Unstable approach involving Boeing 787, registered VN-A870 near Melbourne, Victoria, on 19 September 2019

Overview of the investigation

The occurrence

On 19 September 2019, the ATSB commenced a transport safety investigation into an unstable approach involving a Vietnam Airlines Boeing 787 aircraft landing in Melbourne, Victoria. During the approach to Melbourne Airport, the aircraft was not appropriately configured for landing or slowed to the approach reference speed, which resulted in an unstable approach. After 2 advisory calls from the Melbourne tower air traffic controller, concurrent with an aircraft-generated configuration alert indicating that the landing gear was not extended, the captain initiated a go‑around.

The incident

On 19 September 2019, at about 0725 Eastern Standard Time,^[1] the crew of a Vietnam Airlines Boeing 787-9 aircraft, registered VN-A870, operating a scheduled passenger service from Ho Chi Minh City, Vietnam, were on descent into Melbourne, Australia. The captain was the pilot flying (PF) and the first officer was the pilot monitoring (PM).^[2]Visual meteorological conditions were present at Melbourne Airport for the arrival.

The crew had planned to track via the ARBEY 4A standard terminal arrival route (STAR)^[3] prior to conducting the runway 34 RNAV-Z^[4] approach. The aircraft was descended in accordance with instructions from air traffic control.

At 0757:15, while the aircraft was maintaining 6,000 ft, the Melbourne approach controller requested that the crew cancel all speed restrictions and hold their speed for as long as possible. The PM responded that they were maintaining 240 kt and the approach controller replied ‘just the best you can do, thank you’.

At 0758:03, the approach controller provided the crew with their clearance to descend via the STAR to 2,500 ft and that they were cleared for the RNAV-Z approach to runway 34. From 0758:28 to 0801:02, the crew incrementally reduced the aircraft’s speed from 240 kt to 185 kt and selected 2 stages of flaps (flaps-1 then flaps-5).

During the STAR, a tailwind, in combination with the instruction from air traffic control to hold their speed for as long as possible resulted in an average groundspeed of about 280 kt, requiring the crew to use the speedbrake to decelerate and descend.

At 0802:13, after the aircraft had commenced the turn to intercept the approach, the approach controller instructed the crew to contact the Melbourne tower controller. After initial frequency congestion, the PM contacted the tower controller and confirmed they were cleared for the approach.

At 0804:18, the aircraft passed the final approach fix, 4 NM (7 km) from the runway, at 1,493 ft, about 157 ft below the intended glidepath. The aircraft configuration remained at flaps-5 with the landing gear up. The airspeed was about 186 kt, which was 26 kt above the maximum procedure approach speed of 160 kt and about 36 kt above their calculated flaps-30 approach reference speed of 150 kt. The autopilot captured the glidepath at 0804:25, just beyond the final approach fix, at an altitude of 1,493 ft, which was about 1,059 ft above field elevation (AFE).^[5] At 0804:30, the tower controller cleared them to land.

At about 0804:45, the Essendon Fields Airport tower controllers, located about 8 km south-east of Melbourne Airport, visually identifed that the landing gear was retracted. The aircraft was descending through 1,305 ft (871 ft AFE) at an airspeed of 181 kt and about 3.0 NM (6 km) from the runway 34 threshold. At about that time, the PM reportedly prompted the PF to continue the configuration for landing.

The Essendon tower controller advised the Melbourne tower controller via an internal coordination hotline ‘Vietnam 781 check wheels’. At 0804:56, the Melbourne tower controller relayed this to the crew as ‘Vietnam 781 check wheels’, at which time the aircraft was at 960 ft radio altitude (RA).^[6] However, the PM misheard the advisory call as a ‘check wind’ request from the tower and replied ‘Vietnam 781, wind three-six-zero [360] twenty-five [25] knots’. The Melbourne tower controller immediately recognised the advisory call was misunderstood and provided a second call to the crew ‘Vietnam 781 check your wheels, they were observed up’.

At 0805:06, as the aircraft descended through 1,014 ft (780 ft RA and 580 ft AFE) at 183 kt with flaps-5 and the landing gear up, the crew received a master warning alert with an associated ‘CONFIG GEAR’ message.^[7]In response, the PM moved the landing gear handle to the down position, while the PF announced ‘go-around’ and selected the autothrottle take-off go‑around^[8] button. The PF disconnected the autopilot and the PM reported to tower ‘Vietnam 781 go-around’. The aircraft’s lowest recorded altitude was 862 ft (600 ft RA and 428 ft AFE) at about 1.5 NM (3 km) from the runway 34 threshold. Following the go-around, a second approach was conducted without further incident.

Investigation activities

During the investigation, the ATSB:

• interviewed the crew and air traffic controllers involved
• reviewed air traffic control audio recordings and aircraft recorded flight data
• reviewed the operator’s Standard Operating Procedures and crew fatigue information
• reviewed ATSB occurrence data of similar events.

