Narrative:

This airplane is an early serial number falcon 50 which was updated with TCASII, rvsm, and a new interior 7 months ago. Since returning from the completion center it has been plagued with TCASII problems, autoplt hardovers, false altitude alerts, etc. The problems are almost never hard failures. Our problem began when our TCASII failed. We switched to the #2 transponder, the TCASII came back, and we continued. Yawn. Just another failure. We were close to our home airport in the chicago area and ready for our descent. I tried to pick up the ATIS, but all I could hear was silence or a rapid clicking noise like someone keying a microphone. I figured they were changing the ATIS. I tried calling home base but couldn't hear any sidetone when I keyed the yoke microphone. Finally I scanned the circuit breaker panel. A circuit breaker had popped. This time it was the 'B' side of the emergency feeder bus for radio/navigation. I pointed this out to the copilot who was flying. We then heard ATC call with an altitude change from FL330 to FL240. I acknowledged, but again heard no sidetone. ATC repeated the call and this time the copilot had to use the hand microphone to answer. We were back in business. Our volts, amps, batteries, and generators all showed normal. We agreed we didn't smell smoke. I tried to figure out if a popped circuit breaker on one half of the emergency feeder bus for the radios was causing our odd transmitting problems. It didn't seem likely since as far as I knew we weren't using the emergency battery to power any radios. Then the copilot acknowledged a transmission which I hadn't heard at all. In addition she said ATC sounded like it was fading away. She tried calling them again. Nothing. We agreed we had lost our communications. She had the good idea of trying voice over a VOR, but she couldn't get an identify on a VOR. We squawked 7600. We were at FL240, rapidly approaching our destination, and getting deep into the chicago arrival ATC structure. I wanted to get down below FL180 so we could continue VFR to our destination. I finally decided to reset the emergency feeder circuit breaker to see if it would have any affect on our communications. Sure enough, resetting it caused ATC to re-enter our headsets. It also caused the circuit breaker to pop almost immediately. The copilot and I agreed to reset the circuit breaker, tell ATC our problem, and get a clearance below FL180. I had to constantly push the circuit breaker each time it popped while we briefly talked to ATC for each part of our descent and landing. The communication failure occurred during descent into a busy area. It was not instantaneous, but it developed from a series of human error and mechanical fault. We had been told to fly with the emergency battery switch in the 'on' position. In theory this allowed the emergency battery to be charged. Because of this incident, we have discovered the switch should be in the 'off' position until radio failure at which time the crew can then select it to the 'on' position. There is no flight manual documentation on the position of the switch for normal operation. A short developed internally in the emergency battery which should have tripped a circuit breaker for that battery. Unfortunately it was discovered that the circuit breaker was corroded to the point that it required 2 hands to manually pop it. The circuit breaker which finally popped relaxed a relay so that our radios were only being powered by the already faulty battery. The failure of the #1 transponder should have called for an immediate circuit breaker check, but I was so used to intermittent problems with the airplane and so close to home base that I lost some time before realizing I had a more significant problem. I was willing to push in the circuit breaker because the immediate alternative was to continue our routing, arrive over our chicago destination at FL240, and then descend in a holding pattern right next to ord. If the circuit breaker drill had failed, we could have tried the flight phone.

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Original NASA ASRS Text

Title: FLC OF A DASSAULT FALCON 50 (DA50), TEMPORARILY LOST COM DURING DSCNT WHEN THE EMER BATTERY WAS DRAINED OF PWR DUE TO LEAVING THE SWITCH IN THE 'ON' POS. THE ACFT BUS BARS WERE CAUSING THE INTERMITTENT AUTOPLT, TCASII, ALT ALERT AND COM RADIO OUTAGES COMS WERE RE-ESTABLISHED BY PUTTING THE CTLING CIRCUIT BREAKER IN EACH TIME IT POPPED OUT.

