Narrative:

On dec/wed/01 at approximately XA55 hours, my lead mechanic gave me a gate call. He told me aircraft X had just arrived at the gate and it had a fuel filter problem. I immediately left knowing I needed to do quick troubleshooting in order to prevent a possible delay. When I arrived at the gate, the passenger had already deplaned and the captain was waiting for me in the jetway. He told me that the 'filter bypass' light came on after landing while taxiing to the gate. He also stated that the light went out after the engine was shut down. While interrogating the electronic engine control, I received the message 'sensor signals disagree' with error code 734-31072. With that information, I called the -700 desk in ZZZ1 (maintenance control) and consulted with mr X. I gave him the message and fault code. I asked him if there was any MEL relief. He said I would have to pull the filter and inspect for debris, change the sensor and then run it to verify the fix. I told him I was familiar with this procedure (because I thought we were both referring to 'oil bypass condition' which I had performed in the past). Obviously, I was thinking 'oil bypass' and was reading the fim for 'fuel bypass light.' I don't recall if I told mr X 'fuel' or 'oil.' the time now was approximately XB10 hours. The plane was scheduled to depart at XB15. As I was talking to mr X, the captain handed me the logbook with the write-up. I glanced at the logbook. The discrepancy was stated as 'during taxi in, #2 engine filter bypass light illuminated. Stayed on until engine shutdown.' I told mr X that I would call him back. I needed to talk to the captain. Knowing my past experience with 'oil bypass' problems on -700, I told the captain it would be at least 15 mins for me to do the job. I left to go get the parts. When I entered the line room, there were no other mechanics on evening shift to assist me. I saw lead mechanic, and I hurriedly told him what the situation was with my plane and how I was going to handle it. I went back to the stockroom to get the parts. I was having difficulty finding the 'oil differential pressure sensor.' our stock clerk was trying to help me find the parts. By radio, I told the stock clerk I could not find the parts and I would be returning to the aircraft to get part numbers and start the task. After opening the cowlings, I called stock clerk by radio and gave him the part number of the 'oil differential pressure sensor.' he said 'don't worry about it...I'm going to get the number from the PIC.' I pulled the 'oil filter' out and inspected and removed the differential pressure sensor. He said he was on his way with the part. He came with a 'fuel' differential pressure sensor and said he was on 'delay' himself and so were a few other mechanics. He said he had to go. After unpacking the part, I realized that it didn't look familiar to me. In comparing the 2 parts, I knew the part brought to me was not an effective replacement for the 'oil differential pressure sensor' that I had just removed. He had handed me a different part altogether. I then asked the pilot if he had any fault lights. The pilot said everything looked good. I 'bit' the electronic engine control fault history again. The electronic engine control showed no current fault for that engine cycle. So with the information from the pilot and the electronic engine control fault information, I determined the problem was fixed. I signed the logbook, the door was closed, and the plane immediately departed. The time was approximately XA40 hours. As I was returning to the line office at approximately XA55 hours, I started reviewing my paperwork from aircraft X in preparation for data entry. It was then that I discovered my mistake. I had changed the 'oil differential pressure sensor' when I should have changed the 'fuel differential pressure sensor.'

Related reports:

Google
 

Original NASA ASRS Text

Title: A B737-700 WAS DISPATCHED IN NON COMPLIANCE WITH AN OIL FILTER BYPASS SENSOR INSTALLED FOR A LOG RPT OF A FUEL FILTER BYPASS LIGHT ILLUMINATED.

