B757 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Confusion; Workload; Troubleshooting; Situational Awareness; Human-Machine Interface; Distraction
Aircraft Equipment Problem Less Severe
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft; Procedure
Event that is the subject of this report was first observed on ILS approach. Approaching the airport; we received radar vectors for the transition to the ILS approach from the approach controller. A prior event; (may or may not be related to this event); occurred about 30 minutes prior to TOD and was managed and documented with Maintenance Control. A CDU issue occurred as follows: Selecting either NAV RAD (Navigation Radio) on either CDU caused the respective FMC to 'Timeout'. Followed by a loss of LNAV; VNAV; and autothrottles. VNAV speed and cruise data were also lost in the FMC. All autoflight functions were successfully restored; route was checked and verified; and the respective FMC returned to full function without NAV RAD available. Autoflight; Autothrottles; LNAV; VNAV; all restored. Maintenance Control proposed a test: selecting both FMCs to source 'L' and retry NAV RAD. Same results as above: 'TIMEOUT' on respective side FMC where NAV RAD CDU key was selected; loss of LNAV; VNAV; autothrotte. Again; all these functions were manually reselected and restored. We were VMC at this point; prior to Top of Descent (TOD).Next we tried both FMCs source both 'R'; same results as above. Maintenance Control advised. (Dispatch advised he was monitoring our ACARS COMM with Maintenance Control). Maintenance Log entry made as per SOP. All functions; including all auto flight functions were operating from TOD through approach phase. NAV RAD was N/A on either CDU. What follows is the subject of this report. I don't know if the event below and the issue documented above are related.On approach; aircraft configuration was managed as per profile; SOP. Gear was selected prior to FAF. Flaps 20 at FAF. Inside FAF; PF observed unusual amount of control wheel displacement. Winds were relatively steady; little or no crosswind; mostly a direct headwind; reported at 10 knots. Fuel was balanced. Captured on LOC on GS; PF managing speed and flaps (Flaps 30 planned; briefed) to target values. Landed Flaps 30.Inside FAF; PF and PNF both observed left control wheel displacement of about 3-4 degrees wing down. We were IMC transitioning to VMC below a variable layer at about 500-1000 ft. Visibility was good; reported at 10 NM. Captain directed and FO confirmed; autopilot and autothrottles off for the balance of the approach. Autopilot and autothrottles were disconnected. At disconnect; PF observed and stated to the effect: 'the flight controls (in roll) were sloppy or lose' i.e.; flight controls did not feel typical for this phase/configuration. The aircraft was fully controllable. The yoke had more 'play' or 'slop' but was responsive; in all axis. The PF and PM both physically observed and verified the roll degradation from typically observed in this configuration at these speeds. We were not slow. Target was 135 KIAS. A normal approach; flare; landing and rollout were all accomplished. After clearing all runways both pilots made a control check of ailerons and elevator. Both pilots observed an unusual amount of free play in the roll axis up to and through about 4 degrees left and right of the null (or 0 point) on the control wheel. I did not declare an emergency and determined the safest course of action at the time was to land in these conditions with improving to good visibility and consult with maintenance at our destination. Maintenance was advised at taxi in. Maintenance Log entries made. Met and debriefed verbally with Maintenance tech at the gate. The Duty Manager was advised verbally.
We had a CDU/NAVRAD/Autoflight issue. We believe it is unrelated. The CDU worked fine; but when you pressed either NAV/RAD button; both CDUs would lock up; timeout and kick the Autoflight system off. We coordinated with Maintenance Control and the flight continued. We got a 1500 lbs fuel imbalance within 30 min; after 3+ hours of balanced tanks. We balanced the fuel to even. ZZZ weather was approximately 500-600 ft ceilings. The autoflight system had trouble maintaining speed during descent and approach; it would try to maintain 15-25 knots fast. It took multiple manual interventions to maintain assigned speed. On final about 1000 ft I noticed the yolk was tilted 30-45 degrees to the left. I immediately knew this was odd with the winds being in line with the runway. At approximately same time as we broke out (600 ft) I clicked off the autopilot and realized there was a flight control issue. I could move the yolk about 30-45 degrees either side of center before the aircraft reacted. The other two axis (pitch and yaw) were normal. The aircraft was stable; on speed; on glide path and while there was system degradation; the aircraft was controllable. I quickly discussed with the captain what I was feeling and thinking. We agreed to land and I did without incident. On the ground we contacted base Maintenance and Maintenance Control. We debriefed Maintenance at the gate. This report is being filed out an extreme abundance of caution. Both the Captain and I believe we acted in accordance with all company and FAA guidance.
B757 flight crew reported aileron movement in excess of 30 degrees was needed before an aileron response was detected. An unrelated FMC 'TIMEOUT' anomaly followed by LNAV; VNAV; autoflight; and autothrottle disconnect when either left or right navigation radio was selected.