Narrative:

This is my account of the events concerning dhc-8-200 aircraft. I arrived at the ZZZ maintenance base of air carrier X. Aircraft was brought into the hanger for maintenance with a discrepancy 'autoplt will not stay engaged.' I was the avionics technician on duty and I performed the maintenance on this discrepancy. I determined through the ground maintenance test that there was a hard failure message of 'right/H command cw and ccw fail' in the elevator servo test area indicating a need to replace the elevator servo. In researching the ipc; I found that there are two part numbers for the servo in maintenance manual. There is a pre-modsum 8q101245 and a post-modsum 8q101245. The modsum chapter of the amm does not call out a serial number identifier for the difference; only that 'autoflt -- to eliminate uncommanded autoplt SM300 servo engagement.' I used a 'partial part number search' in part ordering computer to check the availability of the part and found that there are indeed multiple part numbers. In bringing down the cursor to X or highlighting the part number availability at ZZZ; I may have entered the X on the wrong line. In checking the two 'class control numbers' for this servo I found one marked 'do not use on dhc-8-300's' in the stores comment area. As there are pre-modsum and post-modsum entries; this made sense to me. I ordered the part in parts ordering computer by 'cut and paste' of the ccn and proceeded to right&right the part in accordance with amm. After installing the servo; I performed the 'ground maintenance ground power-up test' concerning elevator servos getting a displayed message; 'left elevator servo pass;' and 'right elevator servo pass.' this message was the basis for my continuing the process of installation. I completed my task by closing the panels; checking for return of tools used; and making paperwork entries in the aircraft log book and on the rotable tag. I recorded the part number from the old part and noticed that the part numbers were different as I filled out the rotable tag; but as I had previously seen two part numbers in the ipc and in parts ordering computer; I was not alerted to this as a concern. I have since found that there are two servo types: servos that can be used in either the elevator or aileron position; but only on dhc-8-300 series; and servos that can be used only in the elevator position on dhc-8-100/200 series. This information in the 'stores comment' would have alerted me to investigate the applicability of the part I used on this aircraft. The part I did use had a comment '-300 only' and the part itself had a label '-100/200 only' on it; and the difference in the part numbers that I entered on the rotable tag was consistent in my mind with the two part numbers called out in the ipc. I have also learned that the ground maintenance test for elevator servos only tests that the servo has received a command to power the motor to rotate and has reported back the command and response by the servo. The possibility that the servo clutch may not have engaged is not reported; and a defective servo may be installed and still pass the test. In light of the possibility of the ground maintenance test for elevator servos passing a servo that does not move the flight control surface; a defective part and an incorrect part will test the same. This resulted in a displayed message; 'left/right elevator servo pass.' I had followed the test procedure as written and decided that the installation was good and continued with the process of completing the maintenance. If an error was committed; it was in not verifying before ordering the part number both in the ipc and parts ordering computer; but as well as checking the part number taken from the removed part both in the ipc and in the parts ordering computer for the correctness of that part. I will do this in the future.

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Original NASA ASRS Text

Title: AN AVIONICS TECH NOTICES THE 'GND MAINT TEST' PROC FOR ELEV SERVOS WILL SHOW A 'SERVO PASS' VERIFICATION DISPLAY; EVEN THOUGH A DEFECTIVE PART; OR INCORRECT PART; MAY BE INSTALLED ON DEHAVILLAND DHC-8-100.

