In addition, the shorter bars before and after the Decision Bar are spaced either 100' or 200' apart depending on the ALS type. If the procedure calls for at least 1/2 statute mile flight visibility (roughly 2600'), spotting the Decision Bar at the marker would indicate enough flight visibility to continue the procedure. For example, if the aircraft is at the Middle Marker, and the Middle Marker is located 3600' from the threshold, the Decision Bar is 2600' ahead. ![]() It also is situated such that at Decision Altitude, the Decision Bar is just appearing to pass under the cowling of the plane.Īpproach Light Systems are designed to allow the pilot to quickly and positively identify visibility distances in Instrument meteorological conditions. The Decision Bar is always located 1000' from the threshold, and it serves as a visible horizon to ease the transition from instrument flight to visual flight. In both cases, the brightness of the lights can be adjusted for day and night operations.Ī key ingredient of all Approach Lighting Systems in the US is the Decision Bar. At uncontrolled airports, Pilot Controlled Lighting may be installed which can be switched on by the pilot via radio. The runway lighting is controlled by the air traffic control tower. ![]() ALS usually serves a runway that has an instrument approach procedure (IAP) associated with it and allows the pilot to visually identify the runway environment once he or she has arrived at a prescribed point on an approach. An approach lighting system, or ALS, is a lighting system installed on the approach end of an airport runway and consists of a series of lightbars, strobe lights, or a combination of the two that extends outward from the runway end.
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