Narrative:

Per the captain's authorization; [a flight crew member] was in the cabin for takeoff and I was in the first observer seat. Weather was good with calm winds. Takeoff weight [was] 872;100 [pounds]. First officer (first officer) was flying pilot. On takeoff; we were cleared to fly the bekol 3A RNAV departure. The first officer flew the aircraft in VNAV and shortly after takeoff; turned the autopilot on. Per the SID; he engaged speed intervene at 220 KTS until passing porpa and then asked for a high speed climb to accelerate past the flaps 5 speed to have the power reduction to climb power. At that point; I reminded the flying crew of the 15700 foot crossing restriction at bekol. First officer acknowledged and said he would climb at flaps up speed plus 20 KTS. Approximately 10 miles from tung lung; hong kong assigned us a heading of 060 then asked if we would be able to make the crossing restriction at bekol. Both captain and first officer agreed they could and responded 'yes.' first officer continued the climb at flaps up +20 speed. Climbing out of about 11000 [feet]; hong kong gave us a clearance to fly direct bekol and climb to 16000 [feet]. Given our heavy weight and low airspeed; the aircraft was flying at a deck angle close to the pitch limit indication. At 6 miles from bekol; first officer stated we will not make the restriction. I assumed captain would inform hong kong control of our limitation but instead he instructed first officer to fly in vs (vertical speed) mode at 3000 [feet] per minute and climb at the clean maneuvering speed. First officer immediately complied by engaging vs at 3000 fpm. Already in a high deck angle; the aircraft further pitched up to achieve the 3000 feet per minute vertical speed and the airspeed abruptly bled off below clean maneuvering speed. I called out 'airspeed low' and first officer disengaged the autopilot to reduce the deck angle. The aircraft began a descent and I replied 'don't descend.' first officer pitched up to stop the descent but did so too aggressively which cause the aircraft to fly into the pitch limit indicator and activate the stick shaker. First officer pitched down to correct the situation and descended to regain airspeed to flaps up plus 20 KTS. During the recovery; the aircraft lost several hundred feet of altitude and hong kong control assigned us a heading of approximately 280. Once established back in the controlled climb and normal flight; hong kong cleared us back on course.there was no further discussion with air traffic control concerning the situation. This departure scenario is not uncommon. That flight is normally near max gross takeoff weight and we are normally assigned the bekol crossing restriction. Sometimes; we are able to make the restriction and sometimes not. I watched this scenario unfolding but wrongfully assumed that captain would inform ATC that we were unable to make the restriction. The time lapse from when captain instructed the use of vs mode to the point of abrupt airspeed loss was so fast; I didn't have time to provide any other input other than react with my 'airspeed low' callout. The situation could have easily been avoided by staying in a normal climb and informing hong kong that we would not be able to comply with the 15700 [feet] above crossing restriction at bekol.

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Original NASA ASRS Text

Title: B 747 Captain; First Officer and Relief Officer reported getting slow on the BEKOL3A SID from VHHH thus causing activation of the stick shaker.

Narrative: Per the Captain's authorization; [a flight crew member] was in the cabin for takeoff and I was in the first observer seat. Weather was good with calm winds. Takeoff weight [was] 872;100 [pounds]. FO (First Officer) was flying pilot. On takeoff; we were cleared to fly the BEKOL 3A RNAV Departure. The FO flew the aircraft in VNAV and shortly after takeoff; turned the autopilot on. Per the SID; he engaged speed intervene at 220 KTS until passing PORPA and then asked for a high speed climb to accelerate past the flaps 5 speed to have the power reduction to climb power. At that point; I reminded the flying crew of the 15700 foot crossing restriction at BEKOL. FO acknowledged and said he would climb at Flaps Up Speed plus 20 KTS. Approximately 10 miles from Tung Lung; Hong Kong assigned us a heading of 060 then asked if we would be able to make the crossing restriction at BEKOL. Both Captain and FO agreed they could and responded 'yes.' FO continued the climb at flaps up +20 speed. Climbing out of about 11000 [feet]; Hong Kong gave us a clearance to fly direct BEKOL and climb to 16000 [feet]. Given our heavy weight and low airspeed; the aircraft was flying at a deck angle close to the Pitch Limit Indication. At 6 miles from BEKOL; FO stated we will not make the restriction. I assumed Captain would inform Hong Kong Control of our limitation but instead he instructed FO to fly in VS (Vertical Speed) mode at 3000 [feet] per minute and climb at the Clean Maneuvering Speed. FO immediately complied by engaging VS at 3000 fpm. Already in a high deck angle; the aircraft further pitched up to achieve the 3000 feet per minute vertical speed and the airspeed abruptly bled off below clean maneuvering speed. I called out 'Airspeed Low' and FO disengaged the autopilot to reduce the deck angle. The aircraft began a descent and I replied 'don't descend.' FO pitched up to stop the descent but did so too aggressively which cause the aircraft to fly into the Pitch Limit Indicator and activate the stick shaker. FO pitched down to correct the situation and descended to regain airspeed to flaps up plus 20 KTS. During the recovery; the aircraft lost several hundred feet of altitude and Hong Kong Control assigned us a heading of approximately 280. Once established back in the controlled climb and normal flight; Hong Kong cleared us back on course.There was no further discussion with Air Traffic Control concerning the situation. This departure scenario is not uncommon. That flight is normally near Max Gross Takeoff Weight and we are normally assigned the BEKOL crossing restriction. Sometimes; we are able to make the restriction and sometimes not. I watched this scenario unfolding but wrongfully assumed that Captain would inform ATC that we were unable to make the restriction. The time lapse from when Captain instructed the use of VS mode to the point of abrupt airspeed loss was so fast; I didn't have time to provide any other input other than react with my 'Airspeed Low' callout. The situation could have easily been avoided by staying in a normal climb and informing Hong Kong that we would not be able to comply with the 15700 [feet] above crossing restriction at BEKOL.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.