Every large air traffic modernisation programme passes through a phase where the old system is still running, the new one is partly live, and controllers are working across both. The current programme is squarely in that phase, and it is the point at which such projects most often stall.
Why dual running is expensive
Running two systems means maintaining two sets of procedures, two training syllabuses and two failure modes. It also means that the safety case for any change has to be made twice. Controllers describe the cognitive cost plainly: the mental model of what the system will do next differs between the two, and switching between them mid-shift is tiring in a way that is hard to quantify but easy to feel.
The efficiency benefits, meanwhile, only appear when a whole sector operates on the new system with adjacent sectors doing the same. Partial deployment delivers most of the cost and a fraction of the benefit.
The trajectory-based promise
The core of the new system is trajectory-based operation: instead of clearing aircraft from waypoint to waypoint, controllers agree a four-dimensional path — three spatial dimensions plus time — and manage exceptions. In simulation it reduces controller workload per aircraft substantially and allows tighter, more fuel-efficient routings.
In practice it requires the aircraft to be able to fly the agreed time to a tight tolerance, which not all of the fleet can do. Mixed-equipage airspace is where most of the theoretical benefit disappears.
What would unstick it
Three things, in roughly this order of difficulty.
- A firm equipage mandate with a date, which converts an airline capital decision from optional to scheduled.
- Sector-by-sector cutover rather than function-by-function, so that the benefits arrive somewhere rather than nowhere.
- Retirement of the legacy system on a published timetable, which is the step everybody agrees is necessary and nobody wants to sign.
None of these is technical. The engineering problems in this programme were largely solved several years ago. What remains is a coordination problem across a large number of organisations with different budget cycles, and those are considerably harder.
