Level Segment during ILS Procedures?
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Level Segment during ILS Procedures?
Recently heard that as per some ICAO DOC, a 2.5nm LEVEL flight segment is MANDATORY on the localizer prior to intercepting the glidepath.
So far we'd try and arrange our descent to be AT glideslope intercept altitude AT the point of glideslose capture- prefrebably extending flap and gear so that there is minimum thrust lever change. Also noticed that the FMC builds a 2.5nm level flight segment between the G/S anf CF(localizer intercept point).
Any views/location of the relevant ICAO Doc would be much appreciated.
Thanks
So far we'd try and arrange our descent to be AT glideslope intercept altitude AT the point of glideslose capture- prefrebably extending flap and gear so that there is minimum thrust lever change. Also noticed that the FMC builds a 2.5nm level flight segment between the G/S anf CF(localizer intercept point).
Any views/location of the relevant ICAO Doc would be much appreciated.
Thanks
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From an ATC point of view, the college of knowledge teaches us to try and give you 1/2 to 1 mile of level flight before intercepting the glide, however, I've noticed that most crews when given descent prior to localiser intercept, seem to delay it and go for the continuous descent on the ILS
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Radar 707. Re level segments. Boeing (in the 737 anyway)recommend that initial flap selection on approach be carried out in level flight meaning that the flaps should not be used as speed brakes. This recommendation is commonly ignored. Flaps 1 through to flaps 5 are selected while the aircraft is going downhill at speeds sometimes well in excess of the recommended especially if the aircraft is closing in towards the localiser during en-route descent. Depends on the pilot's skill I suppose.
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Quid-
"Do you mean 2.5 nm in the procedure design, or 2.5 when flying the approach? In the US, I've not heard of this. ???"
2.5nm when flying the approach....
Hudson-
"Boeing (in the 737 anyway)recommend that initial flap selection on approach be carried out in level flight "
Can't find any such recomendation in the FCTM- atleast the new version- though I do remember reading about "not using flaps as speedbrakes". Even on a descent if you would be extending flap to say 5 from UP, and were in say LVL Change mode, the ROD would reduce to about 500fpm and the speed would reduce down to the selected maneuvering speed. So I dont think extending Flap during a descent should be construed as "using Flap as Speedbrakes".
Thanks all for sharing your thoughts- Keep em Coming!!
"Do you mean 2.5 nm in the procedure design, or 2.5 when flying the approach? In the US, I've not heard of this. ???"
2.5nm when flying the approach....
Hudson-
"Boeing (in the 737 anyway)recommend that initial flap selection on approach be carried out in level flight "
Can't find any such recomendation in the FCTM- atleast the new version- though I do remember reading about "not using flaps as speedbrakes". Even on a descent if you would be extending flap to say 5 from UP, and were in say LVL Change mode, the ROD would reduce to about 500fpm and the speed would reduce down to the selected maneuvering speed. So I dont think extending Flap during a descent should be construed as "using Flap as Speedbrakes".
Thanks all for sharing your thoughts- Keep em Coming!!
Most German approaches specify a mandatory continuous descent technique and low drag approach; their radar vectoring usually facilitates it.
In a rather elderly 4-jet, at a typical aerodrome we used to fly through the overhead (airpace restriction) at 4000 ft aal and 210 KIAS, then descend to 2500. At 7 DME outbound, select flap and slat to the 'take-off' setting and decelerate to 170 KIAS, then at 9 DME, select gear down and start a descending base leg turn to level at 2000 ft and not below Vat + 30. Intercept the localiser, then select approach flap just prior to GP intercept, maintaining not below Vat + 20. At 1500, select land flap and maintain not below Vat + 10 until 200 ft aal, then decel to Vat.
This is quite noisy, so the low drag equivalent with a continuous descent technique becomes:
Through the overhead at 4000 ft aal and 210 KIAS. Maintain this to 9 DME outbound, start the base turn then select flap and slat to the 'take-off' setting, decelerate to 170 KIAS and select gear down on a descending base turn to intercept the GP (but not outside localiser coverage). Keep descending on the GP as the localiser is captured, maintaining 170 KIAS to 4 nm from touchdown, then select flap to approach and subsequently to land, increasing thrust as required to stabilise at not below Vat + 10 until 200 ft aal.
