As the pilots of the doomed Boeing jets in Ethiopia and Indonesia fought to control their planes, they lacked two notable safety features in their cockpits.

One reason: Boeing charged extra for them.

For Boeing and other aircraft manufacturers, the practice of charging to upgrade a standard plane can be lucrative. Top airlines around the world must pay handsomely to have the jets they order fitted with customized add-ons.

Sometimes these optional features involve aesthetics or comfort, like premium seating, fancy lighting or extra bathrooms. But other features involve communication, navigation or safety systems, and are more fundamental to the plane’s operations.

Many airlines, especially low-cost carriers like Indonesia’s Lion Air, have opted not to buy them — and regulators don’t require them.

Now, in the wake of the two deadly crashes involving the same jet model, Boeing will make one of those safety features standard as part of a fix to get the planes in the air again.