SkyWest Airlines Flight 3567

After initial contact with the flight, the air traffic controller issued the pilots a clearance to cross the initial approach fix CEGAN at or above 7,800 feet and cleared the flight for the published instrument procedure. The published altitude for the instrument procedure was at or above 10,000 feet from CEGAN until BRKET while established on the arc. The flight crew accepted the ATC clearance, and descended from 12,000 feet to 7,800 feet while established on the arc. The minimum vectoring altitude (MVA) for the airspace containing the arc was 7,800 feet, however, just prior to BRKET the floor of the MVA raised to 8,700 feet. The MVA altitudes as depicted on the radar display are for air traffic control and are not available to flight crews. Interviews with the controller indicated there was an expectation that the pilot would not descend below the 10,000 feet as published despite being assigned the "at or above 7,800 feet" crossing restriction. The controller introduced risk by assigning the lowest altitude in the MVA area containing the fix CEGAN (7,800 feet) and expecting the crew to stop their descent at the higher published altitude of 10,000 feet. There was no operational or procedural advantage gained by assigning the flight crew 7,800 feet when the controller expected the crew to stop at 10,000 feet. Had the controller issued the published altitude of 10,000 feet and issued the approach clearance, the incident likely would not have occurred because the crew could have descended to 10,000 feet and then descended according to the published procedure and not below the MVA for that segment. In the incident sequence, the controller instructed the flight crew to cross the initial approach fix (IAF) CEGAN at 7,800 feet, and, the flight did not become established on the published procedure until after CEGAN when established on the arc. The controller was required to assign an altitude to maintain until being established on the procedure, in this case at or above 10,000 feet as published. When the flight crew received the approach clearance that included a descent below the published altitude, they did not query the controller or stop the descent at the published altitude as required in accordance with 14 Code of Federal Regulations (CFR) Part 121. As a result of the incident, the FAA initiated an education program with briefings and information graphics to the air traffic control workforce to emphasize MVA and MSAW conditions. The topics included the use of MVA maps, assignment of appropriate altitudes, ensuring correct altitudes are maintained, and a reminder to know approach procedures and appropriate altitudes. During the incident investigation, it was determined that an antenna adjacent to the IAF BRKET was not depicted on the Jeppesen produced approach chart for the VOR DME C current on the day the incident. Jeppesen changed the approach chart to reflect the antennae and a new obstacle height of 7,614 feet. Additionally, Jeppesen conducted a review of the terrain surrounding the MFR airport to support produced navigation products.

Verbatim NTSB analysis and probable cause from the NTSB dataset