Among the air traffic controller’s many tasks is to monitor aircraft and issue safety alerts if it appears they might be too low, or flying toward rising terrain. Controllers generally have some help with this task – the minimum safe altitude warning (MSAW) and conflict alert systems installed at terminal and en route facilities. Together with some training and standards, the MSAW system is designed, in part, to help prevent accidents involving controlled flight into terrain, or CFIT. But according to a series of recommendations [PDF] made last week by the National Transportation Safety Board, changes in the existing MSAW and conflict alert systems are necessary “to direct controller attention to CFIT hazards or impending collision.” The recommendations come on the heels of NTSB investigations into 10 CFIT accidents and one midair collision the NTSB says “have caused serious concern” about the MSAW and conflict alert systems’ effectiveness. Accidents examined by the NTSB include the Dec. 17, 2002, near-disaster on Guam involving a Philippine Airlines Airbus A330; the May 10, 2004, fatal crash of a Piper PA-44 Seminole near Julian, Calif.; and the Nov. 22, 2004, accident involving a Gulfstream G-1159A, which struck a light pole adjacent to a roadway and crashed in IMC while on an ILS approach to the Houston (Texas) Hobby Airport. In investigating these and other accidents, the NTSB said it believes changes to the MSAW and conflict alert systems – as well as better controller training – may have prevented them.
Interestingly, the NTSB in its recommendation letter went out of its way to discuss the importance of what it called “good ATC judgment” even when automated warnings were not provided. In discussing the Oct. 24, 2004, crash of a Learjet Model 35A shortly after departing San Diego, Calif., the NTSB noted, “the controller failed to use available information to recognize that he had left the pilot with no viable options.” “Because the controller declined to issue the pilot an IFR clearance until the aircraft reached 5,000 feet (the minimum vectoring altitude in the area), the pilot was effectively unable to climb legally, and the aircraft was caught between the ceiling and the ground in an area of rapidly rising terrain,” the NTSB said in its recommendation letter. Specifically, the NTSB recommended that the FAA:
Redesign the MSAW and conflict alert systems and alerting methods so they reliably capture and direct controller attention to potentially hazardous situations.
Implement any software and adaptation modifications needed to minimize or eliminate unwarranted MSAW alerts.
Perform a technical and procedural review at all ATC facilities with MSAW or conflict alert capability to consistent procedures.
Amend FAA Order 3120.4L, Air Traffic Technical Training, to emphasize that controllers should maintain awareness of aircraft altitudes to detect and effectively react to situations in which a safety alert may prevent an accident.
