Narrative:

While troubleshooting the APU system in this aircraft; problem isolation included swapping the starter/generator on the l-hand engine with the starter/generator on the APU. After troubleshooting; I gave another mechanic the go ahead to swap them back to their original locations. After work had been accomplished; I suggested to the FBO owner that a test run-up of the aircraft would be a good idea so we would be at a fresh starting point on next workday. The owner instructed his employees; who had performed the generator swap to secure the aircraft and perform a ground test run. R-hand engine start up was uneventful; and generator was tied to main buss. Upon l-hand engine start sequence initiation; I heard a loud 'crack' and the l-hand engine failed to spool. After engine shutdown and aircraft secured power off; I approached the aircraft to examine for probable cause; and suggested to the mechanics to look for possible cross wiring. They discovered the l-hand starter/generator main power wires had been crossed (east to B; and B to east). This caused a surge of reverse current to pass through the airframe; causing instant stoppage to the r-hand starter/generator; and literally 'exploding' the interior components of the APU starter/generator. As a result of this occurrence; I advised the FBO owner that there was a good likelihood that the #1 and #2 engine starter generators were internally compromised as well. The FBO owner followed up by having the entire aircraft electrical system checked out by an independent avionics shop. In the future; upon accepting the aid of other mechanics; I will reevaluate their part in the troubleshooting process; and query as to whether or not they had their work inspected prior to further maintenance action; even though it was not my responsibility or job position to do so. Other factors contributing to the maintenance incident could be frustration with the amount of time the troubleshooting process was taking; and the desire of the mechanics to get home early.

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Original NASA ASRS Text

Title: A CESSNA-650 CITATION LH ENGINE FAILED TO SPOOL-UP AFTER A SURGE OF REVERSE CURRENT THROUGH ACFT CAUSED BY CROSSED STARTER/GENERATOR WIRES.

Narrative: WHILE TROUBLESHOOTING THE APU SYS IN THIS ACFT; PROB ISOLATION INCLUDED SWAPPING THE STARTER/GENERATOR ON THE L-HAND ENG WITH THE STARTER/GENERATOR ON THE APU. AFTER TROUBLESHOOTING; I GAVE ANOTHER MECH THE GO AHEAD TO SWAP THEM BACK TO THEIR ORIGINAL LOCATIONS. AFTER WORK HAD BEEN ACCOMPLISHED; I SUGGESTED TO THE FBO OWNER THAT A TEST RUN-UP OF THE ACFT WOULD BE A GOOD IDEA SO WE WOULD BE AT A FRESH STARTING POINT ON NEXT WORKDAY. THE OWNER INSTRUCTED HIS EMPLOYEES; WHO HAD PERFORMED THE GENERATOR SWAP TO SECURE THE ACFT AND PERFORM A GND TEST RUN. R-HAND ENG START UP WAS UNEVENTFUL; AND GENERATOR WAS TIED TO MAIN BUSS. UPON L-HAND ENG START SEQUENCE INITIATION; I HEARD A LOUD 'CRACK' AND THE L-HAND ENG FAILED TO SPOOL. AFTER ENG SHUTDOWN AND ACFT SECURED PWR OFF; I APCHED THE ACFT TO EXAMINE FOR PROBABLE CAUSE; AND SUGGESTED TO THE MECHS TO LOOK FOR POSSIBLE CROSS WIRING. THEY DISCOVERED THE L-HAND STARTER/GENERATOR MAIN PWR WIRES HAD BEEN CROSSED (E TO B; AND B TO E). THIS CAUSED A SURGE OF REVERSE CURRENT TO PASS THROUGH THE AIRFRAME; CAUSING INSTANT STOPPAGE TO THE R-HAND STARTER/GENERATOR; AND LITERALLY 'EXPLODING' THE INTERIOR COMPONENTS OF THE APU STARTER/GENERATOR. AS A RESULT OF THIS OCCURRENCE; I ADVISED THE FBO OWNER THAT THERE WAS A GOOD LIKELIHOOD THAT THE #1 AND #2 ENG STARTER GENERATORS WERE INTERNALLY COMPROMISED AS WELL. THE FBO OWNER FOLLOWED UP BY HAVING THE ENTIRE ACFT ELECTRICAL SYS CHKED OUT BY AN INDEPENDENT AVIONICS SHOP. IN THE FUTURE; UPON ACCEPTING THE AID OF OTHER MECHS; I WILL REEVALUATE THEIR PART IN THE TROUBLESHOOTING PROCESS; AND QUERY AS TO WHETHER OR NOT THEY HAD THEIR WORK INSPECTED PRIOR TO FURTHER MAINT ACTION; EVEN THOUGH IT WAS NOT MY RESPONSIBILITY OR JOB POS TO DO SO. OTHER FACTORS CONTRIBUTING TO THE MAINT INCIDENT COULD BE FRUSTRATION WITH THE AMOUNT OF TIME THE TROUBLESHOOTING PROCESS WAS TAKING; AND THE DESIRE OF THE MECHS TO GET HOME EARLY.

Data retrieved from NASA's ASRS site as of January 2009 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.