B737-800
Flight Crew Air Transport Pilot (ATP)
Flight Crew Total 5
Situational Awareness; Workload; Human-Machine Interface
Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew FLC Overrode Automation
Procedure; Human Factors; Aircraft
Prior to top of descent; I briefed that I would fly the visual approach to RWY XX backed up by the Localizer DME approach.  Landing configuration would be Flaps 30 and Brake Setting #3.  We were cleared the visual to RWY XX by Approach at 3;000 feet MSL.  I decided to start slowing and configuring early and the aircraft was properly configured and on reference speed of 148 KTS plus 5 KTS; approaching the FAF.  The aircraft position was slightly high on visual glide path; so I disengaged the autopilot; left autothrottles engaged; and started a descent to capture normal glide path.  The throttles reduced and the nose was lowered.  When I raised the pitch attitude once the normal visual glide path was attained; I did not notice the autothrottles did not advance.  With the raising of the pitch attitude; the airspeed decreased 15-20 knots below reference speed.  The Captain announced; 'Airspeed' and I immediately overrode the autothrottles and increased power.  The flight path continued on a slight descent when power was increased.  As the airspeed increased; I raised the pitch attitude to level flight and we regained proper pitch; power; airspeed and glide path at approximately 800 feet to 1;000 feet AGL.  All stabilized approach criteria were met before the 500 feet [required] for VMC approaches.  Landing and taxi in were completely uneventful.  Automation is a great tool and works as expected 95% of the time.  I would say that pilots can be 'lulled' into a sense of security when using it.  All the automation in the world does not relieve us of the charge to fly the airplane at all times.  Closer monitoring of approach speed and faster realization of the 'lag' of the autothrottles would have prevented the decrease in airspeed.  Had the situation progressed further; a go-around was; without a doubt; the proper action.  Needless to say; one must remain vigilant in monitoring and assessing all flight parameters at all times.  It's the times when you think you have things 'wired' that you need to maintain total awareness.
B737-800 First Officer; late to recognize slow autothrottle response after raising the pitch attitude on approach; responded to the Captain's 'airspeed' callout and overrode the autothrottles to increase power. Approach was stabilized and preceded uneventfully.