L1011 FLT CREW HAS BRAKE MALFUNCTION DURING TAXI TO PARKING.

Narrative

ON LNDG AT MOJAVE ARPT AFTER A 2+ HR MAINT/TRAINING FLT; ALL 3 REVERSERS FAILED TO DEPLOY. THE REVERSE LEVERS WOULD NOT GO PAST THE BALK. THE AUTO GND SPOILERS ALSO FAILED TO DEPLOY. ROLLOUT WAS COMPLETED SATISFACTORILY USING LIGHT TO MODERATE BRAKING. TAXIING BACK TO THE RAMP; IT WAS OBSERVED THAT ALL 3 ENGS WERE AT FLT IDLE; RATHER THAN GND IDLE THRUST. ALSO DURING TAXI; THE STICK SHAKER ACTIVATED. STALL WARNING SWITCHES WERE TURNED OFF TO DEACTIVATE THE SHAKER. FURTHER TROUBLESHOOTING INCLUDED RESETTING ALL 3 GND IDLE CIRCUIT BREAKERS WITH NO CHANGE -- THE ENGS REMAINED AT FLT IDLE THRUST. THE ACFT WAS VERY LIGHT AND CONSIDERABLE BRAKING WAS REQUIRED TO AVOID EXCESSIVE TAXI SPDS AT FLT IDLE THRUST. AFTER THE FE GOT THE APU ON LINE AND SUPPLYING ELECTRICAL AND HYD BACKUP; THE #1 ENG WAS SHUT DOWN; FOLLOWED SHORTLY AFTER THAT BY #3; JUST PRIOR TO MAKING A 90 DEG L TURN IN TO THE RAMP AREA WHERE THE TUG WAS WAITING TO TOW THE ACFT TO ITS PARKING LOCATION. BRAKING ACTION HAD BEEN SMOOTH AND RESPONSIVE THROUGHOUT LNDG ROLL AND TAXIING UP TO THIS POINT. FOLLOWING GND CREW GUIDANCE TOWARD THE TUG; LIGHT BRAKING APPLICATION WAS APPLIED AT LOW SPD; AN ESTIMATED 75-100 FT FROM THE TUG. SEVERE BRAKE SHUDDERING ACCOMPANIED BY PRONOUNCED ACFT OSCILLATION WAS EXPERIENCED IMMEDIATELY UPON BRAKE APPLICATION; WITH NO APPARENT BRAKING EFFECTIVENESS. BRAKE PEDAL FORCE WAS RELEASED AND REAPPLIED WITH THE SAME RESULTS. ALTERNATE 'C' BRAKE SYS WAS SELECTED AND NO CHANGE IN BRAKE RESPONSE. WHEN IT BECAME APPARENT THAT THE ACFT COULD NOT BE STOPPED BEFORE REACHING THE TUG; THE #2 ENG WAS SHUT DOWN AND A SLIGHT L TURN WAS MADE IN AN ATTEMPT TO AVOID CONTACTING THE TUG WITH THE NOSE GEAR. THE ACFT CONTINUED DOWN THE SLIGHTLY INCLINED RAMP WITH BOTH PLTS APPLYING MAX BRAKE PEDAL FORCE. BY THIS TIME; THE BRAKE SHUDDERING AND AIRFRAME OSCILLATION HAD DISCONTINUED BUT THE BRAKES REMAINED INEFFECTIVE. THERE HAD BEEN NO INDICATION OF IMPACT WITH THE TUG OR THE BUILDINGS WITH MINIMAL WINGTIP CLRNC ON EITHER SIDE OF ACFT. AS THE ACFT PROCEEDED AT A SLOW; BUT STEADY SPD TOWARD A PERIMETER FENCE ACROSS THE RAMP; NORMAL 'B' BRAKE SYS WAS RE-SELECTED WITH NO DECELERATION EFFECT. AT ABOUT THE SAME TIME IT WAS NOTED THAT THE ANTISKID SWITCH WAS ON. THE SWITCH WAS TURNED OFF AND; WITH BOTH PLTS APPLYING MAX BRAKE PRESSURE; THE ACFT CAME TO AN ABRUPT STOP -- LEAVING ABOUT A 2-3 FT SKID MARK. AFTER THE STOP; IT WAS VERIFIED THAT THE ACFT WAS IN THE FLT MODE RATHER THAN THE GND MODE; BUT COULD NOT IMMEDIATELY DETERMINE THE CAUSE. THE MAIN GEAR PROX CIRCUIT BREAKERS WERE IN AND THERE WERE NO OBVIOUS REASONS FOR THIS ANOMALY. FURTHER POSTFLT INVESTIGATION REVEALED THAT THE ACFT WAS AT SUCH A LIGHT WT ON THE FINAL LNDG THAT THE STRUTS DID NOT COMPRESS ENOUGH FOR THE AIR-GND PROX SWITCHES ON EACH MAIN LNDG GEAR TO MAKE PROPER CONTACT. THE REASONS FOR THE BRAKING PROBS WERE MORE OBVIOUS. THE ANTISKID CTL UNIT PROVIDES LOCKED WHEEL PROTECTION ON TOUCHDOWN BY NOT ALLOWING THE ANTISKID BRAKE VALVES TO OPEN UNTIL MAIN GEAR WHEELS HAVE SPUN UP. THE WHEEL SPD THRESHOLD IS ON THE ORDER OF 9 KTS BEFORE ANTISKID BRAKES BECOME EFFECTIVE ON LNDG. IN THIS CASE; BRAKING WAS NORMAL UNTIL TAXI SPEED GOT NEAR THAT SPEED THRESHOLD. WITH THE ACFT SENSING IT WAS IN FLT; THE ANTI-SKID LOCKED WHEEL PROTECTION KICKED IN WHEN BRAKES WERE APPLIED. THE SEVERE SHUDDERING AND AIRFRAME OSCILLATIONS PREVIOUSLY DESCRIBED WERE APPARENTLY THE RESULT OF RAPID; CYCLIC APPLICATION AND RELEASE OF THE ANTISKID BRAKES WHEN THE ACFT WAS ON THE SPD THRESHOLD. AS THE ACFT SLOWED SLIGHTLY AND GOT BELOW THAT SPD; THE LOCKED WHEEL PROTECTION TOOK OVER FULL TIME; CLOSING THE ANTISKID BRAKE VALVES. THIS GOT RID OF THE DISTURBING CYCLIC ACTIVITY BUT THE BRAKES CONTINUED TO BE INEFFECTIVE UNTIL THE ANTISKID SWITCH WAS TURNED OFF AND THE AIRPLANE CAME TO AN ABRUPT STOP.