• 777 Hull loss

    From Ward Dossche@2:292/854 to All on Thu Feb 14 07:05:13 2008
    The 777 that limped into Heathrow has been confirmed a hull-loss,the first 777 since it took to the skies.

    This is what I caught from a pilot-forum so far "with the help of my friends":

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    At about 700 ft AGL, the auto throttle commanded engine acceleration. One engine started to rollback during and the other engine started to
    accelerate then 8-10 seconds later began to roll back. Once the flight
    crew noticed, they pushed the throttles up and the engines' EECs
    responded but the engines did not. It appears that no fuel was getting
    to the engines.

    The investigation continues to look broadly for a cause of the dual
    engine rollbacks. Fuel exhaustion is the only item that has been
    positively ruled out. Aspects that the FAA believes the investigation
    is concentrating on are:

    Ice in the fuel somehow limiting the fuel flow to the engines. A
    maintenance message indicating excessive water in the center tank was
    set during taxi on the two previous flight legs, although it cleared
    itself both times. The airplane was being operated in a high humidity,
    cold environment, conducive to ice formation.

    Small-sized contamination building up in the engine fuel systems
    somehow limited the fuel flow to engine. All the fuel samples have
    ested for contamination of larger particles (sizes outside the fuel pecification). Testing has been started looking for small particles
    greater than 5 microns).

    Engine hardware failures sending inaccurate data to the engine
    electronic control (EEC) causing the EEC to demand insufficient fuel.
    A preliminary review of the EEC data from the right engine shows
    erratic combustor inlet pressure (P30). A leaking P30 sense line could
    cause this, or the EEC receiving a higher than actual fuel flow parameter.

    Software coding problem in the EEC causing the EEC to demand
    insufficient fuel. British Airways installed a new engine EEC software
    revision in December 2007. The software was approved in May 2006. There
    were several changes to the software as part of the revision. Two items
    seem remotely related to the accident: improvements to low power stall
    recovery logic and fan keep out zones for ground maintenance. The first
    two items would be related to a part 25 compliance issue, while the last
    two items would be related to a part 33 compliance issue.

    As stated yesterday in this briefing paper, the electrical system anomalies noted earlier have been resolved, as describe below, and the conclusion now
    is that the electrical buses were powered until impact and performing as expected.

    The auxiliary power unit (APU) began its auto start sequence, even
    hough the buses were still powered. In the days following the event,
    the flight crew has added additional details to their report. The crew
    now believes they turned the APU on prior to impact. There was sufficient
    time before the impact for the APU inlet door to open, but not for the
    APU fuel pump to turn on or the APU engine to start spooling up.

    The quick access recorder (QAR) saved data and shut down approximately
    45 seconds prior to impact. The QAR saves data in batches. It is believed
    the QAR was working properly and was in the process of saving data when
    impact occurred, accounting for the "lost" 45 seconds of data.

    The fuel crossfeed valves were closed in flight according to the flight
    crew, but the switches were found in the open position and only one valve
    was open. In the days following the event, the flight crew has added
    additional details to their report. The crew now believes they opened the
    alves just prior to impact and the airplane lost power before both valves
    moved to the open position.

    The ram air turbine (RAT) was found deployed, even though the buses
    were still powered. It did not deploy until after the airplane came to
    a stop, as determined by the pristine condition of the turbine blades.
    The RAT either deployed due to electrical power loss during impact with
    a failed air/ground signal or the impact unlatched the RAT door.

    Fuel system: Leads regarding water in the fuel and fuel contamination are continuing to be investigated. Fuel testing looking for small-sized contaminants (5 microns) is beginning. The tanks are still being drained
    and the team hopes to start evaluating the fuel system hardware tomorrow.

    Engines: Component testing and teardown of the engine-driven fuel pumps
    and the fuel metering units is planned for later this week. The data from
    the electronic engine controls is still being analyzed. Rolls-Royce is
    planning an engine test, unscheduled as yet, to try and duplicate the rollbacks.

    Crashworthiness: Cabin crew and passenger questionnaires indicate that the evacuation bell was faint, but the evacuation light was seen and the captain's message to evacuate over the passenger address system was heard. Preliminary data indicates that the descent rate at impact was roughly 30 ft/sec. Dynamic seat requirements that became effective at the introduction of the Model 777 series airplanes require seats protect occupants for hard landing impact up to 35 ft/sec. The passenger with the broken leg was sitting next to the point where the right main landing gear punctured the fuselage and pushed into the cabin.

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