Laredo’s localizer back-course approach Runway 36L
THOUGH DWINDLING IN NUMBER, BACK-COURSE APPROACHES STILL OFFER VALUE
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.