AN MD80'S TCAS PROCESSOR SEVERELY DISRUPTED VHF RADIO RECEPTION ON FREQUENCY 128.0.

Narrative

UPON SWITCHING TO FREQ 128.0 THE FREQUENCY WAS BROADCASTING A NOISE WHICH CAN ONLY BE DESCRIBED AS SOMEONE KEYING THE MIC NEXT TO A RUNNING VACUUM CLEANER. I ATTEMPTED TO CONTACT APCH BUT WAS ABLE TO UNDERSTAND VERY LITTLE OF WHAT WAS SAID. WE ATTEMPTED TO USE THE #2 RADIO BUT ENCOUNTERED THE SAME PROB. SUSPECTING ELECTRONIC INTERFERENCE I MADE A PA TELLING THE PAX TO TURN OFF ALL ELECTRONIC DEVICES IMMEDIATELY. THIS DID NOT HELP. I RETURNED TO THE PREVIOUS FREQUENCY AND RPTED THE PROBLEM. I WAS INSTRUCTED TO RETURN TO FREQUENCY 128.0 AS THERE WAS NOT PROBLEM ON THEIR END. THE SAME INTERFERENCE WAS STILL QUITE EVIDENT HOWEVER I WAS ABLE TO UNDERSTAND THE CTLR AND CONTINUED TO AN UNEVENTFUL LNDG. AFTER GATE ARR I REMOVED POWER FROM THE R ELECTRICAL BUS AND THE PROBLEM WENT AWAY. IT WAS OBVIOUSLY A COMPONENT OF OUR AIRPLANE THAT WAS CAUSING THE PROBLEM. THE FOLLOWING ARE THE LOGBOOK ENTRIES RELATED TO THIS PROBLEM. ISOLATED TO TCAS PROCESSOR INTERFERENCE REPLACE TCAS PROCESSOR. PERFORMED REQUIRED CHECKS.