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250kts below 10000ft. Kias or Groundspeed ? (Read 203 times)

Sep 29^th, 2006 at 5:59am

-sam- Offline
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Hi there,

Is this speed limit measured in Kias or Ground Speed ?

Thank You

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Reply #1 - Sep 29^th, 2006 at 7:52am

XP1900 Offline
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kias

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Reply #2 - Sep 29^th, 2006 at 8:01am

Brett_Henderson Offline
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It's KIAS..

When planes capable of going faster than 250kias are below 10,000msl ; chances are that they're near an airport (that speed is reduced to 200kias, once inside of, or under Bravo or Charlie airspace (except INSIDE of Bravo airspace, it can still be 250kias))...

It's mostly for spacing, as they're likely to be near other aircraft. Planes, and their proximity to each other don't care how fast they're moving across the ground. They're closure rates are only relative to the mass of air that they share. If a 747 tried to maintain a 200knot ground speed while entering airspace, with a 40knot tail wind at 9000msl.. it would be flying dangerously slow.

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Reply #3 - Sep 29^th, 2006 at 8:32am

-sam- Offline
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Thank for the answers !!
I´m asking because we are experimenting with Multiplayer
ATC at the moment. And the ATC Controller only gets
GroundSpeed values (at least with the software we are using).
So how could an ATC verify if a plane
is not faster than 250kts if he only gets the Ground Speed ?
Does a realworld ATC Computer calculate these values automatically ?. I could image there is some formula including
wind/direction, Altitude of the airplane, preassure, Groundspeed to calculate the Kias of an airplane.

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Reply #4 - Sep 29^th, 2006 at 10:58am

Nexus Offline
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In real life, the ATC gets aircraft data that is directly derived from the airliners transponders.
Important here is that the transponder is mode- S.
This is a very advanced device which enables airliners to be "Enhanced Surveillance " (EHS) compliants.

With EHS, ATC can see vertical speed, IAS/mach speed, mag heading etc of the target aircraft.

« Last Edit: Sep 29^th, 2006 at 12:07pm by Nexus »

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Reply #5 - Sep 30^th, 2006 at 10:25pm

RitterKreuz Offline
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Real ATC radar indicates ground speed... they frequently ask;

"Delta 123 heavy say airspeed."

if the pilot replies that he is indicating 250 but the controller sees a ground speed on his scope of say 340 he knows something is amiss.

they usually ask your speed when they are going to assign you a speed restriction for example: "Delta 123 cross FORUM intersection at 210 knots or slower." you might cross it indicating 210 even though his scope says 230 or 190 etc. Controllers usually factor this in with their speed assignments and assessments.

generally when you pass 10,000 feet its normal to set the pointer right on 250 knots. if you bump over it by 10 knots who cares - just power back a hair or so.

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