Jetstar A320 at Christchurch on Aug 6th 2019, descent below minimum safe height on approach

Last Update: May 2, 2019 / 15:29:42 GMT/Zulu time

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Photo of Jetstar Airways VH-VGY, Airbus A320 — Jetstar Airways VH-VGY, Airbus A320 (Photo credit: Stilgherrian / Flickr / License: CC by)

Incident Facts

Date of incident
Aug 6, 2019

Classification
Report

Airline
Jetstar Airways

Flight number
JQ-291

Departure
Wellington, New Zealand

Destination
Christchurch, New Zealand

Aircraft Registration
VH-VGY

Aircraft Type
Airbus A320

ICAO Type Designator
A320

A Jetstar Airbus A320-200, registration VH-VGY performing flight JQ-291 from Wellington to Christchurch (New Zealand) with 128 passengers and 6 crew, was on approach to Christchurch's runway 02 when the aircraft, while following the standard arrival procedure MESIX Five Alpha and being cleared to descend to 3000 feet MSL, descended below the minimum safe altitude (MSA) of 2500 feet MSL. ATC noticed the aircraft had descended below cleared altitude and MSA, but did not advise the crew until after the aircraft had landed. The aircraft continued for a safe landing on runway 02.

New Zealand's TAIC released their final report concluding the probable causes of the incident were:

- The aeroplane descended below a published minimum safe altitude for a segment of the arrival procedure, because the flight crew did not maintain adequate situational awareness of their aeroplane’s location in relation to the standard arrival route.

- The flight crew elected to use an ‘open descent’ procedure rather than the available, fully automated ‘managed descent’ mode, which required a higher level of human intervention to keep the aeroplane within permissible limits on the arrival route.

- The operator’s procedures did not encourage the appropriate use of the aeroplane’s automated navigation systems; this increased operational risk by placing more reliance on human performance.

- The air traffic controller observed the aeroplane’s descent below the minimum safe altitude, but did not follow the required procedures and alert the flight crew until the aeroplane had landed.

The TAIC analysed:

Minimum clearance and safe altitudes are set for a good reason: to provide a safety margin between aircraft and terrain or obstacles. When an aircraft breaches these limits, it is operating one step closer to a serious incident or accident. When an air traffic services safety system does not detect or respond to this type of breach, there is a risk of such events becoming normalised and undermining the safety of the system.

...

The captain had not flown domestically within New Zealand for several years, and was therefore less familiar with flying between Wellington and Christchurch than the first officer.

The first officer was more familiar with the route. It had also become common practice for the first officer to delay commencing the descent into Christchurch and to set the aeroplane’s navigation systems to open-descent mode before commencing the instrument approach. Using open-descent mode was not inconsistent with the operator’s standard operating procedures.

In open-descent mode the aeroplane was programmed to descend directly to the altitude set in the FCU (2,000 feet), ignoring the intermediate altitude restrictions contained in the standard arrival route. The first officer had used this descent profile previously at Christchurch and was confident of being able to maintain a steady descent to the commencement altitude for the instrument approach.

However, on this occasion the aeroplane descended below the intended profile and consequently below the 3,000-foot minimum altitude limit between GUKAM and GOMPI, and also below the 2,500-foot minimum safe altitude limit until past GOMPI. The 3,000-foot limit was a procedure limit, while the 2,500-foot minimum safe altitude limit provided separation from terrain along the GUKAM-to-GOMPI track.

With respect to ATC the TAIC analysed:

In this incident the controller observed an aeroplane that had descended below the next waypoint altitude limit of 3,000 feet and the route minimum safe altitude limit of 2,500 feet. There were no complicating circumstances in terms of traffic flow or density.

The Manual of Air Traffic Services sets out the procedures for responding to air traffic situations. The preface to the manual states that it is not practicable for the document to cater for all combinations of air traffic situations, and that controllers are to use their judgement. However, in a straightforward situation with no complicating circumstances, the controller has no reason to deviate from the standard procedure.

In this case the standard procedure was to inform the crew immediately and direct a climb, or at least to alert the aeroplane crew to the exceedance. The controller took neither of these actions. The controller and planner said they had observed the aeroplane level at 2,000 feet and, seeing that it was not descending further, the controller decided not to alert the crew for concern it might distract them at a critical phase of the flight.