What happened
On 31 October 2001, an Embraer EMB-820C Chieftain, registration ZK-RDT, was operating a scheduled passenger service from New Plymouth to Auckland. During the descent into Auckland Airport, the aircraft was being radar vectored and the pilot selected 10 degrees of flap to reduce speed. Upon the extension of the flaps, a loud bang was heard, and a passenger alerted the crew that the cabin door had opened.
While the flight conditions were otherwise routine, the sudden change in airflow and pressure during flap deployment triggered the failure. A passenger seated near the door assisted by two others managed to hold the door in a slightly ajar position using the supporting cables. This effort continued for approximately 10 minutes while the aircraft landed and taxied to the gate. There were no injuries resulting from the incident, though the event caused significant alarm among the passengers.
The investigation
An investigation by the TAIC examined the aircraft's door assembly and maintenance history. The inspection of the lower cabin door revealed that the forward support cable anchor had broken from the fuselage, and the rear hinge was distorted, which prevented the door from being closed properly.
Technicians found that the interior door handle's safety latch mechanism was malfunctioning due to accumulated wear and damage. Crucially, the examination of the door's striker plates revealed that the forward plate was grossly worn, with approximately 40% of the engaging tongue missing. This wear had transformed the contact surface into a 60-degree ramp, which could facilitate the unlatching of the door under pressure.
Findings
- The cabin door became unlatched and opened because of long-term wear and distortion of the latch components.
- The grossly worn forward striker plate was the primary factor that allowed the door to disengage.
- The mechanical deterioration of the latching mechanism should have been identified and corrected by maintenance engineers during routine inspections.
- The failure occurred during a normal flight phase (flap extension) that introduced enough local pressure changes to trigger the defective mechanism.