Boeing 737: Much more than just the Max
Now 50 years old, the 737 family became the best-selling commercial airplane in history. Then came the deadly 737 Max crashes.
Following two crashes that killed 346 people, the Boeing 737 Max remains grounded around the world. Boeing is rushing to fix the MCAS flight control software that's now at the center of both crash investigations, but at present there's no timeline as to when the Max will carry passengers again.
It's a troubling situation for an aircraft barely three years old, but the Max is only part of the 737 story -- other models are still flying. As of the end of March, Boeing had delivered 10,533 of its 737s to hundreds of airlines, making it the best-selling commercial aircraft in history. Chances are you've flown on one -- at any given time, thousands of 737s are airborne around the world, and some airlines, like Southwest and Ryanair, have all-737 fleets.
In 2018, Southwest took delivery of the 10,000th 737. The airline has the world's largest 737 fleet.
When the company delivered the 10,000th aircraft last year before the Max crashes, Boeing Commercial Airplanes President and CEO Kevin McAllister called it the most reliable and efficient single-aisle airplane in the world.
"It represents more than 50 years of success and achievement on the part of thousands of Boeing employees past and present, our supplier partners, and our airline customers around the globe who put their confidence in the 737," he said.
Sure, it lacks the glamor of Boeing's 747 and the novelty of the 787 Dreamliner, but the 737 has been a global workhorse for half a century, with more than 122 billion miles flown under its belt. Here's how the first 737 to fly progressed to the Max 8.
A need to go small
Boeing started developing the 737 in 1964. At the time it had two jet airliners in service, the 707 and 727. The 707, which first flew in 1957, had largely started the commercial jet age and was a fixture on transcontinental and transoceanic routes. The smaller 727, which first flew in 1963, would go on to be a hugely successful airplane that extended jet travel to shorter domestic flights.
Though 727s made Boeing one of the biggest commercial aircraft manufacturers by the mid-1960s, the company realized it needed to fill a hole at the bottom end of its product line. Douglas Aircraft, Boeing's then-archrival, had announced the DC-9 in 1963, and the British Aircraft Corporation was building the BAC1-11. Both aircraft were smaller than the 110-passenger 727 -- the first DC-9 fit 90 passengers -- and with two engines instead of the 727's three, they were cheaper to operate. Boeing needed a new plane to stay on top.
Developed for the short-to-medium haul market, the 727 trijet debuted on Dec. 1, 1962.
Designing an airliner
The 737 was that aircraft. To effectively match the DC-9 and BAC1-11, it also could have only two engines. But instead of mounting them near the aircraft's tail, engineer Joe Sutter decided to mount them under the wings. (Sutter would go on to lead the development of the 747.) That position brought a few advantages: It saved weight, decreased noise in the cabin and allowed for better airflow into the engines. It also let Boeing use the same fuselage cross-section as the 707 and 727, which cut development time and costs and accommodated more passengers through six-abreast seating rather than the DC-9's five-abreast cabin.
The 90-passenger Douglas DC-9 first flew in 1965.
But wing-mounted engines also brought a design challenge. Though maintenance crews could perform repairs without climbing a ladder, their proximity to the ground makes the engines more likely to ingest debris while the plane is taxiing. Attaching the engines directly under the wings rather than hanging them on pylons gave enough clearance. But to operate on unpaved runways -- a reality for an aircraft designed for remote airports -- some 737s required "gravel kits" on the nose gear and engine cowlings to deflect debris. After four years of design and testing, the 737 first flew in 1967 and entered service the next year with Lufthansa.
The Baby Boeing
Sales for the "Baby Boeing" were slow initially -- Boeing even considered selling the program to Japanese firms -- but they picked up after Boeing redesigned portions of the wing to reduce drag and built more effective thrust reversers for landing on short runways. Another boost came a few years later when the Airline Pilots Association removed its objection to eliminating the flight engineer position for US airlines (a two-person flight crew made the plane cheaper to operate).
Ten years after its introduction, the 737 was finally a hit with airlines. Its size made it perfect for short-haul, high-frequency routes, like San Francisco to Los Angeles. Its low position to the ground also meant that it didn't require extensive airport equipment. Ground crews could load bags in the cargo hold without a lift, and some early 737s even had integrated airstairs. All are key to keeping the airplane flying.
