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air safety

Apr 13, 2017

Qantas stick-shaker incident near Hong Kong rated 'serious'

Approaches and landings at Hong Kong airport are often bumpy, but this one crossed a red line

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A Qantas 747-400 leaving Sydney airport.

The Australian air safety investigator the ATSB is sparing in its use of the term ‘serious incident’ which it has applied to the apparent control and turbulence issues that coincided with minor injuries to 15 Qantas passengers in a 747-400 approaching Hong Kong airport last Friday, April 7.

The ATSB has in the past said a ‘serious incident’ was one which had the potential to cause a crash.

That makes this inquiry of the highest importance, but it doesn’t permit premature conclusions to be drawn from the small amount of publicly available information, as carried by various media reports like this.

The fact that the stick shaker warning was activated is an indication that the 747-400 was in a situation where a further decline in its airspeed would put it at risk of a stall.

On the other hand stick shaker warnings are designed to alert pilots to the impending risk of such an event. They do not go off at the very final moment, but at a moment when prompt action will remedy the situation.

There is no suggestion that the Qantas pilots didn’t promptly and professionally respond to the warning and deal with it as effectively as possible. The paucity of information available doesn’t give an insight into whether all of the related systems on the jet were functioning properly, or that the warning was ‘real’, or that the turbulence experienced in the jet was in fact directly related to the onset of low speed buffeting in the airframe.

In short, there is no reason at this stage to jump to conclusions about the answers to what are important questions.

What can be highlighted is that air traffic vectoring on approach to Hong Kong airport is notably complex and naturally prone to turbulence because of a combination of the constraints of surrounding PRC air space management, and disturbances that can be caused by the uneven terrain that is flown over.

A fact based insight into the conditions that prevailed when this incident occurred can be found in this Aviation Herald report.

As this extract makes clear, this was a very bumpy ride.

Data off the ADS-B capable transponder of the aircraft suggest the aircraft was descending to enter the hold at about 340 knots over ground on a track of 315 degrees, when descending through FL229 at 17:47L (09:47Z) the speed decayed to 290 knots over ground still on a track of 315 degrees before increasing to above 400 knots over ground in altitude fluctuations between FL214 and FL230 before levelling off at FL220 at 390 knots over ground subsequently reducing to 340 knots over ground.

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16 comments

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16 thoughts on “Qantas stick-shaker incident near Hong Kong rated ‘serious’

  1. comet

    In the past, stick shaker incidents were confined to Qantas partner airlines like Cobham Air Services, which did this sort of thing while flying with Qantas livery under the Qantas brand.

    Now we’re getting stick shakers on actual Qantas flights.

  2. ghostwhowalksnz

    And the passengers were injured how ?
    Plus the location given by Aviation Herald is over the ocean, not really uneven ground.

    1. Mick Gilbert

      They were entering a holding pattern so there’s ever possibility that they encountered wake turbulence.

  3. Ben Sandilands

    Ghost,
    I’ve been hammered by standing waves coming off the southern alps of NZ in a C-130 several hundred kms to sea coming up on Chi-Chi from McMurdo. I think you have an oversimplified view as to how turbulence can relate to terrain.

  4. comet

    It would be very unusual for two unrelated events – clear air turbulence and stall warning – to occur during the same flight.

    I’m guessing the passenger injuries were related to the stall warning event.

    1. ghostwhowalksnz

      Im thinking at that altitude a plane can do only two things that are quick, climb and lose speed or dive and gain speed

  5. Rainer

    Just shows that as a passenger you should always be buckled up on all flights.

  6. wildsky

    Two comments from Comet are worth correcting, both in regard to context and accuracy.
    First, stall warnings are triggered by angle of attack changes and turbulence, whether encountered in clear air or otherwise, is characterised by inducing rapid changes in angle of attack in what is essentially chaotic airflow. There are many operational situations where turbulence may well induce stall warnings, most often of short duration, or worse when performance margins are low.
    Second, the reference to Cobham without context is problematic. The Boeing 717 incorporates the stall warning system designed for the MD-11, a much heavier aircraft. That system includes a highly sensitive predictive algorithm that is particularly sophisticated but overactive in the much lighter 717. Cobham indeed had a large number of short duration turbulence-induced stick shaker events in the early days, mostly outside the relatively benign East Coast environment, that took both the company and Boeing considerable effort to understand and resolve.
    Comet’s approach to these news items is simple, but the circumstances rarely are.

