Why are parachutes not used on commercial planes?

 You're asking a group of untrained members of the public to strap on a device they have zero training with, and figure out how to exit a plummeting jetliner, without hurting themselves. Passengers are not trained to use parachutes, which contrary to popular belief, involves more than just pulling the cord.

Some people are physically incapable of landing using a parachute safely, for example old people, kids, people with physical disabilities. Parachutes are tailored based on your weight, so what works for one person might not be enough for another. A study of all commercial airline accidents between 1983 and 2000 found that 95.7% of the people on board survived, which means staying with the aircraft is almost always the better option.

There is no convenient way to jump out of typical airliners. Just jumping out of normal side-facing airplane doors or emergency hatches, you would probably hit the wing or the tail. Exit airspeed would need to be 200 mph or less, but commercial jets fly at 500+ mph. Jumping from altitudes of more than 20,000 feet can cause hypoxia, unless you have oxygen to take with you. Most accidents occur at take-off and landing, where parachutes are of no use anyway.

Parachutes are bulky, heavy and expensive. They would not even fit under your seat, they would occupy a lot of space and add a lot of weight. They would also need regular inspection and repacking. To provide several hundred per airplane would add significantly to costs, making flying much more expensive.

Furthermore, accidents that result in deaths are usually the result of sudden catastrophic failure. The kinds of failure that do not allow for people to properly strap on a chute, bring the plane to a proper speed and altitude, and hold that speed and altitude while the passengers jump off in an orderly manner. Nearly every single accident out there is better managed by putting the large metal tube in the hands of a skilled pilot, and attempting to bring the whole thing down in as safe a manner as possible.

Why do planes turn lights off for takeoff and landing?

 First, it is worth clarifying that the pilots don't control the main cabin lighting, and it is actually the flight attendants who dim the cabin lights, not the pilots. The primary reason cabin lights are dimmed during takeoff and landing is safety, and it comes down to how human eyes work. It takes sometimes 30 minutes for eyes to adapt from a well lit environment to darkness, and a human eye can take up to 10 minutes to adapt from bright to dark.

Most airline accidents take place during takeoff and landing, so by dimming the cabin lights, your eyes get adjusted to the darkness outside and you would be better prepared in case of an emergency. The idea is to make the cabin environment similar to the exterior environment.

In case there is a serious emergency during the takeoff or landing and the people have to evacuate through the emergency exits and slides, one of the most likely problems would be that all electrics inside the aircraft go off too. If the cabin lights were very bright, safe evacuation would not be possible, as your eyes would take time to adjust to the outside brightness. Dimming the lights also makes the glow-in-the-dark floor pathways, which point you to the nearest exit, more visible, and people in aisle seats would notice them more easily when the lights are dimmed.

The requirement to raise window shades during these phases is connected to the same safety logic. With blinds raised, you can see potential hazards outside, and you know not to open a cabin door if there is a fire outside it. The passengers sitting at window seats can help other passengers and cabin crews by informing them in case of extreme emergency situations like engine fires. If there is a rescue team outside the aircraft, raised shades also help them see whether any passenger is there inside the aircraft.

As for seats being in the upright position, if there is an emergency situation and you are pushed forward, having your seat reclined means your head has more distance to travel before hitting the seat in front of you, resulting in more injury. In the event of emergency, a reclined seat will also create an obstacle for the person sitting behind you while evacuating.

It is worth noting that there is actually no regulation requiring blinds to be raised or lights to be dimmed during takeoff and landing. It is up to the operator of the aircraft or the airline's policy, though it is pretty rare that this format is not followed.

At what speed do planes usually take off?

 Boeing 737 usually takes off right around 150 MPH. It's also interesting that the acceleration rate is actually quite slow. It picks up speed more gradually than you'd think. Takeoff speeds vary tremendously from one aircraft to the next, and also can change for the same aircraft from one flight to the next based on such factors as the density altitude and the aircraft's weight.

Takeoff speed is determined by a number of factors including the specific type of aircraft, how heavily the aircraft is loaded, flap settings, length of the runway, and altitude of the takeoff airport. The weather can also have an impact as pilots may wish to take off at a higher speed in case of a sudden change of wind direction and resulting tailwind.

For smaller regional jets, takeoff is in the range of 115 to 130 knots. For aircraft such as Boeing 737 and Airbus A320 family, takeoff is in the range of 130 to 150 knots. For mid-size aircraft such as Airbus A330 and Boeing 757/767/777/787, takeoff is in the range of 140 to 165 knots. For larger double deckers such as Boeing 747 and Airbus A380, takeoff is in the range of 145 to 175 knots. Just as a sidenote, Concorde took off at around 200 knots with no flaps when fully loaded.

Most of the time, commercial aircraft with passengers on them will take off around 5 to 10 knots faster than the absolute lower limit for that configuration. This is just to allow the pilot to correct an excessive pitch up or incorrect power setting before it results in a classic departure stall. Takeoffs are broken down into several different speeds called V1, Vr, and V2. V1 is known as the decision speed because this is the speed at which you must commit to takeoff because there isn't enough runway to stop in time. Vr is the rotation speed and is the speed at which the pilot should begin to pull up off the runway. V2 is the safe takeoff speed, and once in the air V2 is the speed that means if an engine failure is suffered the aircraft can continue to climb.

Weight alone has little to do with takeoff speed. The design of the wing doing the lifting is much more important. That's why both an Airbus A340 and a Boeing 747 weighing half again as much take off at about 155 knots under normal conditions from a near-sea level airport.