A jet engine flying in rain?

Jet engines can function normally in heavy rain (usually at during the takeoff and landing phases) since most engines are bypass engines which allows most of the water to pass through the engine and avoid the core compression section.

The water that does pass through the core of the engine turns to vapour, expands and exits out of the engine with no deterioration in thrust.

To avoid the possibility of a flameout the start switches (source for ignition) are set to continuouss to provide constant ignition and avoid a flameout.

Normally start switches are set to continuous during the takeoff and landing phase to increase the safety envelope of any possible flame out (due to bord/rain/snow/hail ingestion) and are then turned back to their normal position during cruise where non of these risks exist.

http://www.youtube.com/watch?v=faDWFwDy8-U

The following video shows the water bypassing the core of the engine.

rain can be a problem on the ground and during engine starts, but does not affect the performance noticeably when flying. The HARRIER Jump Jet actually injects De-mineralized water into the engine to increase power during hovering.

One thing you might not realize -

On heavy rain takeoffs (and with standing water on runway) - we put ignition (spark plugs) ON during takeoff - The engines DO ACTUALLY QUIT several times, during the takeoff roll, but RELIGHT IMMEDIATELY within a fraction of a second...!

When I used to fly 727s, that was quite noticeable -

water is vaporized, the amount of cooling is insignificant.