Boeing wants out of Alaska case

Precursor events. No accident like the 1998 crash of Swissair Flight 111 occurs in a vacuum. Related cases, with less deadly outcomes, often can be found, as in these incidents below:

        January 22, 1996, British Airways B747-400 over Abbeville, France. From the UK's Air Accidents Investigation Branch (AAIB) report of this incident (Bulletin No 3/96, Ref. EW/G96/01/07) these extracts pertain:
        "Passenger in seat 37K drew attention of cabin staff to 'sparks' coming out of floor level cabin conditioning vent, with an acrid burning smell."
        "It was decided to remove the cabin trim panel ... as it was removed the electrical loom aft of the window suddenly emitted flames which reached up to the overhead lockers. The first officer immediately attacked the fire with a BCF extinguisher. He then contacted the flight deck and called for all power to be switched off."
        "The fire had occurred in a bundle of electrical cable ... [which was] part of a loom, the bulk of which originated from power distribution panels ... in the main electronic center ... The loom in the sidewall ran between two insulation blankets." "The heat generated would not have readily dissipated."
        "Two circuit breakers ... had not tripped ... these were 25 amp units, as opposed to the 2˝ amp breakers specified in the diagram"
        Although not an MD-11 like the Swissair jet, this incident had a number of essential elements in common:

·        Fire (sparks and smoke).

·        A "Pan" call.

·        Charred wiring in the main electrical load center.

·        Burning blankets (see photo).

·        Hidden fire in a space with no detection or suppression.

·        Power was initially killed – but later restored (when power was restored to the wiring, the fire flared up tremendously)

·        Globs of melted metal from the arcing.

·        Circuit breakers did not protect (and later were found to be rated incorrectly 1,000 percent higher than they should have been, and were installed after the aircraft was delivered from the factory).

·         Much aromatic polyimide wiring in the airplane, which arcs with explosive effect.


 

        April 28, 1997, Virgin Atlantic B747-200 enroute from Washington, D.C., to London. From the UK's Air Accidents Investigation Branch (AAIB) report of this incident (Bulletin No 10/97, Ref. EW/C97/4/3) these extracts pertain:

As it approached Halifax, Nova Scotia, the cabin crew in the first class section saw smoke and sparks coming from an overhead panel above the beautician's table, which was fitted as part of this operator's interior layout. No passengers were in the area at the time, which was curtained-off, and they remained unaware of the occurrence. The Flight Engineer investigated. Dropping the two Passenger Service Unit panels nearest to where the cabin crew had seen the smoke and sparks, he could see evidence of blackened wires and paint discoloration. He also examined the circuit-breaker panels and found that two had tripped - P14 'Ceiling control' and P15 'Light window right'. The loom comprised about 50 wires, the majority of which had melted at the same location, associated with a 'P' clip which had also partially melted. Secondary damage to a gasper air pipe and sooting/heat damage to adjacent structure and trim panels was also noted. It was evident that the fire had self-extinguished but the loom in the area of the overheat was too badly burned to identify which individual wire had initiated the sequence. The airline uses third-party maintenance. A modification had been embodied to the lighting in the affected section which involved introducing new wires into [the] loom. A considerable amount of 'fresh' debris such as swarf, a solid fastener, a stiffnut and a drill bit was found in the area which had been subject to modification. Chafing or wire-stripping (on pulling the new wiring through the ‘P’ clip) was blamed, however the fire had destroyed any evidence.

        Again, parallels and contrasts to the Swissair disaster:

·        Wiring installed as part of a modification (and Third Party Maintenance or Modification).

·        A Third Man available to actively investigate (remove panels), equate systems losses to CB trips and rapidly resolve the action required (Flt Engineer)

·        Whole wiring bundles (looms) taken out at once by fire (evidence of fresh metal swarf and drilling debris left in situ)

·        Approaching Halifax - but no thought of an immediate landing to examine the situation from the safety of the ground.

·        Fire had self extinguished but only because a mylar blanket wasn’t present (in that area) to propagate.

