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Overspeed

Pro Member Chief Captain
ceetee Chief Captain

I usually fly small props without ever touching the autpilot controlls, but today I decided to fly my new MD-80 from Gatwick, London to Ajaccio, Corsica.

It took me just 1 hour and 45 minutes to fly the 700 mile route which was far quicker than I expected because I kept getting the annoying OVERSPEED sign appearing.

I had my throttle at about 80% in, but I was flying at a speed of about 370 kias. Then after landing, I took off again (just to test it out) and flew level at 10,000 feet with full throtte and I reached a speed of 603 kias!!!

What's going wrong and how can I fix it. Please could someone explain because I'm not to familier with jet aircraft.

Thanks

Guest Ed Guest

ct,

Jets can easily exceed their safe speed; they just have that much power to spare.

Usually, for jets you will see the NTE (not to exceed) speed in both KIAS and Mach number. You should not exceed which ever is LOWER of the two.

Since Mach number depends on your altitude, you usually use the KIAS speed for lower altitudes, say up to about FL260, then you switch over to using the Mach number. On the Lear Jet, I keep it under 250 KIAS up to 10,000 feet, then bump it up to about 300 KIAS until I reach FL260, then switch over to Mach number, going for Mach .81 at cruising altitude.

The easiest way to manage all this is with the autothrottle.

Ed

Pro Member Chief Captain
ceetee Chief Captain

Thanks for the tips Guest Ed,

Now could you or someone else please explain what 'autothrottle' is and how it works?

Embarassed I've never heard of it before...

Pro Member Trainee
FHeselton Trainee

The 'autothrottle' is a function of the autopilot that works similar to the 'cruise control' on your car, it allows you to set the speed (KIAS or Mach) that you wish to fly at.

In some aircraft you must first arm the autothrottle before use. If arming is required, you need only click on the switch on the autopilot to arm the autothrottle then, after you are in the air, click on the "speed hold" button to set the autothrottle. If your aircraft does not require you to arm the autothrottle first, you need only to click on the "speed hold" button to set it.

The aircraft.cfg file determines if the aircraft has use of the autothrottle and if arming is required. Under the AUTOPILOT section you may see something like "autothrottle_available=1" and "autothrottle_arming_required=1"

Looking at your MD-80 Autopilot pannel, from your left to right, the first set of numbers should be your course setting. The next is your speed setting.

Remember if you try to use the autothrottle during landing, that you will not be able to reverse your engines as long as the autothrottle is engaged.

Good Luck.

Pro Member Captain
earthqu8kes Captain

when i first started flightsiming i got so angry that a jet would exceed its safe limit so quickly after takeoff. so if you choose a speed at wich to fly at and set that to the autothottle you should be fine

Pro Member First Officer
beerbadger First Officer

try using auto throttle Smile

Pro Member Captain
Micah Captain

603kias seems rediculously fast!!!

Micah Wink

Pro Member Chief Captain
ceetee Chief Captain

603kias seems rediculously fast!!!

Too right Shocked Thats 0.6 Mach, right? I think prehpas the aircraft.cfg may be a little screwed up because it was meant to be for fs2002...?

And FHeselton, thanks for your autothrotte explanation, but I'm still unsure of where to find the instruments for it in the cockpit. I have taken a screenshot of it below that prehaps you could help me with?

Its proberly really obvious, please excuse my lack of knowlage with jet ac,

Cheers

Pro Member Chief Captain
hinch Chief Captain

top right in your autopilot cluster.

set ias to the speed you want and click ias button underneath. then to arm on you'll need to flick the a/t arm switch to the left.

to change it to mach just click the mach button underneath the setting.

Guest

How come the annoying overspeed sign and ticking comes up when your not even near the top speed of some of the planes?

takes me ages to get places

Pro Member Chief Captain
Matthew Shope (mypilot) Chief Captain

Could be your looking at the wrong speed. The Max Safe speed is given in KIAS or Mach and you may be looking at the ground speed on your gps,

Pro Member Captain
Doyley Captain

Anonymous wrote:

How come the annoying overspeed sign and ticking comes up when your not even near the top speed of some of the planes?

takes me ages to get places

If you are at a low altitude this will happen. Try climing.

Pro Member Trainee
FHeselton Trainee

loSorry it has taken so long to get back, but with the holidays and all, it has been very busy both at home and work.

In answer the A/T ARM switch is the Auto throttle arm switch. Turn this on.

Set the IAS/MACH dial (located between the HDG and ALTITUDE dials). Usually set the IAS/MACH to 250 below 10,000 ft and to activate the A/T click on the IAS button located below the dial. Keep the IAS to 250 or below until crossing 10,000 ft the you can increase this to usually 280 to 300 (just increase the number by rolling the button on your mouse or clicking when the "+" is in the window.

I usually change over to MACH at FL180 (usually setting the speed to .65 - .67). You change over by clicking the MACH button. This will change the IAS/MACH display from a three digit number to a 2 digit decimal number.
(At 280 IAS this will convert to about .57 at FL180). You can then increase your mach number just as you do the IAS value.

You can change back and forth by clicking the IAS or MACH buttons. To disable the A/T you can either click off both the IAS and MACH buttons or turn off the A/T ARM switch.

Best of Luck.

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