Two pilots report on a rudder bias malfunction that occurred during two taxi out checks on their company Cessna 560XL. The First Officer did not notice the rudder pedal movement was opposite of that intended; during their first taxi out check.

Narrative

I operated trip #X. The aircraft had been down for maintenance to work on the rudder bias system which was written up upon completion of the previous leg. On taxi out for departure; the rudder bias system was tested by the pilot flying and was thought to have checked properly per the manual. Flight was completed to destination without delay. The following leg was being flown by me as the pilot flying. On taxi out; the rudder bias system was checked per the manual. I noticed the incorrect movement of the rudder pedals; therefore; yielding a failed test. The aircraft was taxied back to the ramp and shut down. A recovery aircraft was dispatched to complete our flight. Maintenance was notified along with notification to the FDO; and my ACP. Maintenance was performed and the aircraft returned to service. The rudder bias system was tested by the First Officer who was the pilot flying. He noticed movement in the rudder pedals as the check would suggest. Unfortunately; he did not notice that the rudder pedals were moving in the opposite direction from where they should. After a rudder bias system has been maintenance performed; I think both pilots should verify that the rudder bias check operates as is required by the manual. Supplemental information from ACN 821691: The rudder bias test was accomplished prior to the flight as normal; and since both rudders were moving with the advancement of the throttles; there did not appear to be a problem right away. After doing the test again; we realized the problem. Callback conversation with Reporter ACN 821690 revealed the following information: Reporter stated the Citation Excel 560 rudder bias system taxi out check is required prior to each flight. The check requires the pilot to move each throttle forward; separately; and verify the rudder pedals move in the direction that positions the rudder to move towards the engine with the greater thrust during takeoffs and landings. This bias system automatically helps to compensates for a failed engine or loss of thrust from either engine. The bias is achieved through a bleed air line from each engine to a control valve unit that senses engine differential pressure. The system is similar to a rudder boost on heavier aircraft. Reporter stated their aircraft had a previous issue with the rudder bias that required the control valve be replaced because the rudder pedals became so difficult to move during the taxi out bias check. The control valve unit had failed and seemed to neutralize any rudder input. They were the first crew to fly the Excel after the bias control valve change. Reporter stated a maintenance provider facility later found the engine bleed air sense lines to the control valve were crossed; causing the opposite input to the rudder pedals and rudder. The Citation Excel rudder; rudder trim and ailerons are all cable controlled; no hydraulics or electrical power to these flight surfaces. The horizontal stabilizer has two positions; Cruise with flaps up; and Takeoff/Landing; automatically selected depending on flap handle movement.