A B757-300 flight crew reported finding a broken slat loss sensing cable for the left outboard wing tucked inside a flap track canoe fairing during a late night preflight of their B757 aircraft. The inbound flight crew had no indication of a possible slat asymmetry as the leading edge disagree light did not illuminate.
Synopsis
A B757-300 flight crew reported finding a broken slat loss sensing cable for the left outboard wing tucked inside a flap track canoe fairing during a late night preflight of their B757 aircraft. The inbound flight crew had no indication of a possible slat asymmetry as the leading edge disagree light did not illuminate.
Narrative
During preflight on a B757; First Officer conducted the walk-around. This was the night departure. I was also on the ramp; returning from Operations after picking up my required paperwork. We met at the base of the jet bridge stairs and he requested me to look at the left wing. Approaching the wing; I saw nothing wrong. After illuminating the flap track canoe [fairing]; I was able to see a small diameter cable that appeared to be attached under the leading edge of the wing. The aft end of the cable was tucked into the aft end of the canoe; which caused an unsafe aircraft condition.Maintenance was notified; and in their actions they lowered the leading edge slats. It was then noted; the outboard lengthwise cable was broken in the slat asymmetry system. Further; the inbound flight crew had no indication due to the apparent lack of the leading edge disagree light not illuminating. The discovery of this thin; broken cable during nighttime conditions was; in my opinion; an unlikely possibility. Due to the heightened observation by this First Officer and his commitment to safety; this mechanical issue was attended to while the aircraft was still on the ground and before it became an issue after departure or in flight. I would like to commend my co-worker for an outstanding job detecting this broken cable.
NASA callback
Reporter stated he has been flying B757 aircraft for 13 years and never saw a Slat Loss Sensing Cable wrapped up inside a flap track fairing. One of their Line Mechanic's noted there are two separate lengths of Sensing Cable; one length outboard and one inboard of the Left and Right engines. He never saw a Sense Cable break outboard of an engine. Only the inboard section of a Slat Loss Sensing Cable is deferrable under their MEL.Reporter stated no EICAS display message for a 'LE SLAT ASYM;' no AMBER Leading Edge Light illuminated on the P3-1 panel; and no Master Caution Lights on the P-7 panel were reported by the inbound flight crew in the aircraft's Logbook. The broken Sense Cable should have triggered an EICAS message and the warning lights. Reporter stated that if the broken Sense Cable had not been noticed; he might have seen an EICAS message and the AMBER Leading Edge Light appear after they had started their engines and moved the Flap handle during their departure taxi out.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.