Intercepting GS from above.

[z.khalid]

Hi all. Please bare with my questions please, as I am not sure behing this concept.
I understand that if you were above your platform altitude to intercept the GS, but were away from the runway, youre aircraft will catch the signal and you will descend with the glide, is this true?

However if youre close to the runway, and ATC has not descended you to the altitude you should start descending with your glide (FAF) , but cleared your for thr approach, all you do is select VS of 1500, on the alt selector select an altitude above (Missed approach altitude) and wait till the GS signal is caugh and you start descending normally with the glide?

Thanks in advance!

[Nick 1]

Hi,
you need to intercept Loc first , the system'll not track the Glide without Loc.
Then you need to write an altitude higher than the one you'll intercept the Glide ( because if you arrive on glide capture zone with ALT* displayed the system 'll complete first the capture of altitude , so you'll miss the Glide)
then set a V/S as per your SOP regarding altitude and.....remember to push
APP because you are tracking the loc in Loc.

[speedrestriction]

Possible but untidy and usually unwise. Rule of thumb is not to descend at greater than 1000fpm beyond the FAP/FAF. Selecting a higher rate of descent might make it difficult to maintain a stabilised approach depending on the thrust, drag and configuration of the aircraft. Another problem that springs to mind is that you are in an open descent. Finally, unless both crew have plenty of spare capacity you could find yourself in a situation where both crewmembers are losing situational awareness by focusing on capturing the GS and perhaps missing something crucial (checklist, configuration, proximity to terrain, clearance to land, vehicle on runway, flock of birds etc etc)

sr

[macdo]

yes, this is rarely a clean manouvre, but often needed at certain airports where the ATC thinks its cool to do the tightest approach possible. The only points I would add to the post above is to watch out for Vfe exceedance, especially possible on the 321, or when heavy or with a tailwind. If you do this in an Airbus, you go straight into Open Climb, which is very entertaining. If you suspect a capture from above is on the cards, slow down, configure early and if you are VMC and it gets out of hand, fly manually rather than struggling with the automatics. If in doubt, Go Around!

[Intruder]

Details depend on the aircraft and your SOP.

While you cannot legally descend on the glideslope until you are on the localizer, some older automated systems (e.g., 747 Classic) will do it if set up. Newer systems (e.g., 744) will not capture the G/S until the LOC is captured.

An old rule of thumb is the "minute to live" rule -- max 2000 fpm descent below 2000' AGL and max 1000 fpm below 1000' AGL. At high-altitude airports near max landing weight, you may need 2000 fpm or more to get down to the G/S, and may be at 1000 fpm or slightly more when on the G/S.

[ImbracableCrunk]

Boeing A/C have a user option of capturing G/S with or without LOC capture.

[Natstrackalpha]

G/Slope from above - - -yukkie.

There seems to be a popular trend with some companies to entertain this tacky procedure, not procedure in the Procedure sense (although possible I guess) but procedure as in process.

above your platform altitude to intercept the GS, but were away from the runway, youre aircraft will catch the signal and you will descend with the glide, is this true?

Unfortunately, not always. Also and more importantly, there is a false glide slope which is above the real glideslope - this is higher than the true glideslope and if you catch this then you would end up with a very, very steep rate of descent and or completely miss the target and have to go around, at least - not to mention the airspeed - high rate of descent - unreliable signal not good at all.

Are we talking A320? Realising that to intercept from above is unhealthy due to the false glideslope factor and adjusting alts gets a bit loony when she ignores glide because of Alt.

You could SUBJECT TO MSA OCL OCH and TRAFFIC + ATC requirements, including TERRAIN per se` descend slightly below the glide and then intercept from
below. and as mentioned above, make sure you have LOC and also APP PB pushed too. Admittedly each Approch per the airport especially if mountains surround but even these invariably have a steeper glideslope -
you`ll get this in your training,. it must work as they train it but some pilots don`t like it for the above reasons, be very cagey..

