Self-positioned ILS approach
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Self-positioned ILS approach
I am an ATCO at a regional airport in the UK, 30 years experience. It's common practice for us to offer self-positioned approaches to commercial aircraft when it's quiet, rather than giving radar vectors to the ILS, if that's what the crew prefer.
Having watched these take place over several years, I'm struck by the huge variations in the way that flight crews appear to programme their aeroplane to intercept the ILS (typically, A319/320/321 and B737 family nowadays). I've seen LLZ intercepts from 90 degrees to the LLZ and at ranges from 10 down to 5 nm from touchdown, even in very poor weather. I've seen aircraft whistle through the LLZ and (eventually) correct and some which clearly capture the GP from above.
My point is this: if we vectored you in such a fashion, wouldn't you have every right to complain about ATC giving you an unstable approach?! When I teach a student ATCO how to vector to the ILS properly, I always tell him/her to be mindful of the weather conditions and the effect of drift, when selecting a 30/40 degree closing heading, and try to allow a period of level flight before the aircraft captures the GP from below, aiming for a 7-9 mile final. We teach that ATCOs should be mindful of pilot (in)experience and the possibility that the pilot-flying may be under instruction/check-ride.
Personally, I have a strong professional wish to give the crew as stable an approach as possible. Are my views outdated these days, given the abilities of the modern aircraft? Would you expect me to instruct you to go-round if I thought the approach was unstable, from what I observed on radar?
Having watched these take place over several years, I'm struck by the huge variations in the way that flight crews appear to programme their aeroplane to intercept the ILS (typically, A319/320/321 and B737 family nowadays). I've seen LLZ intercepts from 90 degrees to the LLZ and at ranges from 10 down to 5 nm from touchdown, even in very poor weather. I've seen aircraft whistle through the LLZ and (eventually) correct and some which clearly capture the GP from above.
My point is this: if we vectored you in such a fashion, wouldn't you have every right to complain about ATC giving you an unstable approach?! When I teach a student ATCO how to vector to the ILS properly, I always tell him/her to be mindful of the weather conditions and the effect of drift, when selecting a 30/40 degree closing heading, and try to allow a period of level flight before the aircraft captures the GP from below, aiming for a 7-9 mile final. We teach that ATCOs should be mindful of pilot (in)experience and the possibility that the pilot-flying may be under instruction/check-ride.
Personally, I have a strong professional wish to give the crew as stable an approach as possible. Are my views outdated these days, given the abilities of the modern aircraft? Would you expect me to instruct you to go-round if I thought the approach was unstable, from what I observed on radar?
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Are my views outdated these days, given the abilities of the modern aircraft?
Would you expect me to instruct you to go-round if I thought the approach was unstable, from what I observed on radar?
wouldn't you have every right to complain about ATC giving you an unstable approach?!
The difference with accepting vectors to 4nm and flying a self-positioned 4nm final is that issue of the unknown: If we decide to make a 4nm final from, say, 30nm out, it should be no big deal; in the same way if you inform us with a bit of notice that that will be the end result of your vectors, we have plenty of time to decide whether we can achieve it or not. If we are expecting a 9nm final and receive a last-minute 'short-cut' to 4nm, then it can cause real problems.
It is the issue of unpredictibility which causes the most stress in the flightdeck, when considering ATC vectoring: at busy places like LHR, the vectors are extremely consistent (due to the nature of the airspace) and therefore predictable - we can then plan everything to happen when it needs to and acheive nice continuous descents.
The 'problem' with regional airports in quiet airspace is that by nature you have more flexibility, and so our final approaches can take a much wider range of forms.
The key, I believe is to keep pilots informed! Just letting us know early if we are to expect a short approach or if self-positioning will be likely. Updating us on approximate track miles to touchdown is a huge boon when we are trying to plan a continuous descent and a stable approach, something which the 'regionals' don't do so often.
As far as relating what you see on the radar to whether or not you should discontinue the approach, I suspect you are already of the opinion that that is not really your job! Different companies and fleets have widely different standard procedures and performance - it would not be possible to offer that kind of direction sensibly without great experience with the aircraft type or company concerned.
Of course we need your advice if it looks like we are having trouble, either with navigation, descent towards terrain or maybe just appear too high for the approach - and don't be shy! High workload in the cockpit can mean that subtle hints from ATC aren't effective. But let us fly the aircraft!
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ATCO, I think the reason you have witnessed so many variations on a theme (and by the sound of it not all of them sensible) is down to the effect modern technology has on us pilots.
Take the Airbus family. In flying one of these, one can be as lazy or as pro-active as one desires, and this is fine so long as the nav database has all the STARS/SIDS, a sensible intercept onto centrefix, and a sensible vertical profile to match.
