speed reduction

[mgTF]

hi, here's a question for you:
I'm flying into a congestioned airport, atc gives me a speed reduction during descent, how fast should I reduce the speed, and what is the admitted tolerance on that speed?
thanks

[1985]

how fast should I reduce the speed


as quickly as possible


what is the admitted tolerance on that speed?



if given a precise speed to fly then fly it. afaik there is no tolerance.

[Jerricho]

what is the admitted tolerance on that speed?

U.S./Canada regs state plus or minus 10 kts but realistically, unless unable for operational reasons (which you should be telling us), if assigned a speed, it's for a specific reason.

[eyeinthesky]

Reduce at 1kt per second.

[Denti]

Fastest way to bleed off speed without climbing is to level off until the desired speed is reached. So is that what you suggest 1985?

Most annoying though is a required speed reduction with a rather high given rate of descent or even being asked to increase your rate. There are allways more than enough controllers who try that stunt.

[mini-jumbo]

if given a precise speed to fly then fly it. afaik there is no tolerance.

I'll fly a given speed as accurately as I can read the ASI.

[Jerricho]

......and as I overheard a pilot say one day

"Speed brakes are for our mistakes........not yours!"

[yoCu]

Often needing expidite but keep the speed back means something along the line has not gone to plan or something has changed last minute. In that situation would it be better/ easier to issue a ground speed restriction rather than an IAS restriction?
Obviously if it's that much of a problem there's always the option of a vector or an orbit.

[320 or greater]

My mind may be fuzzy, but doesn't the aip state for the london tma inbounds the speed requirements are exact, not the usual plus or minus 10kt otherwise the ac must inform us they are unable the restriction?

[tc_atco]

I'd expect the rate of speed reduction to vary in accordance with your descent profile. If your a bit high and haven't got so many miles from TD, I'd expect you to take a while to lose the speed. I'd take that into account and not stuff you up behind the preceeding. However if its a reasonable descent profile I'd expect a pretty quick speed reduction. Now we have Mode S downloads in the london TMA we can see exactly what speed you're doing and we're aware that A319s (particularly British operators) and 757s are particularly slippery ships.

Regarding speed tolerances, as far as I'm concerned in an approach situation there is no tolerance, fly the speed exactly. If you can't, tell us. Its not a huge deal, but it is if we don't know!

[Jumbo Driver]

I would say it depends on many factors.

First, if you are in the descent, you would be expected to maintain a minimum rate of descent (RoD) of 500'/min. (unless ATC requested otherwise) until you reach your cleared level or altitude.

Operationally, if you are a light twin for example, you will not want to idle your engines so there will be a minimum power level below which you would not choose to reduce further. If you are a heavy jet, you will probably be at idle thrust already, so in either case you will simply trade RoD for speed reduction until the required is achieved, then resume the RoD that the new IAS produces.

In any event, ATC should appreciate that you cannot both "go down and slow down" so, unless there is a need to expedite the decent at the same time as a speed reduction (which usually means an ATC c0ck-up), they will expect your RoD to reduce while you slow and a speed reduction of around 1kt/sec would be a normal descent profile. However, if they do ask you to do both, then convention says they owe you several beers!

You are generally expected to fly any cleared speed within +/-10kts.


JD
:)

[320 or greater]

RE JD, i agree on the expedite / reduce speed scenario but i refer you to the aip for london tma inbounds where there are no speed tolerances permittable unless you tell atc you can't comply

[Jumbo Driver]

320 or greater, can you provide an AIP reference for this please?


JD
:)

[Roffa]

Jumbo Driver,

Here's an example of what the AIP says for Heathrow...

Speed Control: Pilots should typically expect the following speed restrictions to be enforced: 220 kt from the holding facility during the
initial approach phase; 180 kt on base leg/closing heading to final approach; between 180 kt and 160 kt when established on final
approach and thereafter 160 kt to 4 DME. These speeds are applied for ATC separation purposes and are mandatory. In the event of a
new (non-speed related) ATC instruction being issued (eg an instruction to descend on ILS) pilots shall continue to maintain the previously
allocated speed. All speed restrictions are to be flown as accurately as possible. Aircraft unable to conform to these speeds must inform
ATC and state what speeds can be used. In the interests of accurate spacing, pilots are requested to comply with speed adjustments as
promptly as is feasible within their own operational constraints. Pilots should advise ATC if circumstances necessitate a change of speed
for aircraft performance reasons.

Most a/c doing CDAs into LHR seem to be able to go down, slow down and fly the requested speeds fairly accurately and, as mentioned, we can now see who isn't/doesn't.

The belief that there's a +/- 10kt tolerance perhaps stems from flight tests where that may be true. In the day to day operation in busy airspace such tolerance doesn't exist and speeds shown be flown as accurately as possible unless stated otherwise.

[Jumbo Driver]

Roffa, thanks for that. I am familiar with the arrival requirements for LHR. I am also aware that all cleared speeds should be flown as accurately as possible. You are indeed correct that the tolerance of +/-10kts probably stems more from Instrument Rating renewal tolerances than from any ATC published restriction.

However, my question to 320 or greater related to his claim, with regard to London TMA Inbounds, that "there are no speed tolerances permittable unless you tell ATC you can't comply". I am not aware of any publication that says anything like "no speed tolerances are permissible". Even MATS Part 1 is not as prescriptive as that, when it says:

"Pilots are expected to maintain as close as possible the speed value allocated by ATC.
If the aircraft speed is at variance from the allocated speed by 5 kt or more then ATC must be informed immediately."
But maybe that was what he was really referring to ... ?


JD
:)

[shrantk]

If you are transitioning jets while in autopilot setting just command the autopilot how much speed to reduce or if you are in a manual way reduce every 4 knots per 3 seconds