Citation V/Ultra/Encore (C560)
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 100; Flight Crew Total 14000; Flight Crew Type 11500
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Taxiway
Flight Crew Regained Aircraft Control; General Flight Cancelled / Delayed; General Maintenance Action
Procedure
Routine preflight by right seat pilot. Normal startup. Annunciator panel normal. During prep for taxi and obtaining IFR clearance left seat pilot dropped an iPad on the left armrest and breaker panel area. Didn't think anything of it. Obtained taxi clearance. After leaving the ramp area with left seat pilot taxiing the master caution began to flash followed shortly by the failure of the brakes as we approached a 90 degree right turn on the taxiways. Right seat pilot recognized that the power brake annunciator was lit. Reached across the cockpit to reset the breaker for the brakes. Braking action returned immediately. During the few seconds the brakes were inoperative the airplane got off the edge of the taxiway and into the grass. Grass was pretty smooth; relatively flat and we did not contact any taxi lights or anything else while in the grass. Then saw two pieces of a circuit breaker collar on the armrest that had been on the power brake breaker for years. Knew that the dropped iPad had hit the collar which stood taller than the surrounding breakers; tripping the breaker and breaking the collar. Continued taxi with completely normal brake function so felt no reason to delay the trip. After talking to Maintenance the next day decided to replace the breaker. A collar will NOT be put back on that breaker.
[Narrative contained no additional information.]
C560 flight crew reported that a dropped iPad broke a circuit breaker collar and tripped the breaker; causing a loss of brake pressure and a taxiway excursion.