Incident Summary
On July 6, 2024, at 1426 mountain daylight time, a Cessna R172E airplane, registration N23788, sustained minor damage during an instructional flight near Hillrose, Colorado. The flight instructor and student pilot were not injured. The airplane was operated under Title 14 Code of Federal Regulations Part 91.
According to the flight instructor, while retracting the flaps after a practice stall recovery, a loud “pop” was heard. The instructor took over the flight controls and found the ailerons were jammed. An emergency landing was made to a highway using only rudder for directional control, with no flap configuration changes. The landing was completed without incident.
Examination Findings
Postincident examination revealed that the left inboard flap support showed damage consistent with binding. The outboard portion of the left flap had evidence of contact with the inboard portion of the left aileron. The left flap inboard track angle brackets, part of the flap track rib assembly, were pushed forward and detached from their installed location. According to a representative from the airframe manufacturer, these angle brackets did not appear to be components produced by an authorized manufacturer. The rivets on the left flap inboard angle brackets were unpainted, and the brackets themselves were unpainted, unlike all other brackets, which appeared to be original painted parts.
Logbook Review
A review of the airplane logbooks did not reveal any entry for removal or installation of the left inboard angle brackets.
Additional Findings
Inspection panels were removed, and the left flap direct cable was found loose. After applying aircraft power and lowering the electric flaps slightly, tension returned to the cable. The left flap was lowered to its full down position; the motor and down limit microswitch functioned normally. The left flap was removed, and the upper left flap inboard flap roller did not rotate smoothly. No other anomalies were found with the flap rollers or mounting hardware.
Both left flap tracks exhibited mushrooming deformation, expanding the track span to about 0.6 inches. According to the manufacturer, the maximum allowable wear in the flap track slot opening is 0.030 inch, and a slot exceeding 0.6035 inch should be replaced. Wear on the sides of the flap track should not exceed 10% of the track thickness, and there should be no roller wear.
Figure 1: Left inboard flap support damage Figure 2: Left flap and left aileron in jammed position Figure 3: Flap track span (left) and mushrooming deformation (right)