Date: 201201
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Light: Daylight
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Parked
Aircraft component: Trailing Edge Flap
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Technician
Reporter qualification: Maintenance Airframe; Maintenance Powerplant
Human factors: Communication Breakdown; Situational Awareness; Time Pressure; Troubleshooting
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Maintenance
When detected: Taxi
Result: Aircraft Aircraft Damaged; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Company Policy; MEL; Manuals; Procedure; Chart Or Publication; Aircraft; Human Factors
Primary problem: Human Factors

Narrative: Myself; [Mechanic X]; and Mechanic Y were assigned to change the right-hand inboard flap actuators on a CRJ-200 aircraft. I chose the inboard actuator and Mechanic Y chose the outboard actuator. Before our start of this Task; the parts were punched out [issued from Stores] and the correct Maintenance Manual sections were printed out for both of us to have and use for the task ahead. Mechanic Y and I started to remove the flap actuators [per] the Maintenance Manual's Step and Procedures. Once we started the task; Mechanic Y and myself lost communication between each other; [communication] came to a stop. With no communication between me and Mechanic Y; and each of us working our own actuators; we did not realize that we were both pulling our actuators off at the same time. Since we did not realize we were pulling both of them at the same time; nor did we plan removing both at the same time; we did not support the flap like the Maintenance Manual says to: [support] ONLY if both were disconnected at the same time. Once both (inboard and outboard) actuators were disconnected the inboard flap 'relaxed' about an inch and a half. At that point we both reworked our steps to see why this had happened. Realizing that we were both treating this as the Maintenance Manual specifies for a ONE-person removal instead of a TWO-person split task; we had not taken the steps to support the flap in case we both got done at the same point. We informed our Inspector at this point and he inspected the flap and hinges for any damage. After finding no damage at this point; we continued with the installation of the two new actuators with the flap supported. Installation went smoothly and after installation we started on our rigging; Rig Checks and Operational Checks with the supervision of our Inspector. After completing our Operational Checks I realized that on the [flight] crew's EICAS [display] screen; the right-hand flaps were reading 5-degrees different then the left-hand flaps on the [EICAS] Flight Control Page. I informed Mechanic Y; our Inspector and our Lead Mechanic of this problem. Through fault isolation [troubleshooting] and going through the Maintenance Manual steps again; we suspected the 'Crew Reporting Flap Indication Control' located on the outboard flap actuator hinge.The Maintenance Manual states that if both [actuators] are disconnected at the same time and the flap is not supported; damage can happen to this component due to the over-stress of going past '45 degrees' [of flap travel]. Parts were not in stock to replace the crew reporting flap indication control; so Supervisor and Management's decision was to MEL the indication. At this point I had completed the Remove/Replace Task of the actuator and had nothing to do with the aircraft after this point and started on my paperwork and returning the parts into 'Stores'. To my understanding; the MEL was placed on the aircraft (M) function; complied with by Mechanic Z. The [flap] system was operational checked several more times to check the (M) function Operational Check was good and the aircraft was sent to the gate for REVENUE flights. After loading of passengers; the plane returned to gate for a Stall Fail message. Flight was canceled and the aircraft was returned to the hanger where parts were ordered to fix the problem. The event occurred due to no communication between myself and Mechanic Y and due to not realizing at that point that the Maintenance Manual is written for ONE Mechanic to be involved in the task; not TWO or multiple mechanics. Not realizing that when sharing the same task or job with a fellow Mechanic; communication is a must and some steps may have to added; or [that] other steps or policies may have to be complied with when not working alone. Fault isolation was put into place; fault was found. Parts were not in stock; Indication was [placed on] MEL and (M) function complied with.Communication is a must! Also when working/sharing a task witha fellow Mechanic; know that the Maintenance Manual is written for a single person application and that some steps or procedures maybe have to be added and steps or warnings that might not necessarily apply during single person application; can be detrimental when working in teams.

Callback: Reporter stated his Air Carrier has made revisions to their Maintenance Manual (M/M) since the incident that now requires Mechanics to disconnect the Flap Position Transmitter any time a Flap Actuator has to be removed. The arm on the Flap Position Transmitter potentiometer was bent when the inboard flap had moved aft to the flap safety stops; after both actuators were removed. The push-pull arm was damaged and was not designed to move past the 45-degree flap position and caused the 5-degree difference between the left and right flap position indications and probably causing the taxi out 'STALL FAIL' EICAS message. The CRJ-200 flaps are electrically operated using a drive motor turning a flexible drive cable out to flap drive gear boxes and jackscrew type flap actuators.



Synopsis: A Mechanic reports how a lack of communication contributed to a damaged flap position transmitter during simultaneous Removal and Replacements (R/R) of the inboard and outboard flap actuators for the right-hand inboard flap on a CRJ-200 aircraft. The aircraft returned to gate with a 'STALL FAIL' EICAS message due to a bent arm on the flap transmitter.