Page 19 - Volume 16 Number 1

with a standard transponder with an antenna on the belly of the airplane.Transponders work on the principle of line-of-sight transmis- sion. That’s why standard transponder antennae are on the belly – so the airframe doesn’t block the signal to radar interrogations from the ground. Airplane A’s system will detect Airplane B because one or more of A’s antennae can “see” Airplane B’s transponder antenna. The cockpit display shows Airplane A’s pilot where to look for Airplane B. If Airplane B turns toward Airplane A, becoming a real collision threat, Airplane B’s fuselage and wings may blank out its transponder signal. The target disappears from Airplane A’s traffic display – just when Airplane A’s pilot needs to see Airplane B the most.Figure 2 illustrates a limitation of traffic alerting systems. An airplane is in cruise flight (top), while another is climbing from beneath on an intersecting course. The cruising airplane has a traffic detection device, while the climbing airplane is equipped with a standard transponder. When the lower airplane is in position 1, the higher airplane’s traffic detector can “see” its transponder antenna, so a target is displayed. As the climbing target gets closer, however, its wings and fuselage block the signal above, and the climbing airplane disappears from the cruising airplane’s detector. At some point when the climbing airplane is behind the cruising airplane, the two antennae will re-establish line- of-sight and the target will reappear on the cruising airplane’s display.Portable “Fuzzbuster” traffic detectors, the kind that lay on the glareshield or elsewhere, may have even more blind spots for close- in traffic.So, don’t give a sigh of relief if that target closing in on you suddenly disappears from the traffic alerter. The airplane may still be nearby. Traffic detectors are great safety devices further out, but a target thatdisappears from the scope is still a threat to see and avoid visually. Best use of a traffic detector is not to use a target’s penetration of the inner, close-in ring as your prompt to start looking for the other airplane. And, certainly, you cannot see and avoid airplanes entirely by use of the instrument panel device.Instead, traffic detectors are best used to help you find other airplanesvisually while they’re in the two-to- six mile range (or greater, in faster airplanes or when the target is faster). That’s when you have to increase your visual scanning for traffic, to “have the traffic in sight” before it gets close enough to disappear in the blind spots. The alerter does its job by prompting you to look outside – when you have much more than the 12 seconds you need to see and avoidother airplanes.T&T •MAdE IN THE USA$1370 $1785Phone (954) 966-7329 FAX: (954) 966-3584 5614 SW 25 St., Hollywood, FL 33023 web: www.survivalproductsinc.comemail: sales@survivalproductsinc.comJANUARY 2012TWIN & TURBINE • 17