But it has now been involved in two fatal crashes in just five months.

The Boeing 737 Max 8 entered the market in 2017, a part of the 737 Max class and became an instant hit.

Within the first six months more than 4,000 Boeing 737 Max 8 planes had been ordered.

It quickly became the company's best selling plane ever.

The new model was advertised as a rare win-win for both airlines and passengers.

It's going to give them max efficiency, which leads to profitability, max reliability, and to the flying public: max passenger appeal.

The demand for something new.

Boeing debuted the new planes in response to market pressures.

In late 2010, Boeing's archrival, Airbus, had just announced a new fuel-efficient version of its best selling A320.

Boeing countered with the introduction of the 737 Max.

The Max uses 14% less fuel than current 737s.

Its own version of fuel and cost efficient aircrafts.

Their message to customers was: these are new planes that aren't that new.

Newest arrival in the Boeing family of airliners, the 737 attracts a crowd.

Boeing's first 737 model took off in 1967.

"A new queen of the sky."

For the Max class, Boeing upgraded the engine and design.

They added more cabin space, bigger windows and multicolored ceiling lights to help modernize the planes.

But the company kept the 737 name because it evoked a legacy of reliability and built trust.

I'll tell you what, it's just a beautiful, beautiful airplane.

Not only were they able to modernize the airplane with new engines, and new winglets, but they were able to keep that classic iconic 737 look.

But that isn't the whole story.

The new model was also designed to help carriers save money.

Which means CEOs like the Max... Really like the Max.

Major changes to the plane would have required pilots to be retrained.

But Boeing's position was that the new models handled enough like the old ones.

Though the 737 Max 8 planes did actually have a number of changes, including the size and location of the engines.

The higher and more forward position of the larger engines can cause the plane's nose to pitch up, a potential danger.

To compensate for this, Boeing added a computerized system called M.C.A.S. to prevent the plane's nose from getting too high and causing a stall.

But the FAA initially said pilots did not need to be informed of this system update.

Experts say that the lack of training for the new system may have helped cause a deadly crash with a Max 8 off the coast of Indonesia in October, killing 189 people.

All of the Boeing 737 Max 8s in the world are believed to have been grounded, while a second crash in Ethiopia is investigated.

Boeing said it supported the decision to ground the planes and is cooperating with investigators.