BA 747 Crew commended
BA 747 crew commended for escaping near-stall on take-off
By David Kaminski-Morrow South Africa's Civil Aviation Authority has praised the airmanship of British Airways Boeing 747-400 pilots who battled to prevent a low-altitude stall after the leading-edge slats unexpectedly retracted during lift-off from Johannesburg. At 167kt on the take-off roll, fractionally below rotation speed, all the leading-edge slats inboard of the engines on each side automatically retracted, after receiving a spurious indication of thrust-reverser activation. As the aircraft tried to climb out from Tambo International Airport, known for its 'hot and high' environment, the jet lost a "significant amount of lift", says the CAA, and the stick-shaker immediately engaged, warning of an approaching stall. Instead of following the typical climb profile, the first officer - whose aerobatic experience meant he was familiar with buffet - controlled the aircraft through the stall warning and buffeting by executing a shallower climb, while the commander supported the manoeuvre by calling out heights above ground. The slats stayed retracted for a total of 23s. They started to redeploy 7s after the jet became airborne - as the undercarriage was retracting, at a height of 56ft - and were fully extended 9s later. The stick-shaker, which had activated intermittently over a 15s interval, stopped as the airspeed rose to 186kt. In its inquiry report into the 11 May 2009 incident, the CAA says the crew had "no notion" that the slats had retracted before rotation. There is no separate indication in the cockpit for leading-edge slat position. "The flying crew should be commended for the professional way that they controlled the aircraft during a critical stage during take-off," it adds. "During [the incident] the flight-deck crew had no indication or understanding of what had caused the lack in performance of the aircraft." After stabilising the 747's climb, the crew declared to air traffic control that they were experiencing problems with two engines and would be returning to the airport. The aircraft, which had been bound for London Heathrow with 265 passengers and 18 crew members, landed safely. Investigators have concluded that, during the take-off roll, the slats retracted - as designed - in response to signals indicating deployment of thrust reversers on the two inboard Rolls-Royce RB211 engines. The right-hand reverser signal was triggered at 125kt and the left-hand at 160kt. But neither reverser had been activated, and British Airways engineers examined the aircraft (G-BYGA) to trace the source of the false signals. The inquiry concluded that, although the reversers were stowed, their translating cowls were nevertheless seated relatively far rearwards. As the 747's engines wound up to high power, and the aircraft accelerated, sensors monitoring the cowl positions transmitted incorrect 'reverser' signals. The slats retracted because of a logic process designed to prevent them being struck by efflux air from activated reversers. Boeing subsequently developed a safety bulletin for Rolls-Royce-powered 747-400s to disable this reverser-based automated stowing. SF |
Good job. :DThat's why we put "pilots" in the pointy end. thank god they weren't button pushers.
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Yeah - Antonov, tell us again about pilotless aircraft....
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I thought that the auto-restow thing on the thrust reversers was necessary to prevent in-flight deployment. So I wonder how they did the risk balance of robbing peter to pay paul:confused:
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Investigators have concluded that, during the take-off roll, the slats retracted - as designed - in response to signals indicating deployment of thrust reversers on the two inboard Rolls-Royce RB211 engines. The right-hand reverser signal was triggered at 125kt and the left-hand at 160kt. But neither reverser had been activated, and British Airways engineers examined the aircraft (G-BYGA) to trace the source of the false signals. The inquiry concluded that, although the reversers were stowed, their translating cowls were nevertheless seated relatively far rearwards. As the 747's engines wound up to high power, and the aircraft accelerated, sensors monitoring the cowl positions transmitted incorrect 'reverser' signals. The slats retracted because of a logic process designed to prevent them being struck by efflux air from activated reversers. I guess the risk there is the circuit goes bad, and you don't get them when you need them. One could design the circuit so that unless powered, it can't turn thrust reverser function off ... where are the holes in this idea? For one, which wheel? :) Am I right in guessing that an auto-thrust reverse function is very handy in some tight landing situations? |
Wake up at the back! It is
reverser-based automated stowing |
Am I right in guessing that an auto-thrust reverse function is very handy in some tight landing situations? Guess what ? But as just stated - we're not talking about use of reverse in this incident. |
My understanding of the incident was that the sensor on the thrust reversers caused the slats to retract. This has nothing to do with an interlock preventing the thrust reversers from deploying in flight, but instead would be related to braking efficiency once on the ground.
