vapilot2004

The mechanical thrust controls for the A320 consists of three main parts:

The Levers,artificial feel units and control units.

This setup is common for most FADEC equipped aircraft with the only difference between Airbus A320/330/340 and others is the addition of a servo motor to back drive the throttle levers in autothrust mode.


Each thrust lever is connected by a pushrod to the
input of an artificial feel unit. This unit provides friction
and the detents throughout the motion of the thrust levers.

The artificial feel unit's output shaft is connected
to the thrust control unit via a second pushrod.
Within each thrust control unit are 6 potentiometers
and 2 thrust angle resolvers.

The pots provide thrust lever position to the flight control system
while the resolvers are dedicated to the engine thrust control.

A resolver is a sort of rotary transformer that outputs sine & cosine
waves corresponding the the thrust lever angle. The mechanical ratio of the
thrust lever angle and the resolver angle is 1:1.9. For every degree of
movement of the levers, there is a 1.9 degree movement indicated
by the resolver. Resolver units are more accurate and reliable in translating
angular position data than potentiometers and is the reason for their use here.

Each thrust control unit has two resolvers - one for each EEC channel.
A disagreement of more than 15' (1/4 degree) causes the EEC to go into
resolver failure mode.

Each EEC also checks the resolver output for upper and lower limits.
For the IAE engines the limits are from -41 to 88 degrees. Any
value outside of these limits will cause the FADEC system to transfer
engine thrust control to the alternate EEC.



Outside of a jammed feel unit or thrust control unit, a failure of the A320 manual thrust control system seems unlikely.