STUDENT GUIDE FOR T-1A AIRCRAFT SYSTEMS
ATC Transponder Tuning Using the RTU
The fifth line of the CP's RTU displays the transponder active code. Pressing the ATC2 line key
moves the selector star to that line. The code may now be changed using the tuning knobs. The
RTU large tuning knob changes the two most significant digits and the small tuning knob
changes the two least significant digits of the code.
ATC Transponder Tuning Using the CDU
The transponder may be tuned by the CDU when the CDU RADIO TUNING page is selected.
Enter any valid code in the scratch pad line. Press the ATC line key to transfer the code from the
scratch pad line to the ATC location. The old transponder code is discarded and the transponder
is tuned to the new code. If the code entered is invalid or out of range, the CDU last line
displays an error message.
1207. TRAFFIC ALERT/COLLISION SYSTEM
The TCAS II aids the flight crew by detecting the presence of nearby aircraft and providing
warning when the proximity of that aircraft is determined to be a safety threat. The TCAS
interrogates the transponders in the surrounding aircraft and uses the replies from those
transponders to compute their flightpath. From this data, the TCAS evaluates the potential
The TCAS detects and tracks up to 30 aircraft simultaneously.
The type of advisory appropriate for a given threat situation is a function of the aircraft altitude.
These altitude ranges can be seen as sensitivity levels. The types of advisories issued are Traffic
Advisory (TA), Preventive Resolution Advisory (PRA), and Corrective Resolution Advisory
(CRA). The TCAS threat evaluation and resolution is based on a projected Closest Point of
1. Traffic Advisory - A TA is primarily informative in nature, informing the crew of nearby
traffic not presently seen as a threat but can become a threat if conditions change. Aural
annunciation of TAs is provided at altitudes above 500 feet Above Ground Level (AGL).
2. Preventive Resolution Advisory - A PRA, advises the crew not to change the present
vertical flightpath. This means the TCAS has determined the situation is being resolved with the
3. Corrective Resolution Advisory - A CRA is presented to the crew combined in two
forms, aurally and visually. The advisories are issued so the most demanding resolution
(climb/descend) is displayed. When TCAS issues a CRA, the aural form is issued first, then the
visual form is presented.