What happened
On 16 August 2021, a Cessna 421C, registration ZS-JNE, departed from Lanseria International Airport (FALA) in Gauteng, South Africa, bound for Ondangwa Airport in Namibia. The flight was being operated under private (Part 91) regulations.
While climbing to flight level 135, the pilot noticed the left wing was dropping, a condition that progressively worsened. While flying over the Pilanesberg area, the pilot declared an emergency via PAN-PAN and Mayday calls to Lanseria Air Traffic Control. In response to the emergency, ATC diverted the aircraft to Pilanesberg Airport (FAPN). To maintain a stable approach despite the heavy left wing, the pilot performed a 270-degree right turn. The aircraft landed safely at FAPN with no injuries and no damage to the aircraft.
The investigation
Following the landing, a visual inspection of the fuel tanks revealed that the left tank contained significantly more fuel than the right tank. The investigation established that during the pre-flight phase, the pilot had been distracted by an incoming telephone call on a cellular device while performing cockpit checklists. As a result, the pilot failed to notice that both engines had been configured to draw fuel exclusively from the right-side tank during takeoff. This configuration left the left tank with an excess of unutilized fuel, creating the weight imbalance.
Findings
- The primary cause of the wing-low attitude was a fuel imbalance caused by the left tank being heavier than the right tank.
- A significant contributing factor was pilot distraction caused by a mobile phone call during critical checklist procedures.