What happened
On October 19, 2023, a Boeing 767-200, registration SP-MRE, operated by SkyTaxi for Astana (flight TE705), was performing a standard arrival (MEXAD 8J) at Chengdu-Shuangliu Airport (ZUUU) in China. During the approach, air traffic control instructed the crew to turn left to a heading of 105 degrees and cleared them for an ILS approach to runway 02R. The controller further instructed the crew to descend to 1,500 meters once the aircraft had stabilized on the glide path.
Before the aircraft had fully stabilized on the ILS 02R approach, approximately 31 km from the runway threshold, the pilots initiated a descent that caused the aircraft to drop to an altitude of 1,430 meters. The air traffic controller subsequently alerted the crew to the premature descent and ordered them to climb back to 1,500 meters to maintain safe separation from terrain and other aircraft.
The investigation
The investigation examined the communication between the flight crew and air traffic control, as well as the crew's interpretation of the descent instructions. The investigation focused on why the crew initiated a descent to an altitude lower than the instructed 1,500 meters and why the error was not corrected by the controller during the initial readback.
Findings
- The crew mistakenly confirmed a descent to 1,200 meters instead of the instructed 1,500 meters.
- A language barrier, likely caused by the specific accents of Chinese air traffic controllers, led the pilots to misunderstand the instructions regarding the 1,500-meter altitude.
- The crew believed their instructions were correct because the air traffic controller did not issue a correction when the crew read back the incorrect altitude of 1,200 meters.
- The crew's belief was further reinforced by the published RNAV ILS approach chart for runway 02R, which specified a standard descent altitude of 1,200 meters.
Safety action
- An operational bulletin was issued describing this incident as an example of a misunderstanding that could lead to altitude deviations.
- It was recommended that specialized instructions be developed for crews operating in China to increase awareness of regional language barriers.
- The crew was advised to practice greater assertiveness in requesting repetitions of clearances whenever any doubt arises.