Traffic Alert/Collision System

STUDENT GUIDE FOR T-1A AIRCRAFT SYSTEMS

CHAPTER TWELVE

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

threat.

Surveillance

The TCAS detects and tracks up to 30 aircraft simultaneously.

Threat Detection

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

Approach (CPA).

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

current flightpath.

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.

NAVIGATION RADIOS

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