Makes far less noise but is slightly more difficult to fly at the ILS intercept point as things happen rather quickly at that point. Prompt and accurate trimming and thrust management are essential to fly a safe approach from 4 miles - so practice was needed! However, when Wx was close to the limit it was necessary to adopt the 'normal' high drag technique as the autopilot system needed time to stabilise; hence land flap and not below Vat + 10 was established as early as possible on the glideslope after a level segment at 2000 ft aal, giving the autopilot the maximum possible chance to achieve accurate localiser and glideslope tracking with the autothrottles holding the stabilised Vat + 10.
This was in a 35 year old 4-jet with a fairly primitive autopilot system, extremely noisy engines and a 'busy' flight deck. Modern ac such as the Airbus series should be able to cope with low drag continuous descent approaches routinely using AFS/ATS.
In a rather elderly 4-jet, at a typical aerodrome we used to fly through the overhead (airpace restriction) at 4000 ft aal and 210 KIAS, then descend to 2500. At 7 DME outbound, select flap and slat to the 'take-off' setting and decelerate to 170 KIAS, then at 9 DME, select gear down and start a descending base leg turn to level at 2000 ft and not below Vat + 30. Intercept the localiser, then select approach flap just prior to GP intercept, maintaining not below Vat + 20. At 1500, select land flap and maintain not below Vat + 10 until 200 ft aal, then decel to Vat.
This is quite noisy, so the low drag equivalent with a continuous descent technique becomes:
Through the overhead at 4000 ft aal and 210 KIAS. Maintain this to 9 DME outbound, start the base turn then select flap and slat to the 'take-off' setting, decelerate to 170 KIAS and select gear down on a descending base turn to intercept the GP (but not outside localiser coverage). Keep descending on the GP as the localiser is captured, maintaining 170 KIAS to 4 nm from touchdown, then select flap to approach and subsequently to land, increasing thrust as required to stabilise at not below Vat + 10 until 200 ft aal.
Makes far less noise but is slightly more difficult to fly at the ILS intercept point as things happen rather quickly at that point. Prompt and accurate trimming and thrust management are essential to fly a safe approach from 4 miles - so practice was needed! However, when Wx was close to the limit it was necessary to adopt the 'normal' high drag technique as the autopilot system needed time to stabilise; hence land flap and not below Vat + 10 was established as early as possible on the glideslope after a level segment at 2000 ft aal, giving the autopilot the maximum possible chance to achieve accurate localiser and glideslope tracking with the autothrottles holding the stabilised Vat + 10.
This was in a 35 year old 4-jet with a fairly primitive autopilot system, extremely noisy engines and a 'busy' flight deck. Modern ac such as the Airbus series should be able to cope with low drag continuous descent approaches routinely using AFS/ATS.
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Flyingwithoutwings. You are right. The FCTM states that flaps are not normally used for increasing the descent rate...and that normal descents are made in the clean configuration to pattern or instrument approach altitude...if greater descent rates are required, extend the speed brakes. All this adds up to the aircraft should normally be in level flight when reducing speed prior to extending flaps. While the FMC may gradually reduce the speed in the descent before initial flap selection to flaps 1 and 5 - the aircraft is not in level flight - it is still going down and the flaps are therefore being used as speed brakes - in my view.
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ICAO Doc 8168 (Pans Ops), Chapter 21 is the reference, but it is only for procedure design purposes. As a procedure designer, I can tell you that I don't care whether you use it that way or not. It is strictly a procedure design principle that the Intermediate Approach Segment includes a 2NM level segment, as a minimum.
If there's a track change between the Initial and Intermediate segments, greater than 30 degrees, we have to provide additional length in the level segment. I don't have my Pans Ops book in front of me (it's well after hours here now), but I think the minimum distance increases to 2.5 NM for turns of between 30 and 40 degrees between the Initial and Intermediate segments.
From the standpoint of procedure design, this part of the approach is referred to as the Intermediate Approach segment. The sole purpose of this segment is to establish the aircraft on the LLZ prior to GP intercept. That way, if pilots fly the way the procedure is designed, GP intercept occurs from below it.
I recognise that this is not a fuel-efficient way of intercepting the GP.
If I was you, I wouldn't get too hung up on what is built into the design of these approaches. The chances are that your company SOPs and your FMS have already figured out how to deal with it. The only thing that you really need to worry about is the possibility of a "false glidepath" and how to identify it - and I'm sure that your company will have SOPs to address that as well.
