Laredo’s lo­cal­izer back-course ap­proach Run­way 36L


Flying - - CONTENTS - By Rob Mark

In an era of WAAS GPS nav­i­ga­tion sys­tems on board even the small­est air­craft, fly­ing a lo­cal­izer back-course ap­proach could seem rather ar­chaic. In­deed, for years many pi­lots viewed a LOC BC ap­proach as more of an af­ter­thought at air­ports, sim­ply be­cause the pro­ce­dure was built off the back side of a full ILS sys­tem al­ready in op­er­a­tion to the op­po­site end of the same run­way.

But still, to­day, LOC BC ap­proaches, de­spite be­ing non­preci­sion, can serve as a valu­able re­source be­cause they pro­vide fairly pre­cise ground-based guid­ance to pi­lots fly­ing air­planes that might not use ter­ri­bly so­phis­ti­cated avion­ics. All that’s needed to fly a LOC BC to min­i­mums is a VOR re­ceiver with an omni bear­ing se­lec­tor, an in­stru­ment-cur­rent pi­lot and a method of track­ing time in­bound from the fi­nal ap­proach fix. Here are some im­por­tant de­tails of this ap­proach. A. Fly­ing the back-course Run­way 36 Left ap­proach at Laredo Texas (LRD) be­gins when the pi­lot tunes in the lo­cal­izer fre­quency 111.9, which also hap­pens to be the same lo­cal­izer fre­quency used to fly the ILS to Run­way 18 Right.

A back-course ap­proach dif­fers due to some­thing called re­v­erse sens­ing. When op­er­at­ing un­der re­v­erse sens­ing, pi­lot re­ac­tions to move­ments of the lo­cal­izer nee­dle are ac­tu­ally op­po­site to those they’d use if they were fly­ing the front-course ap­proach. Re­v­erse sens­ing can also be ex­pe­ri­enced when track­ing to a VOR on a head­ing with the op­po­site course se­lected. Un­der re­v­erse sens­ing, as the lo­cal­izer nee­dle moves left to in­di­cate an off-course con­di­tion, the pi­lot must bank slightly to the right in or­der to re-cen­ter the nee­dle. B. Mod­ern nav­i­ga­tion sys­tems have eased the bur­den for pi­lots fly­ing LOC BC ap­proaches. For in­stance, with a hor­i­zon­tal sit­u­a­tion in­di­ca­tor (HSI) in­stalled, the pi­lot can sim­ply twist the course se­lec­tor to the out­bound course rather than the in­bound to elim­i­nate re­v­erse sens­ing. On this ap­proach then, a pi­lot us­ing an HSI would set the course se­lec­tor to 178 de­grees, not 358 de­grees. Many mod­ern au­topi­lots of­fer re­v­erse-sens­ing op­tions that can sig­nif­i­cantly re­duce the tra­di­tional work­load of LOC BC ap­proaches, as do pri­mary flight dis­plays show­ing own-ship po­si­tion. C. An­other im­por­tant as­pect of a LOC BC ap­proach is that while the cock­pit glides­lope nee­dle may be­come in­ter­mit­tently ac­tive, the pi­lot must ig­nore any guid­ance they see, since the ra­dio is ac­tu­ally sens­ing an in­ac­cu­rate and er­ro­neous glides­lope sig­nal from the op­po­site end of the run­way. D. Note that “DME is re­quired for ar­rival from the en route en­vi­ron­ment.” The LRD ap­proach can be flown be­gin­ning at the LRD VOR, then by fly­ing south­east­erly on LRD R-132 to the 10 DME point be­fore turn­ing west­erly along the 10 DME arc to in­ter­cept the lo­cal­izer near the in­ter­me­di­ate fix FOMUX. There is, how­ever, no pro­ce­dure turn avail­able on this ap­proach. An IFR-cer­ti­fied GPS or radar vec­tors could sub­sti­tute along por­tions of the ap­proach. E. An­other cau­tion­ary note is to “use I-LRD DME when on the lo­cal­izer course.” If a pi­lot flies to the ini­tial ap­proach fix, the LRD VOR (117.4), then to the 10 DME point and along the arc, he or she must re­mem­ber to change ra­dio fre­quen­cies to 111.9 to re­ceive an ac­cu­rate DME sig­nal for the LOC BC step-down points. F. Un­like many missed-ap­proach pro­ce­dures that fly di­rect, this one de­mands the pi­lot first climb to at least 1,100 feet be­fore turn­ing left to a 290-de­gree head­ing while con­tin­u­ing the climb to 2,600 feet to join the LRD R-319 that leads to the hold­ing pat­tern at BLAME. This re­quires the pi­lot to again switch fre­quen­cies back to the LRD VOR on 117.4. G. In many ap­proach pro­ce­dures, cir­cling is lim­ited due to ter­rain. On this ap­proach, the re­stric­tion is the nearby U.S.-Mex­ico bor­der. Pi­lots must re­main east of both run­ways at Laredo when cir­cling in or­der not to cross the bor­der, but also so as not to in­ter­fere with air traf­fic at the busy nearby Quet­zal­coatl In­ter­na­tional Air­port in Nuevo Laredo, Mex­ico.

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