I was set up for the ILS 32 at EDXW. After breaking through the clouds somewhere between 8000ft and 6000ft I was taken down by ATC to 3000ft while on a heading going almost North. The weather was fine. No clouds below 6000ft and good visibility. There was one IFR departure. That was probably the reason why I was not cleared for the ILS yet but instead was given an vector out of LANAS.
A bit later the departure was out of the way and ATC instructed me to fly heading 300. That had me intercept the localizer at around D8 WES. My avionics did not capture the glideslope as I was intercepting the localizer past the FAF, which is D10.5 WES.
After intercepting the localizer I was a bit puzzled for a second (hmmm?) and then started to loose altitude. It wasn’t really my explicit intention to capture the glideslope from above. My intentions were to circle to land on RWY 24 and I had advised about that early.
While I was getting closer there was a jet waiting to depart and Tower asked me whether I want to cancel IFR so that the jet can depart. I did, the jet got cleared for takeoff and I started my circle to RWY 24 by breaking off to the right.
In all that was all very relaxed and no problem at all. Still it has me thinking. I have little doubt that in IMC ATC would never have vectored me behind the FAF. But then on the other hand I would like to know:
Am I supposed to dive down to the glideslope? I guess I’m not, as the glideslope should be intercepted from below. What would you have done in this situation – given that you want to stick to flying the ILS?
Sure, I could have asked for a visual approach in the first place. I need to remind myself of that on a CAVOK day. Attached is a screenshot of the approach plate.
There’s nothing to stop you intercepting the GS from above, but there are traps for the unwary. You’ll be descending faster and possibly accelerating so it’s possible to get behind the aircraft, miss checks, and end up unstabilised. In order to prevent descending into the ground you need to arm an altitude for capture that will keep you safe it you haven’t captured the GS.
If you can’t capture the GS by the FAF it’s probably best to go around.
We’re allowed to do it in the airline but we have to be stabilised (fully configured, checks complete, on LOC and GS, speed Vref +15 to -0 and power not at idle) by the FAF.
ATC actually quite often leave you with work to do to intercept the glide. Just dirty up and drop down onto it. They “shouldn’t” of course, but they do. It is good practice not to arm the autopilot approach mode when intercepting from above to avoid the danger of false glide slope capture.
We also do a gross error check – ie. 7 miles, 2100agl, looks like the correct glideslope before using the approach mode.
Am I supposed to dive down to the glideslope? I guess I’m not, as the glideslope should be intercepted from below. What would you have done in this situation – given that you want to stick to flying the ILS?
You didn’t say you were cleared for the approach. Unless you are, you’re not allowed to descend.
I have little doubt that in IMC ATC would never have vectored me behind the FA
I believe they have to vector you to intercept at 8 NM the latest.
I guess I’m not, as the glideslope should be intercepted from below.
That’s how it should be but it’s not a given. Intercept from above is quite frequent, especially with a slow aircraft at a busy airport.
Sure, I could have asked for a visual approach in the first place. I need to remind myself of that on a CAVOK day.
Yes, otherwise you’re an annoyance to the airport if it has other traffic. AOCs are usually prohibited from conducting visual approaches (> 5.7t). Everybody is required to do what he can to ensure the orderly flow of traffic and avoid unnecessary delays and that just means doing a visual approach when the weather is fine.
AOCs are usually prohibited from conducting visual approaches (> 5.7t).
No, we can fly visual approaches, and often do, but we can’t cancel IFR.
…AOCs are usually prohibited from conducting visual approaches (> 5.7t).
The 5,7 ton limit is rather an airport/noise abatement thing (like at my home base) than AOC related. Our AOC does not prohibit visual approaches and as business aviators we serve a lot of small airfields that are VFR only, so we can cancel IFR if required and if the conditions permit.
As part of a routine flight calibration check we ensure satisfactory signal strength and correct-sense fly-up/fly-down signals at the equivalent of half scale deflection. There are no guarantees that you will get a suitably strong/correct command bar if you are beyond this point. An additional check is done whereby a level slice is flown (normally 1000ft above landing threshold) where the signal strength is recorded from 0.3-1.75 Theta where Theta is the G/P angle. That said, traditionally, a false lobe will appear at about 2 x the ideal G/P (i.e. if the G/P is meant to be 3 degrees you would get a false lobe, indicating in the incorrect sense at about 6 degrees).
Attacking the G/P from above is not best practise and too many agencies seem to accept it as a matter of routine. All the warnings above about speed, configuration, rate of descent etc hold true and it is imperative that you get a sensible range/alt check at FAF or some other fix. If you don’t like it, throw away the approach and ask ATC to sequence you properly.
How exactly do airlines fly continuous descents, unless they either intercept from the above sometimes or they have some means of calculating and flying a vertical profile which gives them an intercept from below, while starting from 100-200nm back?
In the latter case they would need ATC co-operation for the precise continuous descent, but I have never heard any phraseology on the radio indicating they get anything other than the usual stepped descent clearances so any continuous descent profile has to be “hacked” within that clearance.
I have asked this Q a number of times in a number of places and never got a clear answer, but there must be one since this is done many times every day.
I have been sent above the GS a number times and I suspect it happened because the ATCO was expecting a much higher rate of descent than the 500-800fpm I was probably doing. If it was serious IMC I would probably disable the APR mode, go through the LOC, and tell him right away.
Swedish ATC and Arlanda airport made a lot of fuzz about their green environmentally friendly approaches a few years ago. From what I’ve understood it was a coordinated continous descent.
Perhaps someone else have more info about it, I don’t know how successful. IIRC correct it required something from the operator/aircraft as well.
How exactly do airlines fly continuous descents, unless they either intercept from the above sometimes or they have some means of calculating and flying a vertical profile which gives them an intercept from below, while starting from 100-200nm back?
In the latter case they would need ATC co-operation for the precise continuous descent, but I have never heard any phraseology on the radio indicating they get anything other than the usual stepped descent clearances so any continuous descent profile has to be “hacked” within that clearance.
Modern aircraft calculate a Top of Descent automatically, helped by us entering a “gate” FL/altitude, either an altitude restriction on the STAR (e.g. FL80/220 kt by LAM) or by local knowledge and experience (e.g. 3000 ft/180 kt by 12 nm). If we then carry out a “managed descent” the aircraft does its thing, displaying the “virtual glideslope” or optimum vertical descent path on the PFD (Primary Flight Display).
Closer to the ground, we are expected to fly a continuous descent for noise abatement reasons once we leave the holding fix (LHR: LAM/BNN/BIG/OCK). We usually leave the hold at FL80 and the next descent is to 4,000 ft QNH so we adjust the VS so that we are a little below the GS on base leg with flap 1 and capture the GS without levelling off with flap 2 (for heavy Airbuses). There is no explicit phraseology from ATC and it’s not that hard as long as you’re thinking about it. Airlines’ records on continuous descents from the hold are published – VS are usually among the best performers.
And yes, sometimes we or ATC screw it up and we have to capture the GS from above. Trying to slow down, descend, configure and capture from above in an aircraft weighing up to 259 tonnes (A340-600) is not easy and it can easily go wrong. Don’t ask me how I know.
In the old days we worked it all out manually, “FL / 3” plus or minus 2 nm per 10 kt wind and a weight adjustment. So FL330 divided by 3 = 110 nm plus 6nm for an average 30 kt tailwind on descent – another guess – so we’d ask for descent 116 nm from touchdown. Obviously it went wrong more often in those days…
