Prior to takeoff, we'll need all baggage to be stowed properly.

Your seats move to the upright position and your seat belts securely fastened.

Thank you.

Once everyone's set, the plane lurches away from the terminal and the lights inside the cabin go out.

It happens without mention.

You may not have even fully noticed that it does happen.

One reason has to do with what's called "the 90-second rule."

It's a guideline that dictates many of the mundane, but absolutely crucial in-flight procedures.

In the 1920's, the preflight routines we now know by heart were nonexistent.

Basically, pilots would tell passengers to put on a parachute and briefly show them how to use it.

During that time, commercial air traffic saw a death for every 13,500 miles flown.

It's not good.

But there was one airline that performed much better than the industry median.

That was the government-owned air-mail system and it was run with an eye on safety.

Pilots were selected after careful medical examinations, engines were checked once every 100 hours of flight time, and after every single flight, there was a 180-point inspection checklist.

Because of that thoroughness, the air mail system saw a fatality for every 789,000 miles flown.

The industry took notice and things started to change.

By 1935, the Aeronautics Branch, now called the Bureau of Air Commerce had a list of new safety regulations.

Some of those new rules for planes were the requirement of co-pilots, two way radios, limits on the hours pilots can be in the air, and that planes needed to have multiple engines, get the ability to fly on one engine in the case of an emergency.

By 1937, the number of pilots increased from 1927 by 700 times.

Meanwhile, deaths went down 10 times over that same time period.

In 1967, the Bureau of Air Commerce became the Federal Aviation Administration.

Soon after, they required all airlines to include oxygen masks, flotation devices, and emergency exit markings making it clear to passengers where the closest exits are.

All part of what's called the 90-second rule.

The 90-second rule requires airlines using planes with a capacity of 44 people or more to be able to demonstrate the ability to conduct an emergency evacuation in 90 seconds or less.

Even if half the exits are blocked.

Even today airlines have to run tests to prove to the FAA that they comply.

The Discovery Channel filmed a 90-second test for an Airbus A380.

It's dramatic stuff.

Believe it or not, one of the major hurdles to being successful in the 90-second rule is people trying to grab their belongings to take with them.

Leave your stuff.

So, that leads to our initial question, why do planes turn off their lights within the cabin at takeoff and landing?

The lights inside the cabin are turned off because of the time it takes for eyes to adjust to the dark.

If an emergency during takeoff or landing caused the lights to suddenly go out, no one's eyes would be adjusted making it harder to evacuate, especially in 90 seconds.

The retina at the back of the eye has two kinds of cells, rods and cones, which take light in turning them into neural signals.

The cones help when it's light out and rods handle seeing at night.

When the lights go out, the cones adjust faster—within nine to 10 minutes.

While the rods whose job it is to handle low light can take as long as 30 minutes to see as well as they'll be able to.

There's a good reason why the lights are turned off specifically at takeoff and landing.

That's when most plane accidents occur.

Boeing looked into accidents that led to fatalities from 2006 to 2017.

They found that 13 percent happened within the first three minutes of the flight, which is takeoff in the initial climb, while 48 percent of accidents that caused fatalities happened during the final descent and landing, which are the last eight minutes of the flight.

Along with the lights being dimmed, the whole pre-flight routine is providing passengers with the directions to get to safety as fast as possible.

The only thing that the 90-second rule can't plan and test for is that during an emergency, people are going to panic.

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