Narrative:

When performing task ### failed test. Went to remove and replace power supply and noticed that the converter was missing on power supply. Installed new power supply.callback conversation with reporter revealed the following information: reporter stated the saab-340B aircraft have a pre-mod; or a post-mod emergency power supply jetpack; installed on the aft side of the cockpit aft bulkhead; across from the galley. Both units have different part numbers; but look similar and have the same mount connector in the electrical rack. If the pre-mod power supply unit requires replacement using another pre-mod unit; the (dc) power converter must be transferred from the removed unit to the new replacement pre-mod unit. The post-mod unit has the (dc) converter built into the power supply black box and does not require any transfer of the converter. Reporter stated the jetpack provides emergency standy-by power for their compass and navigation systems and back lighting. Reporter stated the emergency jetpack requires a maintenance test be performed after a certain number of flight hours. This particular test also requires the aircraft right battery circuit breaker be pulled to simulate right battery power loss. When the stand-by compass; navigation systems and the back lighting did not power-up and the test indicated 'failed;' they decided to change the power supply unit; only to discover the converter on the pre-mod supply unit was not attached. Reporter does not know how long the aircraft had been flying without any stand-by power mode capability. There does not appear to be any pre-flight check that would give any indication to the flight crew the stand-by system power supply was not functional; unless this particular maintenance test is performed. The left battery system does not require this test. Reporter also stated there is a separate emergency battery pack for the cabin emergency lighting.

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Original NASA ASRS Text

Title: MECHANIC NOTICES A (DC) CONVERTER WAS MISSING FROM THE ACFT EMERGENCY POWER SUPPLY JETPACK UNIT ON A SAAB-340B ACFT.

Narrative: WHEN PERFORMING TASK ### FAILED TEST. WENT TO REMOVE AND REPLACE POWER SUPPLY AND NOTICED THAT THE CONVERTER WAS MISSING ON POWER SUPPLY. INSTALLED NEW POWER SUPPLY.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE SAAB-340B ACFT HAVE A PRE-MOD; OR A POST-MOD EMERGENCY POWER SUPPLY JETPACK; INSTALLED ON THE AFT SIDE OF THE COCKPIT AFT BULKHEAD; ACROSS FROM THE GALLEY. BOTH UNITS HAVE DIFFERENT PART NUMBERS; BUT LOOK SIMILAR AND HAVE THE SAME MOUNT CONNECTOR IN THE ELECTRICAL RACK. IF THE PRE-MOD POWER SUPPLY UNIT REQUIRES REPLACEMENT USING ANOTHER PRE-MOD UNIT; THE (DC) POWER CONVERTER MUST BE TRANSFERRED FROM THE REMOVED UNIT TO THE NEW REPLACEMENT PRE-MOD UNIT. THE POST-MOD UNIT HAS THE (DC) CONVERTER BUILT INTO THE POWER SUPPLY BLACK BOX AND DOES NOT REQUIRE ANY TRANSFER OF THE CONVERTER. REPORTER STATED THE JETPACK PROVIDES EMERGENCY STANDY-BY POWER FOR THEIR COMPASS AND NAVIGATION SYSTEMS AND BACK LIGHTING. REPORTER STATED THE EMERGENCY JETPACK REQUIRES A MAINT TEST BE PERFORMED AFTER A CERTAIN NUMBER OF FLIGHT HOURS. THIS PARTICULAR TEST ALSO REQUIRES THE ACFT RIGHT BATTERY CIRCUIT BREAKER BE PULLED TO SIMULATE RIGHT BATTERY POWER LOSS. WHEN THE STAND-BY COMPASS; NAVIGATION SYSTEMS AND THE BACK LIGHTING DID NOT POWER-UP AND THE TEST INDICATED 'FAILED;' THEY DECIDED TO CHANGE THE POWER SUPPLY UNIT; ONLY TO DISCOVER THE CONVERTER ON THE PRE-MOD SUPPLY UNIT WAS NOT ATTACHED. REPORTER DOES NOT KNOW HOW LONG THE ACFT HAD BEEN FLYING WITHOUT ANY STAND-BY POWER MODE CAPABILITY. THERE DOES NOT APPEAR TO BE ANY PRE-FLIGHT CHECK THAT WOULD GIVE ANY INDICATION TO THE FLIGHT CREW THE STAND-BY SYSTEM POWER SUPPLY WAS NOT FUNCTIONAL; UNLESS THIS PARTICULAR MAINT TEST IS PERFORMED. THE LEFT BATTERY SYSTEM DOES NOT REQUIRE THIS TEST. REPORTER ALSO STATED THERE IS A SEPARATE EMERGENCY BATTERY PACK FOR THE CABIN EMERGENCY LIGHTING.

Data retrieved from NASA's ASRS site as of May 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.