Heathrow Glideslope Increases

[rolandc]

I hear there are renewed calls for the Heathrow glideslope to be significantly increased to counteract noise pollution from the ideas for new flighpaths in the latest consultation (Airspace and Future Operations Consultation).
Good idea?

[DaveReidUK]

PPRuNe: LHR Glideslope 3.5degrees? (https://www.pprune.org/atc-issues/586352-lhr-glideslope-3-5degrees.html)

[Gonzo]

There is a long term 3.2 RNAV trial going on, and there have been trials of steeper segmented glide slopes (4.0 degrees then changing to 3.0 degrees at 4DME, that type of thing) as well.

There are a few problems.

Once you get above 3.2 then CAT III approaches are not going to be flown (that’s the certification limit for most airliners (well, 3.25)).

Once you get above 3.5 degrees then energy and speed management become very critical, so the chances of aircraft being able to maintain an ATC-specified speed down final approach with minimum separation both ahead and behind become slim to non-existent. On some of the vertical segmented trials, 777s had to be flying at 160kts at 25nm from touchdown joining the 4.0 degree slope to ensure they were still flying 160kts at 4DME and able to slow to finally approach speed. Modern airliners are so efficient in terms of drag that they are difficult enough to slow down without hanging everything down which actually makes them a lot more noisy than a cleaner aircraft on a 3 degree slope.

[DaveReidUK]

Hence the old saying: "you can't go down and slow down at the same time".

[P160]

Perhaps all airlines should be issued with Dash 6's and then a 7.5 deg glideslope can be flown, LCA and Plymouth all over again.

[DaveReidUK]

LCY GS is 5.5°.

[P160]

When originally installed, the glideslope at LCA and Plymouth were commisioned at 7.5 degrees, the DHC Dash 6 was the only type certified to operate this angle of approach. But with production of this aircraft ceased trials were done to certify other a/c types to operate at 5.5 degrees. I'm not sure when the changeover took place but LCA operated at 7.5 deg for quite a few years from its opening date in the late 80's.

[DaveReidUK]

When originally installed, the glideslope at LCA and Plymouth were commisioned at 7.5 degrees, the DHC Dash 6 was the only type certified to operate this angle of approach. But with production of this aircraft ceased trials were done to certify other a/c types to operate at 5.5 degrees. I'm not sure when the changeover took place but LCA operated at 7.5 deg for quite a few years from its opening date in the late 80's.

Interesting - though I think you mean the 50-seat Dash 7s (DHC-7) of Brymon and London City Airways rather than the Dash 6 (DHC-6 Twin Otter).

https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/268x167/dhc_7_g_boay_london_city_aws_lcy_31_10_88_edited_2_c50a46249 a342a9deb638385be4391cf57588b3c.jpg

LCY wouldn't have been viable if only the 19-seat Twotter had been able to operate there.

[P160]

My bad, I meant the four engined DHC dash whichever, sorry. The Bae 146 carried out extensive flight trials to prove it could fly a higher angle than 3 deg but 7.5 wasn't achievable so 5.5 was settled for and since then other types have been certified at this lower angle

[pilotmike]

Perhaps all airlines should be issued with Dash 6's and then a 7.5 deg glideslope can be flown, LCA and Plymouth all over again.

When originally installed, the glideslope at LCA and Plymouth were commisioned at 7.5 degrees, the DHC Dash 6 was the only type certified to operate this angle of approach. But with production of this aircraft ceased trials were done to certify other a/c types to operate at 5.5 degrees. I'm not sure when the changeover took place but LCA operated at 7.5 deg for quite a few years from its opening date in the late 80's.
I was not aware Larnaca ever had a steeper glideslope. But LCY on the other hand.....

[safetypee]

Because of the difficulties discussed above, steep approaches greater than 4 deg (last time I looked at regs) require that the aircraft be specifically certificated for these operations. Basically to show manoeuvre margin and flare / GA handling. The ability to manoeuvre is directly related to drag - slow down, minimum thrust - air bleed / elect gen.
Actual operations encounter further difficulties, as above, particularly with AWO category, and ATC management.

Steep / two-segment approaches have noise advantages - the main issue at LCY.
Modern aircraft are generally quieter and distant nose is minimised with managed drag etc.

High density airport operations have considered wake turbulence - landing rate advantages when intermixing std / heavy aircraft; those capable of steep approach can land long with separate guidance, but see limits above. Possible ATC implications.

Many new types can achieve category 2, steep approach accuracies. Manual landing in these conditions is ‘disliked’ by the authorities - although the crew have a better view than a standard approach. Autoland is a certification cost issue; Avro RJ had ‘the feel’ of an aircraft which could achieve a steep auto-land - manual landing certificated at 6 deg.

RAE showed steep auto-land capability with HS748 and BAC 1-11 in the 1970s.

[Gonzo]

I think it’s 4.49 degrees now, the limit before special training and certification is required.

[P160]

Apologies pilotmike, I'm a retired NATS Engineer and our references to airports were not the same codes as used by the ATCO's. I do now remember when London City was in the planning stage it could not have the designator LCA as it was already allocated, the NDB had its ident as LCY not LCA as requested.

[DaveReidUK]

I'm a retired NATS Engineer and our references to airports were not the same codes as used by the ATCO's. I do now remember when London City was in the planning stage it could not have the designator LCA as it was already allocated, the NDB had its ident as LCY not LCA as requested.

To be fair, LCA is commonly used as an acronym (not a code) for the airport by local councils, the CAA and indeed by the airport itself, in contexts where use of an IATA code would just be confusing.

But probably best not used in the PPRuNe ATC Forum. :O

[poldek77]

Once you get above 3.2 then CAT III approaches are not going to be flown (that’s the certification limit for most airliners (well, 3.25)).


When you look at FRA, there are two ILSes installed for the same runway, e.g. 25R - ILS Y and ILS Z. Different frequencies, GS angles 3 or 3.2 degrees, minimums for Cat I or Cat IIIb. In marginal weather you may expect ILS Z, otherwise Y.
Maybe LHR can have similar system, with descent angles 3 and 3.5 respectively?

[chevvron]

There used to be a list in the AIP showing an extra 'allowance' to be added to DH for GPs above 3 deg in order to compensate for greater drift down when carrying out a missed approach.

[DaveReidUK]

When you look at FRA, there are two ILSes installed for the same runway.

Maybe LHR can have similar system, with descent angles 3 and 3.5 respectively?

In the trials that Heathrow can undertaken over the last few years, the ILS has remained at 3° and arriving aircraft have had a choice between a conventional ILS approach or a published 3.2° RNAV 0.3 approach.

3.2° Slightly Steeper Approach Trial Report (https://www.heathrow.com/file_source/HeathrowNoise/Static/Heathrow_Slightly_Steeper_Approach_Trial_Report.pdf)