By David Morgan

WASHINGTON (Reuters) - Amtrak engineer Brandon Bostian was not talking or texting on his cellphone when his speeding passenger train derailed in Philadelphia on May 12, killing eight people and injuring more than 200 others, federal crash investigators said on Wednesday.

Officials, however, are still trying to determine whether Bostian could have been using the device in some other way that would not have required a wireless connection, such as playing games or reading, according to the National Transportation Safety Board.

Bostian's attorney has said that the engineer turned off his cellphone, as required by federal regulation and Amtrak policy.

The train known as Amtrak 188 derailed along a northbound curve in Philadelphia while traveling at more than twice the 50 mile-per-hour (80 kilometer-per-hour) speed limit.

The NTSB findings represent a milestone for investigators, who had been bedeviled for weeks by complex and contradictory phone service data. But it leaves unanswered the key question of what caused the accident.

"Analysis of the phone records does not indicate that any calls, texts, or data usage occurred during the time the engineer was operating the train," the NTSB said in an investigation update.

Amtrak records also confirmed that Bostian did not use the train's Wi-Fi system to connect to the Internet, the NTSB said.

Officials do not know whether the phone was switched off or in 'airplane mode' at the time of the derailment. Airplane mode prevents a wireless device from transmitting signals but still allows the use of applications that require no data connection.

An NTSB laboratory in Washington has been examining the phone’s operating system in hopes of learning whether the device was turned on. "Investigators are obtaining a phone identical to the engineer’s phone as an exemplar model and will be running tests to validate the data," the agency said.

The 32-year-old Bostian, who suffered a concussion, has been at the center of an intensive effort by federal officials to identify a probable cause. Investigators have been sifting through a range of evidence to determine whether human error or a mechanical malfunction was the cause.

The engineer told investigators that he cannot remember anything after passing through a Philadelphia rail station moments before the accident.

Officials with the Federal Railroad Administration, which regulates passenger and freight rail travel, have pointed to the train's speed as a sign of possible human error.

(Reporting by David Morgan; Editing by Doina Chiacu and James Dalgleish)