B737 flight crew reported the mode control panel (MCP) malfunctioned after they were cleared for an ...

Attributes
ACN	1343657
Time
Date	201601
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	Mixed
Light	Dawn
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Route In Use	Other RNAV Approach
Flight Plan	IFR
Component
Aircraft Component	MCP
Person 1
Function	Pilot Not Flying Captain
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 200 Flight Crew Type 23000
Person 2
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 70 Flight Crew Type 70
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types Inflight Event / Encounter Unstabilized Approach Inflight Event / Encounter Weather / Turbulence

Narrative:

We arrived in poor weather. It was the brand new first officer'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 first officer 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.

Original NASA ASRS Text

Title: 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.

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.

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.

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.