What happened
On November 20, 2007, an Apex CAP 10C, registration F-GYZB, was conducting a local instructional flight at Carcassonne aerodrome. During the final approach to runway 10, the engine experienced several misfires before losing all power. The instructor took control and successfully landed the aircraft. Upon inspection on the ground, the crew discovered that the front fuel tank was completely empty, despite the fuel quantity indicator showing one-quarter full and the low-level warning light remaining unlit.
Prior to departure, the instructor had performed a visual check of the fuel level through the filler port and estimated the quantity to be slightly less than the usual 55 liters. A mechanic had offered additional fuel, but the instructor declined via hand signals. The flight included approximately 40 minutes of circuit work followed by 15 minutes of aerobatic maneuvers.
The investigation
The investigation focused on the discrepancy between the actual fuel level and the cockpit indications. Investigators examined the aircraft's fuel gauging system, specifically the Westach capacitive sender and the Deutsch electrical connector (JG1/JG2).
Technical examinations revealed that the fuel access hatch lacked necessary sealant or mastic, potentially allowing moisture or fuel to ingress. Furthermore, the investigation found that the wires connected to the Deutsch connector were of a smaller diameter than those recommended by the manufacturer. Laboratory tests demonstrated that the presence of liquid (a mixture of water and fuel) within the connector could trigger an oxidation-reduction reaction, creating an electrical potential that provided erroneous readings to both the fuel gauge and the low-level warning light.
Findings
- The primary cause of the fuel exhaustion was an erroneous visual estimation of the fuel quantity before takeoff, which was not verified by checking the aircraft logbook or using a graduated measuring stick.
- The fuel level indicator and the low-level warning light failed to provide accurate information due to liquid ingress in the electrical connector.
- The lack of sealing on the fuel sender access hatch allowed liquid to migrate along the wires.
- The use of wires with a diameter smaller than the manufacturer's specification for the Deutsch connector compromised the connector's ability to maintain a seal.
- The crew's decision to proceed without consulting the logbook, which would have revealed the previous day's fuel usage, contributed to the error.