Departure flight paths
Heathrow is the busiest two-runway airport in the world with about 1,300 combined take-offs and landings a day. Efforts to limit noise mean that fewer people are affected by noise today than at any time since the 1970s. However noise remains an issue for people living near or under the various flight paths used for take-offs and landings at the airport.
On average there are around 650 departures from Heathrow each day. The first departure is around 06:00 and the last scheduled departure is at 22:50.
Aircraft taking off from Heathrow follow pre-defined routes, known as Standard Instrument Departures routes (SIDs). The choice of SID used is decided by the airline and is predominately dictated by the destination of the aircraft. Due to the fact that all aircraft perform differently and may be affected by weather conditions which can cause them to drift left or right, there will be some variation as to where different aircraft will fly relative to the centreline of the SID. For this reason, when the SIDs were designed in the 1960s by the Department for Transport (DfT), the Government set corridors, known as Noise Preferential Routes (NPRs), which extend 1.5 kilometres either side of the SID route centreline.
There are 6 NPRs on easterly and westerly operations:
View the easterly operations NPRs (264KB PDF)
View the westerly operations NPRs (235KB PDF)
Aircraft don’t have to follow the centreline of the SID precisely, they just have to be within the 3km wide NPR up to 4,000ft. Under government rules, once aircraft reach an altitude of 4,000ft, NATS air traffic controllers can direct planes off the departure route towards a more direct heading to their destination. This is known as vectoring.
Track keeping (how well aircraft stay within the NPR up to 4,000ft) on Heathrow’s departure routes is very high overall, with about 95% of all departures staying within the published routes. The exception is the Compton route – a departure route used during periods of easterly operations that heads west. Track keeping compliance is much lower on this route, and has been for many years. Both the DfT and CAA are well aware of this. We monitor how well planes stick to these routes and we publish data on track keeping on a daily basis on our Operational Data website and quarterly and yearly in our Flight Performance reports.
The choice of which of the six departure routes aircraft take is a decision for airlines. It is dictated primarily by the destination of the flight but there are a number of other factors that influence this too including international situations and the availability of the route. Heathrow has no power to dictate which route the airline takes.
Rules on aircraft height
The Department for Transport set rules regarding the height of aircraft on departure. The rules state that:
- After take-off aircraft must reach 1000ft at 6.5km from ‘start of roll’ (the departure)
- After passing this point the aircraft shall maintain a gradient of climb not less than 4% to an altitude of not less than 4000ft and
- Aircraft must stay within the departure route (NPR) to 4,000ft.
The climb rates will vary because aircraft climb at different rates depending on factors such as the type of aircraft, weather conditions or how fully laden they are. For example, bigger aircraft such as the Airbus A380s will climb more slowly compared with smaller aircraft such as an A319 or A320, and therefore they may be lower than a smaller aircraft in the same position.
Aircraft not following a departure route
On occasions planes are directed to take a different route by Air Traffic Control the air traffic controller or to leave the NPR below 4,000ft. This could be for a number of reasons such as thunderstorms, severe weather conditions or another aircraft such as a police helicopter that is flying within the departure route.
Late running departures
Although there is not an imposed ban on planes landing or taking off at night, Heathrow is heavily restricted by the Government in terms of the numbers and types of aircraft that are allowed to operate at night. Generally speaking, there are no scheduled departures between 23:00 and 06.00 but we know there are times when flights do depart late causing disruption to local communities. To address this, we have made it one of the steps to tackle as part of our Blueprint for Noise Reduction.
Unfortunately, extreme weather conditions such as strong winds, fog or thunderstorms can also have an impact on our operations. This can mean that the number of departures that are able to take off each hour has to be reduced for safety reasons. The knock-on effect of this is that the normal schedule can be significantly impacted and in order for us to recover from the disruption, some departures are allowed to operate later than usual.