"Small jets can log up to six or seven flights per day," Sutter wrote in his 2006 book, 747. "The less time they spend on the ground between flights, the more time they can be in the air generating revenue for their operators. If I kept the design of the 737 low to the ground, it would turn around more quickly and be back in the air sooner because no time would be wasted positioning equipment."
Today the 737 remains a regional shuttle and it can fly the transatlantic routes the 707 pioneered. Though suppliers around the world contribute parts (the fuselage sections are largely built in Wichita, Kansas), final 737 assembly still takes place at Boeing's factory in Renton, Washington. And over the last 50 years Boeing has continually expanded its size and capabilities, always building on, and never completely replacing, that original 1960s design.
United Airlines encouraged the development of the 737-200.
737 Original
Per the requirements of Lufthansa, the 737-100 could fit 100 passengers and had a range of 1,540 nautical miles or 1,772 miles. As long as it was wide (94 feet by 93 feet), its square, stubby profile gave it the appearance of a beer barrel with wings or a flying football. Only 30 of the 737-100 versions were built, none of which are flying today.
United Airlines took an early interest in the 737, but wanted it to be bigger. That plane became the 737-200, which also entered service in 1968. Six feet longer than the 737-100, it could fit about 120 passengers and had more powerful engines and longer range (2,600 nautical miles) thanks to a higher fuel capacity. A hallmark of both the -100 and -200 were long, cigar-shaped engines that extended forward of and behind the wing.
The long engines of the first two 737 versions fit snugly under the wings.
With the -200, Boeing also built the first cargo 737s and the first versions of its "Combi" aircraft. The Combi is divided in half, with passengers in back and cargo in front. They were popular with carriers like Alaska Airlines for service to rural communities. The -200 remained in production until 1988 after more than 1,000 were built, but it began to leave the skies at the end of the 1990s as airports introduced more stringent noise restrictions. Some -200s remain in service today, but are outfitted with "hush kits" that dampen jet noise.
An Alaska Airlines 737 Combi with cargo space in the front and the passenger cabin in the back.
In 1991, a United Airlines 737-200 crashed on approach to Colorado Springs Municipal Airport, killing all 25 people aboard. It was the first of two 737 crashes -- the second, in 1994 near Pittsburgh, killed 132 people -- that were later blamed on faulty valves that caused the rudder to move without the pilot's command. Following a 1999 FAA order, all 737s received new valves.
737 Classic
By the 1980s, airliners were asking for a larger 737 with more seats, longer range, quieter engines and a cheaper operating cost. Boeing answered with the 737-300 in 1984. It was the first of what's now called the "737 Classic" series. Airline deregulation in 1978 also created more demand for 737s as new and existing airlines added new routes to small airports.
Lufthansa, the 737 launch customers, also flew the 737-300.
"Small jetliners like the 737 brought the jet revolution to towns and cities that hitherto had been served by piston-powered planes, and they spawned a steady growth in air travel," wrote Robert J. Sterling in his 1986 book, The Jet Age.
The 737-300 fit about 140 passengers and had a range of 2,255 nautical miles. The 109-foot-long aircraft ditched the cigar engines for more powerful and fuel-efficient turbofans with a contemporary barrel shape. But because the new engines were bigger, Boeing had to flatten the bottom of the nacelle into a "hamster pouch" design to allow for enough ground clearance without raising the 737 higher (doing so would have negated those ground equipment advantages). The -300 also was the first of the luxurious Boeing Business Jets, which the company sells as VIP private aircraft.
A sample interior of a Boeing 737 Business Jet
Launched in 1988, the 119-foot-long 747-400 had seats for about 160 passengers. Though its range was slightly less than that of the -300 (2,060 nautical miles), it was enough for a route like San Francisco to Chicago. The 737-500 went the opposite direction the next year by shortening the fuselage to 101 feet and cutting the number of seats to about 122, but it boosted range to 2,375 nautical miles. Boeing stopped production of the Classic series in 2000 after building more than 2,000 aircraft (the -300 was the most popular version), but some are still in service today.
The flattened "hamster pouch" engine nacelles on this Qantas aircraft.
737 Next-Generation
The 737 achieved its best-selling status as the 1990s dawned, but Boeing faced a new threat from Airbus. The European consortium in 1987 introduced the A320, which became the 737's biggest competitor when it entered service the next year. Airbus touted the A320's glass cockpit (where electronic displays like and later LCDs replaced mechanical gauges to show flight information like altitude and speed) and the fact that it was a completely new design.
