Posts: 1405
Joined: Fri Aug 25, 2000 2:50 am

What Happens If You're Flying....

Sat Sep 21, 2002 9:41 am

at 11000m, and your 343 is flying at 950 km/h.

The pilot selects on the autopilot the height of 300m.

The plane will go down, but will it fly at the same speed?
Posts: 1048
Joined: Fri Mar 23, 2001 8:10 am

RE: What Happens If You're Flying....

Sat Sep 21, 2002 10:20 am

The autopilot of an aircraft is much more complex than just heading, altitude and speed. There are some 'modes' of climb and descent controlled by the autopilot and autothrottle. You can sort of 'link' the autothrottle with a vertical mode in which you can climb or descend at a specific airspeed, or at a specific N1, or in such a way you meet the vertical speed selected, etc. Another way is you could simply bring the throttle to idle, and adjust the vertical speed of the aircraft to maintain a specific airspeed: nose down faster, not so down slower. Hope it helps some.

Posts: 1405
Joined: Fri Aug 25, 2000 2:50 am

RE: What Happens If You're Flying....

Sat Sep 21, 2002 7:48 pm

Is it possible flying at 950 km/h at 11000 meters and keep the same speed at 300 m?
Posts: 235
Joined: Fri Jun 01, 2001 8:37 pm

RE: What Happens If You're Flying....

Sat Sep 21, 2002 9:35 pm

Do you mean if a plane is able to maintain 950 Km/h at 300 meters after a descend?

The answer is no. That is not possible due to the higher air's density as you descend.
It's important to say that the only speed to consider regarding the Aircraft limits is the IAS (Indicated Air Speed).
The IAS is the TAS (True Air Speed) without any correction (Density - Attitude...)

So, during a descend you can only maintain the IAS. In this case TAS will decrease.
If you maintain the TAS, the IAS would exceed. Exceeding VMO you could damage the plane.

I hope you have understood.


Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: What Happens If You're Flying....

Sun Sep 22, 2002 12:15 am

There are many different types of autopilot on many different types of aircraft.

The simplest autopilots obviously do not have an auto-throttle system so power management is left to the pilot. The simple answer to the original question is "no", the airplane will not maintain speed unless the pilot manually manages the power or he sets up the AFCS/auto-throttle properly if he has those available modes (speed, N1, IAS, VS etc)

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