Vectors to ILS

[Roff]

Is it common to be vectored onto the ILS and expected to intercept the glide path from above? I heard this is bad practice because of false glide path's but Atc have been known to do this on a few occasion's apparently.
Just a bit confused hearing the local's talk mid IMC course :rolleyes:

[Pull what]

No-- ATC should vector you so that you can I/C the glide path from below. Intercepting from above is usually pilot induced by being too high and too fast which can effect the stabilisation target of 1000ft IMC or 500ft VFR

[Big Pistons Forever]

While ATC will always try to vector you so that you intercept the localizer while still below the glideslope,, occasionally circumstances result in you being slightly above the GS on intercept. This is usually due to a wind that pushes you into the ILS early or ATC attempting to squeeze you in ahead of someone else which results in a short gate.

The bottom line is you should have the skill to transition from a moderately above the GS glide ILS capture, to a stabilized on loc, on GS, flight path. Of course continuing the approach is always at your discretion and if ATC leaves you high and dry you may be forced to abandon the approach and go missed.

This is one area where situational awareness is really important. Good SA will alert you to the possibility of an above the GS capture early allowing you to prepare for it.

[Spitoon]

ATC should always vector aircraft to intercept the localiser at a range that permits at least 2 miles of level flight before intercepting the glidepath from below. There are some good technical reasons for this procedure as well as making the flight profile more predictable. But, unfortunately controllers are human and sometimes don't achieve this for one reason or another - typical causes are that the aircraft has not descended as quickly as anticipated or the controller has tried to be helpful by keeping the pattern tight but misjudged it. Life's like that some days! Ideally the controller will keep you informed about how things are going - particularly if you are not going to follow the 'proper' profile. Remember that if the aircraft does not have mode C it is more difficult for the controller to spot if you are not descending as expected. Finally, if at any time you feel that things are getting tight you can ask ATC for a range from touchdown and also ask for some extra track miles if it will help to sort the aircraft out - the earlier you can ask the better and you may end up being repositioned, but never be afraid to ask.

[Pull what]

You havnt flown to Spain much then!!

[Roff]

Some great advice lad's, Lucky that Atc in the North West are really accommodating under any circumstances. I'm sure that help's..

I feel at ease already :cool::cool:

[IO540]

Is it common to be vectored onto the ILS and expected to intercept the glide path from above?

Yes; it happens quite often.

However, usually it happens when ATC have cleared you to descend to the platform altitude and you are descending a bit slower than the -2000fpm which they are used to :)

I heard this is bad practice because of false glide path's

True, but to pick up false glide paths you do need to be quite a bit above.

It is hugely helpful to monitor the situation on a decent size moving map GPS, on which the ILS inbound is displayed, so you can see what you are getting.

[BackPacker]

I think one of the suggested links in the chain of events that led to the Turkish Airlines Flight 1951 disaster (incidentally just a few miles from my home) was that ATC at Schiphol routinely vectored aircraft so that the localizer intercept would happen 5nm out, and they had to intercept the GS from above. This was done to optimize the flow of traffic, particularly during peak times.

[Big Pistons Forever]

It is hugely helpful to monitor the situation on a decent size moving map GPS, on which the ILS inbound is displayed, so you can see what you are getting.

I could not agree more. With the plethora of portable moving maps you are silly not to use one as an aid to situational awareness. The challenge is how to effectively integrate their information into a flight without letting stuff slip because you are mesmerized by the magic box, or use it when you don't need it and don't when you do.

This where training from an instructor who has real world experience flying A to B IFR is hugely valuable. Too many IFR instructors are still stuck in the fantasy land IFR of the flying school standard round robin of departure, hold, and two approaches at always the same two airports, that comprises a flying school IFR "trip". Proper use of moving map technology is a skill which should be taught as part of every IMC/IFR course.

In anticipation of snarky replies from those ludites who contend that "real" pilots don't need the help of a moving, I will say only fools willfully deprive themselves of all available navigational data.

My personal claim to fame is "17 yrs". 1994 was the last year I flew a NDB approach in actual IFR without GPS final track guidance from at least a hand held GPS. :ok:

[IO540]

How do continuous descents on airliners work w.r.t. glideslope interception?

Does ATC still vector them onto the localiser, conventionally, or is the descent worked out to end at an approx 3 degree angle, so the GS is intercepted at more or less the correct angle, and the autopilot is capable of locking onto the GS from both above and below? While locking onto the LOC at the same time of course.