Problem is when there aren't any nice easy approaches loaded, and you then have a choice:
a) Let the FMGS get on with it, trust you can remember the 3x table and hope that it all works out
b) Construct one or two waypoints to ease the lateral phase (turn-on) and associate a sensible vertical profile (constraints) with these waypoints
I suspect the worst excesses you have witnessed stem from the lazy option a) above.
Rgds,
dcd
Take the Airbus family. In flying one of these, one can be as lazy or as pro-active as one desires, and this is fine so long as the nav database has all the STARS/SIDS, a sensible intercept onto centrefix, and a sensible vertical profile to match.
Problem is when there aren't any nice easy approaches loaded, and you then have a choice:
a) Let the FMGS get on with it, trust you can remember the 3x table and hope that it all works out
b) Construct one or two waypoints to ease the lateral phase (turn-on) and associate a sensible vertical profile (constraints) with these waypoints
I suspect the worst excesses you have witnessed stem from the lazy option a) above.
Rgds,
dcd
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Consider it poor airmanship to blast through the localizer myself, when given the invitation to self position some crews may choose to use this approach as training to practice hand flying with the automatics off.
Your recommendation to student ATCO's is spot on in my opinion.
D.L. (small airbus)
Your recommendation to student ATCO's is spot on in my opinion.
D.L. (small airbus)
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Depends on the FMS installed and/or the ability of the navigation system to give the aircraft's position relative to the LLZ. Traffic permitting, I've often requested a no vector ILS and either let the boxes sort it out or used the 10% ground speed/distance to LLZ rule of thumb to make the turn myself. INS and GPS, wonderful inventions, both make it so easy that even a monkey can do it. Reminds me, where did I leave that banana?
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I've seen LLZ intercepts from 90 degrees to the LLZ and at ranges from 10 down to 5 nm from touchdown, even in very poor weather. I've seen aircraft whistle through the LLZ and (eventually) correct and some which clearly capture the GP from above.
No! Radar is 'history' in terms of displayed height and ground speed - we have (naturally) a much greater dynamic picture of the state of the aircraft, in terms of airspeed trends, actual wind readings, and a far better appreciation of the time and distance required to configure the aeroplane and correct back to datums from any deviation.
Agreed that being 'dangerously positioned' more usually relates to a lateral deviation from the FAT, but it certainly would also apply if the aircraft was observed to be 'significantly' below the glide-path.
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it certainly would also apply if the aircraft was observed to be 'significantly' below the glide-path.
Our (aircrew) notion of a 'de-stabilised' approach in a modern, swept-wing aircraft tends to be one where excess height and/or speed cannot be lost prior to touchdown - a low approach can always be improved by adding power; if high/fast and at idle thrust already, one cannot reduce power any further so the situation becomes more critical.
We (our company) can only self-position when in receipt of radar monitoring (unless fully visual), so in that regard we would always expect terrain and traffic advice, as usual - the only difference being that we are doing the nav and speed control.
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ATCOJ30, hey there. I don't know how about you guys, but with us its only possible to have/ request self positioning while in VMC otherwise, if chosen, follow the STAR. Since in VMC a pilot is basically free to choose whatever strategy he likes, but aiming to be stabilized by 500 agl. Self positioning in IMC its risky business and I wouldn't recommend it.
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Flying Daggers,
As long as you intercept the GS from or above the MSA - what would be the dangers involved in self-positioning approaches, even in IMC?
Empty
As long as you intercept the GS from or above the MSA - what would be the dangers involved in self-positioning approaches, even in IMC?
Empty
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I have been on a vector on downwind in IMC and ATC said "cleared the approach". I am not on any portion of the published approach. Sure, I have a nice EFIS MAP display in front of me and it has fancy EGPWS with GPS terrain display. Can I do this? yes. Should I do this? well now that is an important question.
This is how the Chinese are doing it. Never been cleared for this in the U.S. Maybe I have asked for a "short approach" in the past but never just fly my own IMC pattern to an ILS. This is how CFIT happens, maybe not everyday but certainly increases the chances. What is so advantages to this?
ATCOJ30, vector me.......................... I won't complain.
This is how the Chinese are doing it. Never been cleared for this in the U.S. Maybe I have asked for a "short approach" in the past but never just fly my own IMC pattern to an ILS. This is how CFIT happens, maybe not everyday but certainly increases the chances. What is so advantages to this?
ATCOJ30, vector me.......................... I won't complain.
You'll find that when designing ILS procedures, the designer is required to 'build in' a certain distance for stabilised flight on the LLZ prior to GP intercept. In the design this is usually 2nm, but according to ICAO Doc 8168 Table III-21-1 it can vary according to aircraft category and closing angle.
