B737-700
Flight Crew Last 90 Days 179
Situational Awareness; Distraction; Human-Machine Interface
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types
Aircraft Equipment Problem Dissipated; Flight Crew Became Reoriented; Flight Crew FLC Overrode Automation; Flight Crew Returned To Clearance
Human Factors
While on climb-out at about 39;000 FT; I was filling out the logbook; looked up and noticed the airspeed was low. I informed the Captain of the speed. He disconnected the autopilot and lowered nose to gain airspeed back.I informed ATC of our intentions. We descended 1;000 FT and regained normal airspeed. I believe the mode had changed in the FMS and we did not realize the change.
B737 flight crew failed to notice loss of airspeed during climb. When airspeed decay was eventually noticed; corrective action was implemented and ATC was informed of deviation.