    1. comet

      Wildsky, you’re talking rubbish to blame it all on algorithms.

      Here’s some context for you. The two most famous and widely publicised stick-shaker incidents were:

      1. Cobham flight from Brisbane to Gladstone, May 2015. As the 717-200 was in its initial climb out of Brisbane – let me highlight Brisbane – on the East Coast – the stick shaker activated. It was caused by the pilot inadvertently retracting the flaps.

      2. Cobham flight from Perth to Kalgoorlie, 13 October 2010. I know Ben wrote an extensive article about this one on Plane Talking a while ago. No, it wasn’t caused by a mistake in an algorithm. The cockpit inside the 717-200 was in absolute chaos. The crew had miscalculated the weight of the aircraft by ten tonnes. It caused not one but two stick shaker activations. The crew then failed to follow standard stall recovery procedures because they wrongly thought the stall warning was caused by turbulence (are you sure you weren’t piloting that plane?) when in fact the aircraft was travelling at the wrong approach speed. This plane was very very close to crashing, along with more than 100 passengers holding Qantas tickets.

      Have I given you enough context now?

      1. comet

        Just for good measure, I found the link to Ben’s story about Cobham stick shakers in 2012:
        https://blogs.crikey.com.au/planetalking/2012/02/09/atsb-report-into-qantaslink-717-incident-says-crew-entered-wrong-flight-data-and-didnt-follow-operating-procedures/

        And slightly off-topic, but related to the way Cobham is run, is Ben’s story about a Cobham engine fire.
        https://blogs.crikey.com.au/planetalking/2016/05/02/cobham-jet-caught-fire-after-company-failed-to-properly-repair-an-engine/

        So, when you’re boarding a Qantas flight, you might want to check if that red-tailed jet is really being run by Cobham Aviation Services.

        1. ghostwhowalksnz

          Thanks Comet. Whisky seems to just doing PR spin for Cobham
          “turbulence-induced stick shaker events” indeed, I think there was only one for 717 , VH-NXH over WA
          VH-NXD at landing Kalgoorlie was a pilot issue, VH-NXE landing at Alice Springs was similiar ( NXE later had a hard landing at Darwin with structural damage)

        2. Dan Dair

          Comet,
          I’m not taking issue with any of your other examples,
          but you may (or may not) remember that the Cobham BA146/RJ85 engine incident was down to an undocumented engine chamber repair from before Cobham ever owned the aircraft.
          Whatever else Cobham might be justifiably be beaten over the head with, that incident shouldn’t be one of them.

  7. Dan Dair

    My first thought on the basis of the data Ben includes,
    would be an unexpected headwind which caused the speed to decrease during descent.?
    Perhaps the crew weren’t sufficiently monitoring the airspeed & as soon as the stickshaker shook, they upped the throttles to resolve the problem.?

    1. derrida derider

      But wouldn’t an unexpected TAILWIND raise the ground speed but lower the airspeed? A headwind gust would temporarily raise the airspeed.

      1. Dan Dair

        Derrida Derider,
        I’m not entirely certain about that.
        A headwind might give a ‘false’ reading which would effectively leave the aircraft underpowered when the gust stopped.?
        Also, if the headwind was to effectively increase the airspeed, presumably there would be a commensurate increase in lift.?
        (I will happily defer to the people here who specifically understand this detail. As most of you know from my previous errors, it’s not my field of expertise.!!!)

        The point I was trying to make is that you’d not expect the aircraft to decelerate at the same time as it was descending.
        If the wind affected the airspeed & the pilots weren’t paying properly monitoring the airspeed indicator, such an error might occur.
        They were high-enough that height itself wasn’t safety-critical, although clearly it was a safety-issue.?

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