these systems is approximately three − quarter miles. To use the system the pilot positions the aircraft so the elements are in alignment. The glide path indications are shown in FIG 2 − 1 − 8. 

## 2 − 1 − 3. Runway End Identifier Lights (REIL) 

REILs are installed at many airfields to provide rapid and positive identification of the approach end of a particular runway. The system consists of a pair of synchronized flashing lights located laterally on each side of the runway threshold. REILs may be either omnidirectional or unidirectional facing the approach area. They are effective for: 

a. Identification of a runway surrounded by a preponderance of other lighting. 

b. Identification of a runway which lacks contrast with surrounding terrain. 

c. Identification of a runway during reduced visibility. 

## 2 − 1 − 4. Runway Edge Light Systems 

a. Runway edge lights are used to outline the edges of runways during periods of darkness or restricted visibility conditions. These light systems are classified according to the intensity or brightness they are capable of producing: they are the High Intensity Runway Lights (HIRL), Medium Intensity Runway Lights (MIRL), and the Low Intensity Runway Lights (LIRL). The HIRL and MIRL systems have variable intensity controls, whereas the LIRLs normally have one intensity setting. 

b. The runway edge lights are white, except on instrument runways yellow replaces white on the last 2,000 feet or half the runway length, whichever is less, to form a caution zone for landings. 

c. The lights marking the ends of the runway emit red light toward the runway to indicate the end of runway to a departing aircraft and emit green outward from the runway end to indicate the threshold to landing aircraft. 

## 2 − 1 − 5. In − runway Lighting 

a. Runway Centerline Lighting System (RCLS).  Runway centerline lights are installed on some precision approach runways to facilitate landing under adverse visibility conditions. They are located along the runway centerline and are spaced at 50 − foot intervals. When viewed from the landing 

threshold, the runway centerline lights are white until the last 3,000 feet of the runway. The white lights begin to alternate with red for the next 2,000 feet, and for the last 1,000 feet of the runway, all centerline lights are red. 

b. Touchdown Zone Lights (TDZL). Touch- down zone lights are installed on some precision approach runways to indicate the touchdown zone when landing under adverse visibility conditions. They consist of two rows of transverse light bars disposed symmetrically about the runway centerline. The system consists of steady − burning white lights which start 100 feet beyond the landing threshold and extend to 3,000 feet beyond the landing threshold or to the midpoint of the runway , whichever is less. 

c. Taxiway Centerline Lead − Off Lights. Taxi- way centerline lead − off lights provide visual guidance to persons exiting the runway. They are color − coded to warn pilots and vehicle drivers that they are within the runway environment or instrument landing system (ILS) critical area, whichever is more restrictive. Alternate green and yellow lights are installed, beginning with green, from the runway centerline to one centerline light position beyond the runway holding position or ILS critical area holding position. 

d. Taxiway Centerline Lead − On Lights. Taxi- way centerline lead − on lights provide visual guidance to persons entering the runway. These “lead − on” lights are also color − coded with the same color pattern as lead − off lights to warn pilots and vehicle drivers that they are within the runway environment or instrument landing system (ILS) critical area, whichever is more conservative. The fixtures used for lead − on lights are bidirectional, i.e., one side emits light for the lead − on function while the other side emits light for the lead − off function. Any fixture that emits yellow light for the lead − off function must also emit yellow light for the lead on function. (See FIG 2 − 1 − 12.) 

e. Land and Hold Short Lights. Land and hold short lights are used to indicate the hold short point on certain runways which are approved for Land and Hold Short Operations (LAHSO). Land and hold short lights consist of a row of pulsing white lights installed across the runway at the hold short point. Where installed, the lights will be on anytime LAHSO is in effect. These lights will be off when LAHSO is not in effect. 

