WASHINGTON — Texting by the pilot of a medical helicopter contributed to a crash that killed four people, federal accident investigators declared Tuesday, and they approved a safety alert cautioning all pilots against using cellphones or other distracting devices during critical operations.

It was the first fatal commercial aircraft accident investigated by the National Transportation Safety Board in which texting has been implicated. And it underscored the board’s worries that distractions from electronic devices are a growing factor in incidents across all modes of transportation — planes, trains, cars, trucks and even ships.

While no U.S. airline crashes have been tied to electronic device use, the Federal Aviation Administration in January proposed regulations prohibiting airline flight crews from using cellphones and other wireless devices while a plane is in operation.

The regulations are required under a law passed last year by Congress in response to an October 2010 incident in which two Northwest Airlines pilots overflew their destination of Minneapolis-St. Paul International Airport by 100 miles while they were engrossed in working on their laptops.

Regulations already in place prohibit airline pilots from engaging in potentially distracting activities during critical phases of flight such as takeoffs, landings and taxiing.

The five-member board unanimously agreed that the helicopter crash was caused by a distracted and tired pilot who skipped preflight safety checks, which would have revealed his helicopter was low on fuel, and then, after he discovered his situation, decided to proceed with the fatal last leg of the flight.

The case “juxtaposes old issues of pilot decision making with a 21st century twist: distractions from portable electronic devices,” said board Chairman Deborah Hersman.

The helicopter ran out of fuel, crashing into a farm field in clear weather early on the evening of Aug. 26, 2011, near Mosby, Mo., a little over a mile short of an airport. The pilot was killed, along with a patient being taken from one hospital to another, a flight nurse and a flight paramedic.

One board member, Earl Weener, dissented on the safety alert decision, saying the cases cited as the basis for it — including the medical helicopter accident — were the result of bad decisions by pilots without a direct connection to the use of distracting devices.

Other board members disagreed. “We see this as a problem that is emerging, and on that basis, let’s try to get ahead of it,” said board member Chris Hart.

The pilot, James Freudenberg, 34, of Rapid City, S.D., sent 25 text messages and received 60 more during the course of his 12-hour shift, including 20 messages exchanged during the hour and 41 minutes before the crash, according to investigators and a timeline prepared for the board.

Most of the messaging was with an off-duty female co-worker with whom Freudenberg had a long history of “frequent, intensive communications,” and with whom he was planning to have dinner that night, said Bill Bramble, an NTSB expert on pilot psychology.