T.O. BMS1F-16CM-1
BMS 4.34 Change 2.00
BMS 4.34 Dash 1
© Red Dog 2012-2019
Page: 150
1.16. IDENTIFICATION FRIEND or FOE (IFF)
IFF or Identification, friend or foe
is an identification system designed to identify aircraft as friendly.
IFF is based on an interrogator sending radio queries and a transponder replying to queries.
Currently in BMS IFF interrogation is mostly used by human, ATC and AWACS do not interrogate.
AI fighters may interrogate during BVR intercepts. All AI though respond to IFF interrogation with their
transponders.
It is important to realize that despite the name, IFF can only positively identify friendly targets, not
hostile ones!
If an IFF interrogation receives no reply or an invalid reply, the object cannot be identified as friendly,
but is not positively identified as foe. It will therefore remain a bogey. There are in addition many
reasons that friendly aircraft may not properly reply to IFF. For these reasons, do not consider IFF like
the ultimate solution to prevent fratricide kills but rather another tool to help prevent such occurrences.
1.16.1 IFF modes
IFF in BMS features 5 modes and their relevant codes or cryptographic key: Modes 1, 2, 3, 4, and C
.
Mode S can be turned on/off, but there is no support to simulate mode S reply or address entry;
therefore Mode S is considered not implemented.
IFF modes available are specific to aircraft. Not all aircraft in BMS are mode 4 or mode C capable.
•
Mode 1
: military mode, non-crypto. Response is a code in a range of 32 codes between 00
and 73. The reason it is only 32 codes is that the first digit is never above 7, the second never
above 3. Example: 41 and 22 are valid Mode 1 codes, 44 and 81 are not.
•
Mode 2:
military mode, non-crypto. Response is a code in a range of 4096 between 0000 and
7777. Similarly, the digits are never above 7. So 4484 is not a valid code, 4625 is.
•
Mode 3/A:
military and civilian mode, non-crypto. Most if not all aircraft must be equipped with
a transponder Mode 3/A for ATC purposes in the real world. Response is again a code
between 0000 and 7777.
•
Mode C:
civilian mode, non-crypto. Reports the pressure altitude of the transponder aircraft.
•
Mode 4
: military mode, crypto. The closest thing to a true « Identification Friend or Foe ».
The interrogation is actually a sequence of rapid challenges, encrypted using a specific key
and the transponder must reply correctly to those challenges using the same key.
•
Mode 5
is an updated version of Mode 4, not implemented.
•
Mode S
is an updated civilian transponder. Only implemented as eye-candy.
IFF in BMS can be complicated, as it closely models the real system, but in a typical usage scenario it
can be as simple to use as switching the IFF Master Knob to STBY at ramp and then toggling it to
NORM just before take-off. The rest (for the Transponder at least) is largely taken care of by the DTC.
It is important to understand the details though in case complicated IFF scenarios are designed for
TEs or campaign missions.
Read on…
Summary of Contents for F-16C/D 4.34
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