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 computed 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 equipment operator. Navigation fixes based on
conventional NAVAIDs or GPS are provided in the

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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 differential 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 f, Instrument Approach Procedures

Navigation Aids