Incident Overview
On 19 October 2023, a Boeing 767-200, registration SP-MRE, operated by SkyTaxi on behalf of Astana (call sign TE705), was conducting a standard arrival (MEXAD 8J) to runway 02R at Chengdu-Shuangliu Airport (ZUUU), China. During the approach, air traffic control (ATC) instructed the crew to turn left to heading 050° and cleared them for an ILS approach to runway 02R. ATC also directed the crew to descend from 1500 m only after achieving stabilization on the glide path.
Descent Deviation
Before the aircraft was fully stabilized on the ILS for runway 02R, and while still 31 km from the runway threshold, the pilots initiated a descent that brought the aircraft down to 1430 m. ATC subsequently warned the crew about the premature descent and instructed them to return to 1500 m to maintain safe separation from terrain and other aircraft.
Findings
According to the operator's investigation, the crew acknowledged the clearance for the ILS approach but confirmed a descent to 1200 m instead of the instructed 1500 m. Both pilots likely misunderstood the ATC instruction due to the specific accent of Chinese air traffic controllers. When the crew read back the incorrect altitude of 1200 m, the controller did not correct them, reinforcing the crew's mistaken belief that the clearance had been correctly understood and executed.
Contributing Factors
The standard descent altitude for the ILS Z approach to runway 02R, as depicted on the approach chart (11-3, dated 14 May 2021), was 1200 m. This may have reinforced the crew's assumption that they should descend to 1200 m, contrary to the ATC instruction.
Preventive Actions
In response to the incident, the operator recommended developing special instructions for crews operating to China to raise awareness of language barriers in that region. Additionally, crews were advised to be more assertive in requesting repetitions of clearances when any doubt exists. These measures were disseminated via an Operations Bulletin that used this specific case as an example of miscommunication that could lead to altitude deviations.
No safety recommendations were formulated by the investigating body.