British Airways 747 Near-Accident in South Africa Combined Good Piloting and Luck

The details of the British Airways 747 near-accident in South Africa are out, and man, was that scary for the pilots. They did a great job of keeping that bad boy in the air, but it could have ended very differently. Here’s what happened.

On May 11, 2009, BA flight 56 prepared for its evening departure to London/Heathrow. Afternoon rain had cleared out and it was a clear evening with light northerly winds and temps in the mid-50s (something like -358 degrees Celsius, I’m told). Boeing 747 G-BYGA was ready to bring 265 passengers and 18 crew members back to the UK, so it was about 80 percent full. It probably looked a lot like this one (though this was in Cape Town, not Jo’burg):

Cape Town Airport
Photo via Flickr user Sara&Joachim

They buttoned up and headed for the runway. Engines spooled up as usual and they started rocketing to the north on runway 3L for the long flight home. When the airplane hit 167 kts, just about the time for it to rotate, all hell broke loose. Somehow, due to a technical fault, the airplane showed that thrust reversers had been deployed. Thrust reversers deflect the air within the engine to push it forward instead of backward. This is generally only a good idea when you want to stop the airplane, so it happens with wheels on the ground during the landing rollout. Here’s what they look like on a Lufthansa 747.

Lufthansa 747-400
Photo by Flickr user wbaiv

Fortunately, the thrust reversers didn’t actually deploy and it was merely a faulty warning, but it did bring with it some unintended consequences. When the thrust reversers deploy, the slats Krueger flaps automatically retract. What the heck is a slat Krueger flap? I’m glad you asked.

See those little things hanging over the front of the wing? Those are slats Krueger flaps. Like flaps behind the wing, they’re meant to help increase the surface area camber of the wing to provide more lift. When you’re cruising, you don’t want this because it provides drag and slows you down. But when you’re taking off and landing at slow speeds, it makes it more stable and allows you to fly slower. That’s good.

When it’s not good is when they retract just when you need them most. So picture a 747, just about reaching take-off speed, that suddenly loses its slats Krueger flaps because they think it’s time to retract. Lift goes away and the pilots see less and less runway ahead. Holy crap. So what happened? Well, they took off and sat at about 40 feet above the ground trying to pick up speed. It kind of looked like this:

Ok, so I lied. It looked nothing like this. Instead, replace that airplane with a hulking, slat-less 747 barely clearing the terrain below. Yeah, I’d freak out too. Ultimately, the slats Krueger flaps were back in their deployed position a mere 23 seconds after they ran away, but those were the 23 most critical seconds of the flight. The airplane then started climbing, but the pilots weren’t content to continue on. They dumped fuel and eventually returned with everyone safe.

My guess is that there might have been some people in the back wondering what was going on, but it happened so quickly that they unlikely would have had a chance to even register that this was a real issue. The pilots, however, must have absolutely flipped. Fortunately, they did a fantastic job. The pilot in command happened to have aerobatic training and was well-versed in how to fly at near-stall speeds. There’s no question that those guys saved that airplane and all the people onboard.

But it’s not just them. There was some serious luck here. Johannesburg sits a mile high, and that reduces aircraft performance. But had this been in summer instead of winter, it would have been much worse. Hot weather makes it harder for airplanes to gain altitude, so the mild temperature undoubtedly helped here. It’s also a blessing that the airplane was only 80% full instead of 100%. The added weight would have hurt. On the other hand, it certainly didn’t hurt that they had a slight headwind and the the weather was good.

Anytime there’s an accident, it always requires a handful of things to go wrong. In this case, while one awful thing went wrong, everything else went right. And that’s why the airplane was saved. One other thing going wrong could have resulted in disaster. Fortunately, that didn’t happen here and changes required by the FAA mean this particular incident shouldn’t happen again.

Update at 917p on July 9 – Thanks to the readers who corrected me here. There are no slats on the 747 but rather Krueger flaps. Wikipedia has a good explanation of the difference:

While the aerodynamic effect of Krueger flaps is similar to that of slats or slots, they are deployed differently. Krueger flaps, hinged at their leading edges, hinge forwards from the under surface of the wing, increasing the wing camber and maximum coefficient of lift. Conversely, slats extend forwards from the upper surface of the leading edge.


26 Responses to British Airways 747 Near-Accident in South Africa Combined Good Piloting and Luck

  1. Court says:

    This is a classic case of a little phenomenon we in the industry call, “pucker power.”

