Reduced Spacing Trial Coming to NAT This Spring

 - January 10, 2019, 11:38 AM

An upcoming trial of reduced separation standards for ADS-B-equipped aircraft in the Shanwick, Gander, and Santa Maria Oceanic Control areas of the North Atlantic Track (NAT) is scheduled to begin on or soon after March 28. The trial program is known as the Advanced Surveillance-Enhanced Procedural Separation (ASEPS).

According to NATS Bulletin 2018-06, the trial will initially apply to “17 nm longitudinal separation of aircraft operating on the same track or intersecting tracks provided, that the relative angle between the tracks is less than 90 degrees and 14 nm provided the relative angle between the tracks is less than 45 degrees.”

Opposite-direction aircraft on reciprocal tracks might be cleared to “climb or descend to or through the levels occupied by another aircraft provided that the aircraft have reported by ADS-B having passed each other by 5 nm.” The bulletin said a trial implementation of lateral ASEPS will start no earlier than six months after the beginning of the longitudinal separation operational trial.

NBAA emphasized that no special LOA or other approval is needed for ASEPS operations, nor do aircraft need to be ADS-B compliant to operate in NAT airspace. However, to be eligible to participate in the trial, aircraft must be RVSM/HLA approved, ADS-B equipped with dedicated 1090-Mhz Out capability, and meet RNP 4, RCP 240, and RSP 180 specifications.

Starting simultaneously with the ASEPS trial will be changes to contingency and weather and weather deviation procedures for NAT operators. Outlined in NATS Bulletin 2018-05, the revised procedures apply when there is an inability to comply with the assigned clearance due to weather; diversion across the prevailing traffic flow; loss of, or significant reduction in, the required navigation capability; or pressurization failure.