Final answer:
The message 'CHECK TAKE OFF DATA' signals that the pilot must verify and confirm the takeoff performance data after a change in departure runway to ensure the plane's safety and efficiency during takeoff.
Step-by-step explanation:
When the scratchpad message CHECK TAKE OFF DATA appears after correctly updating the departure runway in the Flight Management and Guidance System (FMGS), it indicates that the pilot must verify the takeoff performance calculations. These calculations include factors such as V-speeds, thrust settings, and flex temperature, which may all vary based on runway length, surface condition, obstacles, and aircraft weight.
It is essential to ensure the safety and efficiency of the takeoff by confirming that these variables are correct for the new departure runway. Failure to do so could result in inadequate performance margins during takeoff. Therefore, the flight crew should meticulously review and, if necessary, update the takeoff performance data in line with the new runway's attributes before proceeding with the takeoff roll.