Japanese investigators have found that a Peach Aviation Airbus A320 descended to just 240ft above water after deviating prematurely from its assigned approach altitude.

The aircraft had been conducting an approach to Naha’s runway 18 on 28 April 2014.

It had been flying at 1,000ft but the captain activated the vertical speed knob – which had been pre-set with a descent rate of 900ft/min – at a distance of 5.7nm from the airport.

Japan Transport Safety Board says this was a “considerable distance” from the planned descent initiation point of 3nm.

While the inquiry into the incident attributes the initial descent to the captain’s “unintentional” operation, it adds that both pilots were “less aware” of monitoring the aircraft’s altitude because they had “relied” on the A320’s autopilot to maintain 1,000ft. The first officer had been pre-occupied with completing the landing checklist.

As a result, the inquiry adds, the pilots “did not properly prioritise their tasks”.

It states that the crew’s workload had been complicated by poor visibility in cloud, which prevented sight of the airport and the surface of the sea.

The crew had originally intended to carry out a VOR approach to the airport but subsequently requested precision-approach radar guidance – the captain’s first such approach in “a long time”, the inquiry says.

It says he probably had a “conscious desire” to perform the approach accurately, and adds: “It is probable that the captain was flying while considering various upcoming operations.”

Although the engine tone changed, the investigation points out that captain would not have noticed any change in the thrust-lever position while the auto-thrust was engaged.

The aircraft descended unchecked and had reached a distance of 4nm from the airport when the air traffic controller warned that the flight was too low and needed to maintain 1,000ft.

Around the same time the enhanced ground-proximity warning system on the A320 issued a ‘too low, terrain’ warning and, a few seconds later, a ‘pull up’ instruction.

Flight-data recorder information shows the aircraft reached a minimum height of 241ft before it climbed away as the crew executed a go-around.

Peach Aviation took several measures in the wake of the incident, convening safety meetings to stress the importance of monitoring duties and confirming flight-mode changes while flying under autopilot. The pilots were temporarily suspended from flight operations until they had been given additional training.

Naha’s approach facility also undertook actions to prevent a recurrence, implementing new training regarding precision-approach radar procedures and minimum safe altitude warnings.

Source: Cirium Dashboard