I've always wondered why we have to put our seats upright during takeoff and landing?
There are two main reasons for doing so - firstly, to reduce injuries to the minimum during a crash landing and secondly, the tilt of the economy seats (three inches or so) near the emergency exits may slow down the evacuation process.
How are injuries minimized? When the seat is tilted back, it's unlocked. In the event of an emergency crash landing, an unlocked seat creates more force during the impact. The thrusting forward of that seat can cause a greater impact on the passenger. Just like a catapult, the farther back the seat, the greater distance your head would travel during an impact and more force would be generated.
So, a reclined seat back could also kill or seriously injure the passenger behind if it should come unbolted or if the passenger behind it is thrown forward. Further, people sitting behind a seat that is reclined or unlocked would not be able to adopt the "crash" position or brace properly.
I have mentioned in previous FAQ that the US Regulations (FAR) require the manufacturer of commercial airplanes to demonstrate that all passengers can be evacuated quickly (within 90 seconds) in the event of an emergency on board. So if the seats leading to the exits are tilted, they would definitely impede the movement of passengers considerably.
Even in a non-emergency situation, moving out from the window seat would be an inconvenient process for passengers (or else some have to climb over the laps or seats in order to get to the aisle of the aircraft!)
The economy classes in most aircraft have an average seat pitch (the space between seats in a row) of about 31 inches. This is a tight fit with upright airplane seats. It is easy to imagine how small the space becomes when a seat back intrudes into the already narrow area.
Hence, all passengers are required to put their seats upright during takeoffs and landings.
A typical UA Safety Video Demonstration on a Boeing 777
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