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Author Overspeed Question
chuck

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Posts: 36
Joined: 25.01.07

Posted on 20-03-2007 20:18
I have a few questions about the overspeed warning in jet aircraft. Is there anyway to know when you are approaching your overspeed at a certain alttitude? The checklist doesn't have the figures (That I can tell) and I don't see any gauges that seem to pertain to it either. So I guess my question is, how does everyone prevent this problem.

Thanks for the help..
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Author RE: Overspeed Question
jackfolla

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Joined: 11.04.06

Posted on 20-03-2007 20:20
The simplest way is to use the maximum speed in KIAS as your guide up to FL260 or so, then switch over to Mach number and use that up to your final cruising altitude.

For example, the Lear Jet has Do Not Exceed speeds of 330 KIAS or Mach 0.81. As I'm climbing up to cruising altitude, I'll leave the autothrottle set at 315 KIAS (for a little safety margin). Then as I pass through 26,000 feet, I'll switch the A/T over to Mach and set it to 0.80. When I reach cruising altitude (~FL350), I set it to 0.81.

While I'm climbing, I'll watch the GPS and adjust the rate of climb so that the ground speed is steadily increasing. If I notice the ground speed start to drop, I cut the rate of climb. My goal is to be at cruise speed when I reach cruise altitude.
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Author RE: Overspeed Question
chuck

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Posts: 36
Joined: 25.01.07

Posted on 20-03-2007 20:20
The Learjet is exactly the jet that I had in mind too. I have just noticed that the Boeings have markings on the airspeed indicators that show the speed which overspeed occurs but I can't seem to find anything like that on the Learjet. Seems odd that it wouldn't have one if other jets do but what do I know.

Also what is the benefit of switching to mach over IAS? Sorry I'm new to jets
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Author RE: Overspeed Question
jackfolla

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Posts: 509
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Posted on 20-03-2007 20:21
i think i should give a shot at this. You need to switch to Mach speed at higher altitudes and not IAS.At higher altitudes the pressure decreases and air density decreases and hence what you see is not the actual airspeed.Your aircraft is moving much faster than indicated as less air causes less tension in the airframes.So i don;t think it is a matter of choice of Mach or IAS...
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Author RE: Overspeed Question
chuck

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Posts: 36
Joined: 25.01.07

Posted on 20-03-2007 20:22
How do you set the Auto throttle to work correctly? I am able to switch between KIAS and MACH, but I can never get the auto throttle to actually hold the speed that I have set.
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Author RE: Overspeed Question
jackfolla

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Posts: 509
Joined: 11.04.06

Posted on 20-03-2007 20:23
You need to arm the Autothrottle .Set the speed and press the SPD button.But it entirely depends on the aircraft you are using.Mine is with reference to Boeing 747. And obviously you need to be on autopilot.
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