What are Rapid Exit Taxiway Indicator Lights (RETIL)?

Rapid Exit Taxiway Indicator Lights (RETIL)

Definition

Rapid exit taxiway indicator lights (RETILs) are yellow runway lights that show a landing pilot the distance to the nearest rapid exit taxiway.

RETIL stands for rapid exit taxiway indicator lights. ICAO gives the purpose in a note to Annex 14, 5.3.15. The lights give pilots distance-to-go information to the nearest rapid exit taxiway on the runway. They improve situational awareness in low visibility. They let pilots apply braking action for more efficient roll-out and runway exit speeds.

A rapid exit taxiway is a taxiway that meets the runway at an acute angle. It lets landing aeroplanes turn off at higher speed than on other exit taxiways. This keeps the runway occupancy time short (ICAO Chapter 1, CS ADR-DSN.A.002). The high-speed taxiway page covers the taxiway itself.

Why the pilot needs a distance cue

After a landing, runway occupancy time has a significant effect on runway capacity. RETILs let pilots keep a good roll-out speed until they must slow down for the turn into the exit. Annex 14 Attachment A and EASA guidance give an optimum roll-out speed. It is 60 kt until the pilot reaches the first RETIL.

In low visibility the lights give the pilot useful situational awareness cues. The pilot can then concentrate on keeping the aircraft on the runway centre line.

The light pattern

The lights stand in sets. Each set has its own count of lights, and the counts fall in a 3-2-1 sequence before the exit.

• Sequence. The sets stand at 100 m intervals before the point of tangency of the rapid exit taxiway centre line. Figure 5-25 of Annex 14 shows the three-light set 300 m before that point. The two-light set is 200 m before it, and the single light is 100 m before it.
• Position across the runway. The lights of a set stand 2 m apart. The light nearest to the runway centre line is displaced 2 m from it.
• Side. A set stands on the same side of the runway centre line as its rapid exit taxiway.
• Several exits. Where a runway has more than one rapid exit taxiway, the sets for each exit must not overlap when lit.

A full set for one exit has six lights. The first set that the pilot sees is the three-light set, and EASA calls it a three-light barrette. The barrette page explains the term.

Colour, direction and light output

RETILs are fixed unidirectional yellow lights. They are aligned so that the pilot of a landing aeroplane sees them in the direction of approach to the runway (ICAO 5.3.15.5).

ICAO and EASA refer to the isocandela diagrams of the runway centre line light. CS ADR-DSN.M.700(c)(3) names Figure U-10 or U-11, and the figure depends on the centre line light spacing of 30 m or 15 m. Figure U-10 prints its values for white light, with a minimum average of 5,000 cd in the main beam. Note (c) says to multiply the values by 0.40 for yellow light. For a RETIL on a runway with 30 m centre line spacing, the minimum average is then 2,000 cd.

ICAO and EASA recommend a separate power circuit for RETILs. The aim is that they can work when the other runway lights are off (ICAO 5.3.15.7, CS ADR-DSN.M.700(c)(2)).

When a runway has RETILs

ICAO recommends RETILs on a runway for use in runway visual range below 300 m, where traffic density is heavy, or both (5.3.15.1). EASA states that its specifications do not mean that an aerodrome has to provide RETILs (M.700(a)(1)). EASA guidance says to consider them on a runway for use in runway visual range below 350 m, where traffic density is heavy (GM1 ADR-DSN.M.700(b)).

Where an aerodrome installs RETILs, the location and pattern rules apply (ICAO 5.3.15.3 and 5.3.15.4).

What happens when a lamp fails

ICAO states that RETILs must go dark after any lamp failure or other failure that prevents the full light pattern (5.3.15.2). EASA guidance says that they should go dark (GM1 ADR-DSN.M.700(c)).

A missing light would change the count in a set. See lamp failure for how failures count against other lighting systems.

The rapid exit taxiway

ICAO and EASA recommend these design values:

• Intersection angle. Not more than 45 degrees, not less than 25 degrees, and preferably 30 degrees (ICAO 3.9.18, CS ADR-DSN.D.295(e)).
• Turn-off curve radius. At least 550 m for code number 3 or 4. At least 275 m for code number 1 or 2.
• Exit speed in wet conditions. The radius allows 93 km/h (about 50 kt) for code number 3 or 4. It allows 65 km/h (about 35 kt) for code number 1 or 2.
• Straight distance after the curve. It is long enough for the aircraft to stop clear of any intersecting taxiway.

ICAO Annex 14 refers to ICAO Doc 9157 Part 2 for guidance on where rapid exit taxiways stand along a runway.

RETILs and taxiway centre line lights

Two different sets of lights serve a rapid exit taxiway.

• RETILs stand in the runway, show yellow, and give distance to go before the exit.
• Taxiway centre line lights on the rapid exit taxiway guide the aircraft along the exit. ICAO recommends that they start at least 60 m before the beginning of the curve of the taxiway centre line. They continue to a point where the aeroplane can reach normal taxiing speed. The spacing is at most 15 m, or at most 30 m where the runway has no centre line lights (ICAO 5.3.17.16 and 5.3.17.17).

On an exit taxiway the centre line lights are fixed. They alternate green and yellow near the runway. The alternation stops at the perimeter of the ILS or MLS critical or sensitive area, or at the lower edge of the inner transitional surface. Beyond that, all lights show green (ICAO 5.3.17.7). The taxiway centre line light page covers these lights.

Inspecting RETILs

An inspection of the RETILs of one exit checks these items:

• The set of three, the set of two and the single light are all present, and all six lights work.
• All lights show yellow toward the landing direction.
• The sets stand on the exit side of the centre line. The lights are 2 m apart, and the nearest light is 2 m from the centre line.
• The sets of neighbouring exits do not overlap.
• The whole pattern goes dark when one lamp fails, and it does not show a partial count.

A drone can record the count, colour and position of each light in the runway. TarmacView’s drone airport inspection covers airfield lighting, including lights in the runway.