    We’ve lost many a cockpit seat cushion that way ;)

    The question I have is whether the TR deploy messages happened after V1 (decision speed). The reason being, if it was prior to V1, they should not have left the runway.

    This also reminds me much of the AAL191, the DC-10 crash in Chicago. In that crash, the engine came loose, but what brought down the airplane wasn’t necessarily the loss of the engine, but the loss of slats. When the engine departed, it took out the hydraulics, which retracted the slats on that wing. What the pilots thought was a safe flying speed, was no longer.

    Translate that to this incident. While the DC-10 had the worse asymmetrical slat retraction (on only one wing), BA did lose leading-edge lift devices on both wings. I’m surprised a design flaw like this would exist. Consider if there really was an inadvertent thrust reverser deployment immediately after rotation. The LAST thing you want is for your slats to retract.

    Had this been a real TR deployment and not just a faulty indicator, I’m certain we’d be talking about this incident in a very different light. Boeing needs to address this design flaw, which they certainly will.

    • CF says:

      It does say in the article. Here’s what happened:
      #3 thrust reverser amber at 125.6 kts
      V1 at 150 kts
      #2 thurst reverser amber at 159.9 kts
      slats retracted at 164 kts
      Vr at 168 kts
      rotation 173 kts
      V2 176 kts
      airborne at 176 kts

  2. A says:

    23 seconds at only 40′-0″? That must’ve been a sight to see. Aren’t there homes and businesses all around JNB? Surprised they didn’t clip anything.

    • Nick says:

      3L at JNB is really long – 4,418m, so I’m guessing they were still over the runway for most of those 23s.

  3. Dan says:

    “Fortunately, that didn’t happen here and changes required by the FAA mean this particular incident shouldn’t happen again.”

    How do FAA changes impact a BA 747 flying from South Africa back to LHR?

  4. That was a lot of fuel to dump. Time to come up with fuel tanks that can be released on a parachute and float down to the ground so as to not damage the environment and be reused.

    • Anon says:

      The kerosene being dumped usually never reaches the ground, but instead evaporates (which admittedly may also cause environmental harm of a different sort).

    • Given how rarely fuel dumps happen and that your basically talking about jettisoning part of the wing, parachutable fuel tanks that’ll find their way safely to the ground (and not break and leak upon landing) would be an engineering nightmare that would also reduce airlines profitability even more since we know they can’t raise fare prices.

  5. Andrew says:

    Hoping that someone can help me understand this from a flight perspective, but even without the slats, shouldn’t a 747 at full power quickly accelerate through the speed necessary to climb even without the slats? I mean, even if the plane had to use an extra thousand feet of runway, in that thousand feet I would think the plane would add another 30 or 40 knots…so I guess I’m surprised that the stall speed of the 747 without slats is so high that they would have to fly level, barely above ground, for 20 some-odd seconds. I would just think that a 747 at full power, in flight for 23 seconds, even without slats, would be accelerating quickly and be well through 200 or even 250 kts, and I would be amazed if a speed like that was not enough to keep a 747 in the air.

    Anyone have any insight? What the stall speed of a 747 is without slats?

    • matt weber says:

      What is not stated here, and may not be obvious, is that JNB is far above sea level, and that seriously degrades engine and aircraft performance in takeoff.
      While we think of Denver as high, JNB is actually several hundred feet HIGHER!

      So this event probably would have been a lot easier to handle had it occured at an airport closer to sea level, which would have made for a much more favorable thrust to weight ratio.

      Fortunately the runway at JNB is very long, about 14,500 feet in fact.

      • CF says:

        That was stated here – “Johannesburg sits a mile high, and that reduces aircraft performance.”

        I wish I could answer your question Andrew, but maybe some pilots can chime in with specifics.

  6. Shindig says:

    What also might be of interest is what was the cause of the initial malfunction or “faulty warning”.

  7. scott says:

    It’s not so much that slats [and flaps] increase the area of the wing to increase lift, more that they change the shape (curvyness) of the wing to something that generates more lift at lower speeds (but more drag at higher speeds).

    The big thing they had going for them, was the 14,495ft long runway 03L/21R, one of the longest civilian runways in the world; and temperatures in the low teens (whatever that might be in F), which would make the air a little denser and able to get more lift from the wing than normal for an airport at 5500ft altitude.

