Runway lights provide the means for the pilot to transition from IFR to VFR flight just before landing. The image shows the precision approach lights. There are also light configurations for non-precision approach runways. They are sometimes switched on, even on request, for VFR pilots in reduced visibility conditions with a low sun angle when the runway aligns in the direction of the sun.
To help the pilot fly a safe approach on finals to the runway a system of lights are used to indicate the correct glide-path and alignment on the center line, these lights are located left or right to the runway and are visible some distance away. After completing the landing, the pilot is guided to his parking position by blue taxiway edge lights.
Having intimate knowledge of these airport and runway lights and familiarity with the layout will increase the safety of your night flight operations.
ALS or approach light systems are designed to transition from IFR to VFR and help the pilot keeping the aircraft aligned with the runway centerline for landing. They start out from the threshold to a distance from 2400 to 3000 feet for precision and to 1500 feet for non-precision runways. Some systems have a ball of light (strobe) running and pointing towards the runway.
But seeing the runway on final approach is not the complete picture. The aircraft needs to stay clear of any obstacles in the approach area. For this visual glideslope indicators were developed.
They are visible from 3 to 5 miles during the day and up to 20 miles at night these lights provide the pilot a safe obstruction clearance within 10 degrees from the extended runway centerline to 4 NM from the threshold. Descend should not start until the aircraft is aligned with the runway centerline.
The installation of a VASI (Visual Approach Slope Indicator) consists from 2 up to 16 light units arranged in bars (near, middle and far). Most will have two bars: near and far. The glide slope indicated by a two bar VASI is 3°, the three bar VASI have two glideslopes: 3° and for high cockpit aircraft a glideslope at 3.25°. These glideslope angles may vary due to obstacle clearance requirements.
The PAPI (Precision Approach Path Indicator) is a similar system as a VASI but it has less lights and is installed in a single row of either two or four light and installed on the left side of the runway. Larger GA airports with sealed runways usually have a PAPI as it is less costly than a full VASI installation.
This is a single light system with lenses which projects three different lights: RED for under glide path, GREEN (on glide path) and AMBER (above glide path).
Much like the tricolor system but equipped with a pulsating red light for below glide path and pulsating white for above glide path. Steady red is slightly below and steady white is on glide path.
This is a system with three panels in a highly visible fluorescent color where the middle element is located a bit to the rear and lower than the outer two. While approaching the runway, the pilot must keep the elements in one visual line to remain on the correct glide path.
The runway itself is also marked with lights, predominantly with end identifier, edge, centerline and taxi lights as discussed below.
REIL (Runway End Identifier Lights) are a pair of synchronized flashing lights positively indicating the approach end of the runway. They can be omni or uni-directional and are mainly used in circumstances of reduced visibility.
Used to outline the edges of the runway. Edge lights are white except for instrument runways where the last 2000 feet is yellow. The runway thresholds are either green or red.
These lights have three intensity settings: HIRL, MIRL and LIRL. Meaning: high, medium and low intensity runway lights.
The in-runway lights consists of the Centerline Lighting, Touchdown Zone, Taxiway Lead-off and the Land and Hold Short light systems. The runway centerline and edge light changes color when approaching the end of the runway as an indication to pilots of how much runway is left to roll out.
These have a green centerline and blue edge lighting system. Keep a taxiway map close-by as all those blue lights can be confusing in the dark. These days with GPS equipped tablets and sophisticated navigation software, this should be no problem.