"Put your seat belts and tray tables into their full upright and locked position is usually heard" in an Airplane when the announcements and safety rules are read out by the air hostess prior to take off or landing.

The primary purpose of instructing passengers to put their seat belts on and ensure that tray tables are in the upright and locked position is to prioritize safety. Seat belts are fundamental safety measures, designed to keep passengers securely in their seats in the event of turbulence, sudden maneuvers, or an unexpected change in altitude. This precautionary step significantly reduces the risk of injuries during critical phases of the flight.

Simultaneously, the instruction regarding tray tables serves a different but equally important purpose. Tray tables must be stowed in the upright and locked position to prevent obstruction during takeoff and landing. In the event of an emergency, having tray tables secured ensures that passengers can quickly and easily evacuate the aircraft without any hindrances. Additionally, it helps prevent potential injuries caused by loose objects during critical moments of the flight.

The phrase itself has become a routine part of the pre-flight safety announcements, emphasizing the importance of passenger cooperation in adhering to safety protocols. Flight attendants are trained to communicate these instructions clearly and assertively to ensure that all passengers are aware of the safety measures they need to follow.

So, the next time you hear the familiar command to put your seat belts and tray tables into their full upright and locked position, remember that it's more than just a routine announcement – it's a critical aspect of ensuring a safe and secure journey through the skies.