An intersection take off is a take off that starts at a position different than the beginning of a runway. This means that some of the runway will not be available for the take off run. Benefits associated with intersection take offs include:
- runway capacity improvement
- reduced taxi time
- noise alleviation
- air pollution reduction
An aircraft may be cleared to depart from a published intersection take off position upon request of the pilot, or if initiated by ATC and accepted by the pilot, provided that all the applicable requirements are met. These may include:
- Time of day (e.g. intersection take offs may only be allowed during daytime)
- Visibility (i.e. intersection take offs are only to be performed when the visibility is above certain value)
- Location (i.e. intersection take offs may only be performed from certain positions on the runway)
The process of establishing intersection take off procedures normally includes consultation with aircraft operators and other stakeholders in order to agree on suitable intermediate intersection take-off positions along the runway(s). After that, the reduced runway declared distances are determined and appropriate procedures are established. These are then published in the State Aeronautical Information Publications (AIPs) in a way that makes them clearly distinguishable from full runway declared distances.
In accordance with ICAO Annex 14, an intersection take-off sign should be provided when there is an operational need to indicate the remaining take-off run available (TORA) for intersection take offs. The inscription on this take-off consists of a numerical message indicating the remaining take-off run available in metres plus an arrow, appropriately located and oriented, indicating the direction of the take-off as shown on the picture below.
Examples of intersection take-off signs
The choice between a full-length and an intersection take off is an aspect of the decision making process. While the controller may offer (or approve) an intersection departure it is the responsibility of the pilot in command to assess whether this is a safe option and, if not, to decline the ATC proposal. The potential benefits (e.g. flight efficiency) needs to be balanced against the potential risks, e.g.:
- a Runway Incursion may occur if the controller forgets (e.g. due to distraction) that two or more aircraft are cleared to enter the same runway via different intersections.
- a Runway Excursion following an aborted take-off (e.g. due to engine failure) is more likely to happen when an intersection is used.
- the margin for error (e.g. in calculating the necessary thrust setting) is reduced
- a Reduced Thrust Takeoff, originally calculated for a full-length run, may be inappropriate for an intersection departure
- intersection line ups provide fewer visual ques therefore increasing the chance of a Runway Misalignment or a taxiway take off
- wake turbulence. The effects of wake turbulence start at the point where the preceding aircraft rotates so if an intersection departure is used, it is more likely that the rotation will take place at the same place or further down the runway (since the larger aircraft probably started the take off roll at the beginning of the runway). This may cause Loss of Control as was in the C185, Wellington New Zealand, 1997 event.
There is no standard phraseology to address intersection departures. Therefore, an instruction "Line up runway [number]" issued when an aircraft is at the holding point will result in an intersection take off as opposed to "Backtrack and line up runway [number]" which would mean that a full-length departure will take place.
In some countries specific phraseology has been developed for these situations, e.g.:
- In the United States, when authorizing an aircraft to line up at or take off from an intersection, the controller states that intersection:
- "RUNWAY [number] AT [taxiway designator], LINE UP AND WAIT"
- "RUNWAY [number] AT [taxiway designator] CLEARED FOR TAKEOFF"
- In the United Kingdom, the intermediate holding point designator is included in the line-up instruction (but not in the take-off clearance): "VIA [taxiway designator] LINE-UP RUNWAY [number]". Additional phraseology is available for:
- Air traffic controllers proposing an intersection departure - "ADVISE ABLE TO DEPART FROM RUNWAY [number] INTERSECTION [taxiway designator]"
- Pilot requests for an intersection departure - "REQUEST DEPARTURE FROM RUNWAY [number], INTERSECTION [taxiway designator]"
- Information on the Take-Off Run Available (TORA) (pronounced TOR-AH) from the intersection. This is issued when requested by a pilot or whenever deemed necessary by the controller. "TORA RUNWAY [number] FROM INTERSECTION [taxiway designator] [number] METRES"
Accidents and Incidents
On 18 September 2018, an Airbus A320 crewed by a Training Captain and a trainee Second Officer departing Sharjah was cleared for an intersection takeoff on runway 30 but turned onto the 12 direction and commenced takeoff with less than 1000 metres of runway ahead. On eventually recognising the error the Training Captain took control, set maximum thrust and the aircraft became airborne beyond the end of the runway and completed its international flight. The Investigation attributed the event to the pilots’ absence of situational awareness and noted that after issuing takeoff clearance, the controller did not monitor the aircraft.
On 5 February 2012, an Airbus A340-300 started its takeoff from an intermediate point on the runway for which no regulated takeoff weight information was available and had only become airborne very close to the end of the runway and then climbed only very slowly. The Investigation found that as the full length of the planned departure runway was not temporarily unavailable, ATC had offered either the intersection subsequently used or the full length of the available parallel runway and that despite the absence of valid performance data for the intersection, the intersection had been used.
On 8 December 2011, an Airbus A340-300 did not become airborne until it had passed the end of the takeoff runway at Rio de Janeiro Galeão, which was reduced in length due to maintenance. The crew were unaware of this fact nor the consequent approach lighting, ILS antennae and aircraft damage, and completed their intercontinental flight. The Investigation found that the crew had failed to use the full available runway length despite relevant ATIS and NOTAM information and that even using rated thrust from where they began their takeoff, they would not have become airborne before the end of the runway.
On 18 January 2016, an Embraer 120 crew made a night takeoff from Amsterdam Runway 24 unaware that the aircraft was aligned with the right side runway edge lights. After completion of an uneventful flight, holes in the right side fuselage and damage to the right side propeller blades, the latter including wire embedded in a blade leading edge, were found. The Investigation concluded that poor visual cues guiding aircraft onto the runway at the intersection concerned were conducive to pilot error and noted that despite ATS awareness of intersection takeoff risks, no corresponding risk mitigation had been undertaken.
On 21 July 2017, a Boeing 737-800 taking off from Belfast was only airborne near the runway end of the runway and then only climbed at a very shallow angle until additional thrust was eventually added. The Investigation found that the thrust set had been based on an incorrectly input surface temperature of -52°C, the expected top of climb temperature, instead of the actual surface temperature. Although inadequate acceleration had been detected before V1, the crew did not intervene. It was noted that neither the installed FMC software nor the EFBs in use were conducive to detection of the data input error.
On 30 August 2016, a Boeing 777-300 crew began takeoff from London Heathrow at an intersection one third of the way along the runway using the reduced thrust calculated for a full-length take off instead of the rated thrust calculated for the intersection takeoff. As a result, the aircraft was only just airborne as it crossed the airport boundary and an adjacent public road. The Investigation attributed the data input error to crew failure to respond appropriately on finding that they had provisionally computed performance data based on different assumptions and concluded that the relevant Operator procedures were insufficiently robust.
On 6 October 2014, an A320 crew requested, accepted and commenced an intersection takeoff at Basel using reduced thrust performance data based on the originally anticipated full length takeoff which would have given 65% more TODA. Recognition of the error and application of TOGA allowed the aircraft to get airborne just before the runway end but the Investigation found that a rejected take off from high speed would have resulted in an overrun and noted that despite changes to crew procedures after a similar event involving the same operator a year earlier, the relevant procedures were still conducive to error.
On 1 October 2013, an Airbus A320 took off from a runway intersection at Porto which provided 1900 metres TORA using take off thrust that had been calculated for the full runway length of 3480 metres TORA. It became airborne 350 metres prior to the end of the runway but the subsequent Investigation concluded that it would not have been able to safely reject the take-off or continue it, had an engine failed at high speed. The event was attributed to distraction and the inappropriate formulation of the operating airline's procedures for the pre take-off phase of flight.