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The technical aspects were discussed on this thread;
http://www.pprune.org/rumours-news/3...-incident.html Dave |
I know of one fatal accident where the SOP for crew was to pre-select reverse on finals - KNOWING, FOR SURE - that the weight switch would prevent reverse thrust until touchdown. Along came the 737-300 and 10 feet radar altitude was used to arm the reversers, inevitably a few very hard landings occured as the reversers deployed prior to touchdown. |
why?
why is the slat system hooked to the thrust reversers in any sense at all? I haven't flown the 747400. The last jet I flew...if you wanted thrust reverse with slats deployed, you got it. |
The last jet I flew...if you wanted thrust reverse with slats deployed, you got it. The claim that aerobatic experience helped with recovery from the improper leading edge configuration is remniscent of Captain 'Hoot' Gibson's high altitude TWA 841 upset years ago: http://en.wikipedia.org/wiki/TWA_Flight_841_(1979) Hoot said at the time that his aerobatic training allowed him to regain control of the aircraft. |
protectthehornet
The inboard and midspan leading edge flaps retract automatically when on the ground with reverse thrust deployed, so as to prevent the reverse thrust air damaging the flaps. It is inhibited in the air, which is why they redeployed when airborne. http://www.caa.co.za/resource%20cent.../2009/0717.pdf Dave |
Why were the false signals generated on two engines? As this is a rare occurrence for one engine, to have two in fault seems very curious.
What, if anything, occurred between landing and takeoff that might have contributed? Sir George Cayley |
I know this will generate a lot of flack but these guys certainly the same type of medals and props as the BA038 chaps...
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you mean they did not look at the QRH and actually thought for themselves and used excessive airmanship...bah sack'em;)
and a computer controlled [pilotless] plane would simply say "not in data bank does not compute...Crash" :D |
Originally Posted by Airbubba
The claim that aerobatic experience helped with recovery from the improper leading edge configuration is remniscent of Captain 'Hoot' Gibson's high altitude TWA 841 upset years ago:)
Hoot said at the time that his aerobatic training allowed him to regain control of the aircraft. Had Capt. Hoot not been one to play around with trying to deploy trailing edge flaps (by pulling circuit breakers and repositioning the flap handle) to gain more altitude capability at the existing gross weight (which, by the way, was beyond the authorizations in the manual), he wouldn’t have had to rely on his aerobatic experience to save his backside and that of the rest of the airplane's occupants! :* |
Sir George
See 1.16.2 in the report. Dave |
Rigged by the same engineer, that's why.
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Rigged by the same engineer, that's why. |
isn't 'dual maintenance illegal., not ETOPS?
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dear airclues
my sincere thanks for explaning that the slats retract on landing and why. I now have to say, we are simply making airplanes that are too complex for our own good. KISS. PTH |
Old Piedmont crews used this unauthorized 'technique' on the classic 737's My source was a solicitor acting for the insurers, I've never read the report, and some legal skullduggery ( Shock ! Horror ! Really ? ) was involved when it came to apportioning liability, which is why he was telling me - over a beer one day. Hoot said at the time that his aerobatic training allowed him to regain control of the aircraft |
Lonewolf 50: At risk of sounding vastly ignorant, might a design strategy for such a capability, thrust reversers, tie in to a weight-on-wheels switch? WoW + Thrust reverser deployed -> Stow LE Flaps (to protect them from jet blast or foreign object damage) No WoW for whatever reason -> Deploy LE Flaps as commanded From the original post (emphasis mine): The slats stayed retracted for a total of 23s. They started to redeploy 7s after the jet became airborne - as the undercarriage was retracting, at a height of 56ft - and were fully extended 9s later. The stick-shaker, which had activated intermittently over a 15s interval, stopped as the airspeed rose to 186kt. |
They Actually FLEW It Off The Runway
Instead of following the typical climb profile, the first officer - whose aerobatic experience meant he was familiar with buffet - controlled the aircraft through the stall warning and buffeting by executing a shallower climb, |
I have a grand total of one hour of aerobatic training, about 35 years ago...but I assure you, and I am sure, that any ATP could handle buffet.
wondering why they didn't go to ''firewall '' power. and extend more flaps, I know that is what I would do on my type. |
I know in a freighter I'd have been thinking the weights were wrong. That means speed up, trading altitude until you get flyable. And dump.....
