Cessna R172E N23788 incident near Hillrose, Colorado

Probable cause

The binding of the left flap due to improper maintenance.

NTSB analysis

The flight instructor stated that while retracting the flaps after performing a practice stall recovery during the instructional flight, they heard a loud “pop.” The flight instructor took over control of the airplane from the student pilot and noticed that the ailerons were jammed. The flight instructor elected to make an emergency landing on a highway. While maneuvering toward the highway, the flight instructor did not change the flap configuration and had to use rudder control only for directional control. The flight instructor landed the airplane on the highway without incident.

A post incident examination revealed that the left flap inboard track angle brackets were pushed forward and detached from their installed location by the flap support arms. This allowed the flap to contact the aileron, jamming its movement. The failed angle brackets appeared to have been replaced; however, there was no entry of the replacement in the airplane logbooks. Neither the rivets on the left flap inboard angle brackets nor the brackets themselves were painted, indicating that they were not produced by an authorized manufacturer. In combination with the installation of unapproved parts and the condition of the upper left flap roller, which did not rotate smoothly, the flap track slot was likely worn enough to allow the flap support arms to contact the replacement left flap inboard track angle brackets during the retraction of the flaps.

Text from the NTSB. Open the NTSB docket for CEN24LA270 for the full record.