Narrative:

During climbout on the terpz departure and cleared to FL230; we received instructions from potomac departure to expedite climb thru FL180 climb to FL230. I observed first officer (first officer) change from VNAV path to V/south mode and increase V/south to comply with climb instruction. Over terpz passing 16;000 feet first officer/pilot flying (PF) stated it didn't turn. Autopilot was engaged. First officer/PF selected heading select on MCP and initiated a 30 degree banked turn over terpz to litme; the next waypoint. During the turn; controller asked what departure we were on and I/pilot monitoring (pm) responded terpz; we're late on the turn. Controller responded with a fly heading 220 degrees; which we did. As we completed the turn; the controller cleared us direct ramay. At no time was the autopilot disengaged or revert to control wheel steering (cws) roll mode. The aircraft failed to follow magenta line at terpz. The departure was briefed and crosschecked and was correct and included all waypoints with no discontinuities. The error resulted in a turn over terpz; which put us 1 1/2 to 2 NM west of the magenta line. Remainder of the flight was uneventful and LNAV worked normally.an MEL for DME was current. That MEL required DME updating to be turned off; which I performed and we concurred with each other during preflight. I am uncertain whether this contributed to the event.

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Original NASA ASRS Text

Title: B-737 flight crew reports a late turn at TERPZ during the TERPZ4 departure after being instructed by ATC to expedite climb through FL180. The First Officer surmised that the heading mode was inadvertently selected while making inputs on the MCP to comply with the ATC clearance.

Narrative: During climbout on the TERPZ departure and cleared to FL230; we received instructions from Potomac Departure to expedite climb thru FL180 climb to FL230. I observed First Officer (FO) change from VNAV PATH to V/S Mode and increase V/S to comply with climb instruction. Over TERPZ passing 16;000 Feet First Officer/Pilot Flying (PF) stated it didn't turn. Autopilot was engaged. First Officer/PF selected HDG Select on MCP and initiated a 30 degree banked turn over TERPZ to LITME; the next waypoint. During the turn; Controller asked what departure we were on and I/Pilot Monitoring (PM) responded TERPZ; we're late on the turn. Controller responded with a fly heading 220 degrees; which we did. As we completed the turn; the Controller cleared us direct RAMAY. At no time was the autopilot disengaged or revert to Control Wheel Steering (CWS) Roll mode. The aircraft failed to follow magenta line at TERPZ. The departure was briefed and crosschecked and was correct and included all waypoints with no discontinuities. The error resulted in a turn over TERPZ; which put us 1 1/2 to 2 NM west of the magenta line. Remainder of the flight was uneventful and LNAV worked normally.An MEL for DME was current. That MEL required DME updating to be turned off; which I performed and we concurred with each other during preflight. I am uncertain whether this contributed to the event.

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.