LHR Glideslope 3.5degrees?
 

Theoretically speaking if the LHR Glideslope ever goes to 3.5 degrees (I believe that is a "working principle" of decision to allow 3rd runway??) would it be possible when LHR is on westerlies & LCY on easterlies that LCY inbounds could be at 2,400ft rather than 2,000ft?
(It doesn't "sound" like much difference but could make 1-2 decibels difference to people on the ground - but, given decibels are on a logarithmic scale the combination of higher LHR & LCY inbounds could well be appreciable).
Also, if both airports were on easterlies is the climb gradient/profile for LHR departures OK to allow LCY inbounds to be at 2,400ft rather than 2,000ft?

How's that gonna work in Heathrow fog then? :hmm: Because at 3.5° - under current rules - the system won't be anything better than Cat I; for Cat III: 3° shall be the angle of the GP and the angle of the GP shall be 3°. And I don't know of any ILS installation that has a 'set glidepath angle for the day' switch. Usually any change to GP parameters is subject to a thorough Flight Inspection - especially for Cat III installations.

Ignore current rules then. Would 1000ft separation between LHR westerly arrivals and LCY easterly arrivals at 2400ft be guaranteed?
(And also 1,000ft between LHR easterly departures vs LCY easterly arrivals?)

If it goes to 3.5 degrees it would increase the vertical separation twixt Heathrow and City... or am I missing something?

Yes, I was wondering if you could raise LCY arrivals from 2000ft to 2400ft on base leg for RW09

At this stage, 3.5° approaches at LHR are an aspiration rather than a commitment and the 3rd runway decision isn't going be be conditional on their introduction.

The runway 14 ILS glidepath at Leeds Bradford
is 3.5 degrees and has been since the ILS was commissioned more than 25 years ago. It's only ever been a Cat 1 system and that is the best that can be hoped for apparently. It is technically possible to adjust the GP to 3 degrees but the obstructions on the approach would still be there. This may not be relevant to Heathrow but it presents a wider context.

At present, yes.

Most modern aircraft have the capability to perform up to 3.25° Cat III approaches at suitably-equipped airfields, with one exception being earlier A320s which are limited to 3.15°.

How did the 3.2degree trial go? And was that Cat I only?

When RW14 was RW15 (pre-extension) there was no ILS but the nominal GP angle was 3.25 degrees, used for SRAs. If that were achievable today, perhaps an improvement on Cat 1 would be possible. Anyway, back to Heathrow.

Heathrow Slightly Steeper Approach Trial Summary

Steeper Approach Trial Report

Yes.

Thanks Dave

So, let's say the CAA made an exception that LHR could use 3.15degree Glideslope for noise/environmental reasons rather than obstacle clearance....by my calculations it would be OK when LHR is on westerlies and LCY is on easterlies that the LCY inbounds could be at 2,200ft rather than 2,000ft?

What would be the point in stopping the LCY traffic at a higher altitude?

Higher = quieter for people on the ground

Higher = slightly more fuel efficient/less CO2

As Sainsbury says "every little helps"

(And of course if both LHR and LCY are higher then it is better on both counts....cummulative effect)

Good luck with 160knots to 4miles with a 3.5 degree slope too.

In theory perfectly possible if you're using thrust against drag until that point, however on both the noise and environmental (fuel) points you would be failing miserably to the point of being counterproductive.

That was one of the concerns before the 3.2° trial but which, both evidentially and anecdotally, turned out not to be an issue.

In fact adherence to the 160 to 4DME rule was slightly better for the aircraft involved in the trial than for those making 3° approaches.

Go figure, as they say.

Of course, it was more of a 3.1 degree trial for a lot of the time anyway!

The double slope flights, where the first slope was 4 or 4.49 degrees until merging on to the 3 degreee slope at 4-5nm highlighted the energy management issues.

I have to say a few pages on the report contained operational errors...

The increase in speed control on final was probably due to the fact that crews who flew them were probably in the 'more competant' category and not for any other factor. The fact that as Gonzo stated above it was more like a 3.1 degree trial probably negated that point anyhow! Some of the fleets mentioned in the report don't deploy gear based on altitude, but do so on the DME reading. An RNAV approach isn't a CAT I approach, and you need considerably more than 550m visibility to fly it!

RNAV is counted as a non-precision approach. GLS counts as a precision approach (which is PBN based too)...

The 09L RNAV (Z not the Y in the report) has a MDH around 500'

I'm confused.

The report simply says that all the trial RNAV approaches were made in Cat I conditions (RVR not less than 550m).

As far as I can see, it doesn't assert anywhere that RNAV and Cat I are synonymous.