I don't know if TERPs provides any similar design constraint, so I don't know if American pilots will know about it or not.
If there's a track change between the Initial and Intermediate segments, greater than 30 degrees, we have to provide additional length in the level segment. I don't have my Pans Ops book in front of me (it's well after hours here now), but I think the minimum distance increases to 2.5 NM for turns of between 30 and 40 degrees between the Initial and Intermediate segments.
From the standpoint of procedure design, this part of the approach is referred to as the Intermediate Approach segment. The sole purpose of this segment is to establish the aircraft on the LLZ prior to GP intercept. That way, if pilots fly the way the procedure is designed, GP intercept occurs from below it.
I recognise that this is not a fuel-efficient way of intercepting the GP.
If I was you, I wouldn't get too hung up on what is built into the design of these approaches. The chances are that your company SOPs and your FMS have already figured out how to deal with it. The only thing that you really need to worry about is the possibility of a "false glidepath" and how to identify it - and I'm sure that your company will have SOPs to address that as well.
I don't know if TERPs provides any similar design constraint, so I don't know if American pilots will know about it or not.
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HUDSON-
"While the FMC may gradually reduce the speed in the descent before initial flap selection to flaps 1 and 5 - the aircraft is not in level flight - it is still going down and the flaps are therefore being used as speed brakes - in my view."
I shouldn't think that just because the aircraft is descending with the Flaps out, the Flaps are being used as speedbrakes- as long as you are maintaining the flap maneuvering speed. Even Boeing does NOT have a prblem with this as this is standard procedure say during a "Delayed Flap Approach", where you would be descending with Gear Down Flap15, then extending to landing Flap by 1000 ft agl.
Beagle, Hudson, Spitoon, Ozexpat, reynoldsno1 your replies appreciated.
Actually- the origin of this thread was a General Operating Circular issued by our Flight Operations stating that pilots are intercepting the Glidepath on a continous descent profile, ie., without a level flight segment, and the ATC has objected to this. Hence, they have said that the pilots should be in level flight at the Glideslope intercept altitude, atleast 2.5nm prior to Glidepath capture, and that this was required as per Doc 8168 Vol I/II.
Can ATC object to something that is NOT wrong in the first place- as many have said that the 2.5nm level segment is a DESIGN requirement. I appreciate the ATC could/should do anything that improves flight safety- but waht are they thinking here??????
"While the FMC may gradually reduce the speed in the descent before initial flap selection to flaps 1 and 5 - the aircraft is not in level flight - it is still going down and the flaps are therefore being used as speed brakes - in my view."
I shouldn't think that just because the aircraft is descending with the Flaps out, the Flaps are being used as speedbrakes- as long as you are maintaining the flap maneuvering speed. Even Boeing does NOT have a prblem with this as this is standard procedure say during a "Delayed Flap Approach", where you would be descending with Gear Down Flap15, then extending to landing Flap by 1000 ft agl.
Beagle, Hudson, Spitoon, Ozexpat, reynoldsno1 your replies appreciated.
Actually- the origin of this thread was a General Operating Circular issued by our Flight Operations stating that pilots are intercepting the Glidepath on a continous descent profile, ie., without a level flight segment, and the ATC has objected to this. Hence, they have said that the pilots should be in level flight at the Glideslope intercept altitude, atleast 2.5nm prior to Glidepath capture, and that this was required as per Doc 8168 Vol I/II.
Can ATC object to something that is NOT wrong in the first place- as many have said that the 2.5nm level segment is a DESIGN requirement. I appreciate the ATC could/should do anything that improves flight safety- but waht are they thinking here??????
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Can ATC object to something that is NOT wrong in the first place
I think that, rather than conjecture the reason, it might be a good idea for your company to ask them about it. Perhaps you can suggest that your Fleet Captain put in a polite letter that seeks clarification from them.
Or maybe there's an ATCO or two floating around here who can shed some light on it for us?
I thought that some level segment was always necessary (though maybe not over a specified distance) in order to ensure the GP was intercepted from below. Thus avoiding false lobes. Some of the methods described above don't seem to have that protection. Any thoughts?
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In most cases where I have come across the continuous descent approach, a DME is provided.
Thus while not capturing the glideslope from below does leave the posibility of establishing on a false glideslope, SOPs which require crosschecking of height versus distance on a regular basis and crosschecking rate of descent required against groundspeed can ensure that the correct glideslope is being followed.....regardless of how it is captured.
