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Approach On Papi

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Approach On Papi

Old 22nd Jun 2007, 16:41
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Approach On Papi

(in Supplementary Technique)

APPROACH ON PAPI

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

===> Can anyone explain this in easy words ?
Thank you in advance....
Airbus340.SR is offline  
Old 22nd Jun 2007, 16:50
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Ah! An easy one!

25+20=45

If MEHT for given PAPIS is <45 and you follow them.......got it?

In any case PAPIS should always be 'ignored' below 200' when you should be aiming at a favourite spot on terra firma.
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Old 23rd Jun 2007, 02:25
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The basic location of PAPI provides approximately 50ft threshold crossing height (wheel height); this depends on aircraft type. For those aircraft with larger than average wheel to eye height a second set of PAPIs may be provided for a particular runway (located further down the runway)
I recall the Airbus statement re A340, but do not have the reference to hand. From memory the wording was such that when approaching an airport without a second set of ‘long body’ PAPIs, then the standard PAPIs should be ignored at low altitude.


BOAC
In any case PAPIs should always be 'ignored' below 200' when you should be aiming at a favourite spot on terra firma.
Are you getting mixed up with the old VASIS which were unreliable below 200ft - red/white=pink?
PAPIs are precision devices which project a very accurate beam (sharp transition) between red and white. For most aircraft they are usable to the lowest altitude that you wish, although a visual landing requires the appropriate concentration on the runway as altitude reduces. It may also be impracticable to see the PAPI as they move to the edge of the visual scan, but they might provide a peripheral cue of wind-shear or landing short.
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Old 23rd Jun 2007, 08:01
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PEI - I appreciate your point, but for me at <200' it is where I am going to 'crash land' rather than the PAPIs that I use, and one should be able to sense path deviation from runway clues at that stage? Agreed thay will be part of the 'peripheral' picture but not the driving guide.
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Old 24th Jun 2007, 12:08
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It's Strange, but...

Back over 40 years ago, when the USAF did studies on crashes during low visibility approaches, they concluded that the most critical time was when the pilot(s) transitioned from instrument flying to completing the landing visually.

For example...a standard "200 and a half approach"... You get down there on the glide path, and right at minimums, you see what you need to see to land...and with the low viz, droplets on the windscreen, etc... you crash.

Hence, the invention of the VASI.

These days, there are a number of company SOPs out there that discourage dependence on the VASI or PAPI when you're 'at crunch time'... (Couldn't resist the pun!)

This, coupled with the limitations of the VASI (e.g. does not guarantee terrain clearance beyond 4 nm, etc.) makes me wonder what good these things are anyway.

Many glide slopes (CAT I) do not give good guidance as you get closer to the touchdown...some have signal flare, etc.

Personally, I use the visual aids down low...coupled with the G/S information.... to give me a good 'gut feel' of where I should be. I do not depend on visual aids too far from the runway for reasons stated above.

In reality, there should not be a BIG difference between the electronic glide slope and the visual indicator. If there is, it should be reported.

PantLoad
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Old 24th Jun 2007, 14:12
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I always thought there should be no difference...
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Old 24th Jun 2007, 14:35
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If I become visual at minima on a Cat 1 approach (200 ft), and the PAPIs are not indicating onslope two white/two red, I would be very concerned! In just a few hundred metres visability, the PAPIs may be the only reliable vertical guidance that you have. Pray tell why anyone would ignore them in this case?
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Old 24th Jun 2007, 18:41
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In the Aerad supplement is says to ignore PAPI's below 200ft. If you fly into Heathrow, the PAPI's and glidslope do not match below 200ft on 09L, at least in the aircraft I fly.

As far as I remember without looking it up, the PAPI is not a required light for CAT1 approaches so in theory you don't need it for a CAT 1 approach to minimums. If you do pop out of the cloud to see the PAPI's saying something strange at 200ft, then the visual reference should be enough to land anyway - if its not surely a Go Around is the thing to do. They are good, but not perfect.
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Old 24th Jun 2007, 22:32
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I prefer on a CAT 1 approach (at DA you see two white and two red....) to transition to visual clues and the IVSI to maintain an adequate ROD.

Works everytime for me. Or is that just luck?

L Met
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