Speed Control
 

When ATC say for example maintain 210 kts is there any allowance? Many people say you can fly plus or minus 10 kts without asking permission. Is that correct?

My info is that there USED to be a +/- 10 tolerance, but 6? or so years ago it went to +/- 0 - maybe JAR/PANSOPS? A bit like the 'you always had 10 minutes on CTOT' which I understand is now 0 unless ATC allow.

I am sure the MATS Part 1 says that the tolerance is 5 Kts and the pilot must advise ATC if he varies from that immediately

A Tenner to the bloke with the moderators hat on...

"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."
MATS Part 1 : SI 1/1995

Cat Free,


My policy is, I'll issue the speed restriction once, warn you once to reduce speed, then if you still don't and it starts to create a problem, I will pull you out of the arrival stream, and make you last.

I sequence a large variety of aircraft (C150's to F16's) that make sequencing for the instrument approach challenging, so when I issue a speed restriction I really need it because you might be the Lear that is sequenced behind the C150.

Mike
NATCA FWA

Thanks guys. I'll carry on with +/- 0 (just in case FWA ever controls me:D )

Mr PPrune may be right as far at MATS goes, but in the London TMA there is no leeway with speeds in the approach phase when pilots are expected to fly the speeds as accurately as possible. Pilots who are unable to comply should advise ATC in good time. Ie don't wait until you are established to ask for a slower speed because there might be someone tucked up 2.5nm behind! (Check all this with the AIP under Heathrow - same probably applies to many other aerodromes too)

Canadian AIP and ATC Manops both highlight there is a +/- 10 knot allowance in speeds. However, as HD rightly says, in a busy sequence with 2.5 mile spacing on final approach, 10 kt speed differences can cause a problem.

And from my understanding when Mode S link start, ATC will be able to tell exactly how fast has been dialed in.

'No leeway' and 'accurately as possible' seem to me to be 2 different things. Some pilots or aircraft will be able to be right on the button 100% of the time ... others will be close but not exactly on the numbers (they are as accurate as possible !!).

The definitive answer no one can find is what 'accurately' means :)

A few pilots I spoke to are of the opinion it is +/- 10Kts, the MATS says +/- 5Kts, and we have also had +/- 0Kts put forward.

Seems a grey area !!

Controllers realize that wind is going to play a part in controlling your ground speed, and we take that into consideration when we assign a speed restriction.

We assign the restriction to maintain separation on final or within an arrival stream.

I don't want to be a hard ass, but if you decide to cheat on your speed, you are jepordizing your life, and my livelyhood, so don't and we all will get to go home happy at the end of every day.

Mike
NATCA FWA

Isn't it strange that MATS Part1 says that pilots should inform ATC if they cannot maintain the correct speed +/-5kts, yet there is nothing telling pilots that they should do this!! How are we supposed to know?

I wonder what other else MATS Part 1 says I should be doing, but about which I have no idea? My Part 1 is getting a bit old now and there is no way that I will be buying a new one. Is it available online, or does it cost?

G W-H

The Part 1 and all of it's amendments can be easily downloaded / read here : http://www.caa.co.uk/publications/pu...ils.asp?id=222

I should probably post this in the 'questions' forum, but since the issue has been raised here I will continue.

We (ATC) issue speeds mostly as IAS and increasingly as Mach.
However, what we are really interested in is Ground Speed because that's what's on the radar and it's what counts when trying to stay behind/ahead of other traffic.

Question: What sort of scope is there for us to ask pilots to fly a ground speed? or at least give a max or a min ground speed as I realise that it can fluctuate greatly with level, wind etc.. Probably best used in level flight or when small level changes take place...

And GWH - are you an ex ATCO/TATC? with your old MATS1

VL


:ok:

Vector - the info/capability is there (I believe Airbii have it) but it is going to confuse things - give it 10 years. Up to then be aware of the X,000ft wind from your met info and request IAS/Mach accordingly?

Obviously all a/c at or near the same height will then have the required groundspeed.

VL

I am afraid that using ground speed is a bit of a non-starter at the moment. As BOAC has hinted, there is no automatic function on most Boeings to acheive this and the level of monitoring required to make it work would have a significant effect upon the rest of the operation. A similar arguement applies to asking aircraft to fly tracks (as opposed to radials or headings). Whilst the information is there on the flight deck, it is just too labour intesive and thus not really condusive to being used as a method of separation.

One of the strangest requests I have ever had fom ATC was to fly at a particular TAS. That got the little grey cells working I can tell you!


G W-H

(Sorry VL, can't answer your other question...!)

When ATC says:"Reduce SPEED 210" then they want us to a) fly 210:D and b) to make the reduction at a rate of 1 kt per second. So ideally you'll see a speed trend vector 10 kts long on your PFD:p

But remember, you the pilot ultimately fly the speed you need (BUT, in cooperation with ATC), i.e. as a TEAM (pilots/ATC):ok:

Cheers GW-H

fairy nuff. thought I might have known you that's all......

VL

square leg

You've got me bamboozled with the 1kt/sec rate of speed reduction. Is that from the MATS or the AIP or are you pulling my leg??!

VL

It's not impossible we know each other... But you'll have to give me a clue...

Howzit Giles Wembley-Hogg?! :D

I'll get back to you on this one in hopefully a coupla daze.

Regahds,

:8

I wish somebody had told that to one of my inbounds!!!!

The last speed instruction I gave was 220kts, it was an upper medium d/w left 05 ss. He decided to reduce to appox 160kts whilst downwind!! He had a light behind him gaining on him rapidly!!

It all worked out with some creative vectoring but we have very little room when downwind for 05 at Stansted.

PLEASE PLEASE PLEASE!! If you want to slow down let us know before hand. You never know, we may say yes.
:ok: