Between 7 and 4....

[Duchess_Driver]

Often heard ATC using the phrase....

"The only speed restriction is xxxknots between 7 and 4 miles."

I can uncerstand the need to slow traffic for spacing incoming traffic or to allow a departure. But why the specifics of such a narrow band for the restriction....knowing that closer than 4 miles they'd be slowing below the usual speed quoted for xxx.

TIA

DD

[HEATHROW DIRECTOR]

Never heard that. Speed control for spacing is normally imposed when the aircraft is established on the ILS, whether it's at 6 or 15 miles.

[Duchess_Driver]

More often than not I hear it on Luton. It may be 8 and 4 but usually it's 7 and 4.

Just curious...

[Level bust]

Lazy way of doing speed control?

Used to be specific speeds at specific time/distance in my day.

[Dan Dare]

Pilots need to been stable on approach at some point in order to be allowed to land. Controllers need some predictability in order to move traffic. Aircraft fly most efficiently when clean (no flaps, gear etc.) and therefore quick. The compromise to achieve this has been to work 160 kt to 4 nm (which often requires some extra drag) or 170 kt to 5 nm (which then makes stable approach more of a challenge). Each aircraft type/loading has different requirements.

Once upon a time ATC was there to be safe, orderly and expeditious. Today we live in a world where if there is a blame there is a claim; Managers can be accountable enough to go to jail if it goes wrong; Nobody in their right mind would go from competence controlling air traffic to managing those who do; ATC is often managed by people with little or no understanding of ATC, who compensate by use of key performance indicators, which they do understand a little. KPIs can be used for any irrelevance, but once they have been set then they are the target to be achieved.

A safe, orderly and expeditious world would have experienced, multi-skilled staff managing inbound energy to provide the required time or separation between arrivals. A KPI world doesn't care about any of this provided that every aircraft has had a continuous descent approach and speed control between 7 and 4 miles. To management they may look as though they provide the same thing, but KPIs remove flexibility to provide service and I have yet to experience a set of KPIs without perverse consequences. KPIs allow management to ask why 20% of arrivals did not meet KPIs without understanding that each combination of flights is different.

The future will be a system, which allows time-based spacing and allows pilots to fly the most efficient approaches in a manner which predictably keeps runway movement rates up. Come the revolution KPIs will be chopped, but I won't hold my breath.

[Eric T Cartman]

@ Dan Dare
:D A brilliant post, IMHO, but there again, I have been described as an ATC dinosaur :hmm:

[Gonzo]

The compromise to achieve this has been to work 160 kt to 4 nm (which often requires some extra drag) or 170 kt to 5 nm (which then makes stable approach more of a challenge)

Are you sure? Many airlines I've spoken to would prefer 170 to 5 purely because of the increase in the chances of achieving the landing stabilisation criteria. The most common stability gate is at 1000ft, so 170 to 5 only adds another ten knots on to the speed reduction, but gives an extra mile to achieve it.

[30W]

At busy airports we all accept speed control as the 'norm', and so the final approach speed restriction is only the last of a stream of ATC separation/sequencing tools.

At less busy airfields often no intermediate speed restristion is placed on arrivals, as gaps are such that they're not required. These often resulted in no requirement for a final approach speed restriction to be applied either. Great for the pilot (me), as one could manage the approach hopefully in the most efficient manner.

The above however does create other issues. The lack of predictability to the aerodrome controller in organising departures from a single runway (empty runway time available), has often in my experience resulted in missed departure opportunities, and hence caused ground delay, and consequently less efficient runway usage. For those that don't beleive what range of speeds seem to be flown between 7 and 4, well the radar evidence of the difference is quite staggering between aircraft types, and indeed different operators!

BHX (EGBB) from which I operated until recently was a classic for this, and hence introduced the from '7 to 4' rule to help overcome this issue. Although not immediately visible to the arriving aircraft (especially if no one is ahead of you!), there IS a bigger picture and OVERALL system efficiency and predictability being achieved. As such I'm in full support of the initiative which was introduced :ok:

[HeathrowDictator]

Hi all,

Interesting thread, I am now in the Middle East and use speed control on final approach regularly. With the variety of aircraft we have operating, all seem to want to do different things (even though it's the same company a lot of the time). Sometimes, 320s if not sped are doing 220kts at intercept (11nm), sometimes they are back at 140kts 15nm out.

Generally, 160kt to 5nm works here - occasionally they try and get away with different - those who do ask though sometimes request 160kt to 6nm in order to help stabalise for the approach.

I'm fortunate enough to have good quality tower controllers upstairs who more often than not will spot any discrepancies in speed and sort them out :)

-HD-

[tori chelli]

I think this may be Luton specific. Given that their tower controllers are tower-only (I know this is the case at other Airports with 'London' in their name) it was agreed that all traffic, irrespective of whether there was a sequence, or they were the only one in the sky; would be 'sped' so that the tower controller didn't get caught out entering and backtracking in front of an inbound coming down the ILS very quickly. So everyone gets the same treatment, even if they haven't been 'sped' up to that point in the approach.

I know it seems simplistic overkill, but if you've never done radar, interpreting the trail dots in an aquired art...or maybe its a KPI :E :E

Tori

p.s DD, can a BE76 do 160K on the approach? :eek:

[ZOOKER]

Mr. Cartman,
I once had a young management whippersnapper apply the same description to me.
I politely pointed out that 'Dinosaurs' were amongst the most successful animals ever, surviving for about 160,000,000 years. :ok:
I also pointed out that, had it hot been for the unfortunate trajectory of the K/T impactor, they would probably still be happily roaming the forests where his office now stands! :E

[30W]

I think this may be Luton specific.

Afraid not - read my earlier post. However I'm still a supporter of it, I believe it has benefits for ALL parties.....