Cessna 172N Incident at Prague-Kbely Due to Flap Hinge Bearing Failure (OK-JKV)

Incident Overview and Aircraft Details On 15 September 2004, a Cessna 172N, registration OK-JKV, operated by Aeroklub Praha - Letňany o.s., experienced an incident during a training flight. The aircraft, manufactured in 1979 with serial number 172-72765, had a total airframe time of 4,880 hours at the time of the event. The flight was conducted in the airspace northeast of Prague-Letňany (LKLT) for private pilot license (PPL) training, specifically focusing on emergency landing techniques. ## Flight Progression and Immediate Response The aircraft took off at 08:47 UTC. Approximately 20 minutes into the flight, after completing the emergency landing maneuver with flaps extended, the pilot-instructor attempted to retract the flaps. The left flap jammed in the 20° extended position, while the right flap retracted normally. The pilot-instructor assumed control, notified the tower at Prague-Kbely (LKKB), and requested a landing on runway 24. Due to the asymmetric flap configuration, the aircraft was limited in controllability during descent and approach, prompting the pilot-instructor to request fire assistance. The aircraft landed safely at 09:17 UTC. ## Damage and Personnel The investigation revealed that the incident was caused by the jamming of the flap linkages in the guide tracks of the left wing. The force from the flap control mechanism deformed the central part of the left flap, causing it to deviate 15 mm to the left. This lateral deviation restricted the deflection of the left aileron. No other damage to the aircraft was reported. Both the pilot-instructor and the student pilot were uninjured. ## Technical Findings and Cause The technical examination found that the flap control in the cabin was set to the 0° position, while the left landing flap remained at 15° extended and the right flap was retracted. The flap control mechanism was adjusted according to the service manual. The root cause was identified as damage to the needle bearing in the left flap hinge (catalog position 9, part 7-3). The manufacturer had replaced the flap hinge assembly with a simpler design for aircraft of this serial number range starting in 1981. The final report concluded that the incident was caused by a technical failure of the left flap hinge bearing. No further safety recommendations were issued.