Air carrier crew reported receiving a terrain alert from ATC while descending via a charted transition off the lateral path; while deviating around thunderstorms in mountainous terrain. The flight leveled out then resumed the approach and landing.
Synopsis
Air carrier crew reported receiving a terrain alert from ATC while descending via a charted transition off the lateral path; while deviating around thunderstorms in mountainous terrain. The flight leveled out then resumed the approach and landing.
Narrative
After returning to the flight deck after our rest the captain briefed our arrival in to HKG. We had been expecting 7L; however; we were informed HKG was now landing 25R. The captain had prior experience so he also briefed the RNAV transition from the ABBEY 3B. I was unfamiliar with this approach. We were experiencing many vectors and speed changes for spacing as well as requesting headings to avoid weather throughout the descent. It was a very busy arrival.There was weather south of RUNSU that appeared to encroach on the arrival path. We requested heading 270 before getting to RUNSU so that we would avoid the cell. This was approved by the controller. I am unsure of the following sequence of events. There seemed to be some confusion (either I misunderstood or the controller misspoke) about maintaining 4500 to RUNSU then descend via the transition to ILS 25R. We were passing abeam south (perhaps 1 mile?) RUNSU on a 270 heading. When just outside of SAGNI (not yet on the lateral path) the controller issued a clearance to climb immediately; that our last clearance was to maintain 4300 to SAGNI. We were passing through 4000 to cross SAGNI at 3800. We leveled; then shortly after the controller cleared us to descend via the transition. As I stated above; I am unsure of the sequence of events. There is significant terrain between VH515 and SAGNI.The bottom line is we descended without being on the lateral path of the RNAV transition. I made some significant errors. First; I was unaware of the note 2: 'do not accept radar vectors inside of RUNSU' as well as the other notes under 'Handling' because of the runway change from what was expected and the busyness of the arrival due to multiple vectors and speed changes due to traffic and weather. Second; when we requested the heading for weather near RUNSU I should have requested a hard altitude as per SOP. This heading though; should not have been approved in light of the notes on the plate. We should not have asked and it should not have been approved. I had some difficulty with the language and perhaps the controller had some difficulty with mine as well. In the future I will think twice about using the AUTO function on the radar. I believe it overstated the weather and we did not need to avoid that small cell.It resolved quickly when we rejoined the transition and were cleared for the approach to an uneventful landing.
Second reporter narrative
While on the RNAV transition to the ILS 25R at HKG we had to deviate slightly left of course for moderate/heavy precipitation and possible turbulence on final. The deviation was approved by approach control and we maintained a safe altitude without descending until re-established on course. While left of course; Approach control questioned our location. We were above NAV profile with terrain in sight and on the FO's display. We intercepted final and regained VNAV vertical profile just inside of RUNSU. We were cleared the approach and the reminder of the approach and landing were uneventful.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.