Glossary

We have tried to make the consultation accessible to all, however the operation of airspace is a technical subject, and to fully explain our proposals we have had to use some technical detail. We have provided an explanation of these terms below.

Term Definition
Airports Commission A commission set up by the Government to look into options for the development of runway infrastructure in the South East
Altitude The height in feet, above mean sea level.  Due to variations in terrain, air traffic control measure altitudes as above mean sea level rather than above the ground.  If you are interested in the height of aircraft above a particular location to assess potential noise impact, then local elevation should be taken into account when considering aircraft heights; for example an aircraft at 8,000ft above mean sea level would be 7,500ft above ground level if the ground elevation is 500ft.  All altitudes in the consultation document are defined as above mean sea level
AMSL Above mean sea level
AONB Area of Outstanding Natural Beauty
ATC Air traffic control
ATC intervention This is when ATC instruct aircraft off their planned route, for example, in order to provide a short cut, they may be instructed to fly directly to a point rather than following the path of the published route
ATS licence The Air Traffic Services licence to provide air traffic control services for UK ‘en route’ airspace issued by the government
CAA Civil Aviation Authority
Capacity A term used to describe how many aircraft airspace can be accommodated within an airspace area without compromising safety or generating excessive delay
CAS See Controlled airspace
Centreline The nominal track for a published route  (see Route)
City pair The departure and arrival airport for a flight. The city pair generally dictates the flight path to be taken – ie there are standard flight paths for each city pair
CO2 Carbon dioxide
Concentration Refers to a density of aircraft flight paths over a given location; generally refers to high density where tracks are not spread out; this is the opposite of Dispersal
Consultation swathe This is the broad area within which we will need to position a route
Continuous climb  A climb that is constant, without periods of level flight – referred to as steps
Continuous descent A descent that is constant, without periods of level flight – referred to as steps
Controlled airspace Generic term for the airspace in which an air traffic control service is provided as standard; note that there are different sub classifications of airspace that define the air traffic services available in defined classes of controlled airspace   Usually abbreviated to CAS
Conventional navigation The historic navigation standard where aircraft fly with reference to ground based navigation aids
Conventional routes Routes defined to the conventional navigation standard
Davies Commission See Airports Commission
Departure interval The time gap required between successive departures taking off from the same runway
Dispersal Refers to the density of aircraft flight paths over a given location; generally refers to low density – tracks that are spread out; this is the opposite of Concentration
Easterly operation When an runway is operating such that aircraft are taking off and landing in a easterly direction; see Runway 09 and Runway 08 respectively for definition of easterly operations at London City and Gatwick airports
Enabled fuel benefits NATS’ measure for improved fuel efficiency; it relates to a definition of the planned fuel, or trip fuel, which aircraft have to carry for a journey – see Part G for details
FAS See Future Airspace Strategy
Final approach path The final part of a flight path that is lined up with the runway; aircraft usually join final approach between 8nm and 15nm from the runway
Flight paths The tracks flown by aircraft when following a route, or when being directed by air traffic control
Flight plan The flight path that an aircraft has to carry fuel for, which covers the whole route, not including any changes to the flight path made tactically by air traffic control – which may be either to shorten the flight path when it is not busy or lengthen the flight path when there is a queue to land (such as time spent in the hold)
ft Feet, the standard measure for vertical distances used in air traffic control
Fuel uplift The amount of fuel that aircraft have to carry on a journey, this includes the fuel for the flight plan, contingency fuel for airborne delay and contingency for emergencies
Future Airspace Strategy The CAA’s blueprint for modernising the UK’s airspace. The CAA explains the background to FAS here: www.caa.co.uk/default.aspx?catid=2408
GA See General Aviation
GAL Gatwick Airport Limited
General Aviation All civil aviation operations other than scheduled air services and non-scheduled air transport operations for remuneration or hire. General aviation flights range from gliders and powered parachutes to corporate jet flights
Holds/Holding Stacks An airspace structure where aircraft circle above one another at 1,000ft intervals when queuing to land
Intermediate airspace Airspace with routes between 4,000ft and 7,000ft in which NATS has accountability for safe and efficient air traffic service but in which airports may also have local requirements (see Part A paragraph 2.3 for details)
LAC London Airspace Consultation
LAMP London Airspace Management Programme
Low altitude airspace Airspace in the vicinity of the airport containing arrival and departure routes below 4,000ft. Airports have the primary accountability for this airspace, as its design and operation is largely dictated by local noise requirements, airport capacity and efficiency
MOD Ministry of Defence
NATS The UK’s licenced air traffic service provider for the en route airspace that connects our airports with each other and the airspace of neighbouring states
Nautical mile Aviation measures distances in nautical miles. One nautical mile (nm) is 1,852 metres. One road mile (“statute mile”) is 1,609 metres, making a nautical mile about 15% longer than a statute mile.
