B737-800 pilot reported flap malfunction during cruise flight. Flight diverted and landed safely.
Synopsis
B737-800 pilot reported flap malfunction during cruise flight. Flight diverted and landed safely.
Narrative
During cruise at FL 370 the LE (Leading Edge) FLAPS TRANSIT LIGHT on the forward panel illuminated in association with the #4 TRAILING EDGE FLAPS green light on Leading Edge Devices Annunciator Panel overhead. There was no flap split indicated on the flap indicator; only the amber LE FLAPS TRANSIT light and #4 TRAILING EDGE FLAP green light. Flap handle was solidly in the zero detent with both flap needles indicating UP. In order to clarify the discrepancy between what the flap indicator was showing and LE DEVICES ANNUNCIATOR PANEL; we safely disconnected the autopilot and confirmed a continual slight left rolling tendency. We [advised ATC] and made the decision to divert to ZZZ. All related QRH procedures were completed beginning with the LE FLAPS TRANSIT checklist to include the Non-Routine Landing Considerations checklist. A zero flap landing below max landing weight was performed in ZZZ per QRH procedures. After taxiing clear of the runway; communications with rescue vehicles was difficult as neither us or them could hear one another on any given frequency. Ultimately; both sides communicated individually through the local ground frequency where it was determined the aircraft was safe to continue taxiing to the gate which we did without further incident.Cause: Upon maintenance inspection in ZZZ it was determined a faulty sensor was causal.
Second reporter narrative
While cruising at FL370; we received an amber LE (Leading Edge) FLAPS TRANSIT indication on the forward panel and a green extended #4 flap indication on the aft overhead panel. No other indications. The flap handle was completely seated in the 0" detent. Both needles on the forward panel flap indicator were matched at the UP position. I was the pilot flying. The aircraft was trimmed right aileron. As part of our troubleshooting; we disconnected the AP (Autopilot) and the aircraft started a slight left roll. CA ran the associated QRH procedure beginning with the LE FLAPS TRANSIT indication. CA [advised ATC] and we diverted to ZZZ. We completed the checklist and performed an uneventful no-flaps landing to runway XX. Aircraft weight was approximately 121;000# at touchdown. Emergency equipment met us at the runway and followed us to the gate without incident. After speaking with maintenance; it seems a faulty sensor caused the issue."
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.