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

4 red but on glide slope

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

4 red but on glide slope

Old 27th Jul 2022, 08:28
  #41 (permalink)  
Thread Starter
 
Join Date: Jan 2018
Location: London
Posts: 85
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Capn Bloggs View Post
I have no doubt, no. And had he been flying down the 2W2R PAPI with the ILS tuned, he would have been outside tolerance above the glideslope below 200ft.

Pilots should not be jumping from one reference to the other below 200ft.
This is exactly why I was trying to get some clarification because I will be flying the same approach probably next week, and I guess Iíll prioritise the PAPIS (itís a long runway anyway) and be above the GS.
PelicanSquawk is offline  
Old 27th Jul 2022, 08:28
  #42 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 8,259
Likes: 0
Received 0 Likes on 0 Posts
4 reds before touchdown on an autoland (at 1min 20sec):

Capn Bloggs is offline  
Old 27th Jul 2022, 08:32
  #43 (permalink)  
Thread Starter
 
Join Date: Jan 2018
Location: London
Posts: 85
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Capn Bloggs View Post
4 reds before touchdown on an autoland (at 1min 20sec):

https://www.youtube.com/watch?v=t3RteTPWaUU
the issue is the 4 reds were probably more around 150ft for meÖ.the ltc in his comments wrote that I was strangely on GS when I got 4 reds. Which is the confusing part I guess, but also the reason he was happy for it to continue.
PelicanSquawk is offline  
Old 27th Jul 2022, 08:37
  #44 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 8,259
Likes: 0
Received 0 Likes on 0 Posts
I’ll prioritise the PAPIS (it’s a long runway anyway) and be above the GS.
Then you'll get a flogging from the FDAP manager for being unstable above the GS! Life's tough, and then there's grumpy captains!!

The main measure of success or otherwise: if you touch down in the touchdown zone with no big pushes or pulls, job done.

Remember, the reason that the PAPI is not at the 300m point with the ILS GS antenna is because the runway is long enough for long-bodies. Landing distance should normally not be an issue even if you flew down the PAPIs instead of the GS.
Capn Bloggs is offline  
Old 27th Jul 2022, 10:04
  #45 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Not commuting home
Age: 44
Posts: 3,966
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by PelicanSquawk View Post
the issue is the 4 reds were probably more around 150ft for meÖ.the ltc in his comments wrote that I was strangely on GS when I got 4 reds. Which is the confusing part I guess, but also the reason he was happy for it to continue.
Yes, I've noticed.

We had been discussing 4 reds being a geometric necessity
- where GS intercet pt. and PAPI have significant lateral shift (150m, more than a 100).
- below roughly 50 feet as the parallel 3 deg path slices through the PAPI segments downwards.

​​​​Whereas your airport has
- distance rom GS to PAPI only 70 meters
- you had 4 reds just below 200 feet, around 1 km to runway still.

That is a profile which needs retraining. Or it does not add up.

The piece where you say it was on GS and with 4 reds does not match the puzzle. On a CAT II instalation even less so.

This needs to happen and will when both of the conditions described above are satisified but neither was by your description.
​​​​​


​​​​​​



​​​​


​​​​​

​​​

Last edited by FlightDetent; 27th Jul 2022 at 12:53.
FlightDetent is offline  
Old 27th Jul 2022, 10:55
  #46 (permalink)  
 
Join Date: May 2022
Location: California
Posts: 5
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Capn Bloggs View Post
You should feel aggrieved. Perhaps you guys operate differently, but there is no way I'd let this slide. If for no other reason, to find out exactly what your training captain wants you to do when you reach the DA (at 200ft). This is precisely the point where most people come unstuck these days, with undershoots and overshoots, early flares, late flares, overcorrecting, floating a big cause of prangs. He is your instructor. He's paid for it. It's his job to know this stuff and as importantly, teach you what you need to know to fly safely from 200ft to touchdown.
It's also his job not to give you contradictory instructions where you will necessarily fail at one or the other.
InnerLoop is offline  
Old 27th Jul 2022, 11:03
  #47 (permalink)  
 
Join Date: Jan 2008
Location: U.K
Posts: 86
Likes: 0
Received 0 Likes on 0 Posts
If I remember right they turn the papi off for CAT3 landings, maybe for this very reason
simmple is offline  
Old 27th Jul 2022, 11:45
  #48 (permalink)  
 
Join Date: Sep 2006
Location: Out of a bag
Posts: 601
Likes: 0
Received 0 Likes on 0 Posts
I donít think anyone has mentioned the disparity you often get between GS angle and PAPI angle. Numerous airfields I fly to have PAPI set to 3 degrees when the GS angle is less than or greater than 3 degrees. You need to brief at what point you will disregard the FD and fly visually with reference to the PAPI, or brief what you will see when sticking to the ILS.
Flying Wild is offline  
Old 27th Jul 2022, 16:57
  #49 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Not commuting home
Age: 44
Posts: 3,966
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by simmple View Post
If I remember right they turn the papi off for CAT3 landings, maybe for this very reason
Surely you don't want to confuse the autoland.
FlightDetent is offline  
Old 27th Jul 2022, 17:19
  #50 (permalink)  
 
Join Date: Jan 2008
Location: U.K
Posts: 86
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by FlightDetent View Post
Surely you don't want to confuse the autoland.
haha.. confused me obviously.
I really canít remember if they were turned off for CAT 2, we had the option of manual landing off them.
Probably donít remember because never looked at them.
Do remember there was a few airfields that if you did fly the papi (accurately) you would set the glide slope warning off.
Yes that contradicts the never looked at them!
We were allowed to fly manually, even approaches, after a few ignored glide slope warnings doing this we were told if doing manual visual approaches press the g/s inhibit button.
simmple is offline  
Old 28th Jul 2022, 04:54
  #51 (permalink)  
 
Join Date: Jul 2007
Location: Perth
Age: 54
Posts: 30
Likes: 0
Received 0 Likes on 0 Posts
CAT2, CAT3 PAPI possibly disconnected.

