Incident: Southern B772 at New York on Nov 15th 2020, stall on departure : 財團法人中華民國台灣飛行安全基金會

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Incident: Southern B772 at New York on Nov 15th 2020, stall on departure

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admin - News | 2020-11-19 01:45:32

By Simon Hradecky, created Wednesday, Nov 18th 2020 00:37Z, last updated Wednesday, Nov 18th 2020 00:37Z

A Southern Air Boeing 777-200 freighter, registration N702GT performing flight 9S-947 from New York JFK,NY (USA) to Seoul (South Korea), was climbing out of JFK's runway 22R climbing through about 5000 feet when the crew contacted departure advising they were climbing to 5000 feet. They were cleared to climb to 11000 feet, the aircraft continued climb, the pilot monitoring read back the clearance to climb to 11000 feet when he shouted, obviously to the pilot flying but with radio microphone open: "Stall! Stall! Stall! Stall! Stall!", then added "Standby" (obviously directed at ATC). The speed over ground had decayed from about 273 knots to 256 knots while climbing above 5000 feet, the aircraft began to descend from 5150 feet and stabilized about 200 feet lower. In the meantime the controller received several requests from other aircraft and just replied "Standby" to the other aircraft. The controller queried whether they were ready to climb now, the crew again replied "Standby". About 90 seconds after the stall calls the speed had recovered to 277 knots over ground and was accelerating, the crew indicated they were ready to climb again, everything was good again and were cleared to continue their climb. The controller also resumed normal service to all aircraft. The B772 continued their flight to Seoul where the aircraft landed safely about 14.5 hours later.

https://flightaware.com/live/flight/SOO947/history/20201115/1825Z/KJFK/RKSI

Reader Comments: (the comments posted below do not reflect the view of The Aviation Herald but represent the view of the various posters)

Sh*t Happens...
By Anony on Wednesday, Nov 18th 2020 21:03Z

Some alarms are going off in the background in the audio recording. Stalls are usually predicated on AOA, still airspeed is a factor. They were just climbing on departure, if the AP was on which is pretty much SOP @ SAI there should not be unusual pitch attitudes, so the speeds don't really correlate - even if heavy.

Could have been a false shaker, which I have seen in turbulence, maybe even that specific aircraft. PM just called out the indication.

@ ATCGermany
By 777, 747 Guy on Wednesday, Nov 18th 2020 20:47Z

Your statement that there are no exclusions about speed exceeding 250k below FL100 means that the After Takeoff Checklist that is electronically displayed in the B777 will be incomplete until reaching 10,000 ft which if levelled off at allows acceleration to standard climb speeds, circa 300-330.

In my experience, if there is any doubt, a call to ATC on Departure requesting speed waiver to accomplish Clean maneuvering speed until 10K is always accommodated unless there is some special need to not exceed, eg trailing lighter traffic that is at 250 speed. Even in really congested areas like SFO where there is a requirement for strict speed control, a courtesy call to ATC is always met with approval. Heavies like 777, A380, 744/8 rarely are held at 250 to 10K - hauling along with climb thrust with Flaps 1 or 5 only increases noise and pollution where sensitive airports and countries want us to avoid behaving like fighter pilots!

Sh*t Happens...
By Anony on Wednesday, Nov 18th 2020 19:49Z

TOGW's > 720K #'s will usually require a flaps up minimum speed > 250 kts. Not as bad as with the 744 which would require greater speeds. I would usually brief higher than 250 kts

250kt below F100
By ATCGermany on Wednesday, Nov 18th 2020 18:42Z

To Anonymous: just because the Aircraft has a clean Speed above 250kt doesnt implicate it is allowed to fly faster below 100. If it is in Airspace E for example, here in Germany max Speed is always 250kt without exclusions

@FBW
By 737 pilot on Wednesday, Nov 18th 2020 14:06Z

Not quite, it may respond to many different parameters. Speed is definitely one of them, it may also be N1 (giving a preset N1 value, irrespective of speed).

Bottom line: the FMA tell you what it is responding to. If the FMA says SPD, then indeed it will give thrust to match the speed you require. If it says N1, it will go to a certain N1 setting, irrespective of speed.

But it might also show THR HLD (meaning thrust hold, as in fixed thrust), or ARM (autothrottle armed). In both cases the autothrottle will not move, until a new mode is selected (either automatically or manually).)

I do not know the 777 autothrottle logic, but I would expect in this level-off that the autothrottle would be in ARM mode, in anticipation of a further climb. This was not yet initiated, since the PM was busy talking to ATC, and did not yet have the time to set 11.000ft in the MCP window and select a new mode.

@737 pilot
By FBW on Wednesday, Nov 18th 2020 13:45Z

The autothrottle responds to speed and not altitude and will only move if the speed of the plane is above or below the selected speed. If the PF raised the nose of the A/C to climb to 11000 ft, the A/T would have moved forward if it was engaged in anticipation of the speed bleeding.

By 737 pilot on Wednesday, Nov 18th 2020 13:21Z

Possible scenario (one of many):

PF flying manually, autothrottle on.
Autothrottle reduces power in anticipation of level-off at 5000ft.
PF hears clearance to climb to 11.000ft and raises pitch, failing to notice FMA in ALT HOLD (or similar)
Thrust does not increase because plane wants to maintain altitude, not climb.

Stall
By Steve on Wednesday, Nov 18th 2020 12:31Z

The 777 when heavy actually has a clean speed that is above 250. If the pilots inadvertently selected 250 after clean flap retraction, the aircraft by design will lower the nose and protect Vls before going into stall if autopilot is engaged. A low speed message will display however which may have got the PM to speak up.

FDR
By (anonymous) on Wednesday, Nov 18th 2020 10:41Z

Hope they can secure the FDR and eventually CVR. This needs to be investigated.

By (anonymous) on Wednesday, Nov 18th 2020 07:47Z

Note: the 777 is one of the few planes that, depending on its weight, may have a clean minimum maneuvering speed of above 250kts (and hence is allowed to fly faster than 250kts below 10,000ft). Even without wind, if the plane was at 5000 ft and the ground speed was 253, the airspeed may have been 230~240 kts, and even less if they were flying with a tailwind.

Those speeds can be enough to activate the stickshaker, especially if you pull up a bit (for example to initiate or increase a climb).

Stall speculation
By AOA Jockey on Wednesday, Nov 18th 2020 04:33Z

Ground speed is not a key consideration in stall evaluation as airspeed has much more influence on AOA.Whether the 200 foot altitude loss was due to pushing the control column forward remains to be determined.

If the sticker shaker activated it should be audible on ATC freq.

Not an arm chair pilot
By (anonymous) on Wednesday, Nov 18th 2020 04:20Z

Not enough details. Could be wind change, pilot error, mechanical, too quick a climb rate. But I'm probably going to rule out mechanical failure.

By Yikes on Wednesday, Nov 18th 2020 03:28Z

Interested to hear from non-armchair pilots on this one.

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