mickjoebill
2nd Oct 2007, 15:00
Heard a story that a UK travel company left an airbus parked up for three days during a cold spell "without ground power or heating"
On startup 3/4 of the LCD screens in seatbacks had failed.
So the story goes....
It is a fact that LCDs can fail if left in freezing conditions, is this enough reason to heat an aircraft whilst it is on the ground for more than a few days in freezing conditions? or is it it standard practice?
Mickjoebill
CJ Driver
2nd Oct 2007, 22:05
This story sounds unlikely as described - LCD technology is not particularly susceptible to damage in cold conditions.
Most people know that when they are sufficiently cold, the crystal properties in LCD glass become so slow that the displays become unusable. This behaviour is completely reversible; when the glass warms up again the display works normally.
Less widely known is that in extremely cold temperatures (around -30 C, depending on the material used) the liquid in the display does actually freeze. The "ice" crystals formed can be large enough and sharp enough that they physically damage the inner surface of the display. When the display warms up again, the crystals melt, and the display works as usual. But, the crystalisation process may have damaged the screen leading to "cosmetic" defects that were not already there (stuck pixels, for example). In fact, the freeze-thaw damage cycle is a game of statistics - most of the time you will get away with it without any visible damage at all, but sometimes you will be unlucky and spoil the display. The suggestion that a single freeze/thaw cycle would destroy 3/4 of the LCD's is therefore very unlikely.
There are other ways this could have happened - mostly involving poor choice of thermal coefficients of expansion on adjacent materials - but none of them sound particularly likely in modern electronic design.
I'm not familiar with Airbus systems, but I imagine that all the plumbing (galleys, toilets, etc) would represent a problem if a ground cold soak passed zero C - long before anything electronic might be expected to break.