Today the Federal Aviation Administration (FAA) gave Boeing the approval for the 737 Max to fly again.
The 737 Max was grounded for around 20 months, due to two crashes that killed 346 people.
Investigators focused on anti-stall software that Boeing had devised to counter the plane's tendency to tilt nose-up because of the size and placement of the engines. That software pushed the nose down repeatedly on both planes that crashed, overcoming the pilots' struggles to regain control. In each case, a single faulty sensor triggered the nose-down pitch.
According to Boeing the cost for the process of approving the plane again, cost more than $20 billion.
The FAA action is only the first step in allowing 59 airlines which own the 387 grounded planes to fly them as part of their schedule. The FAA said in a statement before any of the planes can be flown with passengers again, the necessary changes to the 737 Max identified in the approval process must be installed, the FAA must inspect the individual planes. The pilots must also complete additional training.
The FAA will let Boeing resume delivery of newly produced 737 Max aircraft, which will have the design changes in place.