Vectors For ILS Approach

[Jon Wilder 1268033]

I've noticed for quite a while that controllers seem to like vectoring you in a fashion where you're capturing localizer and glideslope simultaneously. While this sounds cool in theory, this only works if you're hand flying the approach. If you're doing a CATIII approach, the autopilot wants to capture the localizer first, then capture the glideslope. Knowing this, it makes more sense to bring them in below glideslope, let them capture the localiser, then fly into the glideslope.

 

Is this something controllers can work on in their vectoring?

[Evan Reiter]

We should be vectoring you to intercept from below the glideslope, as a standard. It can happen the other way around, and the best practice (if you're not hand flying) would probably be to use Flight Level Change or a Vertical Speed mode to descend below the glideslope before arming the approach.

 

Agree that vectoring to join above/on the glideslope is something controllers should strive to avoid (but it's not strictly-speaking illegal as far as I know).

[Andreas Fuchs]

I can only [Mod - Happy Thoughts]ume that those ATCOs do it unintentionally. Best is if you give feedback to your ATCO next time this happens in order to make sure he understands that it is advisable to always allow 2NM to 3NM on the LOC before reaching the Final Approach Point (GS-intercept).

If an ATCO realizes that him turning you onto the ILS was a bit too optimistic, he can give you to the option "descend with the glide" to avoid intercepting the GS from above. Obviously this can only be done in situations where obstacles are not an issue.

[Simon Kelsey]

Fairly common, however, in the UK (at least) where continuous descent approaches are often mandated - the objective is to minimise or eliminate level segments prior to glidepath intercept and this is how the vectors are typically arranged. At Heathrow in particular there are also limits on how low you can be cleared when establishing on the westerly runways (generally not below 3,000ft outside 10NM) due to both noise constraints and interactions with London City departures.

 

As a pilot it is obviously incomebent on you to manage the descent in such a way that you are able to both achieve a continuous descent (defined in the UK as no more than one period of level flight exceeding 2.5nm below 6,000ft) and establish safely (and this is why the controller should give you the number of track miles to touchdown, so that you can do the maths), and there are times when it may be necessary to request lower if you are about to level off at the cleared altitude and you can see that you are going to get high, but from a technical point of view on most aircraft there's no issue with intercepting the localiser and glidepath more or less simultaneously, provided you are on or just slightly below the glidepath when LOC annunciates.

 

If everything has worked out perfectly both from your point of view and the controller's, you should get a nice full house on the FMA as you establish with SPD | LOC | GS all lighting up simultaneously!

 

(NB: none of the above applicable Stateside where the expectation is that any descent clearance is achieved at the maximum rate, i.e. with idle thrust).

[Andreas Fuchs]

Of course it is possible to intercept LOC and GS simultaneously, but us pilots absolutely detest it. I prefer having a clean LOC intercept and then a separate GS-intercept and if it is just with a gap of 10 or 20 seconds in between. It's especially the UK with this "intercept localizer, when established on localizer descend with the glide" phraseo, where it could just say "cleared ILS approach runway xx". I know, I know, the super special UK phraseo wants to make sure that pilots will maintain the last [Mod - Happy Thoughts]igned altitude until intercepting the glideslope, but the rest of the world has solved this nearly impossible task by saying "maintain xxxx ft until established on the ILS". Wohoooo!

[Kirk Christie]

Depending what aircraft you are flying, in terms of PMDG ect, there is often options to allow the aircraft to capture the glide slope before the LOC, and vise versa.

[Andreas Fuchs]

But please don't do it, it is unrealistic.

[Kirk Christie]

But please don't do it, it is unrealistic.

 

So is flying a 747 at 16 years of age across entire countries on unicom, whats your point?

[Steven Perry]

Jon,

 

I'm guilty from time to time and I do apologize.

 

By the book, I am not allowed to vector aircraft to final in the USA when I am working an en route center sector and covering 100,000 square miles. The FAA has some requirements regarding display ranges and I often am not meeting them.

 

That said, I often find pilots are unclear of what to do when I give a full approach clearance from an IAF.

 

So, I give the option - "would you like the full approach or vectors to final"? If you take vectors, my vectors can be sloppy. I do err on the side of a long final rather than being too high to capture the GS though.