I know this is not a 737 but I have noticed, during some tests, that the KFC225 autopilot I have will lock onto the GS from both below and from above, which suprised me. Not all GA autopilots will do that.

The other thing which I vaguely recall from my JAA IR theory ;) is that false glideslopes have the two lobes the wrong way up so if you locked onto one of them, an UP indication on the HSI actually means you have to fly DOWN. I have no idea if this is true but it sounds entirely plausible. It also means that no autopilot will be able to lock onto it because while a lot of APs have a REV button (for tracking a LOC back course) none I know of have a REV button for the GS :) Another thing is that modern EHSI-type avionics (e.g. the Sandel 3500 I have) suppress the GS indication if the LOC is displaying backwards e.g. if you are flying backwards along the LOC; this is correct since the back course approaches (used in the USA, not here) never have an authorised GS. So a false GS would be really bad news all around.

[Lord Spandex Masher]

How do continuous descents on airliners work w.r.t. glideslope interception?

It's sort of a judgement thing really. ATC give you the odd range check, we adjust our vertical profile to suit. We do attempt to intercept the LOC and the GS pretty much simultaneously and yes, occasionally, the GS from above. Although we're also prepared for an early turn in or a longer downwind.

Range checks seem to be a bit...erm...inaccurate depending where you are!

[mad_jock]

You know about what height you should be at anyway and there are those that use formula's to get it right and there are others that use the "force" and using a combination of ADF DME etc just get everything looking right so you get "capture capture, missed approach level set"

[RTN11]

As above, it is usually when they only clear you to the platform alt of say 2200', you then intercept the GS without having the LOC. If I see this happening, I would immediately request further descent they'll then usually let you drop further, to say 1800', to make sure you intercept from below.

[GeeWhizz]

Much of what's been said already answers many questions. So FWIW and to be explicit, we all know that a 3 deg GP descending from 2000' commences at approx 6.5nm out. (Not sure that unless absolutely necessary I'd like to fly an ILS without DME). A 7.5-10nm base leg is usual and sufficient for most aircraft types. Admittedly my knowledge of the airliners is limited.

If ATC are turning you in earlier without a descent to 1500' lets say (as in a Short Pattern Circuit) you should be going missed and asking for another feed IMO. It's a challenge to intercept the LOC, play with the RT, and track the GP all at the same time in the GA world. Even more so if you're not expecting the intercepting inbound turn and you've forgotten you're pre-landing checks ;)

I'm a non-moving map luddite, and like it that way... perhaps due to the lack of GPS equipped ac at my club, but looking forward to some training on it in good time.

[FlyingStone]

To be established on the localizer 2 miles before glideslop capture is usually privilege, which is not extended to small (slow) aircraft.

I think most problems during vectors appear with high winds aloft (20-30 kts+), since most controllers doesn't expect such an increase in speed with turns. Two weeks ago I was vectored for a localizer approach (G/S was unserviceable) followed by circling. When flying downwind (but effectively into the wind), TAS was about 130 kts, while GS was ~ 90kts. Since I expected problems, I requested descent 2 times, which ATC denied. Couple of minutes later, I got turn for base, and descent clearance - and the GS went from 90 to 140 kts. Despite trying to reduce speed and lose altitude, I was still high on the profile, but hell came loose when he gave me the intercept heading for the localizer, which increased my groundspeed significantly. I did everything I could, including extending gear, but still came overhead FAF 1000ft too high. Since the weather was quite nice (night with runway in sight, few clouds, I intercepted the non-precision approach from above (to fly it as CANPA), which I did 2 miles later and continued to a non-eventful circling approach and landing on the opposite runway. In theory, I would be vectored to the localizer to be established 2 miles before, be fully configured at FAF - if not, one should abort the approach and ask for a new one. I say again, in theory :)

On the topic of false glide slopes - you won't get near one if you're even 1000ft high at 8 miles, since at 8 miles you should be roughly 2400ft AAL, but for the 6° glideslope this height is 4800ft AAL. False glides slopes do appear and one can easily spot them following a departure in the opposite direction of the ILS (e.g. from runway to ILS FAP). I saw one go from full up to full down deflection when I was at ~ 700ft AAL overhead the middle marker when the 3° glideslope should obviously appear somewhere close to 200ft AAL.