Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

Approach On Papi

Tech Log The very best in practical technical discussion on the web

Approach On Papi

Old 22nd Jun 2007, 16:41
  #1 (permalink)  
Thread Starter
Join Date: Jun 2007
Location: canada
Posts: 2
Approach On Papi

(in Supplementary Technique)


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
  #2 (permalink)  
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,584
Ah! An easy one!


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.
BOAC is offline  
Old 23rd Jun 2007, 02:25
  #3 (permalink)  
Join Date: Mar 2006
Location: England
Posts: 842
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.

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.
PEI_3721 is offline  
Old 23rd Jun 2007, 08:01
  #4 (permalink)  
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,584
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.
BOAC is offline  
Old 24th Jun 2007, 12:08
  #5 (permalink)  
Join Date: Jul 2006
Location: USA
Posts: 447
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 is offline  
Old 24th Jun 2007, 14:12
  #6 (permalink)  
Join Date: Apr 2006
Location: uk
Posts: 759
I always thought there should be no difference...
old,not bold is offline  
Old 24th Jun 2007, 14:35
  #7 (permalink)  
Join Date: May 2002
Location: GC Paradise
Posts: 1,023
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?
FlexibleResponse is offline  
Old 24th Jun 2007, 18:41
  #8 (permalink)  
Join Date: Oct 2002
Location: Heathrow
Posts: 291
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.
Jetstream Rider is offline  
Old 24th Jun 2007, 22:32
  #9 (permalink)  
Join Date: Dec 2006
Location: Glasgow
Posts: 281
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
londonmet is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.