A LEAR 45 WITH APU UNIT INOP PER THE MEL LEVELS OFF AT FL270 AND GETS CREW ALERT WARNING ON R GENERATOR FAIL. R ELECTRICAL BUS FAILED.

Narrative

DURING AN INTERMEDIATE STOP TO PICK UP PAX; WE ATTEMPTED TWICE TO START THE APU. BOTH ATTEMPTS WERE UNSUCCESSFUL DUE TO A MECHANICAL PROBLEM. THE APPROPRIATE CHKLIST WAS COMPLETED AND AFT COMPARTMENT WAS INSPECTED BY CREW. A VERY FAINT ODOR OF OZONE WAS NOTED BUT DISREGARDED AS ONLY A RESULT IN FAILED APU STARTER/GENERATOR. A CALL WAS MADE TO OUR COMPANY MAINT DEPARTMENT AND EVENTS DISCUSSED. IT WAS AGREED THAT THE APU WOULD BE MEL'D. THE APPROPRIATE ENTRIES WERE MADE; HOWEVER THE MEL WAS NOT EXAMINED FOR 'M' PROCS. LATER IT WAS FOUND THAT THE 'M' PROC WAS A NEW ADDITION TO THE MEL. THE CREW DISCUSSED THE RESULTS OF THE MEL'D APU AND CONTINUED TO FINAL DEST. ENG START AND PRE-TAXI CHKLIST WERE COMPLETED AND NO ANOMALIES WERE NOTED. TKOF AND CLB WERE UNEVENTFUL UNTIL LEVELING AT AN INTERMEDIATE ALT OF FL270. WE WERE IN CONTACT WITH CTR AND SUDDENLY WE NOTICED AN AMBER CAS MESSAGE INDICATING THE R GENERATOR HAD FAILED. IMMEDIATELY AFTERWARDS NUMEROUS CAS MESSAGES BEGAN FLICKERING ON AND OFF. THE CREW NOTED THAT THE APU 'AVAIL' AND 'ON' LIGHT HAD ILLUMINATED ON THE ELECTRICAL PANEL; AS WELL AS THE AMBER 'START' INDICATION ON THE R ENG. IN ADDITION; WE NOTICED THE APU PANEL INDICATED THE APU 'START' HAD BEEN INITIATED. THE APU MASTER WAS OFF. DUE TO NUMEROUS CAS MESSAGES THE CREW PRIORITIZED CHKLIST USAGE. ONCE THE 'R GEN FAILURE' CHKLIST WAS COMPLETED A PHONE CALL TO COMPANY MAINT WAS MADE BY PNF. AT THAT TIME; PF NOTICED THAT THE NUMBER 2 RADIO (THE ONE USUALLY USED DUE TO CLOSE PROXIMITY TO PNF) WAS INOP AS INDICATED BY DASHES ACROSS ALL NUMBERS. THE PF MADE NUMEROUS ATTEMPTS TO CONTACT ATC ON 121.5 TO OBTAIN RADIO FREQ. NUMEROUS ACFT RESPONDED BUT ALL FREQS WERE INCORRECT. CONTACT WAS MADE WITH JACKSON FSS AND A CORRECT FREQ WAS OBTAINED AND COMS WERE ESTABLISHED. ATC WAS ADVISED OF OUR PARTIAL LOSS OF TCAS AS WELL. WE ADVISED THAT NO EMER EXISTED AT THIS TIME. DURING THIS TIME THE RTE WAS FLOWN AS CLRED AND LNDG WAS MADE UNEVENTFUL AT DEST. UPON EXAMINATION BY MAINT TECHNICIANS; IT WAS DETERMINED THAT THE APU STARTER/GEN GND CABLE HAD WELDED AND CREATED A SHORT IN THE R REAR POWER DISTRIBUTION PANEL IN AFT COMPARTMENT. REPLACEMENT AND TESTING OF THE APU STARTER/GEN AND R REAR PDP WAS COMPLETED AND ACFT RETURNED TO SVC. THE PROBLEMS THAT AROSE COULD HAVE OCCURRED BY OVERLOOKING THE MEL 'M' PROC BOTH ON THE CREW'S PART AND THE MAINT TECHNICIAN'S PART. ALTHOUGH AT THE TIME OF THIS SUBMISSION; BOMBARDIER HAS INDICATED THE PDP MAY HAVE ALREADY BEEN 'TOASTED' TO A SIGNIFICANT POINT. IN ADDITION TO THE MECHANICAL DIFFICULTIES PRESENTED; A MAJOR PART OF DISTRESS PRESENTED ITSELF FROM A FROM A LOSS OF COMS WITH ATC JUST PRIOR TO BEGINNING A STAR. THE OVERALL REASON FOR THE LOSS OF COMS WAS THE IMPROPER USE OF RADIOS. THE NUMBER 2 RADIO (USED PREDOMINATELY DUE TO EASE AND CLOSE PROXIMITY TO PNF) LOAD SHEDS IF THERE IS A DUAL GENERATOR FAILURE OR IF THERE IS A 'START' INDICATION NOTED. IN OUR CASE THE FAULTY 'START' ANNUNCIATION; ALTHOUGH FALSE; SHED THE NUMBER 2 RADIO THUS PROHIBITING COMS. THE SOLUTION TO THIS PROBLEM IS TO OPERATE THE RADIOS IN THE MANNER TO WHICH THEY WERE DESIGNED. THE NUMBER 1 RADIO IS ON NOT ONLY THE ESSENTIAL BUS BUT THE EMER BATTERY AS WELL AND INCLUDES A REMOTE HEAD FOR EMER OPERATIONS AS WELL. IN ALL THE FLT CREW HANDLED THE SITUATION VERY WELL AND PRIORITIZED EVENTS AS NEEDED. HAVING FOLLOWED THE MEL MUCH CLOSER AND NOT WANTING TO LEAVE PAX STRANDED AT A REMOTE LOCATION WITH NO MAINT PLAYED A MAJOR ROLE IN INCIDENT. TWO DIFFERENT INDIVIDUALS CONFIRMED THE ACT OF MEL'ING THE APU BUT NEITHER LOOKED TO REVIEW THE APPROPRIATE PROC. IT WAS IDENTIFIED ONLY AFTER THE PARTIAL ELECTRICAL FAILURE OCCURRED AND LNDG MADE AT DEST.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE SPECIAL PROCS FOR DEFERRING THE APU WERE NOT ACCOMPLISHED BY THE GND CREW. AT LEVEL OFF AT FL270; RPTR STARTED TO GET CREW ALERT WARNINGS 'R GENERATOR FAIL' AND FLICKERING 'APU AVAIL;' 'APU START;' AND 'ON.' NOEMER WAS DECLARED AND THE RTE WAS FLOWN AS FILED. ON LNDG MAINT FOUND THE APU STARTER/GEN GND CABLE WAS SHORTED IN THE AFT POWER DISTRIBUTION PANEL AND HAD DAMAGED ALL THE R ELECTRICAL DISTRIBUTION ELECTRONICS. THE FIX WAS CABLE REPLACEMENT; APU STARTER; AND R ELECTRICAL DISTRIBUTION PANEL REPLACEMENTS.