This has nothing to do with it... It doesn't matter what the Air-Cycle machine does... The only thing that the AC might do is cool the air so much that Ice-pellet starting to fly out from the ducts... but this is not the case of the water dripping from the ceiling...


However, YVR Cockroach is correct... it has all got to do with relative humidity... with Hong Kong (and most of South East Asia and most of tropics) being so humid, once the Air-Cond is fire up after Engine start (ground cooling doesn't count as they are not very powerful), the Air-Cycle machine will often cool down the air too quickly... a lot of time with a very warm cabin, it will pump out cold air from the pipe that is only a few degree Celsius, as the system is trying its best to cool the cabin to the preset temperature set at the cockpit / flight attendent panel (hence the ice pellet or the white moist air coming out from the vent)... however air this cold will also cause condensation at the inside of the aircraft fuselage inside the overhead crown space (just above the overhead bins)... once enough condensation occurs, water starts to fall into the cabin between the overhead panels...

This is especially worse on Boeing 747 and 777 because the overhead crown space (space between the overhead ceiling and overhead bin and the actual fuselage) is so much bigger than any of the Airbus aircraft... hence there are more moisture trapped...

So this is not a problem with CX... it is a fundamental design of the Boeing 747 & 777... It also sometimes happens on Airbus on a very moist and humid day as well...

Just my two cents...