Self Explanatory ??????
FAA Advisory Circular (AC) 150/5340-24 Runway and Taxiway Edge Lighting Systems, published in September 1975, described standards for design, installation, and maintenance of runway and taxiway lighting for airports. Appendix 2 of the AC included diagrams of acceptable methods of light arrangements. On page 3 of the appendix, two locations for placement of threshold lights are shown, both outboard and inboard of the runway edge.
In April of 2004, AC 15/5340-24 was incorporated into AC 150/5340-30, Design and Installation Details for Airport Visual Aids. This AC no longer included the diagram showing threshold lights installed outside the runway edges, except for instances where usable pavement, such as a taxiway, extended beyond the threshold. The AC was revised in April of 2005, and became AC 150/5340-30A. It was again revised in August of 2006 and was renamed AC 150/5340-30B. Neither of these revisions included the former method of installing threshold lights outboard of a runway, except when usable pavement extended beyond the threshold. It is noted that the 2004 and 2005 versions of the AC stated, "The standards contained herein are effective for all new construction. Upgrades for all future lighting systems should use this standard." There was no mention in either AC of any requirement to proactively upgrade existing installations. Figures 3 and 4 show currently approved standards for threshold lighting.
Page 1 of AC 150/5340-30B, stated that: "All lighting configurations contained in this standard including declared distances and yellow-green taxiway centerline lead-on lines are the only means acceptable to the Administrator and must be incorporated within 6 months after signature of this AC." Safety Board staff asked the FAA whether or not this requirement applied to existing threshold lighting configurations, as stated in the AC. In an official response dated March 15, 2007, the FAA replied:
"This change was not included in the paragraph, Principal Changes, in AC 150/5340-30 because it was not intended that existing systems be modified to conform to the new standard. When AC 150/5340-30B was published, it stated, "All lighting configurations contained in this standard including declared distances and yellow-green taxiway centerline lead-on lights are the only means acceptable to the Administrator and must be incorporated within 6 months after signature of this AC." This change was intended to rapidly implement new taxiway/runway intersection lighting standards, which could be accomplished in the time period specified because the change would only require changing lenses on lighting fixtures. The language, which conveyed a requirement to upgrade taxiway end lighting was inadvertently included. This could not reasonably be accomplished in six months, and it was not our intention to include such a requirement. However, after further consideration, we are currently reviewing our standards for runway end lighting and anticipate additional changes. We expect to make such changes mandatory, and will specify a reasonable compliance period."
Safety Board staff also asked the FAA how many runways in the United States had threshold lights that did not meet the current standard. The FAA replied that they "do not keep any records that indicate the number of Part 139 airports that have threshold lights not meeting the standards in AC 150/5340-30B." It was noted that, in addition to runway 12/30, runway 8R/26L at MIA had similar threshold lights that did not meet the current standards.