SDRs and Mx Alerts

Canadair CL-600: A repair station technician investigating an intermittent circuit breaker fault for this aircraft's upper anti-collision light wrote: "[I] discovered the L/H elevator control cable had torn through the wiring conduit in the vertical stabilizer. The cable wore through the conduit and shorted out the wiring for the upper beacon. [I] repaired the wiring conduit, replaced the wiring, and replaced the control cable in accordance with the manufacturer's instructions." He described ensuring sufficient clearance between the cable and surrounding conduits, but wondered about the origins of this defect. "[It] is unclear if the conduit was installed at the factory or at the time of [aircraft] completion. [I] suggest inspection of this area on other, similar aircraft. [It is a] difficult [defect] to notice due to the accessibility of this area in the tail."

Cessna 750: "The L/H thrust reverser performed an un-commanded stow during thrust reverser use after landing," wrote a mechanic. "After accessing the throttle quadrant, it was noticed the wires connected to the L/H deploy switch were stretched very tight when the `T/R' piggy-back levers were in the deploy position. After running diagnostics using software provided by Cessna, it was determined the deploy switch was faulty. During the process of accessing the wires to replace the switch, a wire was found to be broken where it was spliced. The shrink-wrap around the wire bundle contributed to the intermittent nature of the defect. The splice was repaired, and an operational check of the T/R system confirmed the system had been fixed." Part total time: 115.7 hours.

Dassault F50EX: Excessive oil covering number three engine and its nacelle quickly caught this mechanic's attention on postflight inspection. Oil had collected primarily around the oil tank. Subsequently, both engine and cowling were cleaned prior to engine run. Shortly after engine start "...oil was observed coming from a small .50 inch crack in the oil tank wall. [This] crack was located approximately 2.25 inches below the top of the tank and 3.50 inches above and left of the oil filler cap. [It] appears to originate from an internal weld, or a welded baffle internal to the tank assembly." He described installing a new Honeywell direct replacement tank (P/N 3060720-4), but noticed this new tank had a similar, possible defect of a dent or depression in the exact same area of the original cracked tank. Having discussed this with Honeywell, an upgraded tank (P/N 3060720-5) was to be shipped for exchange. (Engine listed is Honeywell TFE731-2B.) Part total time: 2,873.6 hours.

Piper PA31-350: This aircraft's "R/H wing exploded on take-off roll," stated the submitter, "...due to ignited fuel vapors trapped in the empty wing cavity outboard of the fuel cells." Investigators determined about 700 feet into the takeoff roll the left engine began to loose manifold pressure and the pilot began to abort the takeoff. While the pilot was decreasing power, the outboard section of the right wing exploded. The aircraft was stopped on the runway and the pilot and his six occupants evacuated the aircraft without injury.

This submitter went on to state, "Further inspection revealed the R/H main fuel cell vent nipple was broken off and very brittle and deteriorated, allowing fuel vapors to accumulate in this cavity." The submitter also pointed out, "...the aircraft was previously fitted with Colemill wingtip and landing light modifications."

The modification was done in accordance with STC SA1151SO. The 28-volt power wire for the wingtip and landing light assemblies "...had been routed from root to tip following an aft stringer and passing through ribs via stringer cutouts--with no protection. This wire was found to be shorted and burned off with evidence of arcing at the approximate wing station number 148...causing ignition of the above fuel vapors."

The submitter recommended, "...the incident could have been avoided with proper fuel cell [and nipple] inspections [in accordance with the manufacturer's instructions] and routing wires properly using guidance in Advisory Circular 43.13-1B." The subsequent FAA investigation revealed the wing and landing light wiring had not been installed in accordance with the approved STC, which required the wiring to follow existing navigation light wiring along the front spar and not through the rear fuel cell cavity.

The FAA's Philadelphia Flight Standards District Office is initiating a safety recommendation to require all PA31 operators incorporating STCed Colemill wingtip assemblies to check for proper wiring, electrical protection, and installation conformity. In addition, it is recommended all operators of similar aircraft using rubber fuel cells perform a visual check of the exterior of the aircraft wings and/ or fuselage for signs of leakage, fuel wetness, or color dye stains, especially in the vicinity of vents and compartment drains, and have certificated mechanics investigate the source to determine proper corrective action prior to flight.