By James Gaskell, BALPA ATS group member When flying the Atlantic, does it amaze you as much as it does me that, although we never see ships ploughing their white wake in the ocean beneath us, we regularly see aircraft really quite close to us? This is thanks to the organised track system (OTS). And, because all the aircraft are given strict instructions on track, speed and flight level, risks of mid-air collision are mitigated. The North Atlantic Safety Oversight Group (NATSOG) uses a target level of safety (TLS), both for planning and monitoring, for the probability of a mid-air collision of 5 x 10-9 per flight hour in the vertical domain and the same in the lateral plane. Emergencies are not considered in this figure. The IFALPA Regional Vice President, who attends North Atlantic meetings, is concerned that there is insufficient transparency, and that more attempts to achieve TLS should be made before reducing separation. The trial of 30nm tracks (rather than 60nm separation, laterally) is well under way. IFALPA supports improvements such as advanced surveillance enhanced procedural separation (ASEPS). The NATS trial of ASEPS using automatic dependent surveillance-broadcast (ADS-B) in the Shanwick Oceanic Control Area went live in April 2019, and runs until November 2020. Growing numbers RISKY BUSINESS Is the risk of a North Atlantic mid-air collision increasing? Is this scaremongering, Luddism, or are the figures getting worse? The vertical operational collision risk for 2018 was estimated by the NATSOG maths sub-group to be 76 x10-9 without the strategic operational offset procedure (SLOP), and 16.9 x10-9 with SLOP (10.5 x 10-9 in 2017). This is more than three times the TLS, and growing. Nearly half the traffic uses the centre line, while only 10 to 20 per cent use a 2nm right offset. Decimal offset can now be used with suitably equipped aircraft. The number of reduced vertical separation minima (RVSM) levels crossed without prior ATC clearance has doubled since 2017. The number of minutes spent at an unprotected flight level has increased by 50 per cent over the same time period. The lateral collision risk for 2018 was estimated at 13.8 x10-9 (12.8 x 10-9 in 2017), nearly three times the lateral TLS. The number of minutes on an incorrect track has increased, since 2017, by 400 per cent. Three times as many tracks were crossed without an ATC clearance as a year earlier. Conditional ATC clearances (for example, ‘climb FL 350 after 20 west’) are more likely to induce errors than other kinds of clearance, which can result in loss of separation with other aircraft or flying at an incorrect level or on the wrong track. As flight crew, we should report all errors and our belief as to why they happened, and take particular care when receiving conditional clearances or re-routes. TECH LOG