Cloud busting By John Ellis, Deputy General Manager, Swanwick Operations Controllers have a lot to consider when a pilot asks to avoid bad weather, not least of which is how to get your colleagues out of the way. What can you do to help? “I imagine, as a pilot, it doesn’t always seem like this,” he says, “what with the extended routings and seemingly restrictive descent conditions. These are, however, part of the system that allows for a more predictable traffic flow – and more predictability means lower complexity. Less complexity means controllers can handle more aircraft at once, and more aircraft in the sky – safely – means greater capacity and less delay.” The rules change, however, when bad weather gets thrown into the mix. A conflict solution that would have taken one transmission and plan A to solve, suddenly needs three transmissions and plans B through to E being torn up, explains Boyle. “Aircraft that normally enter your sector at Bovingdon arrive heading 90 degrees in the wrong direction over Clacton; Heathrow inbounds that you never normally talk to are suddenly presented to your sector,” he says. Big gaps appear on the radar screen that would normally be filled with the busy trail of dots of normal traffic flow. No-go zones. “Sorry London, we’re going to need a 30-degree turn to the right to avoid.” Oh no, you think – but don’t say. Bad enough if the 40,000ft Cb was parked, unmoving, in the middle of your airspace: back to predictability being the friend of air traffic. But these slippery devils move; they shape shift, appear and disappear. “We control with a hand tied behind our back,” says Boyle. “We can’t see what you can see.” ASKING TO AVOID WEATHER INTRODUCES AN ELEMENT OF RISK INTO THE ATC SYSTEM, BECAUSE AIRCRAFT ARE NOW POTENTIALLY INTERACTING WITH TRAFFIC FLOWS WITH WHICH THEY ARE NOT DESIGNED TO INTERACT Weather avoidance In a nutshell, bad weather means it gets busier for the controller. We battle internally between a need for it to be less complicated (we like it busy, but we’re not masochists) and the deep understanding that “I’m busy – like, really busy – but these guys are looking out of their window at a big black cloud, dead ahead, with an internal pyrotechnics display”. We get it; we’d be concerned, too. And that tone in your voice – the one that says we really need that turn as soon as possible, London. We hear that; we just need to get your colleagues out of the way first. “Our systems are designed to minimise the need for controllers to talk to each other; electronic communication and ‘standing agreements’ mean that we can spend more time talking to aircraft and problem-solving,” says Boyle. Weather avoidance typically entails a request to turn off the standard route and, sometimes, impacts on descent or climb profiles. This triggers an exponential requirement for controllers to coordinate with each other. At best, aircraft enter the next sector off track or at an unplanned level; at worst, they enter a sector that they were never expected to enter in the first place. The controllers’ workload rapidly increases, but we can’t allow safety to be affected – so the only answer is to reduce the capacity of the affected sectors until the weather dissipates. We do this by localised measures or by application of a regulation via the Eurocontrol system, which is when slots are issued. Leaving Epsom heading 125 degrees is pretty much guaranteed to shoot the gap between the Ockham and Biggin hold, and allow some climb against the next flurry of Heathrow inbounds. These strategies, says Andy Hogg, Supervisor, Terminal Control, are the ‘normal’ way of operating and give controllers the predictability they need to control high levels of traffic safely. “When we get convective weather, these headings become a pipe dream – the weather, rather than other traffic, dictates where you need to fly,” he says. “When you ask for a heading for weather, it is rarely turned down. However, this leads to a disproportionate increase in workload for the controller, as they make calls to coordinate traffic with adjacent sectors and adjust plans that they had for other aircraft that were not in conflict with you previously.” In terminal airspace, sectors are smaller and closer together, and controllers are allowed to use 3nm separation because aircraft are operating at lower levels and speeds within an area of high-density surveillance coverage, which allows for more traffic in the sectors. Tailored response As a pilot, it can be extremely frustrating to be informed, as you sit ready to taxi, that there is a delay because of weather. You look out of the cockpit and see a grey, but otherwise benign sky, and the tower controllers are pushing the radar controllers to allow aircraft to depart. What they don’t see is that, 30 miles down route, all hell is breaking loose; aircraft are flying 100 miles off the normal track or orbiting wherever they can, because they cannot approach the hold. “The knock-on effect of convective weather is huge – not only to adjacent air navigation service providers, but also to the airfields,” says Hogg. “If aircraft can’t depart, stands can become an issue; subsequent aircraft cannot land and the system quickly becomes clogged.” Since 2016, meteorologists have been based at Swanwick, 24/7, with access to the latest ground-based weather radars and modelling tools. Supervisory teams are supported with up-to-date observations and predictions, allowing a more tailored response to all types of weather – convective, strong winds, low cloud, mist, fog and snow. But what can you, as a pilot, do to help us? When asking to avoid weather, it is helpful to be given as much notice as possible – and include a clear idea of what you need and for how long. In terms of the overall management of aviation safety, controllers are aware that flying through convective weather creates a risk for the pilots, their crew, passengers and aircraft. Equally, asking to avoid weather introduces an element of risk into the ATC system, because aircraft are now potentially interacting with traffic flows with which they are not designed to interact. It is your judgement as to the level of risk you are taking by flying through weather, but a good measure of the increased activity – and, therefore, risk – in an airspace sector typically lies in frequency saturation. And, in some cases, non-visual clues, such as the tone of voice of the controller managing it. When it comes to air traffic control, bad weather – particularly extensive and significant cumulonimbus (Cb) activity – is about as helpful as a fender bender on the M25 on a Friday evening. While flight crew may see it or have it painting on their radar, our sector controllers cannot see it. We want our radar display to be as ‘clean’ and accurate as possible when it comes to showing aircraft, so we process out everything else – birds, for example, and weather. Weather tends to be very level-specific anyway, so the idea of controllers having a weather overlay is not feasible, given that they can be controlling airspace sectors that are 20,000ft deep or more. Different airlines, pilots flying various aircraft types, and even crews within the same airline apply different interpretations and varying operating procedures when flying through weather phenomena. So, it would be very difficult for controllers to apply consistent judgement about – and take responsibility for – what to avoid, even if we could see weather accurately. Controlled airspace is ordered and structured, and Damian Boyle, Sector Controller, Area Controller, at NATS, believes it is organised in the best way possible to meet the various requirements of all users. WEATHER