Narrative:

During crew change; off-going captain described a problem where a-side hydraulic pressure seems to climb a little during engine starts. Off-going captain made a logbook write-up and reported condition to maintenance control and dispatch. We were issued an amended release with MEL 29-10 (with time and initials). First officer and I discussed the issue after reading MEL; and decided to start #2 engine while attached to towbar; and wait to start #1 until after disconnect of towbar; in case hydraulic pressure leaked into a-side. At push time; I advised tug crew of our intentions and that they could commence the pushback. Our a-pumps were 'off' as per the checklist; and we were given clearance to start #2 from tug crew. First officer (after hearing my conversation with tug crew about waiting to start #1) thought I had asked to start #1; which he did. Just after N2 rotation; the towbar broke; tug crew advised us; and I set the parking brake. I secured the engine which was at 16% N2. Tug crew asked if we had started #1 and I said yes and apologized. They quickly replaced towbar (as another aircraft was waiting for our gate) and we departed normally. I was not verifying my first officer's hand on start switch to prevent wrong engine from being started! MEL should be clear to not have ground crew attached to aircraft during starts of either engine (to prevent this kind of mistake from leading to a more serious event).

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Original NASA ASRS Text

Title: B737NG is dispatched on MEL 29-10; A side engine driven pump cannot be deactivated. First officer misunderstands and starts number one engine during push back causing tow bar to break. Flight departs after replacement tow bar is found.

Narrative: During crew change; off-going Captain described a problem where A-side hydraulic pressure seems to climb a little during engine starts. Off-going Captain made a logbook write-up and reported condition to Maintenance Control and Dispatch. We were issued an amended release with MEL 29-10 (with time and initials). First Officer and I discussed the issue after reading MEL; and decided to start #2 engine while attached to towbar; and wait to start #1 until after disconnect of towbar; in case hydraulic pressure leaked into A-side. At push time; I advised tug crew of our intentions and that they could commence the pushback. Our A-pumps were 'off' as per the checklist; and we were given clearance to start #2 from tug crew. First Officer (after hearing my conversation with tug crew about waiting to start #1) thought I had asked to start #1; which he did. Just after N2 rotation; the towbar broke; tug crew advised us; and I set the parking brake. I secured the engine which was at 16% N2. Tug crew asked if we had started #1 and I said yes and apologized. They quickly replaced towbar (as another aircraft was waiting for our gate) and we departed normally. I was not verifying my First Officer's hand on start switch to prevent wrong engine from being started! MEL should be clear to not have Ground Crew attached to aircraft during starts of either engine (to prevent this kind of mistake from leading to a more serious event).

Data retrieved from NASA's ASRS site as of April 2012 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.