A software fault on Apple iPads used by American Airlines pilots for navigation charts delayed some flights on Wednesday after affecting operations overnight.

About 40 flights ran late over Tuesday night and into early Wednesday, according to American Airlines and data compiled by tracking service FlightAware.com.

Pilots have been given instructions to fix the issue involving an application from a third-party vendor, said Andrea Huguely, an airline spokeswoman.

The fault isn’t affecting iPads used by all pilots, Huguely said. In some cases on Tuesday night, planes had to return to terminal gates so pilots could access Wi-Fi to fix the issue, Huguely said.

Pilots use iPads as part of their “electronic flight bag,” which was adopted by the airline in 2013.

It replaces more than 35 pounds of paper-based reference materials and manuals that flight crews carried onboard in the past.

Electronic navigation devices became available in recent years to private pilots before regulators approved the units for use in commercial operations, starting with charters.

The first such authorization came in December 2010.

- Bloomberg