Vasi / Papi

[6 degrees of motion]

Gentlemen, I would like to call upon all experienced pilots to help settle a debate about PAPI and VASI. We are in agreement that at larger airports these facilities are generally tuned for B747 aircraft. What we disagree on is when smaller aircraft are on the approach (ILS autoland or manual on the glideslope) do you see two red and two white ALL the way down (Down to DH). You inputs will be much appreciated as we have exhausted our trigonometrical analysis with no resolution to our debate.

[OzExpat]

Where a PAPI is installed on a runway served by an ILS, ICAO requires the PAPI to be "harmonised" to the ILS GP. That way, everyone should, in theory, see the same two whites and two reds.

[FE Hoppy]

I dont think the picture is the same for all types on the ILS. The pilots eye height is very different in a 747 and an a320. I dont have a copy but ive seen in a US DoD en-route sup pictures of vasi/papi relating to various ac types i.e. 1 red 1 pink 2 white etc.

[Truckmasters]

My understanding is that the VASIS will give you a 3 deg (or whatever it is published as for the particular serodrome) glidepath regardless of whether you fly one dot high or low. All that alters with the VASIS is the actual height above the threshold that you will cross at. ie if flying one dot low in a particular type it will correspond with a touchdown pt of 500 ft in but still on a 3 deg glidepath.

On the otherhand with a PAPI the change in lights provide you with the feedback of the different angle of approach. In all cases with the PAPI however your impact/touchdown point remains the same.

[BOAC]

Where a PAPI is installed on a runway served by an ILS, ICAO requires the PAPI to be "harmonised" to the ILS GP. That way, everyone should, in theory, see the same two whites and two reds. Not quite! As ´FEH´ says, a 747 following NORMAL vasis will be below the calibrated approach due to the fact that where the VASIS are ´seen´(ie the cockpit) is significantly higher that where they are ´seen´ 'n a ´normal´ a/c. Hence the so-called ´long-body´VASIS?

Perhaps Jumbo drivers could help by telling us what they do if landing on ´short-body´ VASIS?

I THINK the VASI/PAPI approach path ´harmonistaion´ is based on wheel height? Anyone know?

[square leg]

Due to both system tolerances and differences in eye-to-wheel height of various types of A/C, deviations from the ideal glide path may occur close to the ground.

When an ILS glide path is available, VASIS/PAPI should be disregarded, since both paths may not be compatible.

Don't use them below 200 ft.

[604guy]

Generally in Canada, as I suspect most jurisdictions, VASIS and PAPI relate to the type of aircraft that the airport is intended to serve. Consequently you may have V1 (2-bar VASIS for aircraft with an EWH of up to 3 metres) V2 (2-bar VASIS for aircraft with an EWH of up to 7.5 metres and V3 (3-bar VASIS with an EWH of up 14 metres). Similarly the same criteria apply to PAPI, P1, P2 and P3. The nice thing about the V3 system is that it can serve a wide variety of aircraft on the same runway. The upwind and the middle bars for aircraft with EWH of up to 14 metres (i.e. B747) and the middle and downwind bars for more “conventional” aircraft. Also when there is both VASIS and a precision guidance system serving the same runway the VASIS are normally turned off in conditions of low ceiling and or low visibility to preclude the possibility of any contradiction.

Not quite answering the original post I realize but offered for what it’s worth.

[Jetstream Rider]

Don't have docs to hand, but if you look in the Europe and Middle East Aerad supplement it has a bit on the different types of VASI/
PAPI in the front. It says all should be ignored below 200ft.

Also on AERAD Aerodrome plates, the little number in brackets next to the PAPI descriptor indicates the Minimum Eye Height above the threshold in feet. This will vary, even at places like LHR on the 4 runways.

:)
JR

[safetypee]

Based on the original equipment build specs and definitions circa 1980s, PAPI is very much superior to the then-days VASI as it is based on a focused / projected light beam. This gives a clean red/white changeover at all heights, eliminating the ‘pink’ VASI. Thus PAPI can be used below 200 ft and due to its higher power is better in poor visibility. More recent installation definitions (the equipment is basically unchanged) use mixed terminology and in some instances we have PAPIVASI or PVASI (Precision VASI). Our OZ friends have ‘T’VASI, which has a completely different ground installation; it is reported as being even better.

