Date: 201701
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: 0.5
Light: Daylight
Aircraft: B737 Next Generation Undifferentiated
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: It was the last leg of a 6-day sequence (2 to 3 days trips) for me; last leg of a 3-day reserve block for my First Officer (FO). All (but one) flights were flown on NG aircraft. We deiced during our originator flight (first leg). Then (second leg) I tried to coordinate some weight issues with the Dispatcher and Ops Agent; related to: freight; dead headers; and the fact that [there] was only [one] qualified alternate around ZZZ; due to low visibility in the area. During the Cruise portion of the flight we discussed and planned for any approach in ZZZ; alternate courses of action as well as establishing our Bingo fuel. As we approached ZZZ it was evident (by listening on the radios and monitoring our TCAS information; as well as the ATC Controllers voice) that ZZZ was extremely busy. In over a decade flying in and out of ZZZ I don't recall it been so busy. ZZZ was using both Runway XY. We were assigned XYR. Visibility (SM) was below minimums but RVR was good. I flew the ILS XYR; which ended in a missed approach.The go-around went well; but we got distracted with a 'Using Reserve Fuel' message and started to discuss options. We were given an easterly heading and leveled off at 3000 feet MSL. After reducing power and crosschecking my ADI; I engaged the Auto Pilot (AP) and went back to look at the weather information on the FO's MCDU. As I quickly returned to crosscheck my instruments; I saw the airspeed decreasing through 180 knots and almost simultaneously (with the corner of my eye) I saw a blinking BUFFET ALERT message (no other indications). I immediately added power; quickly returning to the assigned speed (210). I then realized that during my attempt to silence the AP Disconnect Warning horn I inadvertently disconnected the Auto Throttle (out of 'old' habit patterns). I reengaged the AT and verified appropriate FMA indications. The remainder of the flight was uneventful; as we landed on XYL after flying the second ILS; all the way down to minimums. Maybe consider having the Pilots practice several go-arounds by the use of the Take Off Go Around (TOGA) buttons only (i.e. reduced/full AT). I fully support our efforts and transition to [company SOP]. It works!! Last; but not least; this goes to prove that things like these can happen to the best of us; in spite of our best efforts; training; and planning. For me (and anyone who would listen); this is my reminder....Stay with the BASICS: (1)(Aviate; Navigate; Communicate); (2) Hack the clock or count backwards before rushing; there was no need to discuss actions until we established ourselves on downwind; and (3) in spite of best advances in technology/automation the laws of aerodynamics still make the aircraft fly.


Second narrative: [Report narrative contained no additional information.]


Synopsis: B737NG flight crew reported disconnecting the autothrottles and aircraft slowing to BUFFET ALERT message airspeed after missed approach.