The practice of selling fundamental features like communication, navigation, or safety systems as “add-ons” is rife within the airline industry, the New York Times reports.

What if: We can’t say for sure, but if they had been included, these two features might have helped the pilots involved in the Ethiopia Airlines and Lion Air crashes to detect erroneous readings. Investigators are closely inspecting new anti-stalling software included in the Boeing 737 Max planes, which are now grounded around the world. The system, called MCAS, is supposed to help push the plane’s nose down automatically to prevent it from stalling. It’s a measure that was included to counterbalance the jet’s larger engine.

The upgrades: One of them is called the “angle of attack indicator” and displays the readings of the two sensors that determine whether the plane’s nose is pointing up or down, relative to oncoming air. The other, a “disagree light,” turns on if those sensors contradict each other. They were missing from the cockpits of the planes that came down in Ethiopia earlier this month and Indonesia last October, according to the Times. Ethiopia Airlines and Lion Air had opted not to purchase the features. Many airlines choose not to buy them to save money, and regulators do not require them.

Damage control: Boeing is scrambling to respond to the crashes. It’s being investigated by the US Justice Department amid one of the worst airline scandals in years. Boeing has promised to release a software update to the new plane models next year and has said it will make the disagree light standard on all new 737 Max jets.

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