Date: 201601
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: Mixed
Weather elements / visibility: Cloudy; Windshear; 5
Light: Dawn
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: MCP
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Troubleshooting; Situational Awareness; Distraction; Confusion
Second reporter function: Pilot Flying; First Officer
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Contributing factors: Aircraft; Human Factors; Weather
Primary problem: Aircraft

Narrative: We arrived in poor weather. It was the brand new FO's leg. We planned landing on Runway XX via RNAV Approach. We were cleared for approach. The FMC/CDU locked up heading to the IAF. By the time I realized this; I evaluated the approach was not salvageable; and we went around. Since the FO was new; the weather was bad; and we seemed to have a malfunction of some sort; I took the aircraft. (CDU was frozen and would not respond to any input attempts).We informed ATC of our situation and requested vectors for an ILS to Runway XX. We received vectors to intercept the Localizer; but were unable. The Localizer would capture; but then swing full scale deflection both left and right. Unable to lock onto the Localizer; and unable to descend; we informed ATC of our need for an additional go-around. ATC gave us a small descent to de-conflict with traffic; and then gave us another G/A vector/altitude. The aircraft behind us reported the same problems. NOTE: On downwind; our CDU began responding to input attempts again. We requested and received clearance for another try at an LNAV Approach monitored by Approach Control; with altitude monitoring; to marginal VMC below the bases; for a visual final approach to Runway XX. Around five miles out the Localizer and glideslope became stable; and was our backup to the HGS assisted visual approach. This attempt was successful and uneventful. We informed Maintenance of the issues we had faced with the aircraft; and they troubleshot the instrument/navigational panels; eventually replacing the MCP panel. We had no further problems with the aircraft after that.


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


Synopsis: B737 flight crew reported the Mode Control Panel (MCP) malfunctioned after they were cleared for an RNAV approach so a go-around was executed in poor weather. On vectors for downwind; the MCP returned to normal and a successful ILS approach was subsequently flown.