Digital glitch caused 2015 NZ comms blackout

A digital malfunction that caused a 2015 communications blackout at Christchurch air traffic control underlines the need for continuous risk management, a review by New Zealand air safety officials has concluded.

In June 2015, controllers lost contact with an aircraft for four minutes due to back-up systems failing to work as expected during a software programme update.

A review by the Transport Accident Investigation Commission said guidelines need to be updated to take into account technological developments, something which the country’s transport ministry has agreed to review.

The report stated that although the sector controllers had alternative radio frequencies and standby radios to contact aircraft, not all of these systems worked as expected. The telephone system was also disrupted by the outage, which prevented normal communication between those controllers and the airport control towers around New Zealand.

“The radar, radio and telephone services of the national air traffic control system were integrated in a digital data network,” stated the report. “The interruption of services occurred when activities during an upgrade programme to migrate remaining services on another part of the digital data network inadvertently caused a ‘broadcast storm’. The storm prevented normal digital data traffic from reaching the control centre and thereby interrupted radar surveillance and communication systems.”

Investigators found that the broadcast storm was caused by a software code error in a device and that the broadcast storm subsided and the systems returned to normal when that device was removed. Air traffic services were brought back to full service in a controlled manner within a few hours.

In its review, the Commission found that rules which define how an aeronautical telecommunications network is managed was ‘not contemporary’ for the digital network technology used by Airways New Zealand.

It found that Airways’ digital data network did not have the resilience necessary to support an air traffic control service and that the Civil Aviation Authority of New Zealand did not have the appropriate capability to determine independently if the Airways’ aeronautical telecommunications network would perform as the rules required.

Airways has since engaged an external specialist organisation to critically review the architecture of its digital data network and has implemented many of the recommendations made by the external reviewer.

The Commission concluded that the the incident was a reminder that effective risk management is a continuous process that applies to all aspects of an organisation’s activities and that well-defined processes are critical to the efficient and safe operation of a system.

Posted in CAAs/ANSPs, Communications, News, Safety

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