Regards,
DFC
Thus while not capturing the glideslope from below does leave the posibility of establishing on a false glideslope, SOPs which require crosschecking of height versus distance on a regular basis and crosschecking rate of descent required against groundspeed can ensure that the correct glideslope is being followed.....regardless of how it is captured.
Regards,
DFC
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OzExpat- Our flight dept./fleet capt. seems to agree with the ATC interpretation of the PANS OPS., or if not agree, have anyhow issued instructions to pilots to follow the ATC interpretation. I wanted to basically find out and get views on the ATC inerpretation.
keithl-
"I thought that some level segment was always necessary (though maybe not over a specified distance) in order to ensure the GP was intercepted from below. Thus avoiding false lobes. "
The Boeing737 FCTM says that the Glideslope may be captured from above or below. Besides there are numerous ways to detect if you are on a false glideslope (also mentioned in the Boeing FCTM):
1. Abnormal altitude range distance relationship (Normal would be aprox. 300ft HAT per NM of distance from the runway for a 3 degree glideslope)
2. Abnormal pitch and ROD would be apparent on a flase glidepath.
Also don't have my GSP handy at the moment, but remember reading that the first false lobe of the glideslope would be occur at a sufficient height, that it would be very obvious that your are getting a false glideslope. Infact, I remember getting a false glideslope at an altitude of about 8000ft at a distance of some 17nm to touchdown on the localizer ( please don't ask how we got there
)
DFC- totally agree with you.
Cheers....
keithl-
"I thought that some level segment was always necessary (though maybe not over a specified distance) in order to ensure the GP was intercepted from below. Thus avoiding false lobes. "
The Boeing737 FCTM says that the Glideslope may be captured from above or below. Besides there are numerous ways to detect if you are on a false glideslope (also mentioned in the Boeing FCTM):
1. Abnormal altitude range distance relationship (Normal would be aprox. 300ft HAT per NM of distance from the runway for a 3 degree glideslope)
2. Abnormal pitch and ROD would be apparent on a flase glidepath.
Also don't have my GSP handy at the moment, but remember reading that the first false lobe of the glideslope would be occur at a sufficient height, that it would be very obvious that your are getting a false glideslope. Infact, I remember getting a false glideslope at an altitude of about 8000ft at a distance of some 17nm to touchdown on the localizer ( please don't ask how we got there
)DFC- totally agree with you.
Cheers....
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Hudson - I think someone in your company has got a little bit confused! Extending flap in descent is NOT, as others have said, NECESSARILY using it as a speedbrake. Do your SOPs require a level off if ATC ask for a manoeuvre speed during your descent that requires flap extension? In the UK that would get ATC quite excited!
Most (UK) companies try to conform to the BAA/CAA requirements for CDAs and the false GP capture is guarded against with a check of altitude (height) against position (DME or NDB) as discussed here and at length on another thread.
Most (UK) companies try to conform to the BAA/CAA requirements for CDAs and the false GP capture is guarded against with a check of altitude (height) against position (DME or NDB) as discussed here and at length on another thread.
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keithl... You would probably only need to fly level if your company SOPs tell you to do so. The point raised by DFC, subsequent to your post, is valid and relevant. The design of the procedure does not account for a false GP and the procedure designer doesn't care whether a pilot opts to intercept from above or below the GP.
The design of the procedure includes the level segment for the pilot who wants to fly level to help slow down and make any necessary configuration changes prior to GP intercept. We figure that pilots will have ways to determine whether or not they have intercepted a valid GP.
FWW... perhaps I misunderstood you intially. It would now seem that what I should have suggested was that, as your Fleet Captain has agreed with the ATC ruling, you're stuck with his directive as a SOP. That being the case, it's a bit irrelevant as to whether or not ATC's ruling is correct.
The design of the procedure includes the level segment for the pilot who wants to fly level to help slow down and make any necessary configuration changes prior to GP intercept. We figure that pilots will have ways to determine whether or not they have intercepted a valid GP.
FWW... perhaps I misunderstood you intially. It would now seem that what I should have suggested was that, as your Fleet Captain has agreed with the ATC ruling, you're stuck with his directive as a SOP. That being the case, it's a bit irrelevant as to whether or not ATC's ruling is correct.