Garmin GNC 420W Pilots Guide - Page 192

SECTION 11 ADDITIONAL FEATURES TIS displays up to eight traffic targets within 7 nautical miles horizontally from 3000 feet below to 3500 feet above the requesting aircraft (Figure 11-1). 3,500 ft TIS Limitations NOTE: This section on TIS Limitations is not comprehensive. Garmin recommends the user review the TIS Limitations section of the Aeronautical Information Manual, Section 1-3-5. 7.0 nm Not to Scale Figure 11-1 TIS Coverage Volume 3,000 ft TIS is not intended to be used as a collision avoidance system and does not relieve the pilot responsibility to see and avoid other aircraft. TIS should not be used for avoidance maneuvers during IMC or other times when there is no visual contact with the intruder aircraft. TIS is intended only to assist in visual acquisition of other aircraft in VMC. No recommended avoidance maneuvers are provided for, nor authorized, as a direct result of a TIS intruder display or TIS advisory. TIS Operational Procedures TIS warns the user with voice and visual traffic advisories when it predicts an intruder to be a threat. The user should not start evasive maneuvers using information from the GNC 420 display or on a traffic advisory only. The display and advisories are intended only for assistance in visually locating the traffic, due to the lack in resolution and coordination ability. The flight crew should attempt to visually acquire the intruder aircraft and maintain a safe separation in accordance with regulatory requirements and good operating practice. If the flight crew cannot visually acquire the aircraft, they should contact ATC to obtain any information that may assist concerning the intruder aircraft. Based on the above procedures, minor adjustment to the vertical flight path consistent with air traffic requirements are not considered evasive maneuvers. NOTE: The main difference between TIS and TCAS is the source of surveillance data. TCAS uses an airborne interrogator with a half-second update rate, while TIS uses the terminal Mode S ground interrogator and its Data Link to provide about a 5-second update rate. The range accuracy of TIS and TCAS is similar. While TIS is a useful aid to visual traffic avoidance, it has some system limitations that must be fully understood to ensure proper use. Many of these limitations are inherent in secondary radar surveillance. In other words, the information provided by TIS is no better than that provided to ATC. TIS only displays aircraft with operating transponders installed. TIS relies on surveillance of the Mode S radar, which is a 'secondary surveillance' radar similar to the ATCRBS. TIS operation may be intermittent during turns or other maneuvering. TIS is dependent on two-way, line-ofsight communications between the aircraft and the Mode S radar. When the structure of the client aircraft 11-2 GNC 420(A) Pilot's Guide and Reference 190-00140-20 Rev. K