8/15/19 3/15/07 12/31/20 AIM  7110.65R CHG 2 AIM special instrument approach procedure to allow aircrews to verify the TLS guidance.  d. Special Category I Differential GPS (SCAT − I DGPS) 1. The SCAT − I DGPS is designed to provide approach guidance by broadcasting differential correction to GPS. 2. SCAT − I DGPS procedures require aircraft equipment and pilot training. 3. Ground equipment consists of GPS receivers and a VHF digital radio transmitter. The SCAT − I DGPS detects the position of GPS satellites relative to GPS receiver equipment and broadcasts differen- tial corrections over the VHF digital radio. 4. Category I Ground Based Augmentation System (GBAS) will displace SCAT − I DGPS as the public use service. REFERENCE − AIM, Paragraph 5 − 4 − 7 j, Instrument Approach Procedures 3. TLS instrument approach procedures are designated Special Instrument Approach Procedures. Special aircrew training is required. TLS ground equipment provides approach guidance for only one aircraft at a time. Even though the TLS signal is received using the ILS receiver, no fixed course or glidepath is generated. The concept of operation is very similar to an air traffic controller providing radar vectors, and just as with radar vectors, the guidance is valid only for the intended aircraft. The TLS ground equipment tracks one aircraft, based on its transponder code, and provides correction signals to course and glidepath based on the position of the tracked aircraft. Flying the TLS corrections com- puted for another aircraft will not provide guidance relative to the approach; therefore, aircrews must not use the TLS signal for navigation unless they have received approach clearance and completed the required coordination with the TLS ground equip- ment operator. Navigation fixes based on conventional NAVAIDs or GPS are provided in the Navigation Aids 1 − 1 − 38