Narrative:

Aircraft X had a rockwell MCP; the one with the small pushbuttons; instead of the traditional classic paddle switch MCP. It worked without incident our first leg. During taxi out for the second leg; the first officer (first officer) asked; 'do you want that?' and pointed to the cws a light illuminated on the MCP. Somehow either it had engaged itself or we had somehow inadvertently pushed it. He looked puzzled. Since I was familiar to this from my safety work and having had it previously; I said; I would explain this in-flight and pushed the autopilot disconnect button. We got the autopilot disconnect horn; and the cws a light extinguished. We rechecked everything and took off. Everything worked fine the next two legs. I was fortunate to have a very sharp first officer who first noticed the trim wheel moving without pilot input during taxi. It seems these new style mcps may be incompatible with the older model aircraft. I know we have had several rejected takeoffs when the trim started to run with un-commanded pitch and roll commands during takeoff roll.it seems in the interest of safety we need to get a full understanding of this anomaly and either correct the situation or provide adequate training and or procedures to prevent this from creating an undesired aircraft state. Note: we didn't write it up because we couldn't tell if we had inadvertently pushed it or it had turned itself on. From a human factors perspective; it would be very easy to unknowingly lightly push it while the first officer performs his flows.

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Original NASA ASRS Text

Title: During taxi for takeoff; a B737 Mode Control Panel (MCP) Control Wheel Steering (CWS) engaged and began trimming the horizontal stabilizer. The First Officer caught the trim movement and disengaged CWS.

Narrative: Aircraft X had a Rockwell MCP; the one with the small pushbuttons; instead of the traditional classic paddle switch MCP. It worked without incident our first leg. During taxi out for the second leg; the First Officer (FO) asked; 'Do you want that?' and pointed to the CWS A light illuminated on the MCP. Somehow either it had engaged itself or we had somehow inadvertently pushed it. He looked puzzled. Since I was familiar to this from my Safety work and having had it previously; I said; I would explain this in-flight and pushed the autopilot disconnect button. We got the Autopilot Disconnect horn; and the CWS A light extinguished. We rechecked everything and took off. Everything worked fine the next two legs. I was fortunate to have a very sharp FO who first noticed the trim wheel moving without pilot input during taxi. It seems these new style MCPs may be incompatible with the older model aircraft. I know we have had several rejected takeoffs when the trim started to run with un-commanded pitch and roll commands during takeoff roll.It seems in the interest of safety we need to get a full understanding of this anomaly and either correct the situation or provide adequate training and or procedures to prevent this from creating an undesired aircraft state. NOTE: we didn't write it up because we couldn't tell if we had inadvertently pushed it or it had turned itself on. From a human factors perspective; it would be very easy to unknowingly lightly push it while the FO performs his flows.

Data retrieved from NASA's ASRS site 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.