On July 25, 2012, a Cessna 172M, registration N73115, crashed into the water near Fernando Luis Ribas Dominicci Airport (TJIG) in San Juan, Puerto Rico. The flight, which originated from Arecibo, was being conducted under visual flight rules in visual meteorological conditions. The pilot sustained 1 fatal injury.
What happened
At approximately 14:13 AST, the pilot established contact with the tower at TJIG and was instructed to perform a straight-in approach for runway nine. At 14:18, the pilot radioed the tower, stating, "i think i $\text{got my aileron cable broken}$ ah i am unable to maintain level flight so i'll continue the descent and land." Shortly after this transmission, the aircraft impacted the water.
Eyewitnesses and security footage showed the aircraft maintaining level flight before banking to the right and descending. The airplane struck the water's surface with its right wingtip in a right-wing-down attitude and subsequently submerged. The wreckage was recovered from approximately 44 feet of water, roughly 1,490 feet from the runway 9 threshold.
The investigation
Investigators examined the wreckage and found that the right aileron control direct cable had separated due to tensile overload. While most flight control cables were lubricated, a specific section of the aileron control cable near the top left doorpost pulley was devoid of lubrication.
Examination of the cable and the associated doorpost pulley revealed the following:
- The cable exhibited severe corrosion at the fracture point.
- The doorpost pulley and its bearing showed moderate to severe corrosion, and the bearing would not rotate when manipulated by hand.
- The NTSB Materials Laboratory confirmed that the majority of the cable wires were completely corroded through at the separation area.
Maintenance records showed an annual inspection had been completed approximately six months prior to the accident. The aircraft operated in Puerto Rico, which the manufacturer's service manual classifies as a "severe" corrosion zone.
Findings
- The failure of the doorpost pulley to rotate due to corrosion likely created excessive tension on the right aileron control cable.
- The aileron control cable suffered from severe corrosion that was not detected during the previous maintenance inspection.
- The mechanic likely failed to detect the internal corrosion because the cable was difficult to inspect visually and was not properly lubricated.