In 2004, a helicopter flying at night over the Gulf of Mexico plunged into the water, killing all 10 people on board. Had the aircraft been equipped with a system to warn the pilots of the impending impact, the crash could have been prevented, investigators for the National Transportation Safety Board determined.

The board urged federal regulators to require installation of the system on all helicopters. “It is well past time for the benefits from these standard safety devices to be made available to passengers on helicopter transports,” the board’s acting chairman said when announcing the recommendation in 2006.

Fourteen years later, use of the system is still voluntary. The helicopter that plowed into a fog-shrouded hillside near Calabasas, Calif., on Sunday, killing the retired basketball star Kobe Bryant and eight other people, was not outfitted with the system, known as a terrain awareness and warning system, or TAWS, said the N.T.S.B. board member Jennifer Homendy.

“Certainly, TAWS could have helped to provide information to the pilot on what terrain the pilot was flying in,” Ms. Homendy said at a news conference on Tuesday.