Narrative:

My day started with a phone call. I was informed that our flight had been canceled and to stand by for further instructions. Later that morning the captain and I were told to ferry an airplane to ZZZ1. The flight to ZZZ1 was uneventful. Upon arrival to ZZZ1; we were told to ferry another airplane to ZZZ2. We performed our normal preflight duties; including the origination preflight. I specifically remember many switches being out of the normal position (pressurization was set up manual and so forth) and this was all corrected as we complied with our normal procedures and checklist functions. We did not notice that one stab trim switch was possibly out of its normal position. The cockpit was busy with maintenance being in and out of the cockpit before as well as after our origination preflight checklist was performed. We were finally ready and departed. After departure we noticed some abnormalities: the autopilot would not engage and the feel diff pressure light was illuminated. We complied with the QRH procedure for this light and it said no crew action required in flight. We continued troubleshooting and noticed one stab trim switch being in the off position. The switch was engaged and all functioned normal at this time. While troubleshooting we had noticed system a hydraulic quantity slowly decreasing. We continued to monitor system a and it decreased to approximately 79%. As a precautionary measure; we decided to return to ZZZ1 in order to make sure there was not a slow leak in hydraulic system a. On the ground in ZZZ1; the airplane was inspected and no hydraulic leak was found. We got a new release from dispatch and departed for ZZZ2. I am still not sure if we missed the one stab trim switch being in the off position or if it was inadvertently moved to off by mechanics or a crew member. After troubleshooting in the air; we were able to resolve the problem; but decided to return to ZZZ1 because of hydraulic system a. In conclusion: 1) we did complete all of our preflight checklists; including the electrical power up; the preliminary preflight procedure; the exterior walk around inspection; the cockpit preflight procedure as well as all of our checklists. 2) our before starting engines checklist does not contain a challenge and response for stab trim cutout switches. 3) this was a non revenue fight; and we opted to return the aircraft to ZZZ1 due to system a hydraulic appearing to slowly decrease. Returning to ZZZ1 was a precautionary measure; and it was; in our opinion; the safest thing to do.

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Original NASA ASRS Text

Title: B737 First Officer reports once airborne A stabilizer trim cutout switch was found in the off position and system A hydraulic quantity was noted slightly low. The switch position was corrected but the crew elected to return for the system A quantity.

Narrative: My day started with a phone call. I was informed that our flight had been canceled and to stand by for further instructions. Later that morning the Captain and I were told to ferry an airplane to ZZZ1. The flight to ZZZ1 was uneventful. Upon arrival to ZZZ1; we were told to ferry another airplane to ZZZ2. We performed our normal preflight duties; including the origination preflight. I specifically remember many switches being out of the normal position (pressurization was set up manual and so forth) and this was all corrected as we complied with our normal procedures and checklist functions. We did not notice that one stab trim switch was possibly out of its normal position. The cockpit was busy with Maintenance being in and out of the cockpit before as well as after our origination preflight checklist was performed. We were finally ready and departed. After departure we noticed some abnormalities: the autopilot would not engage and the Feel Diff Pressure light was illuminated. We complied with the QRH procedure for this light and it said no crew action required in flight. We continued troubleshooting and noticed one stab trim switch being in the off position. The switch was engaged and all functioned normal at this time. While troubleshooting we had noticed system A hydraulic quantity slowly decreasing. We continued to monitor system A and it decreased to approximately 79%. As a precautionary measure; we decided to return to ZZZ1 in order to make sure there was not a slow leak in Hydraulic System A. On the ground in ZZZ1; the airplane was inspected and no hydraulic leak was found. We got a new release from dispatch and departed for ZZZ2. I am still not sure if we missed the one stab trim switch being in the off position or if it was inadvertently moved to off by mechanics or a crew member. After troubleshooting in the air; we were able to resolve the problem; but decided to return to ZZZ1 because of Hydraulic System A. In conclusion: 1) We did complete all of our preflight checklists; including the Electrical Power Up; the Preliminary Preflight procedure; the exterior walk around inspection; the cockpit preflight procedure as well as all of our checklists. 2) Our before starting engines checklist does not contain a challenge and response for Stab Trim cutout switches. 3) This was a non revenue fight; and we opted to return the aircraft to ZZZ1 due to System A Hydraulic appearing to slowly decrease. Returning to ZZZ1 was a precautionary measure; and it was; in our opinion; the safest thing to do.

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.