Approach Lighting Systems (ALS) provide the basic means to transition from instrument flight to visual flight for landing. Operational requirements dictate the sophistication and configuration of the approach Lighting system for a particular runway. Where displaced thresholds are required and/or intersections with another runway require such an application, lights may have to be placed in pavement to permit aircraft and vehicular traffic on the pavement. Semi flush lights primarily assist by providing visual guidance in precision approaches.
Semi flush lights must not only withstand the stresses and strains of aircraft, but also endure snow plows and heavy equipment transversing them. Lights must be installable onto L-868 light bases. To avoid excessive damage, the units must be able to withstand snow removal chemicals; have a stainless steel or aluminum top cover; have a maximum input power to the light unit of 200 watts (500 watts for ALSF-2); and have the torqueing instructions provided on an attached metal plate. Lights must have 1,000 hour minimum lamp operational lifetime and must have an internal flange to restrain each lens, or alternatively a wedge shaped lens and mating aperture. Further, units must be able to be repaired and returned to service within 12 minutes, weigh under 44 pounds, have 1/16 minimum radius of curvature on exposed exterior surfaces, and ½maximum projection above the runway pavement.
FAA Technical Lead in ATO: Leonixa Salcedo - (202) 493-5182
Current Status: There are a few thousand semi flush units in the NAS . Principal manufacturers include Crouse Hinds, Multi Electric Manufacturing, Inc.