Narrative:

The aircraft was grounded at ZZZ which required me to travel to the remote location and perform maintenance on the ramp. After determining the cause of the front engine's failure to start was a faulty fuel pump; I ordered the replacement part which came a few days later. I replaced the failed fuel pump and had to disconnect and reconnect the landing gear hydraulic lines. Someone came to talk to me while I was installing the fuel pump and was asking me questions for several minutes. Because the project was taking longer than I had told the owner it would take (the owner had been there the whole time overseeing the project and his wife was sitting in the lobby with her packed bags waiting to go); I was beginning to get 'hurried;' plus the visitor was distracting me. I then tested the systems (hydraulic and fuel). The landing gear doors opened and shut; but I was not able to perform a complete retraction test as the aircraft was not in the shop. The fuel pressure came up normally. The engine was then started and the ground run-up was completed successfully. I checked for any fuel or hydraulic leaks and found none. At this point I declared the aircraft airworthy and signed the logbook including the part number and serial number of the fuel pump; returning the aircraft to service. While landing at ZZZ1 (their stop after leaving ZZZ) the landing gear did not fully extend and the pilot made an emergency gear up landing. Investigation revealed that the fuel pump was installed incorrectly; resulting in the failure of the landing gear to extend. The owner/pilot told me that the hydraulic and fuel vent lines were crossed. Even though the lines are labeled throughout the system; it would be helpful if they would be labeled at that connection and/or the fuel drain line could be made a different size; so they cannot be hooked up incorrectly (which is easy to do). This critical safety item; which can result in a dangerous and costly situation; should be addressed.callback conversation with reporter revealed the following information: reporter stated the nose gear had locked ok in the down position; but not the mains. Realizing a gear up landing would be required; the pilot/owner tried to shut down the aft engine of the cessna-337 puller/pusher aircraft early enough; but propeller strike damage still occurred. Reporter stated he has not seen the aircraft since he replaced the fwd engine electric fuel pump in the nose gear well area. He does remember removing and reconnecting hydraulic lines to get access to the fuel pump. He was told; because the hydraulic line was connected to the fuel vent line; the hydraulic fluid for the landing gears was pumped overboard; preventing the mains from locking in the down position. Reporter stated no reports of any engine problem or hydraulic fluid in the engine fuel system after the hour plus flight following the fuel pump change. This was the first time in twenty years of aircraft maintenance that he's had any issue of maintenance work. Reporter stated changing the size of the fuel line end connection fitting to the vent line would be the easiest to accomplish by the manufacturer.

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Original NASA ASRS Text

Title: AFTER REPLACING THE FWD ENG'S FAULTY FUEL PUMP ON A CESSNA-337; A MECHANIC IS INFORMED THE PILOT MADE AN EMERGENCY LANDING. THE HYDRAULIC AND FUEL VENT LINES WERE INADVERTLY CROSSED DURING LINE REINSTALLATION.

