Shemya, AK, USA
N773AN
BOEING 777 - 236
A loss of required separation occurred near Shemya, Alaska, between a Boeing 777-200 en route to Shanghai Pudong International Airport, Shanghai, China, and a Boeing 747-400 en route to Ted Stevens Anchorage International Airport, Anchorage, Alaska. There was no damage to either aircraft, and no injuries were sustained by the passengers or crewmembers. The flight crew of the Boeing 777 requested to climb from flight level (FL) 360 to FL 370. Given the Boeing 777's position at the time, the requested climb would have conflicted with two other airplanes that were traveling at FL 370 but in the opposite direction. The air traffic controller identified the potential conflict between the Boeing 777 and the first airplane, but he did not identify the conflict between the Boeing 777 and the second airplane, the Boeing 747. The controller instructed the flight crew of the Boeing 777 to remain at FL 360 until they passed the first airplane and then to climb to FL 370. The flight crew of the Boeing 777 acknowledged and complied with the clearance, which resulted in a loss of required separation with the Boeing 747. Both flight crews received and responded to resolution advisories from their onboard traffic alert and collision avoidance systems after the controller issued the climb clearance. The Federal Aviation Administration (FAA) estimated that the minimum separation between the two aircraft was 1.04 miles laterally and 900 ft vertically. Typically, two types of automated conflict detection were available to controllers in the Shemya radar coverage area: a "conflict probe" that provided controllers with extended warning time for future conflicts and a short-term conflict alert system that looked about 2 minutes ahead to detect conflicts between radar-observed aircraft. However, the FAA had intentionally disabled the extended conflict probe in the Shemya radar coverage area because of unresolved performance issues, and the only automated conflict detection assistance available to the controllers in this area was the short-term conflict alert system; this removed a layer of backup to controller judgment and reduced the overall safety of flight operations in this area. Postincident corrective actions resulted in the extended conflict probe being returned to service. If the extended conflict probe had been available at the time of the incident, it is likely that it would have detected the conflict and alerted the controller about it before he issued the incorrect clearance and that no loss of separation would have occurred.
On August 15, 2014, about 2133 Alaska daylight time, an air traffic control loss of separation occurred near Shemya, Alaska, between American Airlines flight 183 (AAL183), a Boeing 777-200 en route to Shanghai Pudong International Airport, Shanghai, China, and China Airlines flight 5254 (CAL5254), a Boeing 747-400 (B744), en route to the Ted Stevens Anchorage International Airport, Anchorage, Alaska. Both flight crews responded to resolution advisories from their onboard Traffic Alerting and Collision Avoidance System (TCAS). The FAA estimated the minimum separation between the two aircraft was 1.04 miles and 900 feet. There was no damage to either aircraft and no injuries to passengers or crew. At 2113:08, ZAN sector 11R (radar) received a controller–pilot data link communication (CPDLC)[1] message from CAL5254 requesting a climb from flight level (FL) 360 to FL 370. CAL5254 was established eastbound on R-590. Sector 11R responded via CPDLC to "climb to FL370 by 0520." (2120 local time.). At 2116:08, sector 11R received a request from AAL183 to climb from FL360 to FL370. AAL183 was westbound on the Pacific Organized Track System (PACOTS) track "E" from AMOND direct to OPAKE to join the northern Pacific R580. At 2118:43, sector 11R used the time passing tool from the Advanced Technologies and Oceanic Procedures (ATOP) Ocean 21 system and determined the separation between Korean Airlines (KAL) 035 and AAL183 would be 15.9 nautical miles at 2126 local. At 2118:52, sector 11R instructed AAL183 to "[At] time 0530 (2130) climb to FL370." At 2119:10, AAL183 acknowledged the climb clearance via CPDLC. At 2131:55, a radar-based conflict alert activated between CAL5254 and AAL183. The sector 11R air traffic controller utilized the time passing tool and determined the lateral separation between CAL5254 and AAL183 would be .80 nautical miles (NM) at 2133. At 2132:18, the sector 11R air traffic controller made a blind transmission attempting to contact AAL183; there was no reply. At 2132:25, the controller made a blind transmission attempting to contact CAL5254; again, there was no reply. At 2132:29, CAL5254 made a transmission that they were responding to a TCAS RA and climbing. At 2132:44, the pilot advised the RA was complete and they were descending back to FL370. At 2133:26, AAL183 contacted sector 11R and advised "yeah we had a uh we requested three seven oh, we got a CPDLC message said that at oh five thirty to climb to three seven oh we did that and ah we just got an RA with another aircraft." The sector 11R air traffic controller replied, "American one eighty three roger, yup, that clearance should have been delayed." For additional information, please see the ATC Group Chairman's factual report located in the docket.
The air traffic controller’s failure to identify a conflict between two aircraft and to issue an adequate clearance, which resulted in a loss of required separation. Contributing to the incident was the Federal Aviation Administration’s failure to provide controllers adequate automated conflict detection assistance, which removed a layer of backup to controller judgment and reduced the overall level of safety.
Source: NTSB Aviation Accident Database
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