Holding an autothrust disconnect button for more than how many seconds will cause a loss of ALPHA FLOOR protection for the remainder of the flight?

Holding the autothrust disconnect button for more than 15 seconds will indeed result in the loss of ALPHA FLOOR protection for the remainder of the flight. ALPHA FLOOR protection is an essential safety feature designed to ensure that the aircraft maintains adequate lift under certain conditions by automatically setting the thrust to maximum.

When the autothrust disconnect button is pressed, the aircraft's flight control laws interpret this as an intention from the pilot to override the autothrust system. If this button is held down beyond the specified duration, the system deactivates ALPHA FLOOR protection as a response to what it perceives as a pilot decision to forfeit that protection. This is crucial information for pilots since losing ALPHA FLOOR protection means they will not automatically receive maximum thrust if they encounter a situation where it's critical for maintaining lift and safety.

By understanding this timeframe, pilots can make informed decisions regarding the use of the autothrust system and the associated safety features it provides.