2021-10 · NASA ASRS report 1846634
Flight Crew reported the loss of FMC P in flight and elected to use VOR for navigation to destination airport.
During cruise at FL340 in the vicinity of ZZZ VOR with LNAV/VNAV and Autopilot A engaged; the 'FMC P/RST' (Flight Management Computer Primary Reset) light illuminated; FMC data on Captain's and First Officer's navigation display Map mode disappeared and the FMC prompt at 1L on both CDUs (Control Display Unit) disappeared. The auto flight system reverted to Control Wheel Steering. The pilots advised ATC that aircraft navigation system failure was preventing use of area navigation and the flight was proceeding via conventional VOR navigation. Pilots completed the B737 FM Non-Normals (MAX) FMC FAIL Checklist and reviewed the FMC INFLIGHT RESTART Checklist. The Captain obtained voice contact conference call with Dispatch; Maintenance Control; and Duty Pilot via ARINC VHF. Procedures and options were discussed; and the decision was made to continue to flight planned destination by use of conventional navigation (VOR; DME and ILS). The original flight plan included VOR to VOR direct routing. After the dual FMC malfunction the flight may have inadvertently exceeded the 'operational service volume' distances while navigating between enroute VORs. Upon realizing this the Pilots requested and received ATC clearance via published airways routing for the remainder of the flight. The Captain briefed the Purser on the non-normal. While on vectors for the ILS there was brief pilot confusion as to why the ILS was not displayed on the navigation display. This was promptly resolved by moving the EFIS (Electronic Flight Information System) Control Panel rotating selector from VOR that was used during enroute navigation to ILS for the approach. No declaration of emergency and the flight arrived at ZZZ1 otherwise uneventfully. Captain made an ELB (Electronic Log Book) entry for the malfunction and pilots briefed Maintenance personnel at the arrival gate. Upon arrival at the crew layover hotel the Captain contacted both Dispatch and Duty Pilot by telephone for post event debrief.
VMC near ZZZ level FL340 encountered loss of roll depicted by loss of roll bar; CWS (Control Wheel Steering) and FMC P/RST light. MCP (Mode Control Panel) set with LNAV and VNAV. As a result both FMCs failed with no L1 restart selection available. PF (Pilot Flying) took the controls as I attempted to regain the FMC along with finding the appropriate checklist for FMC Fail. After running the checklist we discovered we could fly in HDG and ALT SEL modes with the AP engaged. We selected the ZZZ VOR and outbound radial to track towards ZZZ2 providing details to ATC regarding the failure as well as we would navigate VOR to VOR. We had no issues pulling up the VOR needles however selection of the VOR mode was delayed as this function is not used enough. ACARS was available for communicating with company. Controls were transferred and Captain reran the QRH items to ensure we didn't miss anything. ATC provided some vectoring towards ZZZ2 as a result of being outside VOR service volume distances. Captain setup ARINC comm with Dispatch; Maintenance Control and Duty Pilot to make a decision as to continue or divert. All agreed to continue via VOR to VOR. Fortunately routing took us over multiple defining VORs to ZZZ1. Between ZZZ-ZZZ2 and ZZZ3-ZZZ4 we operating VOR outside the VOR standard service volume but backed up navigation with IPad GPS locator which was good SA (Situational Awareness) reference. We did receive VOR information throughout the flight. From ZZZ4-ZZZ5 request navigation on XXX complying with VOR service volumes. We arrived into the ZZZ1 area without issue until vectoring for the ILS.We were in the VOR mode therefore the localizer will not work until switching to the MAP mode. Approach was night VMC and landing was uneventful.Weights; Vref and GA power information must be manually input to the aircraft to provide guidance during approach to GA if needed.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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