What happened
On 12 September 2006, an Air New Zealand flight from Auckland to Christchurch, operated by a Boeing 737-319 registered ZK-NGJ, experienced a series of technical failures during its departure. During the take-off roll, an electrical relay failed, resulting in the loss of battery bus power. As the aircraft climbed, the flight crew observed an increasing number of electrical malfunctions, including the loss of speed markers on the electronic flight information system and various warning lights.
Due to the escalating nature of the electrical issues, the pilots elected to return to Auckland International Airport. Upon landing, the aircraft began to fill with smoke, which the crew attributed to overheated residue in the air conditioning system. Consequently, the captain ordered a ground evacuation. All 96 passengers and 5 crew members exited the aircraft safely without injury.
The investigation
Investigators examined the sequence of electrical failures and the subsequent cabin environment. The investigation focused on the specific relay responsible for the power loss and the mechanics of the smoke entry. The inquiry also reviewed the crew's response to the in-flight malfunctions and the effectiveness of the emergency evacuation procedures used on the ground.
Findings
- The primary cause of the electrical failure was a manufacturing defect in the electrical relay, which caused the internal contacts to deteriorate over its seven-year service life. This degradation left the contacts unable to remain closed when subjected to the vibrations of take-off.
- The timing of the failure during the critical take-off phase created a high workload for the pilots, complicating the troubleshooting process.
- While the crew successfully managed the return to land, the investigation noted that a more immediate approach to the evacuation could have further reduced the time required to exit the aircraft.
- The smoke observed during the ground evacuation originated from overheated oil and other materials within the air conditioning system, which ceased once the engines were shut down.
Safety action
Following the incident, the operator implemented several measures, including enhanced monitoring of the specific relay type and updated procedures for handling battery bus power loss. The investigation also led to safety recommendations for the regulator to enhance emergency training, specifically regarding the positioning of crew members during abnormal landings and the management of ground evacuations.