June 22, 1998, Air2000 B757- 200 enroute from Larnaca Cyprus to Manchester UK. From the UK's Air Accidents Investigation Branch (AAIB) report of this incident (Bulletin No 10/98, Ref. EW/G98/6/6) these extracts pertain:
        "When passing FL 255 there was a loud bang and a shower of sparks which emanated from the overhead panel. Simultaneously, the commander's air speed indication reduced to zero' his altimeter OFF flag appeared and multiple OFF flags appeared on his radio distance magnetic indicator (RDMI); the FO [first officer] ... retained control of the aircraft which he leveled at FL 270. By this stage a number of cautionary and advisory messages had appeared on the engine indication and crew alerting system (EICAS) display. The commander selected the alternate air data sources, which restored his ... altimeter. Meanwhile his VOR/DME controller display had gone blank, the center ILS had failed and multiple OFF flags had appeared on the standby attitude indicator which eventually toppled."  The commander completed the appropriate drills for the following EICAS messages: 'Spoilers', 'Left Yaw Damper' 'Standby Bus Off'. He was unable to restore power to the standby bus and since both the main and the Auxiliary Power Unit (APU) batteries were discharging he reset the standby power selector to 'Auto' in accordance with the drill. During the return to Larnaca the commander's flight director and the auto throttle failed and when descending through 5,000 feet the 'Right IRS DC Fail' message appeared on the EICAS and later a 'APU Batt No Stby' appeared. Two wires above the pilot’s head had chafed against a bonding lead, tripping the AC STBY Bus breaker and killing many systems. Other aircraft in the same fleet were also found to have inadequate wire clearance.
        Again, parallels and contrasts to the Swissair disaster:

·        Multiple simultaneous (but wholly disassociated) ongoing systems emergencies associated with a single initial explosive arcing event.

·        Problem for the above development – complex drills for unrelated malfunctions can have a mutually compounding effect (cf the result of SR-111 crew turning off cabin exhaust fans -in accordance with the checklist- leading to the fire propagation reversing its direction of travel into the flight deck)

·        Faulty routing, support and improper stand-off of wires

·        Captain loses most of his critical normal and standby flight instruments…plus some avionics

·        Crew declared an urgent (but not emergency) PAN situation (only) and didn’t upgrade it - despite continuing manifestations of elec failure.

·        Overweight landing carried out

Even the standby attitude indicator failed. All this stemmed from two wires shorting out to each other.



8 Jan. 4, 1998, BAC 1-11, during cruise between Belfast and Birmingham. From the UK's Air Accidents Investigation Branch (AAIB) report of this incident (Bulletin No 2/98, Ref. EW/C98/1/1) these extracts pertain:
        "Flight crew heard a series of 'popping' sounds and observed smoke coming from the 'hat rack' stowage area behind the captain's seat."
        "Senior cabin attendant ... saw an orange flame ... and fired a ... burst of extinguishant into the area ... but it reignited and two additional bursts ... were needed."
        "After closing the flight deck door, the flight crew donned their oxygen masks and transmitted 'Mayday.' " "A one-inch gap existed between the rear of the top shelf and the fuselage trim panel, which had allowed the oxygen mask pouch to fall onto the cables that were connected to the rear of the relay receptacle."
        "The relays ... formed part of a modification to the cabin lighting system."
        "The pouch acted as a thermal insulation blanket such that the normal amount of heat energy ... could not be dissipated at its usual rate, leading to elevated temperatures and eventual combustion of the pouch material and cable insulation.
        "There would have been no significant change n the current passing through the cables, thus explaining why the associated circuit breakers did not trip."
        "The 'popping' noise heard by the crew was not fully explained, but ...was probably due to the pouch material combusting." Photo
        Again, elements in common with the Swissair crash:

·        A post production modification.

·        Breakers not tripping.

·        Arcing, burned material resulting from a debris deposit

Mayday Emergency declared and a diversion to an immediate landing.
        All told, that makes four precursor events not long prior to the Sept. 2, 1998, in-flight electrically-stoked fire that downed Swissair Flight 111. Different aircraft, but common circumstances and common latent hazards. Four strikes, then death.*



Another case of wiring sandwiched next to flammable material, burned insulation blankets and circuit breakers which did not trip. In this case, the breakers installed were of the incorrect rating. Source: AAIB


 
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