What's one plausible relationship between:
1. the incident below at bottom (which, according to latest ATSB revelations a few days ago, remains insoluble),
2. BA038 and
3. the A320 crash off Perpignan [Toulouse] (and maybe a few others)?
.
Answer:
The ability of water to free-flow migrate to different parts of a labyrinthine piped system, be it LP fuel or static air line - and coalesce into a static and blocking frozen mass, obstructing flow-rates and constricting sensor input data pick-offs. Think suddenly replacing engine oil with heavy duty grease.
Explanation:
A. When water is in solution in fuel or merely a frozen lump attached to a crevice in a tank, it's harmless. When water is free-flowing in a pneumatic static air pressure system all it does is slightly/imperceptibly dampen rates (ASI speed-changes, VSI, altimeters).
However when an icy lump dislodges due to fuel level changes, turbulence, warming, structural flexure etc, it can rapidly move, without any symptoms, to a position where it can critically obstruct flows.
.
B. When water in a static line moves to an area where it can freeze and obstruct ambient pressure changes from reaching sensitive transducers, then ADIRU data can become corrupted. This can happen suddenly and, courtesy of the software, produce abrupt and unexpected results. Think the difference between anti-skid braking on a slippery surface at 100knots - and simply selecting the parkbrake ON (at that speed).
The point being made is that the metamorphosis from free-flowing water to static and obstructionist ice-block is very capable of defeating system design software and producing sudden unexpected outcomes.
Not a lot is known about the behavior of water in a system of non-homogenous temperatures that is also subject to a wide range of flow-rates
.
When that metamorphosis is transitory and ephemeral, the phenomenon can be a difficult one to envisage, let alone replicate. It's the same problem with a wiring fire. Did the wiring flash-over and a fire cause the crash OR was all that burnt wiring just burnt in the post-crash fire?
.
Those of us ho have experienced the rapid confusing loss of flight instrumentation in the climb due to frozen pitot or stati lines will be ready converts to this theory. Those who went on to fly modern aircraft where the same systems can become flummoxed by such data corruptions would be less easily convinced - unless they were participants in the incidents mentioned (or similar). If you're not convinced about the effect that water can have upon a computer, I urge you to empty an ice-tray on your keyboard and stand back.
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At 0932 local time (0132 UTC) on 7 October 2008, an Airbus A330-303 aircraft, registered VH-QPA, departed Singapore on a scheduled passenger transport service to Perth, Australia. On board the aircraft (operating as flight number QF72) were 303 passengers, nine cabin crew and three flight crew. At 1240:28, while the aircraft was cruising at 37,000 ft, the autopilot disconnected. That was accompanied by various aircraft system failure indications. At 1242:27, while the crew was evaluating the situation, the aircraft abruptly pitched nose-down. The aircraft reached a maximum pitch angle of about 8.4 degrees nose-down, and descended 650 ft during the event. After returning the aircraft to 37,000 ft, the crew commenced actions to deal with multiple failure messages. At 1245:08, the aircraft commenced a second uncommanded pitch-down event. The aircraft reached a maximum pitch angle of about 3.5 degrees nose-down, and descended about 400 ft during this second event.
At 1249, the crew made a PAN emergency broadcast to air traffic control, and requested a clearance to divert to and track direct to Learmonth. At 1254, after receiving advice from the cabin crew of several serious injuries, the crew declared a MAYDAY. The aircraft subsequently landed at Learmonth at 1350.
Currently available information indicates that one flight attendant and at least 13 passengers were seriously injured and many others experienced less serious injuries. Most of the injuries involved passengers who were seated without their seatbelts fastened. This constituted an accident under the ICAO definition outlined in Annex 13 to the Chicago Convention and as defined in the Transport Safety Investigation Act 2003.
Examination of flight data recorder information indicates that, at the time the autopilot disconnected, there was a fault with the inertial reference (IR) part of the air data inertial reference unit (ADIRU) number 1. From that time, there were many spikes in the recorded parameters from the air data reference (ADR) and IR parts of ADIRU 1. Two of the angle-of-attack spikes appear to have been associated with the uncommanded pitch-down movements of the aircraft.
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