What happened
On 17 August 2021, at 11:01 UTC, the Boeing 777-300ER, registration HZAK26, operating as Saudia 366, was climbing through FL230 approaching COP SONAK after being released to Malta Radar from Tunis Control. The crew requested a cruising level of FL370.
To maintain separation from Kuwaiti Air Force C17 aircraft (KAF3209) maintaining FL320, the pilot was initially cleared to climb only to FL310. After passing the first restricting traffic, the pilot was subsequently cleared to climb to FL330, with the crew correctly reading back the instruction. However, while climbing through FL328 at a rate of 1600ft per minute, the aircraft triggered a TCAS RA.
Following the resolution advisory, the crew descended to FL326 and requested information regarding traffic above them. Malta Radar acknowledged the RA and provided information regarding reciprocal traffic (KAF3211) maintaining FL340. The crew subsequently reported resuming their climb as per the original clearance back to FL330.
The investigation
The investigation examined surveillance recordings, communications, and Mode C readouts. The authority reviewed the ATC clearances provided by Malta Radar and the corresponding readbacks from the Saudia 366 crew.
Findings
- The ATC clearances issued by Malta Radar were correct, and all readbacks by the crew of HZAK26 were accurate.
- A minimum vertical separation of 1000ft was maintained throughout the event.
- Neither Short Term Conflict Alert (STCA) nor Medium Term Conflict Detection (MTCD) were triggered.
- The TCAS RA occurred while the aircraft was passing FL328, approaching a level of FL330, with reciprocal traffic positioned at FL340.