TRANSPONDERS IN GLIDING Presented by Bill Kendall CFI

TRANSPONDERS BY THE END OF TONIGHT YOU WILL HAVE A BASIC UNDERSTANDING ABOUT: Primary and Secondary Radar in New Zealand Phraseology used with Air Traffic Controllers Transponders used by Taupo Gliding Club

RADAR SYSTEMS IN NZ PRIMARY RADAR: This type of radar can detect and report the position of anything that reflects its transmitted radio signals including, depending on its design, aircraft, birds, weather and land features. SECONDARY RADAR: Secondary surveillance radar (SSR)[1] is a radar system used in air traffic control (ATC), that not only detects and measures the position of aircraft i.e. range and bearing, but also requests additional information from the aircraft itself such as its identity and altitude.

Primary Radar

Secondary Surveillance Radar SSR Secondary radar works by sending out a signal from the radar aerial which causes the aircraft to send a reply signal back to the radar receiver. The range of secondary radar is 250 miles. There are 6 secondary radar installations in New Zealand situated at various locations to provide the required coverage. The disadvantage is that only aircraft fitted with serviceable transponders will be detected

3 PSR 6 SSR Flight plan details IFR and some VFR The Computer Auckland Oceanic Ohakea Christchurch Control Towers National Briefing Office

ATC Transponder Phraseology Some phraseology may vary from that listed below, just remember, unless otherwise stated, you should read back or acknowledge instructions. “SQUAWK” (e.g. “SQUAWK 3714”) which means:- set the code as instructed i.e. change the code on your transponder to that given. You are required to read back:- “SQUAWK 3714”

“RESET SQUAWK (Mode/Code)” (e.g. “RESET SQUAWK 3714” Which means: reset the assigned mode/code. This phrase could be used if it appears to the controller that you have dialled up a wrong mode or code on your transponder. You should read back: “RESET SQUAWK 3714” “Ooops sorry”

“CONFIRM SQUAWK” (e.g. “CONFIRM SQUAWK 3714”) Which means: confirm the (mode Alfa) code set on your transponder. Your response would be to check that you have the correct code (numbers) selected on your transponder and read this code back to the controller.

“SQUAWK CHARLIE” Which means: set your transponder so that it will transmit your altitude information (mode C). With most transponders you achieve this by selecting the ‘ALT’ function. NOTE: ‘ALT’ is the function you should normally have selected except when in the circuit at a controlled aerodrome If your transponder does not have Mode C, advise the controller.

“SQUAWK (code and) IDENT” Which means: press the button on your transponder labelled ‘IDENT’. (Some transponders may have a different method / labelling for this function.) This causes your radar symbol to flash so that the controller can identify you. You do not need to respond to this instruction.

“CONFIRM” (Level) Which means: check and report your altitude (to the nearest 100ft). Before ATC can use your Mode C read out on the radar screen for separation purposes there is a requirement to check that it is accurate. ATC’s read out must be within 200ft of your actual altitude, therefore, be accurate when reporting your altitude

“CHECK ALTIMETER SETTING AND CONFIRM” Which means: check that you have the correct setting on your altimeter subscale (correct QNH set) and report your altitude (to the nearest 100ft). One reason why the Mode C read out on the radar screen could be different from your actual altitude could be due to your not having the correct QNH. An example of a response to this is: “ALTIMETER 1015, LEVEL 4,500ft””

“STOP SQUAWK CHARLIE WRONG INDICATION” Which means: having tried the previous transmission and procedure to correct a wrong read out of your altitude, it is still not within acceptable limits. It could also be that your altitude read out on the screen is erratic. It is better not to transmit Mode C information rather than have wrong information. To stop squawking Charlie (Mode C) you set your transponder to the ‘ON’ function.

“STOP SQUAWK” Which means: terminate transponder operation, select OFF. “SQUAWK STANDBY” Which means: select ‘SBY’ on your transponder. Having done this there is no longer a transponder symbol for you on the radar screen “SQUAWK MAYDAY” Which means: the controller wishes you to squawk the emergency code 7700

“SQUAWK NORMAL” Which means : return to normal transponder operation, i.e. select the transponder function that is normally used, i.e. ‘ALT’. A controller could request you to do this should it appear that you have your transponder still set to the OFF or SBY function

TRANSPONDER MODES MODE “A”: Each time your transponder is interrogated by radar it transmits a 4 digit code. These codes range from 0000 to 7777 and provide a 4-digit identification for your aircraft. MODE “C”: Combines mode A with your altitude provided by your encoder. This gives the controller 4-digit identification plus your altitude. MODE “S”: On interrogation transmits a 24 bit address which has two components, the nationality code assigned by ICAO and a code corresponding to the identification number. This will become the standard in 10 to 15 years

Transponder Code Allocation

EMERGENCY SSR CODES

Taupo Gliding Club Transponders Terra 250 Microair T2000 Becker ATC 4401-175 GTG GSD, GML ZK-GME, GBD

Microair T2000SFL

X – SBY A – Mode A C – Mode C I - IDENT R – Normal reply operation

Pressure Altitude QNH Feet

Select Mode Knob

Terra TRT250

Becker ATC 4401-175

ANY QUESTIONS OR DISCUSSION The Transponder manuals are available for reading, printing or download on www.taupoglidingclub.co.nz