| Occurrence Briefs are concise reports that detail the facts surrounding a transport safety occurrence, as received in the initial notification and any follow-up enquiries. They provide an opportunity to share safety messages in the absence of an investigation. |
What happened
On 16 May 2018, at about 0700 Eastern Standard Time (EST), an Airbus A330-303 was beginning its descent into Melbourne, Victoria (Vic.). The aircraft was on a scheduled passenger flight from Tokyo, Japan with 12 crew members and 297 passengers on board.
The flight crew received clearance from air traffic control (ATC) to conduct a descent to 9,000 ft. Shortly after commencing a managed descent,[1] the first officer (FO) observed the aircraft was slow of its commanded speed. The FO selected OP DES[2] and the aircraft accelerated towards a managed speed of 310 kt. The aircraft’s maximum allowable operating speed (VMO) was 330 kt.
Passing through flight level (FL) 320[3], the wind direction shifted from a crosswind to a headwind and consequently the aircraft rate of descent increased. The flight crew deployed the speed brakes and levelled the aircraft, by selecting ‘PUSH TO LEVEL OFF’ on the flight control unit, to reduce speed. Despite these actions, the aircraft continued to accelerate. During the descent, the aircraft reached a maximum speed of 336 kt for 6 seconds.
The aircraft landed at Melbourne without further incident. There was no damage to the aircraft or injuries sustained to crew or passengers.
Engineering Inspection
Following the incident, the operator’s engineering team examined the details of the occurrence and determined that the maximum speed obtained was within the permissible limits of the aircraft maintenance manual. No inspections of the airframe were required, and the aircraft was returned to service.
Safety message
This occurrence highlights that unexpected changes in weather can occur at any time. Sudden shifts in wind direction can have a significant impact to aircraft speed. Flight crews should pay particular attention to monitoring the aircraft’s speed during descent when operating with a reduced margin to VMO as the impact of a wind gradient can result in an airframe overspeed. In particular, when flying close to the wind direction or in turbulent conditions, flight crew should adjust the speed target to allow adequate margin below VMO.
About this report
Decisions regarding whether to conduct an investigation, and the scope of an investigation, are based on many factors, including the level of safety benefit likely to be obtained from an investigation. For this occurrence, no investigation has been conducted and the ATSB did not verify the accuracy of the information. A brief description has been written using information supplied in the notification and any follow-up information in order to produce a short summary report, and allow for greater industry awareness of potential safety issues and possible safety actions.
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- In the managed descent mode, the aircraft follows a pre-computed descent profile that allows for aircraft deceleration and airspace restrictions along the active flight planned route.
- OP DES: allows the aircraft to climb or descend uninterrupted toward flight control unit selected altitude, maintaining a target speed (managed or selected) with a fixed given thrust.
- Flight level: at altitudes above 10,000 ft in Australia, an aircraft’s height above mean sea level is referred to as a flight level (FL). FL 320 equates to 32,000 ft.