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Mach-nr or IAS?

Old 10th Jan 2019, 20:23
  #1 (permalink)  
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Mach-nr or IAS?

Hi folks,

Recently i was cleared to descend from FL340 down to FL240, with a restriction of flying 260 kts.
I asked if the 260 kts restriction was on conversion, but no, he wanted it right now! (from leaving FL340)

I was educated to fly Mach number on conversion in the climb.
I had numerous clearances to fly 260 IAS (or so) on conversion, but never to fly IAS above FL290, in my case descending from FL340.

Is this correct or just another german atc typical way of doing it their way......?

Thanks!
testpanel is offline  
Old 10th Jan 2019, 20:48
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Join Date: Jul 2004
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Lack of understanding...
Talkdownman is offline  
Old 10th Jan 2019, 20:59
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Join Date: Dec 2004
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You'll get in the UK too. It's not a lack of understanding at all.

For example, I can see traffic off the ocean inbound to London that is currently doing 250kts at FL350. I know it's flying on a Mach number at the moment, but the Mode S is showing 250 knots so it's not hard for the pilots to keep it at that. If the traffic situation warrants it, and inbound to Heathrow it usually does, then I'll tell the pilot to keep the speed at 250kts from now. It's up to them to manage that through a combination of Mach number and deciding when to convert to IAS

In the case above, if you can't come back to that speed at that level then say something - we've always got a Plan B up our sleeve
The Many Tentacles is offline  
Old 11th Jan 2019, 09:35
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I'd stick with Mach number at or above FL280 and IAS below that. It's easier for everyone as ATCOs know the Mach number range for most jets above that level but we certainly couldn't tell you what a good, assured IAS would be above that without a few questions first as to whether you can make the speed or not. I haven't heard IAS used at all above FL280 ; that's after 38 years of controlling, mostly in upper airspace.
ATCO1962 is offline  
Old 11th Jan 2019, 11:33
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Originally Posted by ATCO1962 View Post
I'd stick with Mach number at or above FL280 and IAS below that. It's easier for everyone as ATCOs know the Mach number range for most jets above that level but we certainly couldn't tell you what a good, assured IAS would be above that without a few questions first as to whether you can make the speed or not. I haven't heard IAS used at all above FL280 ; that's after 38 years of controlling, mostly in upper airspace.
Given that for any aircraft at any level, assuming they're Mode S equipped which is 99.5% of our traffic, we can see what IAS they're flying regardless of whether or not they're flying on a Mach number, then we can have a reasonable stab at what might be a suitable IAS to keep them in the air. Things have changed in 38 years
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Old 12th Jan 2019, 20:07
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Join Date: Dec 2008
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Originally Posted by testpanel View Post
Hi folks,

Recently i was cleared to descend from FL340 down to FL240, with a restriction of flying 260 kts.
I asked if the 260 kts restriction was on conversion, but no, he wanted it right now! (from leaving FL340)

I was educated to fly Mach number on conversion in the climb.
I had numerous clearances to fly 260 IAS (or so) on conversion, but never to fly IAS above FL290, in my case descending from FL340.

Is this correct or just another german atc typical way of doing it their way......?

Thanks!
What kind of airplane were you flying so that reducing to 260IAS sounded weird? Does it mean you never fly IAS above FL290? How weird is that?! Is there any particular FL at which you changeover? I know one stupid point in DOC4444 that states ATC should consider using IAS below FL250 and MN above, but how ridiculous is that? Would any ATCO speak to Q400 at FL260 in terms of MN?
For instance, if you fly 270IAS you keep flying IAS until FL340. Only after reaching approx. FL340 you catch up with .78 or so.
pilotnik is offline  
Old 12th Jan 2019, 20:29
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Join Date: Nov 2002
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ICAO says FL260 is the cut over. Mach until then. Over.
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Old 13th Jan 2019, 09:05
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I was educated to fly Mach number on conversion in the climb.
Do you understand why?
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