How safe is it to fly with best pilots?

Ever wondered why air crashes happen so frequently even with the best of pilots flying state-of-the-art automated jets? That's because humans are poor at monitoring tasks, according to a NASA-initiated study.

No wonder then that a majority of air crashes can be attributed to human error rather than technical glitches.

"Our study really does suggest that vigilance is a very difficult task for people," said co-researcher Jonathan Schooler from University Of California-Santa Barbara.

Pilots have to constantly monitor aircraft position, speed, altitude and an array of other automated functions as they appear on a computer screen during flight.

"Extended uninterrupted monitoring can be draining. The antidote to that is interruptions that break up the monotony, but we also found that the interruptions themselves contributed to lapses," Schooler explained.

"And people will spontaneously mind-wander, and that can also contribute to monitoring difficulties. It's a trifecta of things working against effective monitoring," he added.

Schooler and NASA pilot Steve Casner teamed up to examine why monitoring failures happen even among experienced and highly trained airline pilots.

For their study, they asked 16 commercial jet pilots to monitor the progress of a simulated routine flight in which high levels of cockpit automation handled the tasks of navigating and steering the airplane.

The researchers found that the cockpit environment is busy enough that pilots were often sidetracked by other tasks, such as talking to air traffic control or configuring the airplane's systems, which curtailed fatigue.

But they also discovered that these pop-up tasks could themselves cause pilots to miss important events during flight.

Most interesting, Schooler and Casner said, is what happened when the pilots weren't interrupted.

Rather than focusing solely on monitoring the flight, they instead created their own distractions by engaging in what the researchers call "mind wandering".

All in all, the researchers found, pilots missed 25 percent of all altitude crossings they were charged with monitoring. That's scary, no?

The study appeared in the journal Consciousness and Cognition.