oicur12.again
In the airline I work for CC are allowed to contact the flight deck during the "Critical phase" (There are two: "From application of take off power until wheels-up" and "From Wheels down until exiting the runway")
There is only one situation where they are allowed to do so: and that is if they see visible flame in the cabin. If they do, they use the emergency call function and (when the pilot answers) state "cabin fire" and hang up.
Pretty simple.
DIVOSH!