The crash led to widespread public mourning for the retired basketball star and several lawsuits, and prompted state and federal legislation.
There was no sign of mechanical failure and the pilot was not under the influence of drugs or alcohol, investigators said.
But NTSB investigator-in-charge Bill English said the system, which was not on the helicopter, would probably not have prevented the crash.
Federal lawmakers have sponsored the Kobe Bryant and Gianna Bryant Helicopter Safety Act to mandate the warning systems on all helicopters carrying six or more passengers.
Island Express Helicopters Inc. denied responsibility and said the crash was “an act of God” that it could not control.