I SEE MOOSE"S POINT & I'll RAISE YA ONE ..( Im assuming you are talking about the RJ200 ) - THE CRJ700/900 have no problems like this ..
The FAA issued an airworthyness directive on the Bombardier/Canadair CRJ200 pertaining to an unsafe flight control ( trailing edge flap ) asymmetry ( skewing ) condition. This was caused by unforeseen excessive loading of the flap actuators during operations in particular areas of the flight envelope at certain flap settings. In this condition, the EATON ballscrew actuators break teeth in their hypoid gearsets resulting in a jam condition. The unsophisticated open-loop design, does not detect the problem and therefore allows the power drive units to continue to drive the jamed actuator resulting in a torsional skewing on the associated flight control – resulting in unsafe asymmetric control and potentially loss of roll control of the aircraft. In response, a team was formed between Bombardier; EATON and ELDEC/CRANE to 1) determine design responsibility and 2) solve the problem. It is my understanding the FAA mandated ( AD ) a skew detection system to be implemented – hence ELDEC/CRANE’s involvement. In parallel, EATON responded by redesigning the gearset to non-SAE standards – the challenge to realize a gearset that would fit the existing space envelope and load requirements. This was done by deviating from SAE practices by optimizing the gear cut and choice of materials. The new EATON product has exceeded expectations in robustness. The AD comprised an odeometric position sensing system on all actuators where the synchronicity of the flap actuators is monitored and compared. Actuator position disagreements will cause an immediate shutdown of the flap actuation system. The system resembles a variation approach to the ELDEC supplied 737 NG / 757 ballscrew target. Wherein the Boeing systems rely on a ballscrew-end target. The CRJ200 solution relies on a target that resembles a ballscrew “slip-ring” – similar to a slip ring on an electric motor armature – located “at the other end” of the ballscrew, adjacent to the actuator housing. The system works basically very similarly – perhaps identically to the Boeing system. Either way, Bombardier has responded & beat this thing to death - should be no more issues with it - Even Luftansa Tecknic has jumped on the bandwagon & has engineered their own actuator for the CR200 ..