Reference: T34C NATOPS, Chapter 19, Transponder (TDR950); Part VI, IFF/SIF.
Although it is considered a piece of identification equipment the transponder (Figure 48) will be
discussed here since it is used in conjunction with navigation equipment.
The transponder set is an identification, position tracking, and emergency tracking device. An
operating transponder receives, decodes and responds to interrogation by search radar.
Use of the transponder involves the setting of proper codes, setting the function selector to the
desired mode of operation and use of the reply/ident button.
Figure 48 Collins Transponder
Each code selector switch is used to set a digit 0 through 7. The function switch can bring the unit
from an OFF to a STANDBY condition. In the ON position the unit is in operation, without the
altitude encoding function. Placing the switch in the ALT position enables this function. In the
TEST position illumination of the reply lamp indicates operational capability.
The reply/ident button will flash on and off in response to interrogation by radar. This occurs in the
ALT or ON mode. The intensity of the flashes can be controlled by rotating this button. If the
button is depressed while in the ALT or ON Mode the reply lamp will light for approximately 20
seconds. At the same time the radar operator will see a distinct reply on his scope which facilitates
identifying your aircraft.
Basic airspeeds and configurations used in executing the various Radio Instrument Procedures
are listed below.
1. 170 knots
2. Approximately 750800 ftlbs
INTRODUCTION TO RADIO INSTRUMENTS 4-11