PAPI location is determined by the eye to wheel height of the largest aircraft regularly using the runway to give 50 ft threshold clearance.
I wish is offline  
Old 28th Jul 2022, 05:15
  #52 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Not commuting home
Age: 44
Posts: 3,966
Likes: 0
Received 0 Likes on 0 Posts
And then they fly the GS for autoland leaving only 29. Oh yes.

​​​​​​Somebody link the VIS/RVR facility degradation table, so we can see the penalties for PAPI inop.

Except, is an aid not a facility.
To be used for the approach not landing.
During visual manouvering, not instrument flight.

======

Where I am now 4 reds on PAPI is a mandatory GA below 1000 ft. If it is there use it, within its applicable scope.

​​​​​​

​​​​
FlightDetent is offline  
Old 28th Jul 2022, 07:29
  #53 (permalink)  
 
Join Date: Jan 2006
Location: Between a rock and a hard place
Posts: 1,174
Likes: 0
Received 0 Likes on 0 Posts
It may be an interesting academic discussion. But in my opinion we are doing ourselves (and the OP) a disservice if we pay this much focus to PAPIs and G/S indications at low altitude.

I have aimed at the zebra stripes on short slippery runways. I have aimed at half way down the runway at AMS where the exits are at the far end. Know your plane, know your surroundings.
172_driver is offline  
Old 28th Jul 2022, 10:07
  #54 (permalink)  
 
Join Date: Jul 2006
Location: Somewhere over the rainbow
Posts: 919
Likes: 0
Received 0 Likes on 0 Posts
Agreed with 172 Driver. For the last few hundreds feet assuming you are visual, outside reference is the primary reference. Below 200 feet, you should focus on the aim marker and not focus on the glide slope or Papi at this point. In fact you should disregard them at this point or you might end over controlling the aircraft.
Mentour explains it pretty well on this video after the 4min mark.
pineteam is offline  
Old 28th Jul 2022, 12:10
  #55 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Not commuting home
Age: 44
Posts: 3,966
Likes: 0
Received 0 Likes on 0 Posts
pineteam There you go, at #36.



FlightDetent is offline  
Old 28th Jul 2022, 12:42
  #56 (permalink)  
Thread Starter
 
Join Date: Jan 2018
Location: London
Posts: 85
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by pineteam View Post
Agreed with 172 Driver. For the last few hundreds feet assuming you are visual, outside reference is the primary reference. Below 200 feet, you should focus on the aim marker and not focus on the glide slope or Papi at this point. In fact you should disregard them at this point or you might end over controlling the aircraft.
Mentour explains it pretty well on this video after the 4min mark.
https://youtu.be/8GG9RIhpH3w
thanks thatís a good video.
PelicanSquawk is offline  
Old 28th Jul 2022, 15:18
  #57 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 8,259
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by C172 Driver
I have aimed at the zebra stripes on short slippery runways. I have aimed at half way down the runway at AMS where the exits are at the far end. Know your plane, know your surroundings.
Nonsense. We're trying to get people into the same box over the threshold each time so there's less variables, not John Wayneing it. Landing half way down the strip so you can taxi off quicker will get you a free tea and bikkies pretty quickly. You ever heard of FOQA/FDAP/FDM?

Originally Posted by Pineteam
For the last few hundreds feet assuming you are visual, outside reference is the primary reference. Below 200 feet, you should focus on the aim marker and not focus on the glide slope or Papi at this point. In fact you should disregard them at this point or you might end over controlling the aircraft.
Nobody's suggesting you concentrate wholly on the guidance below 200ft. But they (GS or PAPI) should be front of mind until 200ft. Re the "last few hundreds feet" is where it often all goes pear-shaped because of slack glidepath control.

That is an interesting video. His comment about being coordinated with the ILS is rarely valid these days. The PAPI is almost always further in, to suit long-bodies on longer runways. Also, I don't agree with his philosophy of use. The first thing you do is nail the PAPI, to the dot, stay on it then, at 200ft, start transitioning to the visual aim point by holding that spot steady in the windscreen. It is impossible, for a newby at least, to start assessing the aim point moving or not on the windscreen at 1000ft, as he is suggesting. Even I can't do it. The touchdown zone is so far away that any minor pitch movements throws this spot on the windscreen around chaotically. Only when you get in closer does "holding the aim point" become doable. I notice a commentor has a similar view to me.

For Pelican, a commentor also mentioned a PAPI that looked odd and which was later found to have been run over by a vehicle and bent out of shape. So you never know, the PAPIs at your airport might be skewiff, or the glideslope bent!

Last edited by Capn Bloggs; 29th Jul 2022 at 04:02. Reason: Grammar.
Capn Bloggs is offline  
Old 28th Jul 2022, 16:03
  #58 (permalink)  

Only half a speed-brake
 
Join Date: Apr 2003
Location: Not commuting home
Age: 44
Posts: 3,966
Likes: 0
Received 0 Likes on 0 Posts
At night, impossible to see the markings and read the aiming point from them, sure pilots need to pick up the 'collision' point by obesrving the visual field expand.

About 500 is the first feeling I get for it, the centreline lamps become distinct one from another. The key is flying the GS / FDs well with a steady pitch so the outside image is stable. Around 300 it starts making sense to the brain, not earlier than that to me. If no GS until that point, PAPI + V/S are the tools, Mk II eyeball + V/S and a little gut when below.
FlightDetent 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 - Do Not Sell My Personal Information

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.