Narrative: ON DEC/WED/01 AT APPROX XA55 HRS, MY LEAD MECH GAVE ME A GATE CALL. HE TOLD ME ACFT X HAD JUST ARRIVED AT THE GATE AND IT HAD A FUEL FILTER PROB. I IMMEDIATELY LEFT KNOWING I NEEDED TO DO QUICK TROUBLESHOOTING IN ORDER TO PREVENT A POSSIBLE DELAY. WHEN I ARRIVED AT THE GATE, THE PAX HAD ALREADY DEPLANED AND THE CAPT WAS WAITING FOR ME IN THE JETWAY. HE TOLD ME THAT THE 'FILTER BYPASS' LIGHT CAME ON AFTER LNDG WHILE TAXIING TO THE GATE. HE ALSO STATED THAT THE LIGHT WENT OUT AFTER THE ENG WAS SHUT DOWN. WHILE INTERROGATING THE ELECTRONIC ENGINE CONTROL, I RECEIVED THE MESSAGE 'SENSOR SIGNALS DISAGREE' WITH ERROR CODE 734-31072. WITH THAT INFO, I CALLED THE -700 DESK IN ZZZ1 (MAINT CTL) AND CONSULTED WITH MR X. I GAVE HIM THE MESSAGE AND FAULT CODE. I ASKED HIM IF THERE WAS ANY MEL RELIEF. HE SAID I WOULD HAVE TO PULL THE FILTER AND INSPECT FOR DEBRIS, CHANGE THE SENSOR AND THEN RUN IT TO VERIFY THE FIX. I TOLD HIM I WAS FAMILIAR WITH THIS PROC (BECAUSE I THOUGHT WE WERE BOTH REFERRING TO 'OIL BYPASS CONDITION' WHICH I HAD PERFORMED IN THE PAST). OBVIOUSLY, I WAS THINKING 'OIL BYPASS' AND WAS READING THE FIM FOR 'FUEL BYPASS LIGHT.' I DON'T RECALL IF I TOLD MR X 'FUEL' OR 'OIL.' THE TIME NOW WAS APPROX XB10 HRS. THE PLANE WAS SCHEDULED TO DEPART AT XB15. AS I WAS TALKING TO MR X, THE CAPT HANDED ME THE LOGBOOK WITH THE WRITE-UP. I GLANCED AT THE LOGBOOK. THE DISCREPANCY WAS STATED AS 'DURING TAXI IN, #2 ENG FILTER BYPASS LIGHT ILLUMINATED. STAYED ON UNTIL ENG SHUTDOWN.' I TOLD MR X THAT I WOULD CALL HIM BACK. I NEEDED TO TALK TO THE CAPT. KNOWING MY PAST EXPERIENCE WITH 'OIL BYPASS' PROBS ON -700, I TOLD THE CAPT IT WOULD BE AT LEAST 15 MINS FOR ME TO DO THE JOB. I LEFT TO GO GET THE PARTS. WHEN I ENTERED THE LINE ROOM, THERE WERE NO OTHER MECHS ON EVENING SHIFT TO ASSIST ME. I SAW LEAD MECH, AND I HURRIEDLY TOLD HIM WHAT THE SIT WAS WITH MY PLANE AND HOW I WAS GOING TO HANDLE IT. I WENT BACK TO THE STOCKROOM TO GET THE PARTS. I WAS HAVING DIFFICULTY FINDING THE 'OIL DIFFERENTIAL PRESSURE SENSOR.' OUR STOCK CLERK WAS TRYING TO HELP ME FIND THE PARTS. BY RADIO, I TOLD THE STOCK CLERK I COULD NOT FIND THE PARTS AND I WOULD BE RETURNING TO THE ACFT TO GET PART NUMBERS AND START THE TASK. AFTER OPENING THE COWLINGS, I CALLED STOCK CLERK BY RADIO AND GAVE HIM THE PART NUMBER OF THE 'OIL DIFFERENTIAL PRESSURE SENSOR.' HE SAID 'DON'T WORRY ABOUT IT...I'M GOING TO GET THE NUMBER FROM THE PIC.' I PULLED THE 'OIL FILTER' OUT AND INSPECTED AND REMOVED THE DIFFERENTIAL PRESSURE SENSOR. HE SAID HE WAS ON HIS WAY WITH THE PART. HE CAME WITH A 'FUEL' DIFFERENTIAL PRESSURE SENSOR AND SAID HE WAS ON 'DELAY' HIMSELF AND SO WERE A FEW OTHER MECHS. HE SAID HE HAD TO GO. AFTER UNPACKING THE PART, I REALIZED THAT IT DIDN'T LOOK FAMILIAR TO ME. IN COMPARING THE 2 PARTS, I KNEW THE PART BROUGHT TO ME WAS NOT AN EFFECTIVE REPLACEMENT FOR THE 'OIL DIFFERENTIAL PRESSURE SENSOR' THAT I HAD JUST REMOVED. HE HAD HANDED ME A DIFFERENT PART ALTOGETHER. I THEN ASKED THE PLT IF HE HAD ANY FAULT LIGHTS. THE PLT SAID EVERYTHING LOOKED GOOD. I 'BIT' THE ELECTRONIC ENGINE CONTROL FAULT HISTORY AGAIN. THE ELECTRONIC ENGINE CONTROL SHOWED NO CURRENT FAULT FOR THAT ENG CYCLE. SO WITH THE INFO FROM THE PLT AND THE ELECTRONIC ENGINE CONTROL FAULT INFO, I DETERMINED THE PROB WAS FIXED. I SIGNED THE LOGBOOK, THE DOOR WAS CLOSED, AND THE PLANE IMMEDIATELY DEPARTED. THE TIME WAS APPROX XA40 HRS. AS I WAS RETURNING TO THE LINE OFFICE AT APPROX XA55 HRS, I STARTED REVIEWING MY PAPERWORK FROM ACFT X IN PREPARATION FOR DATA ENTRY. IT WAS THEN THAT I DISCOVERED MY MISTAKE. I HAD CHANGED THE 'OIL DIFFERENTIAL PRESSURE SENSOR' WHEN I SHOULD HAVE CHANGED THE 'FUEL DIFFERENTIAL PRESSURE SENSOR.'

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.