Originally Posted by
FlyingStone
That's not true. 737 A/T has two servomechanisms, one per each lever. Have a look at
this BITE test, particularly around 0:45, where you will see that A/T can move each thrust lever separately.
This functionality is required to synchronize the engine RPM, as the same thrust lever angle might not result in exactly the same N1, depending on many factors, particularly with these hydromechanically-controlled engines.
Indeed, the OM says in the Autothrottle System description:
The A/T moves the thrust levers with a separate servo motor on each thrust lever.
So I would expect this to be common knowledge among 737 Classic drivers.
I wonder where the seemingly widespread idea originates that there is a single motor driving both levers.
It also seems that a "Thrust Split Monitor" is available as an option, described as follows:
Additionally, on some airplanes, a thrust split monitor disengages the autothrottle if autopilot roll control requires significant spoiler deployment and thrust levers become separated. The thrust split monitor is active when flaps are less than 15, and the A/T is not engaged in the takeoff or go-around mode.
How common is this thrust split monitor? It seems it might have been helpful in this case. The very fact that it was available indicates that someone thought it might be a good idea in some cases, but I know nothing about its history.