What happened
On 23 July 2018, a Cessna T2/210M, registration ZS-MBU, was conducting a type conversion training flight from Wonderboom Aerodrome (FAWB) when the pilot discovered the nose gear had failed to extend. During downwind checks, the instructor noted the gear remained retracted. To verify the status of the landing gear, the crew performed three separate landing approaches. While air traffic control confirmed the main landing gear was down, the nose gear remained up.
In an attempt to rectify the situation, the pilot utilized the emergency landing gear extension system, but the gear failed to deploy. The pilot subsequently declared a "Pan Pan" emergency. The aircraft subsequently landed on Runway 29 with the nose gear retracted, causing substantial damage to the propeller, the nose cowling, and the nose gear doors.
The investigation
SACAA AIID investigators examined the hydraulic systems and the aircraft's recent maintenance history. The investigation noted that the aircraft had flown only 24.2 hours since its last mandatory periodic inspection (MPI) in December 2017. During that previous inspection, maintenance personnel had discovered and replaced non-approved fiberglass nose gear doors with approved aluminum versions.
Investigators also reviewed the hydraulic mechanics of the Cessna T210M. The system requires hydraulic pressure to reach 400 psi to open the nose gear doors before the gear can extend. The investigation also looked into the emergency hand pump operation, noting that the emergency system relies on the same hydraulic pathways as the primary system.
Findings
- The primary cause of the incident was a blockage and/or leakage within the nose gear door check valve system.
- This failure prevented hydraulic fluid from reaching the nose gear door actuator, meaning the system could not achieve the 400 psi required to open the doors.
- Because the doors could not open, the priority valve failed to trigger, preventing the nose gear from extending.
- The emergency extension system was rendered ineffective because it utilizes the same check valve pathway that was obstructed.
- The landing resulted in substantial damage to the aircraft's nose section and propeller.
- Weather conditions at the time of the incident were calm and clear (CAVOK).