Narrative:

I was assigned to do a service check on X. The aircraft came in with a write-up for '#1 engine slow to spool on engine start.' after doing my normal service check and having only a few discrepancies; I began to troubleshoot the problem. After talking to the pilot; he stated that it was like a weak APU. The first thing I did was to troubleshoot the air supply problem. I started both engines to see if I could duplicate the problem. During my troubleshooting; I was starting both engines several times. During my engine starts; I noticed that the air supply was dropping to around 11-12 psi. On a couple of the starts; the start was normal with the air pressure staying well above 20 psi so I had an intermittent problem. During all of my troubleshooting; the air pressure was normal for pack operation and such but only dropped when trying to start an engine. I wanted to see if the APU was just not putting out enough air so I hooked up the huffer start cart and received better results that were almost normal. This action told me that either the APU was not putting out enough air for some reason or there was an air leak at the APU. I checked for air leaks at the APU and found none. I also did a brief check to see if I could find any other air leaks with none found. During my starts I noticed that the APU egt was not getting up to temperature as it should. With the workload we had for the night; my lead suggested that I add all the information that I obtained and just put the APU bleed air on MEL. I followed the maintenance procedures and installed the MEL. After installing the MEL; I found that I had a little more time before the morning flts to do a little more troubleshooting. At that time I reinstalled the APU bleed valve electrical connector D474. I proceeded to troubleshoot a little further to make sure the turbo control valve was not stuck in the open position which was suggested for me to check from technical services. After this; it was getting time for the morning departures and I was assigned to do the air start on this aircraft. I hurried to close up the APU cowling and get set up for the air start. I started the aircraft and it left on time. Tonight I was informed by my supervisor that a mechanic in ZZZ was working another write-up for the same problem. At that time he noticed that the electrical connection for the APU bleed valve (D474) was still hooked up. My supervisor was notified and in turn notified maintenance control. At no time do I think there was any danger to the aircraft. The APU was working normal but was just not putting out enough air for an engine start. I initially did do the maintenance procedures as stated in the MEL on log but in hindsight did not disconnect it the second time. No other factors really added to the mistake I made. No excuses; I just forgot.

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Original NASA ASRS Text

Title: A B737-400 ACFT DEPARTED WITH AN APU BLEED AIR CONTROL VALVE ON MEL DEFERRED. BLEED VALVE CONNECTOR NOT DISCONNECTED PER MEL REQUIREMENTS.

Narrative: I WAS ASSIGNED TO DO A SVC CHK ON X. THE ACFT CAME IN WITH A WRITE-UP FOR '#1 ENG SLOW TO SPOOL ON ENG START.' AFTER DOING MY NORMAL SVC CHK AND HAVING ONLY A FEW DISCREPANCIES; I BEGAN TO TROUBLESHOOT THE PROB. AFTER TALKING TO THE PLT; HE STATED THAT IT WAS LIKE A WEAK APU. THE FIRST THING I DID WAS TO TROUBLESHOOT THE AIR SUPPLY PROB. I STARTED BOTH ENGS TO SEE IF I COULD DUPLICATE THE PROB. DURING MY TROUBLESHOOTING; I WAS STARTING BOTH ENGS SEVERAL TIMES. DURING MY ENG STARTS; I NOTICED THAT THE AIR SUPPLY WAS DROPPING TO AROUND 11-12 PSI. ON A COUPLE OF THE STARTS; THE START WAS NORMAL WITH THE AIR PRESSURE STAYING WELL ABOVE 20 PSI SO I HAD AN INTERMITTENT PROB. DURING ALL OF MY TROUBLESHOOTING; THE AIR PRESSURE WAS NORMAL FOR PACK OP AND SUCH BUT ONLY DROPPED WHEN TRYING TO START AN ENG. I WANTED TO SEE IF THE APU WAS JUST NOT PUTTING OUT ENOUGH AIR SO I HOOKED UP THE HUFFER START CART AND RECEIVED BETTER RESULTS THAT WERE ALMOST NORMAL. THIS ACTION TOLD ME THAT EITHER THE APU WAS NOT PUTTING OUT ENOUGH AIR FOR SOME REASON OR THERE WAS AN AIR LEAK AT THE APU. I CHKED FOR AIR LEAKS AT THE APU AND FOUND NONE. I ALSO DID A BRIEF CHK TO SEE IF I COULD FIND ANY OTHER AIR LEAKS WITH NONE FOUND. DURING MY STARTS I NOTICED THAT THE APU EGT WAS NOT GETTING UP TO TEMP AS IT SHOULD. WITH THE WORKLOAD WE HAD FOR THE NIGHT; MY LEAD SUGGESTED THAT I ADD ALL THE INFO THAT I OBTAINED AND JUST PUT THE APU BLEED AIR ON MEL. I FOLLOWED THE MAINT PROCS AND INSTALLED THE MEL. AFTER INSTALLING THE MEL; I FOUND THAT I HAD A LITTLE MORE TIME BEFORE THE MORNING FLTS TO DO A LITTLE MORE TROUBLESHOOTING. AT THAT TIME I REINSTALLED THE APU BLEED VALVE ELECTRICAL CONNECTOR D474. I PROCEEDED TO TROUBLESHOOT A LITTLE FURTHER TO MAKE SURE THE TURBO CTL VALVE WAS NOT STUCK IN THE OPEN POS WHICH WAS SUGGESTED FOR ME TO CHK FROM TECHNICAL SVCS. AFTER THIS; IT WAS GETTING TIME FOR THE MORNING DEPS AND I WAS ASSIGNED TO DO THE AIR START ON THIS ACFT. I HURRIED TO CLOSE UP THE APU COWLING AND GET SET UP FOR THE AIR START. I STARTED THE ACFT AND IT LEFT ON TIME. TONIGHT I WAS INFORMED BY MY SUPVR THAT A MECH IN ZZZ WAS WORKING ANOTHER WRITE-UP FOR THE SAME PROB. AT THAT TIME HE NOTICED THAT THE ELECTRICAL CONNECTION FOR THE APU BLEED VALVE (D474) WAS STILL HOOKED UP. MY SUPVR WAS NOTIFIED AND IN TURN NOTIFIED MAINT CTL. AT NO TIME DO I THINK THERE WAS ANY DANGER TO THE ACFT. THE APU WAS WORKING NORMAL BUT WAS JUST NOT PUTTING OUT ENOUGH AIR FOR AN ENG START. I INITIALLY DID DO THE MAINT PROCS AS STATED IN THE MEL ON LOG BUT IN HINDSIGHT DID NOT DISCONNECT IT THE SECOND TIME. NO OTHER FACTORS REALLY ADDED TO THE MISTAKE I MADE. NO EXCUSES; I JUST FORGOT.

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.