Aviation occurrence briefs

Inadvertent early slat retraction involving Boeing 717-200, near Perth Airport, WA, on 5 August 2018

Status: Completed
Investigation completed


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 the 5 August 2018 at about 1545 Western Standard Time, a Boeing 717-200 operating between Perth and Broome, Western Australia, departed from runway 21 at Perth Airport.

Following a normal departure, Air Traffic Control (ATC) advised that the Standard Terminal Arrival Route (STAR)[1] speed and altitude restrictions were cancelled. The aircraft captain (AC) briefed the first officer that the crew would maintain normal programmed departure speeds. Shortly thereafter, the AC was alerted to a low speed warning on the primary flight display (PFD). The AC stated that as slat retraction had not been called for, the AC initially thought that the crew were experiencing an unreliable airspeed event. The AC checked the thrust and altitude parameters and identified they were within expected limits. As the airspeed was increasing at a normal rate, and there was no stick shaker or under-speed protection engagement, the AC elected to leave the autopilot engaged and monitor the situation. The AC then identified that the slats had been retracted prior to the AC calling for that action. As all flight parameters appeared normal, the crew continued the flight to Broome. Subsequent discussions identified that the first officer misinterpreted the AC’s instructions to maintain normal departure speeds and prematurely retracted the slats.

Safety action

As a result of this occurrence, the aircraft operator has advised the ATSB that they have issued an Operational Safety Alert, reminding flight crews of the importance of positively identifying and confirming actions prior to selection and taking the time to ensure tasks are done correctly.

Safety message

This incident highlights the importance of inter-crew communication to preventing, trapping and mitigating error. Flight crews should ensure they use procedures such as cross check, or identify and confirm to support effective communications and develop a shared understanding of the aircraft state.

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.



  1. STARs are procedural methods to control the flow of traffic within the vicinity of an aerodrome. Flight crews are to comply with published speeds and altitudes unless they are specifically cancelled or amended by ATC
General details
Date: 05 August 2018   Investigation status: Completed  
Time: 1545 AWST    
Location   (show map): Perth Airport    
State: Western Australia    
Release Date: 22 November 2018   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft manufacturer The Boeing Company  
Aircraft model 717-200  
Type of operation Air Transport High Capacity  
Sector Jet  
Damage to aircraft Nil  
Last update 12 December 2018