WASHINGTON (AP) — A safety program that encourages air traffic controllers to voluntarily disclose their mistakes in exchange for amnesty from punishment needs significant improvement before it can work effectively, according to a report released Monday.

The program has been FAA’s primary answer to the problem of controller errors that bring planes dangerously close together. It encourages greater reporting of mistakes by promising not to punish controllers who disclose errors within 24 hours of an incident as long as the errors aren’t the result of gross negligence. The idea is to use the data gathered to better spot safety trends and take corrective action.