Narrative: THE ACFT WAS GROUNDED AT ZZZ WHICH REQUIRED ME TO TRAVEL TO THE REMOTE LOCATION AND PERFORM MAINTENANCE ON THE RAMP. AFTER DETERMINING THE CAUSE OF THE FRONT ENG'S FAILURE TO START WAS A FAULTY FUEL PUMP; I ORDERED THE REPLACEMENT PART WHICH CAME A FEW DAYS LATER. I REPLACED THE FAILED FUEL PUMP AND HAD TO DISCONNECT AND RECONNECT THE LANDING GEAR HYDRAULIC LINES. SOMEONE CAME TO TALK TO ME WHILE I WAS INSTALLING THE FUEL PUMP AND WAS ASKING ME QUESTIONS FOR SEVERAL MINUTES. BECAUSE THE PROJECT WAS TAKING LONGER THAN I HAD TOLD THE OWNER IT WOULD TAKE (THE OWNER HAD BEEN THERE THE WHOLE TIME OVERSEEING THE PROJECT AND HIS WIFE WAS SITTING IN THE LOBBY WITH HER PACKED BAGS WAITING TO GO); I WAS BEGINNING TO GET 'HURRIED;' PLUS THE VISITOR WAS DISTRACTING ME. I THEN TESTED THE SYSTEMS (HYDRAULIC AND FUEL). THE LANDING GEAR DOORS OPENED AND SHUT; BUT I WAS NOT ABLE TO PERFORM A COMPLETE RETRACTION TEST AS THE ACFT WAS NOT IN THE SHOP. THE FUEL PRESSURE CAME UP NORMALLY. THE ENG WAS THEN STARTED AND THE GROUND RUN-UP WAS COMPLETED SUCCESSFULLY. I CHECKED FOR ANY FUEL OR HYDRAULIC LEAKS AND FOUND NONE. AT THIS POINT I DECLARED THE ACFT AIRWORTHY AND SIGNED THE LOGBOOK INCLUDING THE PART NUMBER AND SERIAL NUMBER OF THE FUEL PUMP; RETURNING THE ACFT TO SVC. WHILE LANDING AT ZZZ1 (THEIR STOP AFTER LEAVING ZZZ) THE LANDING GEAR DID NOT FULLY EXTEND AND THE PLT MADE AN EMER GEAR UP LANDING. INVESTIGATION REVEALED THAT THE FUEL PUMP WAS INSTALLED INCORRECTLY; RESULTING IN THE FAILURE OF THE LANDING GEAR TO EXTEND. THE OWNER/PLT TOLD ME THAT THE HYDRAULIC AND FUEL VENT LINES WERE CROSSED. EVEN THOUGH THE LINES ARE LABELED THROUGHOUT THE SYSTEM; IT WOULD BE HELPFUL IF THEY WOULD BE LABELED AT THAT CONNECTION AND/OR THE FUEL DRAIN LINE COULD BE MADE A DIFFERENT SIZE; SO THEY CANNOT BE HOOKED UP INCORRECTLY (WHICH IS EASY TO DO). THIS CRITICAL SAFETY ITEM; WHICH CAN RESULT IN A DANGEROUS AND COSTLY SITUATION; SHOULD BE ADDRESSED.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THE NOSE GEAR HAD LOCKED OK IN THE DOWN POSITION; BUT NOT THE MAINS. REALIZING A GEAR UP LANDING WOULD BE REQUIRED; THE PILOT/OWNER TRIED TO SHUT DOWN THE AFT ENGINE OF THE CESSNA-337 PULLER/PUSHER ACFT EARLY ENOUGH; BUT PROP STRIKE DAMAGE STILL OCCURRED. REPORTER STATED HE HAS NOT SEEN THE ACFT SINCE HE REPLACED THE FWD ENGINE ELECTRIC FUEL PUMP IN THE NOSE GEAR WELL AREA. HE DOES REMEMBER REMOVING AND RECONNECTING HYD LINES TO GET ACCESS TO THE FUEL PUMP. HE WAS TOLD; BECAUSE THE HYD LINE WAS CONNECTED TO THE FUEL VENT LINE; THE HYD FLUID FOR THE LANDING GEARS WAS PUMPED OVERBOARD; PREVENTING THE MAINS FROM LOCKING IN THE DOWN POSITION. REPORTER STATED NO REPORTS OF ANY ENGINE PROBLEM OR HYD FLUID IN THE ENGINE FUEL SYSTEM AFTER THE HOUR PLUS FLT FOLLOWING THE FUEL PUMP CHANGE. THIS WAS THE FIRST TIME IN TWENTY YEARS OF ACFT MAINT THAT HE'S HAD ANY ISSUE OF MAINT WORK. REPORTER STATED CHANGING THE SIZE OF THE FUEL LINE END CONNECTION FITTING TO THE VENT LINE WOULD BE THE EASIEST TO ACCOMPLISH BY THE MANUFACTURER.

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.