Narrative:

Before pushback; contract maintenance had to be called because of a thrust reverser issue involving both thrust reverser's. Both thrust reverser lights remained on after landing on our previous inbound flight and one reverser failed to stow with the levers stowed. Both pilots were in the flight deck to assist the contract maintenance mechanic in troubleshooting the problem. The mechanic was on the ground crew's flight interphone headset and directed myself; the captain; to turn on all hydraulic pumps and operate thrust reverser levers. The problem was eventually cleared and the malfunction was signed off. Prior to the troubleshooting I had interacted with dispatch and maintenance control over the telephone and also face to face with the ground operations; ramp personnel; the fueler; and flight attendants to ensure everyone was in the loop with the problem. After all the coordinating; the boarding process began for 135 passengers. The first officer and I did the before start originating checklist because of the maintenance performed. The flight pushed back 16 minutes late and during the start of #1 the tug driver reported a broken tow bar. The first officer asked why there was a system hydraulic pressure and I looked up and noticed the hyd system switches were in the configuration of the parking checklist with the electric pumps off and engine pumps on. I remember being careful to restore that configuration after operating the switches for troubleshooting but failed to turn the a pumps off for my before start flow. I also must have been thinking about electric pumps instead of a pumps for the before start checklist and when I reported 'a's off brakes set' to the ground crew on headset; my broken habit pattern and lack of attention to detail broke the tow bar on the last leg of a long day. We were not rushed with the checklist I just saw what I thought was normal and didn't confirm what I reported. I lost situational awareness in the process of an abnormality. This incident has taught me to pay extra attention to detail on the basic checklist items; especially after a break in routine!

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Original NASA ASRS Text

Title: After dealing with a maintenance issue with contract maintenance; B737 Captain omits turning off 'A' engine driven hydraulic pump during before start checklist causing tow bar to fail when number 1 engine is started.

Narrative: Before pushback; Contract Maintenance had to be called because of a thrust reverser issue involving both thrust reverser's. Both thrust reverser lights remained on after landing on our previous inbound flight and one reverser failed to stow with the levers stowed. Both Pilots were in the flight deck to assist the contract maintenance Mechanic in troubleshooting the problem. The Mechanic was on the Ground Crew's flight interphone headset and directed myself; the Captain; to turn on all hydraulic pumps and operate thrust reverser levers. The problem was eventually cleared and the malfunction was signed off. Prior to the troubleshooting I had interacted with Dispatch and Maintenance Control over the telephone and also face to face with the Ground Operations; ramp personnel; the fueler; and flight attendants to ensure everyone was in the loop with the problem. After all the coordinating; the boarding process began for 135 Passengers. The First Officer and I did the Before Start Originating checklist because of the maintenance performed. The flight pushed back 16 minutes late and during the start of #1 the tug driver reported a broken tow bar. The First Officer asked why there was A System Hydraulic pressure and I looked up and noticed the Hyd system switches were in the configuration of the Parking checklist with the electric pumps off and engine pumps on. I remember being careful to restore that configuration after operating the switches for troubleshooting but failed to turn the A pumps off for my Before Start flow. I also must have been thinking about electric pumps instead of A pumps for the Before Start checklist and when I reported 'A's off brakes set' to the Ground Crew on headset; my broken habit pattern and lack of attention to detail broke the tow bar on the last leg of a long day. We were not rushed with the checklist I just saw what I thought was normal and didn't confirm what I reported. I lost situational awareness in the process of an abnormality. This incident has taught me to pay extra attention to detail on the basic checklist items; especially after a break in routine!

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.