The localiser deviation displayed on the ADI/PFD or the HSI/ND ILS display, after capture, may become erratic or may maintain a continuous offset with corresponding unpredictable autopilot control or flight director guidance. With the flight director turned on and localiser or approach mode selected, the flight director will initially command a turn to track the inbound course, just like a normal capture. With the autopilot engaged and localiser or approach mode selected, the airplane will initially turn to acquire the inbound course, just like a normal localiser capture. Some of these indications are applicable to all airplanes, while some are unique to airplanes equipped with EICAS and/or EFIS displays. False capture occurs when these signal variations satisfy the automatic flight control system’s localiser capture logic.įalse captures can produce the following indications depending on the flight deck instrumentation. The false capture occurs due to significant scalloping, or signal reversals, in the region of the localiser where the signal is normally saturated. It is believed that a large number of occurrences are never reported since flight crews are generally trained to detect this anomaly, and false capture events are often not recorded in pilot flight logs.įlight crews should be aware that repeated false localiser captures can occur at certain airports due to the radiated signal characteristics of the localiser facility even when the airplane systems are functioning normally. Occurrences of false localiser captures during autopilot and flight director approaches have been reported at a number of airports throughout the world.
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