DIVERSIONS Requesting a diversion As we move back towards busier skies, the likelihood of diversions will increase. Heres what to expect By Phil Tanner, Air Traffic Controller and member of the Guild of Air Traffic Control Officers (GATCO) hen an aircraft requests a diversion, for whatever reason, there is a sequence of actions that need to be taken before we can start vectoring you there. The first thing we need to check is that the nominated airport can accommodate the diversion. This involves a series of discussions, starting with the individual controller informing either the watch supervisor at an airport or the airports group supervisor at Swanwick, who is responsible for overseeing the approach functions into most major airports in the southeast of England of the request. They, in turn, will pass the request onto the tower supervisor at the requested diversion airport, who will coordinate with the airport authority. After considering factors including the current and forecast traffic levels, stand, and handling agent availability they will determine whether the airport can accept the diversion. They will also look into any additional restrictions that might be imposed, such as a time limit for how long the aircraft can remain on the ground, whether passengers are permitted to disembark, or if only a splash and dash for fuel is permitted. They will then relay their decision back down the chain. This process takes time to action, and the wait for a response can be just as frustrating for controllers as it is for pilots. On a quiet day, with little disruption, it might only take a minute or two to receive a response. But on a high workload day with go-arounds, strong winds, low visibility or airport unavailability resulting in multiple diversion requests it can take much longer: potentially up to 10 minutes in extreme cases. Procedures In the event of mass diversions for example, the drone incident at Gatwick in 2018 or the Valentines Day storms in 2014 there are procedures in place that can expedite the process slightly. However, once airports start reaching capacity for the number of diversions they can accept, finding an available destination can become more timeconsuming. It is also not uncommon on busy summer days for it to take two or three attempts to find an airport that has sufficient capacity to accept non-emergency diversions. Once a diversion has been approved, we can start the process of vectoring an aircraft to the diversion airport. This involves coordination between the original sector usually the approach sector of the original destination and the en route sector, to plan a route. It is generally a relatively quick process involving a phone call between the relevant sector groups to negotiate a route. However, in high workload situations, such as weather avoidance, mass diversions, and complex traffic situations, this can take longer. Controllers will endeavour to provide as short a route as is practical. However, because of the nature of UK airspace, especially around London, it will inevitably involve additional track miles compared with a direct route. For example, an aircraft in the Biggin hold for Heathrow requesting to divert to Birmingham will almost certainly be vectored eastbound for 10-20nm to climb above aircraft holding in the Lambourne and Bovingdon stacks, before being routed towards Birmingham. Similarly, a Gatwick inbound holding at WILLO, intending to divert to Luton, will probably be vectored eastbound, away from Heathrow and London City traffic, before continuing northbound towards Stansted and then Luton. Given the above, it is often useful to inform us of intentions a few minutes before requiring to divert. That way, we can start asking the right questions to the intended diversion airport to check whether it is likely to be feasible. That does not mean the situation will not change, especially if there are multiple other diversions around the same time. However, at least we will be able to inform you if the intended diversion airport is not accepting non-emergency diversions and a new plan is needed, so as not to waste critical planning time. This will also allow us to starting routing you to the diversion airport a lot sooner when you finally need to divert. It is not uncommon on busy summer days for it to take two or three attempts to find an airport that has sufficient capacity to accept diversions In an emergency It goes without saying that none of the above applies to aircraft that have declared an emergency or require to divert for time-critical reasons, such as disruptive passengers or a security situation. In these cases, we will pull out all the stops to vector you to the destination of your choosing using the shortest practical route, bearing in mind that this is not always a direct route because of the extremely complicated nature of UK terminal airspace. I hope that provides a useful insight into what goes on from an ATC perspective when diversions occur. It may not always seem like it at the time, but we will always try our best to accommodate your request as quickly as possible. Sometimes, though, it just cannot be done. The more notice you can give us of your intentions, the better we will be able to assist and, if you have any questions, we will always try to find time to answer whenever possible.