A 737-800 in the livery of Ryanair, another large 737 customer.
Boeing struck back with the 737 Next-Generation series, which would go on to include four models. These were the first 737s with winglets, full glass cockpits and the range to fly long overwater routes like the US West Coast to Hawaii. There were other changes throughout like a redesigned cabin, a new wing for more efficient aerodynamics and a new electrical system. Despite the changes, though, the 737 Next-Generation was built to be familiar to 737 Classic pilots. According to Guy Norris and Mark Wagner in their 1999 book, Modern Boeing Jetliners, it was a deliberate choice.
The 737-900ER is still in production.
"Boeing was trying to sell the Next-Generation to as many existing 737 operators as possible," they wrote. "It would be a lot easier to convince them to buy the aircraft if the same crews could fly both types without expensive retraining."
To date, almost 7,000 Next-Generation 737s have been built, with all but the -600 still in production.
737 Next-Generation Versions
| 737-600 | 737-700 | 737-800 | 737-900ER | |
| First flight | 1998 | 1997 | 1997 | 2006 |
| Length (in feet) | 102 | 110 | 129 | 138 |
| Seats | About 123 | About 140 | About 175 | About 193 |
| Range | 3,235 nautical miles | 3,445 nautical miles | 3,085 nautical miles | 3,235 nautical miles |
737 Max
Boeing's newest airliner, and the latest generation of the 737 family, was another response to a move by Airbus. Introduced in 2016, the Airbus A320Neo promised lower operating costs from completely new engines that burned less fuel. Though Boeing initially considered replacing the 737 with a brand new airliner, it instead followed Airbus' lead by adding new engines to the existing fuselage. The reason? As The Air Current's Jon Ostrower wrote earlier this year, designing a new airplane is immensely expensive and would have taken years. On the other hand, revamping Boeing's baby again would get the Max in the air faster to compete with the A320Neo. What's more, like with the transition from the Classic to the Next-Generation, existing 737 pilots would be able to fly the Max without training on the aircraft anew. After the crashes, though, that decision and the FAA's certification process, are being criticized.
The engines Boeing adopted were more powerful and efficient and larger still. In order to fit them in that same position under the wing, the company's designers had to move the engines slightly forward. But that modification changed how the plane handled in the air, creating a potential for the nose to pitch up during flight.
Of the four 747 Max versions, only the Max 10 has yet to fly.
To overcome that action -- raising a plane's nose too high during flight can cause it to stall -- Boeing then added the Maneuvering Characteristics Augmentation System (MCAS) system, which automatically pushes the Max's nose down when sensors on the fuselage detect it's too high. And it's that chain of decisions -- larger engines and the need to add MCAS -- that's now under scrutiny. According to the preliminary investigations from both 737 Max crashes, faulty sensors may have been feeding incorrect data to MCAS, constantly activating it when it wasn't needed. As the airplanes continually dove just after takeoff, flight crews struggled unsuccessfully to regain control.
Up until the crashes, Boeing called the 737 Max the fastest-selling airplane in its history. To date it has delivered 387 aircraft, with another 5,012 on order. Boeing is still building the plane and few airlines have cancelled their existing orders. There are four versions in the series.
737 Max Versions
| 737 Max 7 | 737 Max 8 | 737 Max 9 | 737 Max 10 | |
| First flight | 2018 | 2016 | 2017 | Still in development |
| Length (in feet) | 116 feet | 129 | 138 | |
| Seats | About 153 | About 178 | About 193 | About 204 |
| Range | 3,850 nautical miles | 3,550 nautical miles | 3,550 nautical miles | 3,300 nautical miles |
More 737s?
With the Max only a few years old, Boeing is a decade away at least from announcing another 737 version, if it does so at all. If history is a guide, though, we won't see another. The 747, which first flew in 1969, is now at the end of its life.
In any case, Boeing's focus for now is on getting the Max back in the air and regaining the confidence of airlines and passengers. And after 346 deaths, the company has a lot of work ahead of it. But grounded aircraft have gone on to enjoy success before -- the Douglas DC-10 had a long career after two catastrophic crashes in the 1970s that killed 617 people and the now-popular 787 was briefly grounded after nonfatal battery fires in 2013 -- so the 737 Max will likely return to the skies again.