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Re: Self-positioned ILS approach
Originally Posted by Empty Cruise
Flying Daggers,
As long as you intercept the GS from or above the MSA - what would be the dangers involved in self-positioning approaches, even in IMC?
Empty
As long as you intercept the GS from or above the MSA - what would be the dangers involved in self-positioning approaches, even in IMC?
Empty
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Re: Self-positioned ILS approach
Hi Flying Daggers,
Yes - a procedure might be designed around a 3 deg. GS intercept @ 3000 ft. AAL, i.e. 9 NM. However, if you are operating with a MSA of 2000 ft. (assuming zero AD elevation) - what would be the problem if you had been cleared to descendt to altitude 2000 ft. - and then self-position for a 7 NM final (with GS capture @ 6 NM)?
My point is - above the MSA, yes, it's doable & safe. Below the MSA - oh, no! Not on my watch!
The problem is only one of geometrics, i.e. what distance to aim for in order to intercept the GS at or above the MSA. Whit high MSAs, there is no gain in this. With low MSAs and high procedural altitudes, there might be a gain. But it's not about economics - it's a question of safety & legality.
Brgds
Empty
Yes - a procedure might be designed around a 3 deg. GS intercept @ 3000 ft. AAL, i.e. 9 NM. However, if you are operating with a MSA of 2000 ft. (assuming zero AD elevation) - what would be the problem if you had been cleared to descendt to altitude 2000 ft. - and then self-position for a 7 NM final (with GS capture @ 6 NM)?
My point is - above the MSA, yes, it's doable & safe. Below the MSA - oh, no! Not on my watch!
The problem is only one of geometrics, i.e. what distance to aim for in order to intercept the GS at or above the MSA. Whit high MSAs, there is no gain in this. With low MSAs and high procedural altitudes, there might be a gain. But it's not about economics - it's a question of safety & legality.Brgds
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Re: Self-positioned ILS approach
E.C. well, again I think there are a lot of legal aspects involved in that, like ATC's responsibility for the safe path, traffic separation, and correct positioning, if I'm right. Following the published appr./ radar vectors you follow a protected area/safe area and the responsibility bears with ATC. I haven't found the official definition for self positioning, so who is responsible for what? Finally coming to the MSA, does MSA include temporarily man maid obstacles? (which you usually find in the notams), I don't think so. Where do you start self positioning? Out of 30 nm or 15? Do you follow standard traffic pattern, basically as you would do a visual, or is that 5,7,9 nm? Do you proceed to base turn or join the down wind leg straight? Whereas the flight path (intermediate& final appr.) is the AT C's responsibility and will be kept clear according to the requirements. I have never been cleared for lower, than FINAL LAT G/S capture even if MSA is lower, unless being on LOC already. Its common practice in the eastern countries though, to clear you straight to the base turn and you basically just navigate on your own (self position) to that position, from which you start the approach following published pattern. Bear in mind that's a published procedure (traffic pattern with prescribed dimensions) with respective profile, meaning there are ALT and speeds prescribed and they are compulsory. Whereas in the west there aren't prescribed traffic pattern, except visual one. That's why you see people coming from 15 to 9,7,5 miles final sometimes too high too hot or what is even more dangerous too low. Its different story though.
Well that would be my approach to this issue,
Cheers.
P.S. Sorry for editing.
Well that would be my approach to this issue,
Cheers.
P.S. Sorry for editing.
Last edited by Flying Daggers; 1st Jan 2006 at 18:57.
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Re: Self-positioned ILS approach
...well...
...because they are radar vectoring charts, perhaps? I do not have an uplink to ground-based secondary radar, therefore do not have the means to apply the correct position. It's a bit like flying an ILS approach without an operational LOC reciever, innit?
Empty
...because they are radar vectoring charts, perhaps? I do not have an uplink to ground-based secondary radar, therefore do not have the means to apply the correct position. It's a bit like flying an ILS approach without an operational LOC reciever, innit?
Empty
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Re: Self-positioned ILS approach
Flying Daggers, that's a good remark about the traffic pattern. Having flown one of the eastern made airplanes I can only confirm that even the SOP (approach phase) was adjusted to the standard traffic pattern (5 NM final and 2,5 lateral).
Interesting though was the fact, that SOP prescribed to take the gear first, so you will never face a hot approach as you have to be at the right alt at base anyway. Simple, but very effective.
Cheers.
Interesting though was the fact, that SOP prescribed to take the gear first, so you will never face a hot approach as you have to be at the right alt at base anyway. Simple, but very effective.
Cheers.