View Full Version : g/s capture from above

19th Oct 2009, 15:43
Does anyone now where can I find references for this manuever in a Boeing 737 classics serial? Someone with a good airline policy on the matter because the reference We use come from airbus planes?

19th Oct 2009, 16:29
Glide slope capture from above.
The following procedure should only be applied when established on the localizer.
React without delay to ensure the aircraft is configured for landing before 1000ft AAH.
When cleared to intercept the glide slope:
Lower the Landing Gear
MCP ALT-1000ft AAH
V/S mode- Select 1500FPM initially then as required to maintain Flaps Placard speed minus 20kts.
APP mode-Select
At G/S capture:
MCP ALT-Set to Go Around altitude.

cosmo kramer
19th Oct 2009, 17:58
I my opinion the best way is to disconnect the automatics and switch the FD off, and fly it manually. Gear down, and as long the speed is high do not try to capture the GP but keep following it 1 dot or 1 1/2 high. Configure as you go. Order the FDs to be re-armed, final heading and missed approach alt to be set. Order the Vref to be changed to flaps 40 and configure to flaps 40 for the extra drag if flaps 30 was planned originally. When fully configured get the GP centered, and if you were not much too high from the beginning everything should be fine by 1000 feet, otherwise of course go-around.

With automatics be very careful as the 737 can bite back when doing this and you may exceed the capabilities of the auto throttle. I would recommend taking the throttle manually at least. Otherwise do as vasalis wrote.

Here is where to be careful: if GP capture occurs, configured with flaps 40, speed still high and throttles in idle, the auto throttle will not spool the engines up quick enough and will happily take the speed below Vref without adding the necessary thrust to get it back.

Best is not to get in this situation by taking the thrust manually and predict for youself when the engines should be spooled up.

If you do let the automatics take you for a ride, do not wait and explore the autopilots capabilities of recovery from approach to stall. With flaps 40 it will take a lot of thrust to get just 5 knots below Vref back - 80-85 % N1. Put it in manually immediately!

19th Oct 2009, 18:28
my take...(assuming loc captured already)

Establish landing config...
MCP Alt window - Airfield elev +1000'
LVL Change - Press
Approach mode - Arm

(you will end up going down at about 2000fpm...)

Now, exactly what cosmo says, but a different take. When 1 dot high on the glide (and closing rapidly), then manually increase thrust to about 40% N1 (so they are spooled up a little - A/T will be at arm at this moment). When the glide captures everything should come together - All you need to do is set missed alt on MCP.

But there are a thousand ways....

19th Oct 2009, 20:20
Thank you guys.Really useful and this is what We do in our airline (more or less) What I was looking for is some kind of published version from Boeing on the matter because its well practised manuever in airbus but I couldn't find anything in the FCTM.

19th Oct 2009, 21:57
Probably because they say 'don't'? I'm more with 'cosmo' than the A/P brigade - but I am a 'KOS'.

19th Oct 2009, 22:14
Boeing are negligent in not having this maneuver in their various FCTMs. Most of us operate often into airports where short approaches, fast approaches, sudden track shortening etc are the way of life. Yet the FCTM (and all the Boeing fleets have the same core manual and techniques) depicts a gentlemanly leisurely intercept of the glide slope from below at a sedate speed. Rarely happened to me I must say. Yet there's technique in there for rapid descent after depressurization and engine failure as though those things happened every day.

FOQA data shows a primary cause of stuffed up approaches in the above airports to be ALT Capture above the G/S....difficult to recover when that happens unexpectedly. It would be nice (and they have been asked often) for a Boeing ordained procedure to give guidance.

The Airbus procedure is fine as a starting point. You have to be established on the Localizer of course. Have a good think about whether you're trying to rescue a dodgy approach and be realistic about giving it away. Set 1000 HAA on the MCP. Don't use FLCH down low and don't exceed about 2000 fpm while descending to get the G/S. If you get an alt capture at say 1300 ft and still haven't got the G/S then, especially in bigger Boeings, it's time to be professional and give it away, try again. It's no sin and the passengers would demand it if they knew what you now.

If anyone from Boeing reads this thread.....what about it. Have an FCTM that reflects the real world of SFO, ORD and LAX.

Safe flying

20th Oct 2009, 00:24
I'm just curious as to why you believe there has to be an official Boeing procedure for every contingency. What ever happened to simply flying the airplane?

Procedures and limitations already exist for intercepting the G/S from above: Use V/S, VNAV, or whatever else you have (like your air sense) to descend. Don't exceed 2000 FPM below 2000' AGL, or 1000 FPM below 1000' AGL. Be stable below 1000'. If not, go around.

20th Oct 2009, 08:00
where short approaches, fast approaches, sudden track shortening etc are the way of life- I think Boeing take a more mature view to flying their aircraft in that all those 'events' are within your control as a pilot, so its entirely up to you whether you accept the events or decline the offer. I have never 'blamed' ATC for making my approach 'tight' (the co-pilot, and ATC 'trying to', yes:)). Whenever it has happened it has been because I 'allowed' it to happen - not Boeing.

"depressurization and engine failure" are not within your control as a pilot.

I cannot see why anyone needs to write a 'procedure' for it. Airmanship again?

20th Oct 2009, 08:26
One airline I flew for prohibited glideslope capture from above in their SOP's.
Don't exceed 2000 FPM below 2000' AGL, or 1000 FPM below 1000' AGL. Be stable below 1000'. If not, go around.
Is good advice.
There have been CFIT's where a moderately high V/S was set up to capture followed by a distraction (one that comes to mind was a gear indication problem) followed by CFIT. The high ROD was not huge but it was prolonged due to the distraction and a bit of overload on the crews part.
It should not be a daily event in my opinion.

20th Oct 2009, 09:55
So, what is the B737 'Classic' please? Serious question, I always thought it was the -100 and -200 series where half of the procedure mentioned above wouldn't apply. Thanks.

20th Oct 2009, 10:21
So, what is the B737 'Classic' please?- where have you been?:)

1/200 - 'Jurassic'
3/4/500- 'Classic'
6/7/8/9/1000 - 'NG'

22nd Oct 2009, 00:23
it happened with me last week during the approach,,i disengaged autopilot dived for the gs...
you can do it also using autopilt by engaging V/L and selecting VS with putting higher altitude than the current one ,as soon as u capture select LAND on

22nd Oct 2009, 01:27
-100,-200 = Jurrassic !!! Excuse Me, I well remember......... Oh well never mind! Thanks BOAC.:)

Huffs and puffs out the door.

22nd Oct 2009, 03:16
Huffs and puffs out the door.

Indeed, sir, we are amongst the well-attired, if somewhat equally well-dated, saurian folks within the PPRuNe sandpit ... exits stage left adjusting scaly tail ...

I still have to come by at a respectable hour and drop in for a cup of coffee ... just have to lift my game, I guess.