    • matt weber says:

      Actually 55F/13C at 5500 feet is on the warm side, and air is actually less dense. My thumbnail calculation says the density altitude was probably nearly 7000 feet, which further degrades the performance.

      JNB is what is commonly referred to as a High/Hot airport.

  8. DT says:

    Scott is correct. The primary purpose of the leading edge devices in this case is to increase the effective camber of the wing. I think that the 747 employs both Kruger flaps and conventional slats to achieve the increase in camber.

  9. “On the other hand, it certainly didn’t hurt that they had a slight headwind and the the weather was good.”

    The wind didn’t matter once they were clear of the ground. First, there’s always a “headwind” when you take off, because a headwind makes your ground roll shorter. But once you’re off the ground, it wouldn’t have mattered if there was a 60 knot headwind or dead calm. The plane moves relative to the air, not the ground, and would have had the same problems climbing, since the wing surfaces are moving through… the air. :)

    Now, a sudden *change* in headwind would have been bad, since the inertia of the plane comes back into play. Maybe what you were happy for was no change in the relative wind. And that *was* good.

    • CF says:

      Yes, but this happened before they were off the ground. Without a headwind, they might have been further down the runway when they rotated and that could have causes problems. It’s always a game of inches when it comes to averting disaster.

      • That contradicts your earlier reporting then. You said they were “40 feet off the ground”, which to me (as a pilot) means “they couldn’t get out of ground effect”, even though they were already past the end of the runway. If they hadn’t gotten off the ground at all yet, they would have just aborted the rotate.

        • CF says:

          That’s not what I said. Here’s what I said:

          “When it’s not good is when they retract just when you need them most. So picture a 747, just about reaching take-off speed, that suddenly loses its Krueger flaps because they think it’s time to retract. Lift goes away and the pilots see less and less runway ahead. Holy crap. So what happened? Well, they took off and sat at about 40 feet above the ground trying to pick up speed.”

          The flaps retracted while the airplane was still on the ground. As mentioned in the comments earlier, here’s the way it went:

          #3 thrust reverser amber at 125.6 kts
          V1 at 150 kts
          #2 thurst reverser amber at 159.9 kts
          slats retracted at 164 kts
          Vr at 168 kts
          rotation 173 kts
          V2 176 kts
          airborne at 176 kts

  10. Pay attention. The high, low, or no headwind completely factors out.

    If they had enough runway to make a normal departure (given the expected headwind), then they would have aborted immediately if they failed to rotate by the required time. This is part of your pre-roll calculation… you must rotate by X-thousand feet of runway remaining, or you STAY ON THE GROUND and stomp the breaks and reversers.

    So, if they lost enough lift on the ground to not rotate by the braking point, they wouldn’t have rotated, and they would have made a normal emergency stop.

    If they were able to get off the ground by the required rotate time, even if they couldn’t climb out of ground effect, AGAIN the headwind doesn’t matter, because they’re already in the air.

    See, it doesn’t matter. The only difference is the rotate point.

    • CF says:

      you must rotate by X-thousand feet of runway remaining, or you STAY ON THE GROUND and stomp the breaks and reversers

      Maybe another pilot would like to chime in here, but as far as I know, once you pass V1, you aren’t aborting even if you lose an engine. The flap retraction occurred after V1.

      But this really is beside the point. Let’s get back to my initial reason for saying that headwind matters. With a headwind, you’re likely to get airborne sooner than without, right? So, they’re sitting there hovering a few feet over the runway, waiting to get enough speed before they can climb. With a headwind, they have a little more runway to work with. Without a headwind, they’re further down when they rotate and that means they could be closer to hitting an obstruction.

      • Well, if that’s your claim, a strong headwind is far more interesting than a light headwind. There’s almost never “no headwind”. So you’re arguing against yourself by saying “oh, good thing there was a light headwind”. I’d say “Oh darn, only a light headwind!”

        The most important part was a *consistent* wind. Gusty would have been *very* bad. Even if the average wind was 15 knots, if that was 0 gusting to 30, the chance of this action falling out of the sky would have been much greater than a constant 0 or a constant 30.

  11. Berniece Hutton says:

    Southwest Flight 2361 on July 16, 2009 from Jackson International Airport (Jackson, MS) en-route to Midway International Airport (Chicago, Illinois). Looking to share pictures from that incident.

Leave a Reply

Please use your real name or nickname instead of your company name or keyword spam.