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Aviation: London's airports are full(-ish)

It's a commonly held belief that London's airports are full; that is, there are no runway slots available which can be used to start new services. Five of the UK capital's six airports - Heathrow, Gatwick, Stansted, Luton and City - are IATA Level 3 coordinated, which means that demand for landing and takeoff slots outstrips supply. Only Southend, until a couple of years ago a sleepy backwater, has capacity aplenty but its short runway restricts movements to aircraft with fewer than around 180 seats.

Surprising then that ACL (Airport Coordination Limited), the independent organisation that manages slot bids and allocations for many airports around the world says that there's still some capacity available at London's big five. Indeed the firm goes on to point out that the total number of slots available next summer has actually increased by 31 compared to this year. Unfortunately these new slots aren't distributed across the capital - Heathrow, Gatwick and Luton will be able to handle only the same number of arrivals and departures as summer 2018 while 16 extra movements will be possible at London City, along with 15 more at Stansted. If all of the vacant slots are requested by airlines, four of London's airports will reach their daily take off and landing limits. Heathrow on the other hand cannot use all of the slots its two runways enable, as it is also constrained by a yearly movements limit. Even so with this new capacity, year-on-year increases across the capital will be 1.5%, representing 11,000 more seats and 26 additional take-offs and landings in the London area every day.

London City is getting busier and is constrained by aircraft parking space.

With slots at a premium and being leased or exchanged for millions of pounds, its not surprising that airlines are finding others ways to provide extra capacity. ACL notes that many operators are already using bigger aircraft, and that will continue - there will be 3.4m more seats on offer at London's airports next summer, an increase of 2.5% over 2018. This is particularly the case at London City, where next summer the average will be 91.5 seats per flight versus 85.6 this year.

Taking a closer look

Intrigued, The Aviation Oracle decided to examine the slot situation in London next summer more closely, choosing at random the week ending Sunday August 4, 2019. A tip for anyone reading beyond here: if you're not really interested in the detailed figures just look at the colours - red is bad, orange is not good, green is great when it comes to slot availability.

London Heathrow

The week ending August 4, 2019 at Heathrow is shown below, and its typical of the entire summer period from late March through to late October. The figures in the grid indicate the number of slots being used and the number available (allocated / available), each hour of every day of the week. Red means no slots are free, orange means just one slot is available, and green indicates that there more capacity free. Clearly any new entrant to the market - or an airline wanting to start a new service or increase frequency - would stand a fair chance of be allowed to operate if it only wants to operate on a Saturday, and in particular on a Saturday afternoon. There's also a little bit of wriggle room on Sunday morning if inbound / outbound turn ti