[M.82]

Boeing 737NG Procedure

Once you intersept LOC and you are cleared for the ILS APP.
1) Landing Gear Down and FLAP 15 (you need a lot of drag).
2) Set APP on MCP ( "GS ARM" on FMA)
3) Set 1000 Ft AFE on the MCP.
4) Move V/S wheel and set no more than1500 V/S. (" VS" active on FMA).
5) When GS capture, set landing Flap.

[de facto]

you need to intercept Loc first , the system'll not track the Glide without Loc.

Bit of a general statement,if i remember correctly on the 737CL ,arming APP was not to be done before established on the LOC.
On the 737NG,glide slope will not capture before the LOC.

Boeing 737NG Procedure
Once you intersept LOC and you are cleared for the ILS APP.
1) Landing Gear Down and FLAP 15 (you need a lot of drag).
2) Set APP on MCP ( "GS ARM" on FMA)
3) Set 1000 Ft AFE on the MCP.
4) Move V/S wheel and set no more than1500 V/S. (" VS" active on FMA).
5) When GS capture, set landing Flap.

Landing gear down and flaps 15 when LOc established?is that your airline procedure?in that case you must be living in the gulf where fuel is cheap...
Gear down by boeing is one dot to glide intercept(recommended),still too early if your glide starts at 6000 ft AGL.
The gear normally will be dalyed until a certain dme/alt to comply with your airline stabilized criteria.
If IMC:1000ft aal-speed 180,gear down at 7miles.
If vmc500ftaa-speed 160,gear down at 3.2 miles or speed 180 gear down at 5miles.

[nitpicker330]

De Facto:---- read his post again, he suggests ( correctly ) lowering the gear to maximize drag so you can get down onto the G/S ( whilst controlling the speed within limits )....that is the whole point of this topic is it not?

[nitpicker330]

Indeed just to add to his correct post regarding G/S capture from above in a 737NG I will add the A330 proceedure:---


INTERCEPTION FROM ABOVE

The following procedure should only be applied when established on the localiser, with either LOC* or LOC displayed in green on the FMA. The best rate of descent is achieved with the landing gear extended, FLAPS 2 selected and flying at VFE2 − 5 kt. Speedbrakes may also be used, noting the considerations detailed in Deceleration and Configuration Changes earlier in this chapter. Apply the following procedure without delay:

• Confirm LOC capture and G/S armed.

• Select the FCU altitude above aircraft altitude to avoid unwanted ALT*.

• Select V/S − 1,500 ft/min initially. V/S in excess of 2,000 ft/min will result in the speed increasing towards VFE.

V/S rather than OP DES must be used to ensure that the A/THR is in SPEED mode rather than IDLE mode. Carefully monitor the rate of descent to avoid exceeding VFE or triggering a GPWS warning. When approaching the G/S, G/S* engages. Monitor the capture against raw data. Use normal procedures for the remainder of the approach.

If at any stage it becomes apparent that the stabilised approach criteria will not be met, perform a go-around.

[despegue]

Look, everybody has to intercept the glide from above from time to time. Wether this is your own miscalculation or the result of an overeager ATC...
However, complaining that this is sloppy etc. will not help. Teach young collegues this procedure (yes, it IS a procedure) to be done correctly during sim training and initial line-training and this "sloppy" and "untidy" manoeuvre will become just as smooth and safe as an interception from platform altitude at the FAP. Explain this procedure in the FCTM.

That is the problem nowadays in training. Non-standard, but common scenarios are not included anymore resulting in indeed sloppy, sometimes unsafe handling of the aircraft when this does occur. Fault of the procedure-monkeys SOP-gestapo. Follow the SOP, but be trained to know that aviation is not standard and be taught how to think,aviate and make sound decisions based on trained procedures and knowledge.

[Discorde]

This from 'The Going Down Bit'. It relates to the B757 and was written several years ago so might have been superseded by new techniques.

<<OH NO . . . WE’RE ABOVE THE GLIDESLOPE!