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Lonewolf 50,
The slats retracted whilst the aircraft was still on the ground - that is, with 'weight on wheels' - which I'd suggest would normally be the condition under which reversers would be deployed on landing. Hence an oleo-linked switch would not have prevented the slats from retracting in this instance (given that the slat retraction was based on the reverser indication). Protectthehornet, Maybe they didn't firewall as they believed they had a problem with the inboard engines; certainly, at least a (spurious, apparently) reverser deployment warning. A previous inflight (actual) deployment (Lauda 767 out of Bangkok) resulted in the engine blasting itself off the wing and the loss of the aircraft; maybe the BAW056 pilots were mindful of this. |
taildragger...good point
but I know that if you have a reverser truly deployed, you would have YAW and you would reduce power on the affected engine/s it is beyond me why we are making planes so complex that the added complexity actually works against us. if something can go wrong, it will...so don't put it on the darn thing in the first place. don't get me wrong, the crew flew the plane and should be congratulated. |
"I have a grand total of one hour of aerobatic training, about 35 years ago...but I assure you, and I am sure, that any ATP could handle buffet"
Remember colgan at niagara falls ?? |
Protectthehornet,
but I know that if you have a reverser truly deployed, you would have YAW and you would reduce power on the affected engine/s I guess the point remains that these engines were at take-off power so if they were ever going to shear themselves off a la the Lauda 767, this would've been that time, but maybe the drivers took into account the fact that they appeared to still be working so worked with what they had. Anyway... I think we agree the crew did some good flying using skills developed over years. Well done. |
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Protectthehornet; you'd "firewall" the power would you?
It's a hot and high airfield; probably max take-off weight en-route back to London; do you not think that all of the available thrust was being used anyway? TCF |
wondering why they didn't go to ''firewall '' power. and extend more flaps, I know that is what I would do on my type. The 744 takes off with Flap 20. Flap 25, one extra stage, is land flap. |
Errr, excuse me interrupting....isn't lowering the nose to restore airspeed, aka
controlling the aircraft through the stall warning and buffeting by executing a shallower climb, I accept readily that recognising the situation as one which may be resolved by doing that is the product of experience and knowledge, though. I hope that Easyjet takes note. BTW, isn't "go to firewall power" either Top Gun or FlightSim territory? |
I do not want to take anything away from the excellent work of the crew on this flight, which without doubt prevented a serious incident becoming something worse.
BUT Should the crew not have aborted take off as soon as the No.3 Engine TR ‘REV’ amber EICAS message displayed at approximately 125.6kt i.e prior to V1? Also, hats off to the SACAA for their safety recommendations especially Operators should provide flight crews with more basic hand flying and simulator flight training on new generation aircraft to address the technological developments in aviation, inclusive of effective stall training. The apparent increase in the number of software related incidents involving various type certificated aircraft is becoming a cause of concern. There is also a common thread through many recent accidents and it is time to train for a new type of emergency that addresses the failure modes in highly automated aircraft. The interface between pilots and aircraft automation, as well as how this should be incorporated into aviation training, requires a review. This includes addressing how automation fails, how pilots should cope with it and how to get through the failures |
Should the crew not have aborted take off as soon as the No.3 Engine TR ‘REV’ amber EICAS message displayed at approximately 125.6kt i.e prior to V1? |
I wonder if the 200 hour cadet pilots that my company deem to be of acceptable experience would have handled such a frightening situation with such aplomb.
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sooperfrank
thanks for confirming that all engines were firewalled. TheChitterneFlyer and profeng...see above. profeng...no, ''firewall power'' isn't top gun or fight sim. it is part of our flight ops and aircraft flight manuals. granted , we don't operate 747-400, but we have other modern jet transports. crazyaviator, yes, I do.. your point is well taken...let me change my words to MOST atp's could handle buffet. I do wonder about fatigue in that one, the takeoff crew in the 747 was likely more rested at the start of their flight than at the end of it...as the colgan crew. |
while I've just read the PDF file report, I could not find any indication that the engines were firewalled. HOWEVER it states plainly that the takeoff was a REDUCED POWER TAKEOFF.
going to firewall power would have been a good thing to do...perhaps sooperfrank may have found the information saying that the crew firewalled the engines. so TCF and L377 you might want to read the report...also some 31,000 kg below max to weight...or was it pounds? either way not at full weight. |
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