A blind door is a fake door that is really part of the wall. People use them to make a room look nice.
An up-and-over door is often used in garages. Instead of hinges, it rolls up on rails so that it stays above the opening.
A fire door is a door that does not let fire go through. They are usually made of heavy steel.
A doggie door is a small door for dogs or other small pets. They are usually on the bottom of people-sized doors.
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Boeing 737
The Boeing 737 is a twin narrow-body airliner built by Boeing. At first, Boeing was making it to be a shorter, cheaper airliner than its 707 and 727. However, the 737 has become a family of nine different models. The number of passengers it can carry ranges from 85 to 215. The 737 is the only narrow-body airliner that Boeing is making. The only types of 737 that Boeing is still making are the -700, -800 and -900ER. A version of the 737 with new engines and a new design, the 737 MAX, came into service in 2017 but was grounded in 2019 as unsafe.
Boeing began designing the 737 in 1964. The very first 737-100 flew in 1967. It was first used by an airline in February 1968. The 737-200 started being used in April 1968. The -200 was basically just a longer version of the 737-100. In the 1980s Boeing made the -300, -400, and -500 models. Boeing called these models the Boeing 737 Classic series. The 737 Classics could carry more passengers, and they had new engines: CFM56 turbofans. The 737 Classic planes also had some improvements made to the wings. In the 1990s, Boeing brought out the 737 Next Generation. The 737 Next Generation planes also had redesigned wings, a better cockpit and a new cabin. The 737 Next Generation is made up of the -600, -700, -800, and -900ER models. These models go from to in length.
The 737 is the best-selling jet airliner in history. Boeing has never stopped making 737s since 1967. 7,283 aircraft have been delivered, and the 737 still has 2,759 orders that have not been delivered yet (). Boeing 737s are built at the Boeing Renton Factory in Renton, Washington. The 737's main rival is the Airbus A320 family. On average, 1,250 737s are in the air at any time and two land or leave somewhere every five seconds.
Boeing was looking at designs for aircraft which flew short distances. Boeing wanted to make another aircraft to replace the 727 on short flights. It began designing the 737 on May 11, 1964. Boeing did a lot of research and found that airlines wanted an airliner which could hold 50 to 60 passengers. This airliner would also be able to fly routes long. Lufthansa was the first airline to order a Boeing 737 on February 19, 1965. They ordered 21 aircraft, worth $67 million (1965, $190.28 million in 2008). After Boeing spoke to Lufthansa in winter 1964, they made the 737 bigger so that it could hold 100 passengers.
On April 5, 1965, Boeing announced that United Airlines had ordered 40 737s. United wanted a plane which was a bit bigger than the 737-100. Boeing made a different type of 737 for United, which was longer. This other plane was called the 737-200. Boeing changed the name of the original 737 to the 737-100.
The first 737s were made near Boeing Field (now officially called King County International Airport) because the factory in Renton was too busy building the 707 and 727. After 271 aircraft were made at Boeing Field, Boeing moved the 737s to Renton. This was in 1970.
The first Boeing 737-100 prototype was ready in 1966. It made its first flight on April 9, 1967. On December 15, 1967 the Federal Aviation Administration said that the -100 was allowed to fly with passengers. They gave it the Type Certificate A16WE. Lufthansa got its first 737 on December 28, 1967. On February 10, 1968, Lufthansa became the first non-American airline to fly a new Boeing aircraft. It was the only large airline which bought the 737-100. Only 30 -100s were ever made.
The 737-200 first flew on August 8, 1967. The FAA allowed it to fly with passengers on December 21, 1967. The first flight it made for United Airlines was on April 28, 1968. It flew from Chicago to Grand Rapids, Michigan. Airlines liked the 737-200 much more than the 737-100.
A "thrust reverser" is a part of the engine of a plane. It changes the flow of air through the engine so that it ends up trying to push the plane backwards instead of forwards. The first thrust reversers on the 737 were not very good. They were said to lift the aircraft off the runway when they were used. This meant that the wheels were not being pushed down onto the ground very much, which made the brakes less useful. In 1968, Boeing improved the thrust reverser. This improvement was put onto all aircraft after March 1969. Aircraft which were made before the improvement could have it installed. Boeing also improved the flaps. This improvement allowed the flaps to be used more during takeoffs and landing. All these changes meant that the 737 could hold more cargo and fly further. In May 1971, after the 135th aircraft was built, all of these improvements, as well as better engines and more fuel, were put into the 737-200. This gave it 15% more payload and range than the first 737-200s. This type of 737-200 became known as the 737-200 Advanced.
In 1970, Boeing only got 37 orders for 737s. Since Boeing were running out of money, they thought about stopping making 737s and selling the design to Japanese companies. Boeing cancelled the Boeing Supersonic Transport and started making less Boeing 747s. By doing this, Boeing kept enough money to keep the 737 project going.
In 1988, Boeing stopped making 737-200s. 1,114 aircraft were made and the last one was delivered to Xiamen Airlines on August 8, 1988.
In 1979, Boeing started working on a large improvement for the 737. Boeing wanted to allow the aircraft to hold more passengers and travel further. It also wanted to make improvements to make the aircraft more modern. However, it also wanted to keep it similar to the older 737s. In 1980, information on this new type of 737 (called the 737-300) was given at the Farnborough Airshow.
The CFM56-3B-1 engine was chosen to be the engine for this new 737 type. This engine burned much less fuel and was much less noisy. However, it was also difficult to fit these engines to the aircraft. This was because the 737's wings were not very high above the ground, and the CFM56 had a bigger diameter than the original engines. Boeing and CFM solved the problem by putting the engine slightly ahead of the wing, instead of right under it. They also moved some parts of the engine, which would normally go on the bottom, to the sides. This made the engine look a bit like a hamster pouch, because the engine is not shaped like a circle.
The plane could now carry 149 passengers, because the fuselage of the plane was made bigger. Many changes were made to the wings. The tip of the wing was made longer by . The wingspan was also made bigger. The flaps on the wings were changed. The flight deck (cockpit) was improved with electronic displays. However, airlines could choose not to have these in their planes. The main cabin (where the passengers sit) was also made better. It looked similar to the cabin of a Boeing 757. The prototype of the 737-300 first flew on 24 February 1984. Its pilot was Jim McRoberts.
In June 1986, Boeing said that it was working on the 737-400. The 737-400 made the fuselage even bigger (by ). This change meant that the -400 could carry 170 passengers. The 737-400's first flight was on February 19, 1988. The first airline to use it was Piedmont Airlines.
Boeing made a 737-500 because its customers wanted one. It was a replacement of the 737-200. The -500 is longer than the 737-200. Up to 132 passengers can travel on the 737-500. Cockpits with electronic displays could be installed on the -500, but airlines could choose the use the older cockpit if they wanted.