Nearly 6,000 Airbus A320 passenger planes have now completed a round of software patches. The fix comes about a month after a software error caused a JetBlue flight to unexpectedly lose altitude and make an emergency landing. More than a dozen people were injured.

Airplanes these days are a lot more than engines and wings and tiny bathrooms.

To oversimplify a bit, modern aircraft are flying computers, said Samuel Engel. He researches the economics of air travel at Boston University and said most planes these days are so-called fly-by-wire. 

“That is, the pilots are manipulating a small joystick that is, that is sending messages to the computer,” he said, which then signals the mechanical parts to move. Before, that was done via cables or hydraulics.

All the on-board software has two main jobs, said Mike Stengel of Aerodynamic Advisory.

“Number one is keeping the aircraft in its safe flight envelope. You know, not letting it bank too hard to the left or right. Not letting it enter stall territory,” he said.

The computers also ease the workload for the pilots, Stengel said, “so you can literally reduce the number of switches on a plane.”

He said that since software has become so important to flying, Boeing and Airbus are relying less on outside suppliers for it.

“The aircraft manufacturers have gotten more heavily involved in the designing and developing the software that goes into the aircraft,” Stengel said.

There could be risks in letting computers take on so much work. Dan Bubb at the University of Nevada, Las Vegas, said some investigators think malware contributed to a deadly crash in Spain in 2008.

And even though that hasn’t been confirmed?

“That set off the alarms and made every airline manufacturer aware of, now we have another challenge: cyber attacks,” Bubb said.

Overall though, software has helped make air travel safer, said Nicolas Owens, an analyst at Morningstar. And just like many of the mechanical systems, there’s redundancy built into aircraft computer systems.

“You have more than one flight computer controlling each of the various ailerons and rudders and elevators and so forth,” he said.

And if the computer systems fail at the same time, Owens said there are still ways for pilots to take back some control with their own human hands.