Narrative: THIS AIRPLANE IS AN EARLY SERIAL NUMBER FALCON 50 WHICH WAS UPDATED WITH TCASII, RVSM, AND A NEW INTERIOR 7 MONTHS AGO. SINCE RETURNING FROM THE COMPLETION CTR IT HAS BEEN PLAGUED WITH TCASII PROBS, AUTOPLT HARDOVERS, FALSE ALT ALERTS, ETC. THE PROBS ARE ALMOST NEVER HARD FAILURES. OUR PROB BEGAN WHEN OUR TCASII FAILED. WE SWITCHED TO THE #2 XPONDER, THE TCASII CAME BACK, AND WE CONTINUED. YAWN. JUST ANOTHER FAILURE. WE WERE CLOSE TO OUR HOME ARPT IN THE CHICAGO AREA AND READY FOR OUR DSCNT. I TRIED TO PICK UP THE ATIS, BUT ALL I COULD HEAR WAS SILENCE OR A RAPID CLICKING NOISE LIKE SOMEONE KEYING A MIKE. I FIGURED THEY WERE CHANGING THE ATIS. I TRIED CALLING HOME BASE BUT COULDN'T HEAR ANY SIDETONE WHEN I KEYED THE YOKE MIKE. FINALLY I SCANNED THE CIRCUIT BREAKER PANEL. A CIRCUIT BREAKER HAD POPPED. THIS TIME IT WAS THE 'B' SIDE OF THE EMER FEEDER BUS FOR RADIO/NAV. I POINTED THIS OUT TO THE COPLT WHO WAS FLYING. WE THEN HEARD ATC CALL WITH AN ALT CHANGE FROM FL330 TO FL240. I ACKNOWLEDGED, BUT AGAIN HEARD NO SIDETONE. ATC REPEATED THE CALL AND THIS TIME THE COPLT HAD TO USE THE HAND MIKE TO ANSWER. WE WERE BACK IN BUSINESS. OUR VOLTS, AMPS, BATTERIES, AND GENERATORS ALL SHOWED NORMAL. WE AGREED WE DIDN'T SMELL SMOKE. I TRIED TO FIGURE OUT IF A POPPED CIRCUIT BREAKER ON ONE HALF OF THE EMER FEEDER BUS FOR THE RADIOS WAS CAUSING OUR ODD XMITTING PROBS. IT DIDN'T SEEM LIKELY SINCE AS FAR AS I KNEW WE WEREN'T USING THE EMER BATTERY TO PWR ANY RADIOS. THEN THE COPLT ACKNOWLEDGED A XMISSION WHICH I HADN'T HEARD AT ALL. IN ADDITION SHE SAID ATC SOUNDED LIKE IT WAS FADING AWAY. SHE TRIED CALLING THEM AGAIN. NOTHING. WE AGREED WE HAD LOST OUR COMS. SHE HAD THE GOOD IDEA OF TRYING VOICE OVER A VOR, BUT SHE COULDN'T GET AN IDENT ON A VOR. WE SQUAWKED 7600. WE WERE AT FL240, RAPIDLY APCHING OUR DEST, AND GETTING DEEP INTO THE CHICAGO ARR ATC STRUCTURE. I WANTED TO GET DOWN BELOW FL180 SO WE COULD CONTINUE VFR TO OUR DEST. I FINALLY DECIDED TO RESET THE EMER FEEDER CIRCUIT BREAKER TO SEE IF IT WOULD HAVE ANY AFFECT ON OUR COMS. SURE ENOUGH, RESETTING IT CAUSED ATC TO RE-ENTER OUR HEADSETS. IT ALSO CAUSED THE CIRCUIT BREAKER TO POP ALMOST IMMEDIATELY. THE COPLT AND I AGREED TO RESET THE CIRCUIT BREAKER, TELL ATC OUR PROB, AND GET A CLRNC BELOW FL180. I HAD TO CONSTANTLY PUSH THE CIRCUIT BREAKER EACH TIME IT POPPED WHILE WE BRIEFLY TALKED TO ATC FOR EACH PART OF OUR DSCNT AND LNDG. THE COM FAILURE OCCURRED DURING DSCNT INTO A BUSY AREA. IT WAS NOT INSTANTANEOUS, BUT IT DEVELOPED FROM A SERIES OF HUMAN ERROR AND MECHANICAL FAULT. WE HAD BEEN TOLD TO FLY WITH THE EMER BATTERY SWITCH IN THE 'ON' POS. IN THEORY THIS ALLOWED THE EMER BATTERY TO BE CHARGED. BECAUSE OF THIS INCIDENT, WE HAVE DISCOVERED THE SWITCH SHOULD BE IN THE 'OFF' POS UNTIL RADIO FAILURE AT WHICH TIME THE CREW CAN THEN SELECT IT TO THE 'ON' POS. THERE IS NO FLT MANUAL DOCUMENTATION ON THE POS OF THE SWITCH FOR NORMAL OP. A SHORT DEVELOPED INTERNALLY IN THE EMER BATTERY WHICH SHOULD HAVE TRIPPED A CIRCUIT BREAKER FOR THAT BATTERY. UNFORTUNATELY IT WAS DISCOVERED THAT THE CIRCUIT BREAKER WAS CORRODED TO THE POINT THAT IT REQUIRED 2 HANDS TO MANUALLY POP IT. THE CIRCUIT BREAKER WHICH FINALLY POPPED RELAXED A RELAY SO THAT OUR RADIOS WERE ONLY BEING POWERED BY THE ALREADY FAULTY BATTERY. THE FAILURE OF THE #1 XPONDER SHOULD HAVE CALLED FOR AN IMMEDIATE CIRCUIT BREAKER CHK, BUT I WAS SO USED TO INTERMITTENT PROBS WITH THE AIRPLANE AND SO CLOSE TO HOME BASE THAT I LOST SOME TIME BEFORE REALIZING I HAD A MORE SIGNIFICANT PROB. I WAS WILLING TO PUSH IN THE CIRCUIT BREAKER BECAUSE THE IMMEDIATE ALTERNATIVE WAS TO CONTINUE OUR ROUTING, ARRIVE OVER OUR CHICAGO DEST AT FL240, AND THEN DSND IN A HOLDING PATTERN RIGHT NEXT TO ORD. IF THE CIRCUIT BREAKER DRILL HAD FAILED, WE COULD HAVE TRIED THE FLT PHONE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.