Why Does The 777 Overspeed at 330Knots?

[ncl_uk]

Hi can any one let me know why 777 and 747 overspeed at 330 cause in real life when i flew on continental 777 the spead reached over
440 and on flight simulator 2004 in the description box it says max speed of 747 is 555. Is their anyway to resolve this issue please
HELP!

Thanks
Michael

[Nasder]

This is probably the True AirSpeed (TAS) and not the IAS wich you see in the cockpit.

Sadly, I can't describe the difference between them. Except that TAS is the trueairspeed and IAS is the Indicated Airspeed.

[Anastasios]

when you fly above a certain altitude your IAS maximum speed changes. However, when you look at your ground speed, it should be
about the same. The IAS speed changes because of the pressure. With my boeing 737-700 I fly on cruise level with a IAS speed of 250
knots. My ground speed however is about 470 knots.

Maybe it helps is if you change your IAS hold to MACH hold. Normal speed for a 777 is about .84 MACH, I believe. So let's say, if you use
speed hold, you can use IAS hold till about 28,000 ft and then switch the speed hold to MACH hold.

Maybe this could work.

Tasos.

[ivo]

This is becuase the air up at 35000ft is thinner than the one down at 5000ft. Less air is flowing through the pilot tube, so you don't get a
reading of your ground speed. You get a reading of you airspeed. Even though you gauges might only show 290 knots, you're actually
going much faster at 30000ft.

TAS=True AirSpeed, the speed at which you move through the air.
IAS=Indicated Airspeed, the speed that you gauges show you.
GS=Ground Speed, the speed at which your plane moves over the ground.

[jboweruk]

Max speed on any jet airliner safely is actually around 300 KIAS, so not surprising 330 is overspeed. Mind you that is max safe speed they
will go faster, 330 is around absolute max but one little gust of headwind and you may be looking at damaged wings.

[QF6024]

I always have my gauges reqd the IAS on the gauge. As alluded to the the higher you fly the less dense teh air and you will notice the red line on the
gauge gradually crawl back. so for sake of argument whereas at 30000 ft the overspeed will kick in at 320kias at 40000 the overspeed will kick in at
about 280 kias and continue to decrease the higher you go until the fall is at the critical level where the air canot support the aircraft in normal
flight without a stall being incurred( I think that is gist of it)

[Ham]

Thing is, that there are essentially two critical speeds you may not exceed:

1. Vne This is your critical IAS that you may never exceed, this is typically relevant only at lower altitudes (<~FL280)
2. Mne This is your critical mach number, usually around .80-.86, depending on the type of aircraft (I'm just talking about jetliners, of
course; don't try this in a King Air, please...)

Take the lower one (on the modern aircraft, it is computed and displayed on the EFIS PFD as the upper red candy stripe marker) and
you're fine.

[kvuo]

and the barber pole on an analogue gauge = Vne / Mmo

[jboweruk]

Ham wrote:


2. Mne This is your critical mach number, usually around .80-.86, depending on the type of aircraft (I'm just talking about jetliners, of
course; don't try this in a King Air, please...)

I don't have jets fitted to my KingAir yet, but if I can't go that fast then I'm not giving the guy the hard earned wonga to do the upgrade,
he promised me it would do like 0.99 easy



Post Edited ( 02-02-06 09:50 )