The Boeing 737 Max is likely to be the last version of the best-selling airliner of all time

BoeingA Boeing 737 Max.
  • The Boeing 737 is best-selling airliner of all time.
  • There have been four distinct generations of the plane in the five decades years since the original 737-100 entered service in 1967.
  • The latest version, the Boeing 737 Max, entered service in 2017.
  • The plane we fly on today is very different in design and capability than aircraft that originally debuted.
  • The 737 platform has been effectively pushed the limit of its capabilities with the Max. Boeing will probably need to come up with a brand-new plane to take on the successor to the Airbus A320neo.

The US Federal Aviation Administration last week issued an emergency order to ground all Boeing 737 Max airliners flying in the US.

The decision came after two effectively brand-new 737 Max 8 jetliners crashed under strikingly similar circumstances within four months.

The grounding brings fresh attention to Boeing’s game-changing 737 family of narrow-body airliners.

Over the past five decades, Boeing has sold a whopping 15,000 of the planes, the most of any airliner.

Currently, Boeing boasts a backlog of 5,826 planes worth upwards of $US400 billion; 80% of those orders are for the 737.

Read more: The Boeing 737 Max is embroiled in controversy after 2 deadly crashes in five months. Here’s how the plane came to be.

Since entering service in 1967, Boeing has introduced four distinct generations of the 737, the latest being the Max.

With each new generation, the 737 got bigger, more powerful, more capable, and more advanced.

Boeing 737 100 LufthansaLufthansaA Lufthansa Boeing 737-100.

What started as a 93-foot-long, 100-seat short-range airliner has morphed over the years into something quite different.

The upcoming 737 Max 10 airliner is 53% larger at nearly 144 feet long, and it can carry up to 230 passengers. It can also fly three times as far as the original 737-100.

“The mission today is certainly much more extensive than the mission you would see with the 737-100/200,” Vinay Bhaskara, an analyst for trade publication Airways, said in an interview.

As the 737 expands in capacity and capability, many in the industry are asking just how far Boeing can push the 50-year-old platform.

“Boeing has always made fantastic, safe aircraft,” Ross Aimer, the CEO of the airline consulting and legal firm Aero Consulting Experts, told Business Insider. “But in the case of 737, a simple way to describe it is, how many times can you modify your old 1980s Honda Civic? This is basically what Boeing is doing with the 737.”

Aimer said that the original 737-100 Boeing delivered to launch customer Lufthansa in 1967 is a “totally different aeroplane” than the jet we fly on today. “Now it has evolved into the something else,” he said.

According to long-time aviation analyst Richard Aboulafia, Boeing has pushed the 737 platform to its limit with the Max.

“Yes, it’s the last iteration,” Aboulafia said. “They ran out of steam in terms of range and capacity.”

In other words, the Boeing 737 has maxed out in terms of range and passenger capacity.

“The 737 Max 8 is doing great against the Airbus A320neo, but the 737 Max 9 and Max 10 are getting clobbered by the A321neo,” Aboulafia said. “At the top end of the market, Airbus has the better-sized platform. The market is clearly showing that.”

In other words, the next time around, Boeing will need a brand-new plane to take on the successor to the Airbus A320neo.

The primary limiting factor for the 737 is the space underneath its wings.

Boeing 737 MAX 7BoeingThe 737 Max’s CFM International LEAP 1B engine.

There is a direct correlation between the diameter of a turbofan engine’s fan blades and the amount of thrust the engine can produce. Generally speaking, the larger the fan diameter, the more powerful the engine.

“This is a game of fan diameter and bypass ratio,” Aboulafia said. “Boy, the A320, you can 81 inches of fan diameter under there, the 737 maxed out at 69 inches and change. That’s a big difference.”

The Airbus A320neo, the 737 Max’s archrival, is powered by the new CFM International LEAP 1A engine that boasts a fan diameter of 78 inches and produces a maximum of 35,000 pounds of threat each.

Unfortunately, Boeing couldn’t get that engine to fit underneath the wings of the 737.

After all, the 737 was originally designed in the 1960s to use the Pratt & Whitney JT8D low-bypass turbofan engines that have a fan diameter of about 40 inches.

Airbus A320neoAirbusAn Airbus A320neo.

Instead, Boeing went with the next best option, the LEAP 1B engine that’s smaller and 20% less powerful with 69-inch-diameter fan blades.

Even then, it had to move the mounting point of the 737 Max’s engine forward and farther up.

This change disrupted the plane’s center of gravity and caused the Max to have a tendency to tip its nose upward during flight, increasing the likelihood of a stall. In response, Boeing engineers created the Manoeuvring Characteristics Augmentation System, or MCAS, to automatically counteract this tendency and point the nose of the plane downward.

This brings us back to the tragic crashes of Ethiopian Airlines Flight ET302 and Lion Air Flight JT610. Even though the crash investigation is still ongoing, initial reports from the Lion Air investigation indicate that a faulty sensor reading may have triggered the 737 Max’s MCAS shortly after the flight took off. Observers fear that a similar thing may have happened on the Ethiopian Airlines flight.

Boeing is working on a software update for MCAS.

Rachel Premack contributed reporting.

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