identification lights;
(vi) The visual glide slope indicator;
(vii) The touchdown zone or touchdown zone markings;
(viii) The touchdown zone lights;
(ix) Runway edge lights; or
(x) Other visual references accepted by the Authority.


Precision Approach A pilot may not continue an approach below the Category I decision height ... unless at least one of the following visual references for the intended runway is distinctly visible and identifiable to the pilot:
(i) Elements of the approach light system;
(ii) The threshold;
(iii) The threshold markings;
(iv) The threshold lights;
(v) The threshold identification lights;
(vi) The visual glide slope indicator;
(vii) The touchdown zone or touchdown zone markings;
(viii) The touchdown zone lights; or
(ix) Runway edge lights.

Visual Glide Slope Information plays no part in Category II,Category IIIA or
Category IIIB Operations

[B737900er]

Pull_what - thanks for the reference but all that states is that its part of the visual requirements, it does not state it must be followed or its 'usable height'.

[Capot]

PAPI indicates to the pilot's eye whether or not he/she is positioned above, on or below the glidepath angle to which the PAPI is set. That glidepath meets the ground on a line on which the PAPI are positioned and perpendicular to the runway CL, so in theory you could follow the PAPI guidance down to that point; in practice the increasing angle between the CL and a line to the PAPI from the pilot's eye makes that pretty much impossible.

VASI, with its 2 or 3 rows of lights obviously deteriorates in accuracy as the aircraft gets nearer, and in the final stages must eventually give a "wrong" indication.

I suspect that neither system publishes a minimum height above the TDZ, because many other over-riding restriction/regulations/needs come into effect in the final stages of an approach. I don't recall ever seeing such a limit published.

Personally, I would have said that if, in a hand-flown aircraft, you have visual contact at, say, 300 feet (necessarily if you are using the PAPI!) and need PAPI guidance to stay on the glideslope below that height, you might want to consider going back to basic training. But that's a personal view, and probably completely out of date, so I'm resigned to outraged instructors/pilots telling me off.

[aterpster]

Capot:

I suspect that neither system publishes a minimum height above the TDZ, because many other over-riding restriction/regulations/needs come into effect in the final stages of an approach. I don't recall ever seeing such a limit published.

The FAA publishes them in its Airport/Facilities Directory.

example:

[chevvron]

I was once asked (as an ATCO) what the difference was between VASIs and PAPIs; the person who asked the question was a PILOT!!

[Capot]

aterpster

Thanks for that, we/I live and learn! To complete the lesson, can you tell us/me what, precisely, the "TCH" number is? Is it really a minimum height below which the PAPI cannot be used?

If I had seen that plate out of the context of this thread, I would have guessed at a horizontal distance related to the TDZ......

[aterpster]

Capot:

Threshold Crossing Height.

[Capot]

Many thanks! But not a minimum height for using the PAPI, then? As I see it the TCH is simply a function of the G/S angle and distance of the PAPI from the THR; useful information, but not published as a limitation on using the PAPI?

Academic, really, if you are still using a PAPI as you cross the threshold at 72', let alone 63', you need advice!

By the way, I did look at the acronym glossary on the FAA website; there are many, but not TCH....

[aterpster]

It's discussed in the Aeronautical Information Manual.

For PAPI and VASI it is referenced to the pilots eyes. For ILS it is referenced to the G/S antenna. For LPV and LNAV/VNAV I presume it is a calculated value.

There is no minimum limit for PAPI or VASI, but I don't believe any transport pilot uses it below 100 to 200 feet.

[Togue]

FCOM PRO-SUP-34 P 14/16 27 NOV 13:

Eye to wheel height on approach is 25 ft. and minimum recommended wheel clearance over the threshold is 20 ft. Do not follow Precision Approach Path Indicator (PAPI) or "T"-Visual Approach Path Indicator (T-VASI) guidance below 200 ft when PAPI or T-VASI Minimum Eye Height over Threshold (MEHT) is less than 45 ft

[Centaurus]

This document is well worth reading and shows how you should not be following a PAPI to touch down or to a designated altitude. Chasing the light beams is like chasing the ILS glide slope close in - not advisable

https://www.tc.gc.ca/eng/civilaviati...2-009-1202.htm