The original PAPI design concept assumed that the aircraft ILS Glideslope receiver antenna to pilot eye height was small, circa 5 ft when in the approach configuration / attitude; thus on an instrument approach the ILS glidepath and the visual glide path would be aligned. For small / medium sized aircraft with small pilot eye height to wheel heights (configuration / attitude/ and eye-main wheel longitudinal distance), the wheel clearance at the threshold is acceptable. However, for large / long body aircraft, or aircraft with large wheel / antenna to eye height, the required wheel clearance at the threshold may not be met, thus at some airports there is a second set of PAPIs located further into the runway. Only one set may operate at any time. The larger aircraft use the ‘long’ PAPI, which gives reasonable visual / ILS glidepath correlation and meets the threshold crossing height requirements.

The original concept was for the change in the PAPI lights (2/2 to 3/1) to corresponded with a 1 dot deviation on the ILS glideslope.

PAPI is an angular system (as ILS), thus if the PAPI is flown 1 light high/low the aircraft will still aim at the same visual glideslope origin, only the height over the threshold (or at any range) will change. I understand that some PAPI installations (possibly non instrument runways) have slightly tighter or slacker values between the lights from 2/2 to 3/1 etc. These changes increase / decrease the precision of the system, but due to this, the perceived sensitivity the system makes it more difficult / easier to fly. I also understand that this sensitivity is changed for steep approaches to keep an equivalent sensitivity (height change per lamp) vs range with that value chosen for 3 deg approaches.

[Centaurus]

T-VASIS in Google.
Answers your questions.

http://www.airwaysmuseum.com/T-VASIS%20Pilots%20Notes.htm

[Cap 56]

Don't use them below 200 ft.

I agree fully and that's the way I have been trained.

Some airports have double systems one for the wide body/high cockpit and one for the narrow body.

I am not sure about the correctenes of a technique of just following the Glide Slope once below 200 ft.

It will depend if the G/S is Cat III quality at that moment you use it, because it can have serious bends.

My preferance is to use Flight Path vector and V/S below 200 ft to cross-check what I FEEL and SEE.

Once visual inbound the threshold it's all visual.

[7FF]

6 degrees of motion asked: What we disagree on is when smaller aircraft are on the approach (ILS autoland or manual on the glideslope) do you see two red and two white ALL the way down (Down to DH).

Yes. Providing the ILS GS and the vasis/papi are, as was said earlier harmonised. If they are and they should be, the only thing that changes is the height differences of the aircrafts parts over the threshold.
If the GP/vasi/papi were located 1000' from the threshold on a correct 3* glidepath, a 747-400s main gear will be 30' over the threshold, the ILS GP antenna 53' and the eye height 73' giving a 572' touchdown distance from the threshold.
Which is a bit close so most airports that have 747 movements have 3 sets of vasis and the ILS GP and papis further from the threshold.
If the GP/vasis/papis are not harmonised then get out the graph paper and start plotting. Personally I just aim at the 1500' point marker.

[mcdhu]

Interesting - sort of - that quite a few French airports do not have Papi/Vasi where Ils is installed eg Tls.

mcdhu

[autoflight]

Night LOC/DME approach with definite terrain considerations after passing the minimum altitude. F/O wanted 1200 fpm to follows PAPI false fly down signal. Trouble was, the fog reflected the white lights so much that they disguised the red lights. Lucky there weren't two pilots who believe everything they see. The point is that any time you follow electronic or visual guidance, other parameters must fit the circumstances.

[Hudson]

Main thing to remember is that all VASIS can give erroneous indications under certain weather conditions where dew point and dry bulb are close, low lying mist or light fog just sitting over the runway and finally if there is condensation on the lamps. Under these conditions especially at night with no other visual cues, do not blindly accept what you see. Check the approach angle with ILS if available or suitably sited DME.

A fatal crash at Mount Gambier in Australia where a Kingair crashed 3 miles short and on the extended centre line during the visual segment of a black night VOR approach in misty weather, was thought to be associated with possible erroneous T-VASIS light signals. The T-VASIS at that airport had a long history of reported erroneous indications. It was the first time that the pilot who had over 13,000 hours, had landed at that particular airport at night. The moral of the story is that any VASIS should be treated with great suspicion in moisture laden conditions.