Narrative: THIS IS MY ACCOUNT OF THE EVENTS CONCERNING DHC-8-200 ACFT. I ARRIVED AT THE ZZZ MAINT BASE OF ACR X. ACFT WAS BROUGHT INTO THE HANGER FOR MAINT WITH A DISCREPANCY 'AUTOPLT WILL NOT STAY ENGAGED.' I WAS THE AVIONICS TECHNICIAN ON DUTY AND I PERFORMED THE MAINT ON THIS DISCREPANCY. I DETERMINED THROUGH THE GND MAINT TEST THAT THERE WAS A HARD FAILURE MSG OF 'R/H COMMAND CW AND CCW FAIL' IN THE ELEVATOR SERVO TEST AREA INDICATING A NEED TO REPLACE THE ELEVATOR SERVO. IN RESEARCHING THE IPC; I FOUND THAT THERE ARE TWO PART NUMBERS FOR THE SERVO IN MAINT MANUAL. THERE IS A PRE-MODSUM 8Q101245 AND A POST-MODSUM 8Q101245. THE MODSUM CHAPTER OF THE AMM DOES NOT CALL OUT A SERIAL NUMBER IDENTIFIER FOR THE DIFFERENCE; ONLY THAT 'AUTOFLT -- TO ELIMINATE UNCOMMANDED AUTOPLT SM300 SERVO ENGAGEMENT.' I USED A 'PARTIAL PART NUMBER SEARCH' IN PART ORDERING COMPUTER TO CHK THE AVAILABILITY OF THE PART AND FOUND THAT THERE ARE INDEED MULTIPLE PART NUMBERS. IN BRINGING DOWN THE CURSOR TO X OR HIGHLIGHTING THE PART NUMBER AVAILABILITY AT ZZZ; I MAY HAVE ENTERED THE X ON THE WRONG LINE. IN CHKING THE TWO 'CLASS CTL NUMBERS' FOR THIS SERVO I FOUND ONE MARKED 'DO NOT USE ON DHC-8-300'S' IN THE STORES COMMENT AREA. AS THERE ARE PRE-MODSUM AND POST-MODSUM ENTRIES; THIS MADE SENSE TO ME. I ORDERED THE PART IN PARTS ORDERING COMPUTER BY 'CUT AND PASTE' OF THE CCN AND PROCEEDED TO R&R THE PART IAW AMM. AFTER INSTALLING THE SERVO; I PERFORMED THE 'GND MAINT GND POWER-UP TEST' CONCERNING ELEVATOR SERVOS GETTING A DISPLAYED MESSAGE; 'LEFT ELEVATOR SERVO PASS;' AND 'RIGHT ELEVATOR SERVO PASS.' THIS MESSAGE WAS THE BASIS FOR MY CONTINUING THE PROCESS OF INSTALLATION. I COMPLETED MY TASK BY CLOSING THE PANELS; CHECKING FOR RETURN OF TOOLS USED; AND MAKING PAPERWORK ENTRIES IN THE ACFT LOG BOOK AND ON THE ROTABLE TAG. I RECORDED THE PART NUMBER FROM THE OLD PART AND NOTICED THAT THE PART NUMBERS WERE DIFFERENT AS I FILLED OUT THE ROTABLE TAG; BUT AS I HAD PREVIOUSLY SEEN TWO PART NUMBERS IN THE IPC AND IN PARTS ORDERING COMPUTER; I WAS NOT ALERTED TO THIS AS A CONCERN. I HAVE SINCE FOUND THAT THERE ARE TWO SERVO TYPES: SERVOS THAT CAN BE USED IN EITHER THE ELEVATOR OR AILERON POSITION; BUT ONLY ON DHC-8-300 SERIES; AND SERVOS THAT CAN BE USED ONLY IN THE ELEVATOR POSITION ON DHC-8-100/200 SERIES. THIS INFO IN THE 'STORES COMMENT' WOULD HAVE ALERTED ME TO INVESTIGATE THE APPLICABILITY OF THE PART I USED ON THIS ACFT. THE PART I DID USE HAD A COMMENT '-300 ONLY' AND THE PART ITSELF HAD A LABEL '-100/200 ONLY' ON IT; AND THE DIFFERENCE IN THE PART NUMBERS THAT I ENTERED ON THE ROTABLE TAG WAS CONSISTENT IN MY MIND WITH THE TWO PART NUMBERS CALLED OUT IN THE IPC. I HAVE ALSO LEARNED THAT THE GND MAINT TEST FOR ELEVATOR SERVOS ONLY TESTS THAT THE SERVO HAS RECEIVED A COMMAND TO POWER THE MOTOR TO ROTATE AND HAS REPORTED BACK THE COMMAND AND RESPONSE BY THE SERVO. THE POSSIBILITY THAT THE SERVO CLUTCH MAY NOT HAVE ENGAGED IS NOT REPORTED; AND A DEFECTIVE SERVO MAY BE INSTALLED AND STILL PASS THE TEST. IN LIGHT OF THE POSSIBILITY OF THE GND MAINT TEST FOR ELEVATOR SERVOS PASSING A SERVO THAT DOES NOT MOVE THE FLT CONTROL SURFACE; A DEFECTIVE PART AND AN INCORRECT PART WILL TEST THE SAME. THIS RESULTED IN A DISPLAYED MESSAGE; 'LEFT/RIGHT ELEVATOR SERVO PASS.' I HAD FOLLOWED THE TEST PROCEDURE AS WRITTEN AND DECIDED THAT THE INSTALLATION WAS GOOD AND CONTINUED WITH THE PROCESS OF COMPLETING THE MAINTENANCE. IF AN ERROR WAS COMMITTED; IT WAS IN NOT VERIFYING BEFORE ORDERING THE PART NUMBER BOTH IN THE IPC AND PARTS ORDERING COMPUTER; BUT AS WELL AS CHECKING THE PART NUMBER TAKEN FROM THE REMOVED PART BOTH IN THE IPC AND IN THE PARTS ORDERING COMPUTER FOR THE CORRECTNESS OF THAT PART. I WILL DO THIS IN THE FUTURE.

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.