I am currently in the process of trying to do a flight from Los Angeles-Tahiti on Thomas Ruth's A340-300, and just yesterday discovered that I couldn't get the autopilot to maintain my selected airspeed of 280 knots.  When the Speed Hold switch is engaged, my airspeed doesn't increase or slowly begins to decrease.  I don't know what could be causing this issue, and I tried reducing some of the aircraft's payload, thinking that was the problem, but no such luck.  I have a copy of the autopilot section of the aircraft cfg. file for this aircraft, if anyone needs that: https://1drv.ms/u/s!AuWqP9oV1Utlh7xQ-Euw4V6xNfK0dA?e=Y1cDqw

What altitude are you flying at? At the higher flight levels - in excess of 28000 feet then you should be using Mach hold. A340-300 should possibly be around Mach 0.82 at cruise altitude... which may equate to less than 280 knots INDICATED airspeed..

What do your N1 engine readouts display? If you're at full throttle already then she won't accelerate.. and I've noticed that the Thom Ruth birds seem a little wheezy at high altitudes even though they have enough power to do the job. EDIT - What I mean is that no airliner has very much excess power once it's 7 miles high (unless it's Concorde...)

Edited September 13, 20205 yr by HighBypass

If you disable Speedhold , and give Full Throttle, does the aircraft then reaches (or exceeds) 280 Knots in the same flight conditions ??

If so:
In the aircraft.cfg, raise the value of 

autothrottle_max_rpm = 92

Try 100 - 110 or so.

Rob        
 

 

 

 

 

Hey, guys.  I think you gave me some pretty good suggestions, I will try rcbarend's suggestion and see if it helps.