Network airspace En route’ airspace above 7,000ft in which NATS has accountability for safe and efficient air traffic service for aircraft travelling between the UK airports and the airspace of neighbouring states (see part A paragraph 2.3)
nm See ‘nautical mile’
Noise contours The depiction of noise across a period of the day as a series of contours around the airport; major airports annually publish the noise contours for the ‘daytime’ period of 0700-2300; these are referred to as the Leq(16 hours) noise contours
Noise footprint The depiction of noise from a single aircraft as a ‘footprint’ around the airport
NPR Noise Preferential Route
NPR swathe An area defined around an NPR in which aircraft below 4,000ft are required to stay within.  Today’s NPR Swathes start narrow at the runway and widen to a maximum of 3km.  Their length is based on the distance it would take a slow climbing aircraft to reach 4,000ft.  NPRs for future ‘PBN’ routes are likely to be narrower and shorter to represent improved navigation accuracy and climb performance of modern aircraft
p/a  Per annum (per year)
PBN  See Performance Based Navigation
Performance Based Navigation Referred to as PBN; a generic term for modern standards for aircraft navigation capabilities (as opposed to ‘conventional’ navigation standards). See www.eurocontrol.int/navigation/pbn for details
Point Merge A route system for organising arrivals into an efficient  landing ‘sequence’
PRNAV Precision ‘RNAV’, otherwise referred to as ‘RNAV1’ (both these terms are defined in this glossary)
Radius-to-fix turn A turn on a PBN route where all aircraft fly a turn with a fixed radius, meaning that all aircraft flight paths will be concentrated on the published centreline of the turn.  Other kinds of turn generally result in more variation as a consequence of aircraft flying at different speeds and therefore flying turns with a bigger or smaller radius (the faster the aircraft the wider the turn)
Requested flight level The requested cruising level for a flight. This is dependent on factors such as the aircraft type, its weight and the route being flown
Respite route Additional routes established to spread traffic in a predictable way so that areas beneath the original track get predictable periods of respite
RNAV Short for aRea NAVigation. This is a generic term for a particular specification of ‘Performance Based Navigation’
RNAV1 See RNAV. The suffix “1” denotes a requirement that aircraft can navigate to with 1nm of route 95% or more of the time
RNAV1 transition The part of an arrival route, defined to the RNAV 1 standard between the last hold (or Point Merge structure) and the runway
RNP1 Required Navigation Performance 1. An advance navigation specification under the PBN umbrella. The suffix “1” denotes a requirement that aircraft can navigate to with 1nm of the centreline 95% or more of the time
Route Published routes that aircraft plan to follow. These have a nominal centreline that gives an indication of where aircraft on the route would be expected to fly; however, aircraft will fly routes and route segments with varying degrees of accuracy based on a range of operational factors such as the weather, and technical factors such as the PBN specification
Route system The network of routes linking airports to one another and the airspace of neighbouring states
Runway 08 (London Gatwick) The name given to the main runway at Gatwick when operating in a ‘easterly’ direction (ie taking off and landing on the easterly heading of 080º)
Runway 09 (London City) The name given to runway at London City when operating in a ‘easterly’ direction (ie taking off and landing on the easterly heading of 090º)
Runway 26 (London Gatwick) The name given to the main runway at Gatwick when operating in a ‘westerly‘ direction (ie taking off and landing on the westerly heading of 260º)
Runway 27 (London City) The name given to the main runway at London City when operating in a ‘westerly’ direction (ie taking off and landing on the westerly heading of 270º)
Sequence The order of arrivals in a queue of airborne aircraft waiting to land
SID See Standard Instrument Departure
Simulation modelling Computer based analysis where the air traffic is ‘flown’ through a virtual airspace system; used to assess the effect of changing airspace on the efficiency of air traffic flows
Stacks/stack hold Refer to holds
Standard Arrival Route The published routes for arriving traffic. In today’s system these bring aircraft to the holds, from where they follow ATC instructions rather than a published route. Under PBN the published arrival route would go all the way to the runway
Standard Instrument Departure Referred to as a SID; this is a ‘route’ for departures as specified in the UK’s Aeronautical Information Publication – see www.ais.org.uk
STAR See Standard Arrival Route
Statute mile A standard mile as used in normal day to day situations (eg road signs) but not for air traffic where nautical miles are used
Stepped climb A climb that is interrupted by periods of level flight required to keep the aircraft separate from another route in the airspace above
Stepped descent A descent that is interrupted by periods of level flight required to keep the aircraft separate from another route in the airspace above
Systemisation The process of reducing the need for human intervention in the air traffic control system, primarily by utilising improved navigation capabilities to develop a network of routes that are safely separated from one another so that aircraft are guaranteed to kept apart without the need for IR traffic control to issue specific institutions
T Metric Tonne (1t=1,000kg)
TA See Transition Altitude
Tactical methods Air traffic control methods that involve air traffic controllers directing aircraft off the established routes structure for reasons of safety of efficiency
Terminal airspace An aviation term to describe a designated area of controlled airspace surrounding a major airport or airports where there is a high volume of traffic; a large part of the airspace above London and the South East is defined as terminal airspace (or Terminal Manoeuvring Area – TMA). This is the airspace that contains all the arrival and departure routes for Heathrow, Gatwick, Stansted, Luton and London City from around 2,000ft to 3,000ft up to approximately 20,000ft
Transition (referring to a route) The part of an arrival flight path between the last hold (or Point Merge structure) and the final approach path to the runway
Transition Altitude The altitude at which aircraft switch their altimeter settings from local pressure to the standard international pressure setting; for the purposes of airspace design the transition altitude represents a cap on the maximum height that a departure rote can be defined to; it is currently 6,000ft across the UK but plans to raise it across Europe are being developed – see part A for details.
Uncontrolled airspace Generic term for the airspace in which no air traffic service is provided as standard
Uplift See fuel uplift
Vectored The application of ‘vectoring’
Vectoring An air traffic control method that involves controllers directing aircraft off the established routes structure for reasons of safety of efficiency.
Westerly operations When an runway is operating such that aircraft are taking off and landing in a westerly direction; see Runway 26 and Runway 27 respectively for definition of westerly operations at London City and Gatwick airports