British Airways 777 crash – Boeing’s recommendations

Boeing 777.jpg

I had a chance to talk to Boeing about what they’re now recommendingand why. Although Boeing are not saying so I understand that thevarious manufacturers suspect that the risk only applies toTrent-powered aircraft due to the design of the fuel/oil heating systemwhich Pratt and GE don’t have.

Boeing are investigatingwhether other Rolls-Royce-powered current and legacy models are atrisk. Anecdotally I also understand that it’s by no means certain thatTrent-powered Airbus widebodies will be affected due to different fuel-tank designs. Anyway, below is what Boeing is telling operators. There are two new in-flight procedures to be implemented wheneverconditions resemble those that affected BA038; a new ground procedurelikewise when conditions dictate; and a new non-normal checklist if itall goes wrong (although it wouldn’t have helped BA038).

Thefirst procedure is intended for any flight when the fuel temperaturefalls below 0deg C. It’s pretty simple: when you conduct a step-climb(ie climbing to the next level as the aircraft gets lighter), you do itusing maximum thrust. That’s in order to induce a high fuel-flow andhelp dislodge any ice while it’s still of a size that the fuel/oil heatexchanger can handle that. Something that didn’t happen on BA038.

Thesimple way to achieve that is to use the Vnav function in the FMS -which demands a new flight level – rather than the vertical speed mode(which is what the BA038 crew used.) That’s a change from usualpractice. Crews tend to use vertical speed precisely because it inducesa gentle power change and doesn’t disturb the passengers in the middleof what is often a night-time cruise. Apparently the fuel penalty isnegligible.

The second procedure is basically for use when theoccasion doesn’t arise for a step climb during a flight. So if if youfind yourself getting close to top-of-descent, the fuel temp is below-10deg C (which happens on about half of all flights), and you haven’tdone a high-thrust manoeuvre (like a step-climb) for more than threehours – now’s the time to do one. What you do is go to full thrust for10 seconds or until you reach M0.86 – whichever comes sooner.

Thereis another procedure for use on the ground. Anytime you’re refuellingand it becomes apparent that the fuel will not reach 0deg C, youoperate the fuel pumps at high power for one minute. That was the casefor BA038 at Beijing.

Finally, if you find yourself in the unhappy situation that the BA guysdid, but at a higher altitude, which is still pretty unhappy, thenthere’s a new checklist to follow. You throttle back for 30 seconds onthe affected engine (or engines – one elephant, two elephants, threeelephants….keep smiling…30 elephants) while the ball of slush/icemelts on the heat-exchanger. The shortcomings of this procedure if youare trying to squeak it onto Heathrow 27L without spilling any pints atThe Green Man will be immediately apparent.

Allof this is pretty much predicated on the assumption that the slug ofice getting lodged in the heat-exchanger is probably right. Boeing wasrepeatedly able to replicate that pheonomenon in test circumstances,whereas they were unable to replicate the alternative scenario of iceaccreting in the fuel line and gradually choking it off.

All of this is expected to end up in an airworthiness directive anytime now.

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3 Responses to British Airways 777 crash – Boeing’s recommendations

  1. John S. September 8, 2008 at 2:32 pm #

    Even if true, it was still quite a coincidence to have two slugs of ice block both engines’ fuel flow simultaneously.

    As I understand the 777 fuel system, each engine is fed by it’s corresponding wing tank, with the center fuel tank keeping the wing tanks topped off until it is exhausted.

  2. Capt T V Batu September 11, 2008 at 4:12 am #

    The information was useful to the pilot’s community in addition to the Checklist.

  3. Mutuelle October 4, 2010 at 2:49 pm #

    This is a matter of people’s lives so they have got to do something about it or else we will end up entering aircrafts with a scared feeling. These things should be secured.

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