ATSB observation

Stable approach criteria

The Vietnam Airlines standard operating procedures required the correct flight path, approach speed and aircraft configuration to be met, and all briefings and checklists completed by 1,000 ft above ground level for an approach to be considered stable. The procedures also stated that a go‑around must be initiated immediately if the approach became unstable below this height. The ATSB found that the aircraft was not correctly configured and the aircraft’s deviations from the operator’s stabilised approach criteria were not effectively managed, which resulted in an unstable approach.

Non-standard phraseology

The International Civil Aviation Organization Manual of Radiotelephony (ICAO Doc 9432) recommended that landing gear checks by air traffic control use the phraseology ‘check gear down and locked’, which was consistent with the Airservices Australia aeronautical information publication for a civil aircraft. However, the publication provided alternative phraseology to be used when controlling military aircraft of ‘check wheels’.

Fatigue

Considering the crew’s local home time in Ho Chi Minh City, and the approach into Melbourne was conducted during their window of circadian low, this increased the risk of fatigue for the crew. In addition, information provided to the ATSB from the crew indicated that, at the time of the incident, the captain had been awake for around 15 hours and the first officer for around 21 hours. The extended time of wakefulness also increased the risk of fatigue affecting the pilots.

Safety message

Unstable approaches are known to be a hazard to aircraft operations. According to the International Air Transport Association, between 2012–2016, there was an average of 6 accidents per year, which were preceded by an unstable approach.^[9] The Flight Safety Foundation approach-and-landing accident reduction task force identified several factors that contributed to unstable approaches, which included:^[10]

• crew fatigue
• crew or air traffic control-induced circumstances resulting in insufficient time to plan, prepare and conduct a safe approach, which includes accepting requests from controllers to fly higher/faster or to fly shorter routings than desirednot recognising deviations
• not adhering to parameter-deviation limits
• belief that the aircraft will be stabilised at the minimum stabilisation height or shortly thereafter
• confidence by the PM that the PF will achieve a timely stabilisation.

In March 2019, the United States National Transportation Safety Board published Safety Alert 077 Stabilized approaches lead to safe landings. This reiterated that, failing to maintain a stabilised approach could lead to a landing with too much speed or too far down the runway, and ultimately to a runway excursion, loss of control or collision with terrain. The alert went on to urge pilots of all types and classes of aircraft to comply with standard operating procedures and industry best practice for stabilised approach criteria and go-arounds.

Reasons for the discontinuation

Based on a review of the available evidence, the ATSB considered it was unlikely that further investigation would identify any systemic safety issues or important safety lessons. Consequently, the ATSB has discontinued this investigation.

The evidence collected during this investigation remains available to be used in future investigations or safety studies. The ATSB will also monitor for any similar occurrences that may indicate a need to undertake a further safety investigation.

The ATSB has communicated with Vietnam Airlines and Airservices Australia about some its observations and potential learnings. However, it considered that broader communication of this information would not be of significant benefit to other parties.

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1. Australian eastern standard time (EST): coordinated universal time (UTC) + 10 hours. 
2. Pilot flying (PF) and pilot monitoring (PM) are procedurally assigned roles with specifically assigned duties at specific stages of a flight. The PF does most of the flying, except in defined circumstances such as planning for upcoming stages of the flight. The PM carries out support duties and monitors the PF’s actions and the aircraft’s flight path.  
3. All time reference in this report are in local time (Central Standard Time).</Standard terminal arrival route (STAR): A designated instrument flight rules arrival route linking a significant point, normally on an air traffic services route, with a point from which a published instrument approach procedure can be commenced. 
4. Area navigation (RNAV) approach: A method of navigation, which permits aircraft operation on any desired flight path within the coverage of the ground or space-based navigation aids, or within the limits of the capability of self-contained aids, or a combination of these. 
5. The aerodrome elevation was 434 ft and the threshold elevation for runway 34 was 330 ft. 
6. Radio altitude (RA) is the height above terrain measured by the aircraft, which is equivalent to height above ground level (AGL). 
7. The master warning for CONFIG GEAR activates if any thrust lever is at idle, radio altitude less than 800 ft, and the landing gear is not down and locked. 
8. Take-off/go-around: is an autopilot/autothrottle setting activating take-off or go-around thrust. Depending upon aircraft type, it may be activated by depressing a switch or by manually moving the thrust levers to the appropriate position 
9. IATA (2017). Unstable Approaches – Risk, Mitigation Policies, Procedures and Best Practices (3rd ed.). Retrieved from https://www.iata.org/contentassets/7a5cd514de9c4c63ba0a7ac21547477a/iata-guidance-unstable-approaches.pdf. 
10. Flight Safety Foundation (2020). FSF ALAR Briefing Note 7.1 – Stabilized Approach. Retrieved from https://flightsafety.org/wp-content/uploads/2016/09/alar_bn7-1stablizedappr.pdf