Consultation expired with comments. The proposed Equivalent Safety Finding (ESF) has been updated based on the comments received, and the corresponding Comment-Response Document (CRD) has been completed by EASA.
Details
Identification of issue
A new concept of thrust control is proposed on a CS-25 aeroplane.
Instead of one thrust lever per engine as known from traditional designs, there is a single thrust lever controlling the thrust delivered by two engines and a backup control means is used in case of engine failures requiring different thrust setting between both engines.
In normal operating conditions, the single thrust lever controls both engines thrust at the same time. The pilot inputs, when moving the lever, are acquired, processed and consolidated by the flight control system. A consolidated independent thrust order is then transmitted to each engine.
A backup system is introduced allowing separated thrust management for failure handling. This control knob allows to isolate the command of the faulty engine in order to set the appropriate thrust command on it.
In normal operating conditions, the design of the single thrust lever does not comply with the § CS 25.1143 (a) and (b)(1) requiring separate controls for each engine.
In case of engine failure condition, the backup control means (rotary knob) is used to adjust the thrust of the faulty engine. This control means does not comply with CS 25.777(b) and CS 25.779 (b)(1) defining respectively the directional movement and range of rotary knobs and the directional movement of the thrust control.
Considering all the above, the following Equivalent Safety Finding is proposed.