Explain what “promulgated rules according to the informal rulemaking process” means.

The following three questions begin with a deadly explosion.
In 1988, terrorists bombed Pan Am Flight 103 over Lockerbie, Scotland, killing all passengers on board.
Congress sought to remedy security shortcomings by passing the Aviation Security Improvement Act of 1990, which, among other things, ordered the Federal Aviation Administration (FAA) to prescribe minimum training requirements and minimum staffing levels for airport security. The FAA promulgated rules according to the informal rulemaking process. However, the FAA refused to disclose certain rules concerning training at specific airports. Public Citizen, Inc. v. FAA