On July 6, 2024, at 1426 mountain daylight time, a Cessna R172E airplane, N23788, sustained minor damage when it was involved in an incident near Hillrose, Colorado. The flight instructor and student pilot were not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 instructional flight. The flight instructor stated that while retracting the flaps after performing a practice stall recovery, they heard a loud “pop.” The flight instructor took over the flight controls from the student pilot and noticed that the ailerons were jammed. The flight instructor elected to make an emergency landing to a highway. While maneuvering toward the highway, the flight instructor was only able to use the rudder for directional control and did not change the flap configuration. The flight instructor landed the airplane on the highway without incident. A postincident examination of the airplane revealed that the left inboard flap support exhibited damage consistent with binding, as shown in figure 1. The outboard portion of the left flap also exhibited evidence of contact with the inboard portion of the left aileron, as shown in figure 2. The left flap inboard track angle brackets (that are part of the flap track rib assembly) were pushed forward and detached from their installed location by the flap support arms. According to a representative from the airframe manufacturer, the angle brackets did not appear to be components produced by an authorized manufacturer. The rivets on the left flap inboard angle brackets were not painted, and the brackets were not painted. All other brackets appeared to be original parts and had been painted.

Figure 1. Left inboard flap support

Figure 2. Left flap and left aileron in jammed position. A review of the airplane logbooks did not reveal any entry for removal or installation of the left inboard angle brackets. Inspection panels were removed, and the left flap direct cable was found loose. Aircraft power was applied, and the electric flaps were lowered slightly. Tension returned to the direct cable. The left flap was lowered to its full down position. The motor and down limit microswitch functioned normally. The left flap was removed. 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 .6 in as shown in figure 3.

Figure 3. Flap track span (left) and mushrooming deformation (right) According to the manufacturer, the maximum amount of wear in the flap track slot opening is .030 inch and a flap track slot with a slot that exceeds .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.