Discontinuation notice
Section 21 (2) of the Transport Safety Investigation Act 2003 (TSI Act) empowers the ATSB to discontinue an investigation into a transport safety matter at any time. Section 21 (3) of the TSI Act requires the ATSB to publish a statement setting out the reasons for discontinuing an investigation. The statement is published as a report in accordance with section 25 of the TSI Act, capturing information from the investigation up to the time of discontinuance.
Overview of the investigation
On 25 June 2016, at approximately 1857 Eastern Standard Time,[1] the flight crew of EK407, an Emirates A380 aircraft, registered A6-EDD was conducting a PORTS NINE PAPA standard arrival route (STAR) for the runway 34 required navigation performance (RNP) instrument approach to Melbourne Airport (Figure 1).
Figure 1 - Emirates Charts – Ports 9 STAR (left) and RNAV (RNP) Runway 34 Approach (right)
Source: Emirates
While on a track shortened arrival route, prior to waypoint SUDOS, the transition point between the STAR and the approach, the air traffic controller cleared the aircraft for the approach. The flight crew began the approach immediately. This resulted in the aircraft descending below the minimum assigned altitude for the STAR, and briefly operating outside of controlled airspace (Figure 2). While outside controlled airspace there were no observed traffic conflicts or terrain proximity issues.
On 14 July 2016, at approximately 1940, the flight crew of EK407, an Emirates A380 registered A6-EDM, flew the same STAR, with similar track shortening, and the same approach to the same airport. This flight crew also descended below the minimum assigned altitude for the STAR just prior to the initial approach fix, operating briefly outside of controlled airspace, in a similar location to the aircraft on the 25 June (Figure 2).
Figure 2 - A profile view of the Melbourne airspace to a distance of 14.9 NM along the route taken by A6-EDD on 25 June 2016 and A6-EDM on 14 July 2016
Source: ATSB
In both incidents, the controller intervened to ensure the aircraft stopped further descent until the aircraft reached SUDOS. Once past SUDOS, both aircraft completed the rest of the approach as published, and landed without further exceedances.
During the investigation, the ATSB:
- interviewed the flight crew and air traffic controllers
- reviewed flight and radar data
- examined the operator’s arrival and approach charts, policies, procedures and training for the RNP type approach.
In these two incidents, each crew believed that they were conducting the approach and that descent below 3,000 ft was permitted by the clearance issued by the controller, while the controller believed the clearance would prepare the flight crew, but they would still fly the remainder of the STAR procedure, at the last assigned altitude until passing SUDOS. The plan identified by flight crew was to descend and stabilise the aircraft at 2,000 ft, the minimum safe approach altitude marked on the approach chart between SUDOS and the final approach fix, before commencing the final approach.
The investigation identified a difference in the profile view of the approach charts used by Airservices Australia and those used by Emirates, which may have contributed to the occurrence (Figure 3).
Figure 3 - Comparison between the profile view of the AIP and Emirates Runway 34 RNP approach chart
Source: Airservices Australia and Emirates, annotated by ATSB.
Due to the size of an A380, the aircraft had to land on runway 34, despite runway 27 being in use for all other arrivals. This requirement led to track shortening being issued by the controllers in both incidents to keep the aircrafts’ place in the arrival sequence, and to ensure separation from other arriving and departing aircraft. Analysis of the flight data showed that both aircraft were operating in pilot selected modes as they descended out of controlled airspace, chosen by the flight crew to manage the reduced track distance flown. This meant that protections in the Airbus flight management system which would automatically level the aircraft at the 3,000 ft restriction were inhibited.
Following the incidents, the operator prohibited their A380 flight crew from conducting RNP approaches in Australia and New Zealand.
In May 2017, Melbourne Airport reassessed the standard instrument approach paths in operation at the airport, as part of the implementation of a ground based augmentation system, and the Runway 34 RNP approach was removed.
Additionally, in November 2017, Airservices Australia aligned production of their charts, and the associated phraseology, to International Civil Aviation Organisation standards. This meant that all speed restrictions were published directly onto the chart, and that climb and descent clearances issued via a SID or STAR included an altitude clearance level, in addition to the published limit on the charts.
ATSB comment
Based on a review of the available evidence, the ATSB considered it was unlikely that further investigation would identify any systemic safety issues.
Additionally, the ATSB strives to use its limited resources for maximum safety benefit, and considers that in this case, due to proactive safety action by the operator and air services provider, the ongoing risk is minimal. Consequently, the ATSB has discontinued this investigation.
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