Narrative:

I left home (phx) the day before I was to begin my pc. The plan was to ferry an aircraft from ZZZ to lax; then deadhead back to ZZZ for my pc. I had pulled the paperwork in phx. I did my flight planning in the airplane on the way to ZZZ. Upon arrival at ZZZ; I went to the aircraft; met the first officer and began the process of readying the plane for departure. The first officer mentioned that he had a tight connection in lax to get him back to ord and catch the last flight to his home. I normally do not let myself become rushed; but this may be a contributing factor. We completed the preflight and pushed back from the gate. After receiving clearance; I asked the first officer to start both engines. The left engine was started normally; and he asked if I wanted to start the right. I said yes that it would be a short taxi. As he was in the process of starting the right engine; I was communicating with the pushback crew. With everything done; I received a salute and release from guidance. Then; and I don't know why; I glanced at the engine instruments and believing the right engine was stable; shut down the APU. The engine was not fully started and we got a hung start. The first officer took out the qrc and we agreed that engine should be shut down. Maximum temperature was about 350 degrees; way below maximum start temperature. Up to now; no harm; no foul. As the engine was spooling down; the first officer asked if we should motor the engine to keep the temperature coming down. The right answer was 'what does the qrc say?' my answer was 'ok.' first officer opens the bleed valve and it did not take us long to realize we sheared the starter shaft. My heart just sank. Never done something that dumb in 35 yrs of flying big airplanes. Maintenance changed the starter and we got to lax about 50 mins late. Shutting down the APU during a senior moment was; however stupid; a recoverable error. All we needed to do was complete the 'abnormal engine start' qrc! The very next statement is 'caution: if starter cutout has occurred; do not select ground until N2 is 20% or less. Read also; do not open bleed valve on running engine till below 20%.' I feel awful; starters are expensive; and it did not need to happen. Lessons learned: always; always; always use the checklist.

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Original NASA ASRS Text

Title: A B757-200 FLT CREW GOT A HUNG START BECAUSE THEY SHUT DOWN THE APU PREMATURELY; THEN SHEARED THE STARTER SHAFT WHEN THEY ENGAGED THE STARTER TO MOTOR THE ENG BEFORE IT HAD SPOOLED DOWN.

Narrative: I LEFT HOME (PHX) THE DAY BEFORE I WAS TO BEGIN MY PC. THE PLAN WAS TO FERRY AN ACFT FROM ZZZ TO LAX; THEN DEADHEAD BACK TO ZZZ FOR MY PC. I HAD PULLED THE PAPERWORK IN PHX. I DID MY FLT PLANNING IN THE AIRPLANE ON THE WAY TO ZZZ. UPON ARR AT ZZZ; I WENT TO THE ACFT; MET THE FO AND BEGAN THE PROCESS OF READYING THE PLANE FOR DEP. THE FO MENTIONED THAT HE HAD A TIGHT CONNECTION IN LAX TO GET HIM BACK TO ORD AND CATCH THE LAST FLT TO HIS HOME. I NORMALLY DO NOT LET MYSELF BECOME RUSHED; BUT THIS MAY BE A CONTRIBUTING FACTOR. WE COMPLETED THE PREFLT AND PUSHED BACK FROM THE GATE. AFTER RECEIVING CLRNC; I ASKED THE FO TO START BOTH ENGS. THE L ENG WAS STARTED NORMALLY; AND HE ASKED IF I WANTED TO START THE R. I SAID YES THAT IT WOULD BE A SHORT TAXI. AS HE WAS IN THE PROCESS OF STARTING THE R ENG; I WAS COMMUNICATING WITH THE PUSHBACK CREW. WITH EVERYTHING DONE; I RECEIVED A SALUTE AND RELEASE FROM GUIDANCE. THEN; AND I DON'T KNOW WHY; I GLANCED AT THE ENG INSTS AND BELIEVING THE R ENG WAS STABLE; SHUT DOWN THE APU. THE ENG WAS NOT FULLY STARTED AND WE GOT A HUNG START. THE FO TOOK OUT THE QRC AND WE AGREED THAT ENG SHOULD BE SHUT DOWN. MAX TEMP WAS ABOUT 350 DEGS; WAY BELOW MAX START TEMP. UP TO NOW; NO HARM; NO FOUL. AS THE ENG WAS SPOOLING DOWN; THE FO ASKED IF WE SHOULD MOTOR THE ENG TO KEEP THE TEMP COMING DOWN. THE RIGHT ANSWER WAS 'WHAT DOES THE QRC SAY?' MY ANSWER WAS 'OK.' FO OPENS THE BLEED VALVE AND IT DID NOT TAKE US LONG TO REALIZE WE SHEARED THE STARTER SHAFT. MY HEART JUST SANK. NEVER DONE SOMETHING THAT DUMB IN 35 YRS OF FLYING BIG AIRPLANES. MAINT CHANGED THE STARTER AND WE GOT TO LAX ABOUT 50 MINS LATE. SHUTTING DOWN THE APU DURING A SENIOR MOMENT WAS; HOWEVER STUPID; A RECOVERABLE ERROR. ALL WE NEEDED TO DO WAS COMPLETE THE 'ABNORMAL ENG START' QRC! THE VERY NEXT STATEMENT IS 'CAUTION: IF STARTER CUTOUT HAS OCCURRED; DO NOT SELECT GND UNTIL N2 IS 20% OR LESS. READ ALSO; DO NOT OPEN BLEED VALVE ON RUNNING ENG TILL BELOW 20%.' I FEEL AWFUL; STARTERS ARE EXPENSIVE; AND IT DID NOT NEED TO HAPPEN. LESSONS LEARNED: ALWAYS; ALWAYS; ALWAYS USE THE CHKLIST.

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.