 

Agree that vectoring to join above/on the glideslope is something controllers should strive to avoid (but it's not strictly-speaking illegal as far as I know).

See the 7110.65...

For a precision approach, [vector arriving aircraft to intercept the final approach course] at an altitude not above the glideslope...

[Martin Loxbo]

But please don't do it, it is unrealistic.

 

If you refer to capturing the G/S before the LOC, I agree that's unrealistic as it would be potentially dangerous, as if you're not on the LOC (i.e. on the centreline), you don't know that you have the obstacle clearance to descend below the platform altitude.

 

If you're referring to capture G/S and LOC simultaneously, that's pretty much what we strive for at least in my airline since it's the most fuel and noise efficient way of flying, as ideally the engines will only have to spool up by the time you lower the landing gear (which we normally do at 4 NM from the threshold).

[Andreas Fuchs]

@Martin: Yes, we are talking about intercepting the GS before the LOC. You can do this in VMC and with ATC's approval. As a vATCO I sometimes tell people to "descend with the glide" when I realize that my instructions will put pilots way too close to the Final Approach Point or even past it. This should only be done if there no obstacles around, of course. In places like Frankfurt this kind of recovery of bad vectoring is possible, in Chambery maybe not so much

 

Now, intercepting LOC+GS at the same time: that depends on the type of aircraft! You guys in your airliners can do it, because you have high speed limits for slats/flaps and the landing gear. On my Falcon 2000EX EASy we are somewhat limited. Max speed for flaps is 200 KIAS, the gear must not be moved above 190 KIAS, due to the gear doors. When I intercept the LOC+GS at say 2000ft/6NM and 250 KIAS, I will not be able to slow down without the use of speedbrakes and we all know very well that speedbrakes are for pilot errors only ( <== traces of sarcasm are contained in my previous sentence). In clean configuration the Falcon will keep almost any speed that you have when on a 3 degree glideslope. That's why I am happy to have a short level off phase of 2 NM to 4 NM (depending on weight) to bleed off speed before intercepting the glide and I won't need to touch the thrust levers until lowering the gear. You can say that I should manage my speed better before: yeah, we are trying this, but sometimes vectors can be a bit tight and winter-conditions with its [Mod - Happy Thoughts]ociate use of anti-ice systems make it harder. On top of it our normal descent angle is between 4 and 5 degrees (depending on weight...), as I will have to add quite a bit of thrust when descending at 3 degrees. It is a bit different than an airliner, in this respect.

[Martin Loxbo]

Every aircraft type is different of course, and every SOP as well. The B738s that I fly are very slippery, but we try to slow down fairly early (max 200 knots at 10 NM from the threshold). What we don't like is level segments with thrust on. Thankfully this is rarely forced by ATC, except in cases with parallel approaches where we have to descend early to the platform altitude in order to have 1000' separation to aircraft joining the approach for the parallel runway.

 

I would say, from an ATC perspective, if you tell the pilot to "descend on the glide" because the aircraft is on the vertical profile but not yet on the centreline, and it means the aircraft might go below the MSA or minimum vectoring altitude before being established on the approach, then you've effectively transferred the responsibility for terrain clearance to the pilot.

 

I've only ever heard "descend on the glide" in the context that ATC gives clearance for the ILS approach from a higher altitude than the platform altitude, i.e. expecting that the aircraft will stay at the cleared altitude until meeting the G/S instead of descending to the platform altitude.

 

To play it safe, I would personally clear the aircraft to descend to a lower altitude than the "platform" if necessary (i.e. if intercepting inside the FAP), but only if that lower altitude is still at or above the minimum vectoring altitude.

[Andreas Fuchs]

"Descend with the glide" is not the same as "descend on the glide". The first means that you start descending with the glide while you are still intercept the LOC. The latter means to "descend on the glideslope when established on the LOC". At least to my understanding.

 

And of course you cannot do this at 2000ft AGL... As long as the plane is above MVRA and LOC-intercept is expected before reaching MVRA, there's not problem with it. I have not heard or done it in the real world for a while, but it can happen. Better than messing up an approach, because you have to dive for the glide.

 

Ultimately I do not care too much about the fuel used, because we are primarily employed to fly safely, economy comes second.