Incomplete change management processes contributed to a Batik Air 737 descending below minimum safe altitude during the airline's inaugural Denpasar to Canberra service last year, an ATSB investigation has found.
Early on 14 June 2024, the Batik Air Boeing 737‑800 was descending for what would be the operator's first scheduled landing in Canberra, an ATSB final report details.
Strong tailwinds during a flight from Denpasar put the aircraft significantly ahead of schedule, set to land before 0600 local time when Canberra Tower and Approach air traffic control services were not yet being provided.
The flight crew opted to proceed without delay, and to land using common traffic advisory frequency (CTAF) procedures, where pilots make positional radio broadcasts and coordinate self‑separation with other traffic.
While still in airspace being controlled by Melbourne Centre air traffic control, the aircraft approached the AVBEG waypoint north-west of Canberra and the flight crew planned to use the AVBEG 5A standard arrival route (STAR).
STARs use satellite-based positioning waypoints to transition aircraft from en route flight to, in this case, an initial approach fix waypoint for Canberra Airport's instrument landing system approach, to land on runway 35.
"The crew did not request, nor were they provided clearance to use this route by Melbourne Centre," ATSB Chief Commissioner Angus Mitchell said.
"Air traffic control in Melbourne expected them to follow their cleared track direct to Canberra, which would have descended the aircraft out of controlled airspace as it approached Canberra.
"Instead, the crew deviated from the clearance and flew the AVBEG 5A STAR."
As the aircraft deviated from the cleared track, a shift change occurred in Melbourne Centre.
The oncoming controller observed the 737 deviating from the cleared track while still in controlled airspace, and noted the aircraft was approaching an area of restricted airspace over the Canberra Deep Space Communication Complex at Tidbinbilla, west of Canberra.
After the controller queried their intentions, the flight crew told them they were following the AVBEG 5A STAR.
Acknowledging this, the controller advised the flight crew to maintain at least 10,000 ft to stay above the restricted airspace. Once the aircraft had cleared the airspace, the controller then cleared them to descend.
"The STAR the flight crew was following takes aircraft over the Tidbinbilla restricted airspace at 10,000 ft by design," Mr Mitchell said.
"This intervention by the controller resulted in the aircraft becoming higher than the desired descent profile, as well as the crew becoming confused regarding the airspace classification for the arrival and approach."
Aiming to get the aircraft back onto the desired flightpath, the captain decided to conduct a holding pattern at the approach waypoint of MOMBI.
"This holding pattern was not correctly flown, and the aircraft was manoeuvred significantly below the minimum safe altitude and terrain clearance reduced to a minimum of 924 ft above ground level in darkness," Mr Mitchell said.
Prior to landing in Canberra, and while in uncontrolled airspace, the CTAF was not selected by the flight crew, and the appropriate radio broadcasts were not made.
This meant safety alerts, being issued over the CTAF by an oncoming Canberra tower air traffic controller about to begin their shift, were not heard.
The ATSB's investigation considered factors which contributed to the occurrence, including the preparatory work done by the airline prior to the inaugural flight into a new aerodrome.
"Batik Air's change management processes were not effective at fully identifying and mitigating the risks associated with the commencement of the Denpasar to Canberra route," Mr Mitchell concluded.
"This included the airline not ensuring flight crew completed all CTAF training prior to operating flights into Australia, where use of these procedures could be required - as in this instance."
Batik has taken a range of measures to address the identified safety issues.
These include internal notices to flight crew highlighting the importance of a comprehensive approach briefing, and completing practical and theoretical CTAF training for all flight crew assigned to Australian operations.
"This incident underlines the need for operators to ensure that they have comprehensive and effective change management processes in place to identify all foreseeable risks relevant to a new route, and to implement appropriate mitigations to ensure the safe operation of these routes," Mr Mitchell said.
"In this case, the unfamiliar operating environment included the potential for operations using a CTAF, an uncommon operating procedure for non-Australian operators and crews."
You can find here the final report: Flight below minimum altitude involving Boeing 737, PK-LDK, 19 km south of Canberra Airport, New South Wales, on 14 June 2024