Busy airport - single runway – ATC doing their best to get flights in and out without holding anyone up. The radar controller’s vectors might turn you onto the localiser while you’re still above the glideslope. No problem: get some more drag out. But suppose you then capture your last cleared altitude before you get onto the glide. An ALT CAP is the last thing you need at that point. Here’s a solution: once you have captured the LOC and if you are absolutely sure you’re above the genuine glideslope (by cross-checking range information), arm GS and set the MCP altitude window to final fix altitude. Stay in FL CH (check that speed window!) and use whatever drag is necessary to capture the GS. Remember that the task will be more difficult if you’ve got the TAI on. If you’re not established on the GS by the time you arrive at the final fix, start thinking about a go-around, especially if you are IMC.>>

[Natstrackalpha]

However, complaining that this is sloppy etc. will not help. Teach young collegues this procedure (yes, it IS a procedure) to be done correctly during sim training and initial line-training

fair comment.............he can also make sure he is going for the `real` g/slope (if, from above) by calculating his dist against altitude but he knows that already, right?

If A320 and freq already on MCDU then press APP pb or it may not engage it at all, yes, make sure it engages - definately LOC before G/S. Keep sharp, if she won`t engage, hard tune it using a MAN input into the MCDU rad or tune it on the RMP - And, make sure the "fickle" LOC has not gone off and flirted with the nearest signal from another approach runway nearby, if in Nav make sure she doesn`t go flying up the LOC in the wrong direction

.

[MetoPower]

Whatever the procedure published by Boeing, Airbus or else, no one has ever says it is a SOP (while many new gen pilots appear to believe so).
They only tell you how to come out of an occasional and unplanned situation should you have the time, and conditions to do so!!
The best answer is DON'T do it on purpose nor on a regulat basis (I'd rather save my arse than 100kg (lbs) of fuel), or go around!
I know personally one pilot that was very fortunate to survive the false glideslope captured from above, only to hit the planet at an unexpected location .......... he knows a lot about it.
He NEVER DIT IT AGAIN and NEVER WILL do it again.

But I might be old fashion...

MP

[bubbers44]

Landing at MIA to the east it is a luxury to intercept the glide slope from below on an east arrival. Your downwind is way above glide slope intercept altitude when you turn base to final. You will make your copilot think you are really stupid when you keep letting the aircraft intercept the altitude before glide slope and keep going around when all others are landing. Either keep going around or lower the altitude to let the glide slope intercept first, your choice. It rarely rains in FLA so you can see the airport 30 miles out. I know it rains but they are those fun tropical things.

[Nick 1]

There is another option, but don' t do it at home ! Very dangerous!
Disconnect everything and fly manually ......( if condition permit).

[Intruder]

I know personally one pilot that was very fortunate to survive the false glideslope captured from above, only to hit the planet at an unexpected location .......... he knows a lot about it.
He NEVER DIT IT AGAIN and NEVER WILL do it again.

That's fine. He discovered his limits and will adhere to them.

OTOH, a pilot with an ATP should be able to easily intercept a G/S from above, and use all his other instrumentation to confirm the G/S is reasonable, and not a false one.

On the 744 Vertical Speed and/or hand-flying are good options.

[HamFan]

Hey, Intruder, at least he referred to it as the "glideslope" and not the "glide."

Have some pride in yourselves; use proper terminology. It's not being anal, it's about being precise and removing the possibility of ambiguity. Standard phraseology exists for a reason; don't be so lazy.

"Glide" is what you do when you run out of fuel.

[bubbers44]

Nick1, yes that was the normal way to not let automation take your airplane away from you. I loved how two clicks on a Boeing made you a J3 cub again and let you fly like a real pilot, not a computer monitor guy. My first job was flying a super cub crop dusting flying under power lines and brushing tree limbs. Never forgot the basics and never let automation fly my airplane other than how I wanted it flown. Worked great for 23,000 hrs until I wore out at 60.