Loss of Control in Flight · NTSB ERA12FA484
CESSNA 172M — San Juan, PR
| Date | July 25, 2012 |
| Location | San Juan, PR |
| Aircraft | CESSNA 172M |
| Purpose of flight | Personal |
| Conditions | Day · Visual Meteorological Cond |
| Phase / occurrence | Approach-VFR pattern final Loss of control in flight |
| Pilot age | 57 |
| Pilot total time | 1,175 hrs · Experienced |
| Time in type | 500 hrs |
| Fatalities | 1 |
Probable cause
NTSB findings
- Aircraft-Aircraft systems-Flight control system-Aileron control system-Fatigue/wear/corrosion - C
- Personnel issues-Task performance-Maintenance-Scheduled/routine maintenance-Maintenance personnel - C
- Aircraft-Aircraft systems-Flight control system-Aileron control system-Malfunction - C
- Environmental issues-Task environment-Physical workspace-Access to equipment/controls-Contributed to outcome
- Aircraft-Aircraft oper/perf/capability-Performance/control parameters-(general)-Attain/maintain not possible - C
What happened
About 4 minutes before the accident, the pilot advised an air traffic controller that an aileron cable had broken but that he was continuing to the airport to land. Security video and eyewitness reports revealed that the airplane was at low altitude and appeared to be maintaining level flight until it banked right, descended, and impacted water near the airport in a right-wing-down attitude.
A postaccident examination of the wreckage indicated that all of the airplane's flight control cables were lubricated except for a fractured section of aileron control direct cable near the doorpost pulley, which was likely not properly lubricated. Most of the cable strands and the doorpost pulley and bearing exhibited severe corrosion near the fracture. When manipulated by hand, the pulley bearing would not rotate due to the corrosion. Analysis of the cable, doorpost pulley, and an exemplar cable from a similar make and model aircraft that had been flown in similar atmospheric conditions (in what is considered a severe corrosion zone) revealed moderate to severe corrosion. It is likely that, during the airplane's maintenance inspection 6 months before the accident, the mechanic failed to detect the corroded cable due to the difficulty in visually seeing the cable. It is also likely that the doorpost pulley's failure to rotate resulted in tension on the right aileron control cable, which subsequently caused it to fail due to the severe corrosion. The aircraft manufacturer's maintenance manual for the airplane gives specific instructions for lubricating and inspecting flight control cables and pulleys every 600 hours or 12 months, whichever comes first, including, in part, examining the cables for corrosion and the pulleys to ensure smooth rotation. After the accident, the manufacturer produced a video emphasizing the importance of properly examining and lubricating the cables.