An area symmetrical about the extended runway centre line and adjacent to the end of the strip primarily intended to reduce the risk of damage to an aeroplane undershooting or overrunning the runway
[Source: ICAO Annex 14]
Runway End Safety Areas (RESAs) are a formal means to limit the consequences when aeroplanes overrun the end of a runway during a landing or a rejected take off, or undershoot the intended landing runway.
They are constructed to provide a cleared and graded area which is, as far as practicable, clear of all but frangible objects. It should have a surface which will enhance the deceleration of aircraft in the overrun case but should not be such as to hinder the movement of rescue and fire fighting vehicles or any other aspect of emergency response activity.
Minor aircraft runway overruns and undershoots are a relatively frequent occurrence. Most data sources point to significant occurrences on average once a week worldwide and suggest that runway excursions overall are the fourth largest cause of airline fatalities. It has been stated by the U.S. Federal Aviation Administration (FAA) Airport Design Division that approximately 90% of runway undershoot or overruns are contained within 300 metres of the runway end. The contribution which RESAs can make to a reduction in the consequences of such over-runs has frequently been demonstrated as has the avoidable hazardous outcomes where they have not been present.
ICAO Annex 14 SARPs
ICAO SARPs relating to runways are determined according to runway length using the standard Runway Code categories. Code 1 runways are less than 800 metres long, Code 2 runways are 800-1199 metres long, Code 3 runways are 1200-1799 metres long and Code 4 runways are 1800 metres or more in length.
In all cases, the dimensions of a ‘Runway Strip’ are first defined as it must contain the dimensions of the designated runway surface and it should be flat, firm and free of non-frangible obstructions. For Code 3 and 4 runways, runway strips must extend at least 150 metres either side of the runway centreline and at least 60 metres beyond the end of the runway including any stopway. For Code 1 and 2 runways, the width requirement is reduced to 75 metres and for non-instrument Code 1 Runways, the length requirement is reduced to 30 metres.
ICAO RESA specifications all begin at the limit of the ‘Runway Strip’ not at the limit of the Runway/Stopway surface.
RESA SARPs were revised in 1999 when the then Recommended Practice of a 90 metre RESA was converted into a Standard. The current Requirement is that Code 3 and 4 runways have a RESA which extends a minimum of 90 metres beyond the runway strip and be a minimum of twice the width of the defined runway width. The additional Recommended Practice for these runway codes is that the RESA length is 240 metres or as near to this length as is practicable at a width equal to that of the graded strip. For Code 1 and 2 Runways, the Recommended Practice is for a RESA length of 120 metres with a width equal to the graded strip.
Implementation of these SARPs by State Regulators is ongoing. Many have now prescribed a period within which the ICAO Standard must be adopted and the Recommended Practices carefully considered.
In the case of the USA, the FAA Airport Design requirements specify the minimum dimensions of a ‘Runway Safety Area’ which includes the Runway Strip defined by ICAO. Since 2002, these requirements have included a Runway Safety Area at each end of a runway which takes account of the direction of runway use when specifying the minimum length of the runway end element. The basic standard is defined for instrument runways used by transport aircraft and any such runway with an ‘approach visibility minima’ of less than 1200 metres and is 300 metres for the overrun case and 180 metres for the undershoot case. It is permissible to reduce the overrun case to 180 metres if the runway has either instrument or visual vertical guidance aids and an Engineered Materials Arresting System (EMAS) which can stop an aircraft which leaves the end of the runway at up to 70 kts groundspeed is provided.
It can be seen that the FAA overrun requirement (300 metres) is equivalent to the ICAO RESA Recommended Practice plus the required Runway Strip (also totalling 300 metres) but that the FAA undershoot requirement (180 metres) is only slightly more than the ICAO RESA Standard plus the required runway strip (totalling 150 metres).