ATC requires a transponder code included in the ICAO Surveillance field in order for the flight plan to be accepted.
The transponder code must be one of these: A, C, E, H, I, L, N, P, S, or X
Here are the most common codes installed in aircraft.
A - Mode A only (no altitude)
C - Mode A and C
S - Mode S, Aircraft ID, Altitude
E - Mode S, Aircraft ID, Altitude, Extended Squitter (most ADS-B Out transponders are this code)
L - Mode S, Aircraft ID, Altitude, Extended Squitter, EHS
N - Nil (no transponder)
A full list of ICAO Codes can be found in the ForeFlight Filing Guide.
Information about extended squitters can be found at https://www.garmin.com/us/intheair/ads-b/squit/
Diagram 1. ICAO Surveillance Codes
Diagram 2. ADS-B airspace requirements
In addition to the transponder code, all aircraft equipped with Automatic Dependent Surveillance-Broadcast (ADS-B) must also include the appropriate code along with the transponder code. If you only file an ADS-B code such as B1, B2, U1, or U2, and do not also include a transponder code, your flight plan will be rejected. All flight plans must file a transponder code. (eg. E, B2, not just B2)
ADS-B Out transponders are all 1090ES and UAT Systems are all 978 MHz out. There are no dual-band ADS-B Out systems on the market. The out is what is specified and mandated, the In may only be specified if there is an out of the same frequency. Aircraft equipped with 1090ES transponders are authorized to fly at all altitudes, whereas 978 UAT systems are not permitted above 18,000 ft.
Note, you may only file one ADS-B code. For example, "B2" NOT "B2U2"
Here are the most common ADS-B codes for general aviation.
ADS-B (dedicated 1090) Out capable transponders are filed using B1
ADS-B (dedicated 1090) Out+In capable transponders are filed using B2
ADS-B (dedicated 978 UAT) Out capable systems are filed using U1
ADS-B (dedicated 978 UAT) Out+In capable systems are filed using U2
Diagram 3. ADS-B codes
Other Information Field
In addition to the Surveillance code specifying the ADS-B Out code, two fields found in Other Information should be specified to obtain the best results from ADS-B Out equipage. CODE and SUR. Neither CODE or SUR are mandated.
CODE is the assigned hexadecimal value found in the FAA registry. It is uniquely associated with the registration value (N number) and is always broadcast by ADS-B Out systems. By including it, the FAA association between your flight plan and your ADS-B Out is optimized. This also reduces transponder code reassignment when you fly near another aircraft with the same transponder code having been assigned.
To enter the transponder hex code for your aircraft into an ICAO flight plan, please do the following:
- Go to More > Aircraft and tap on the Aircraft Profile > Scroll down to the FILING section and tap > Other Information > Enter the HEX code for that aircraft in the CODE field.
- Now, when you file a flight plan using that aircraft profile, the Hex code will be included.
SUR is used to indicate that the ADS-B Out is of the variety that is 2020 compliant. This allows you to be routed into airspace or along routes that only ADS-B Out equipped aircraft are permitted. If there is a radar outage, you may still get a direct route through the outage area. There are some routes that will not be assigned unless the aircraft has this code set. There are two values used, 260B for 1090ES and 282B for UAT. These are the RTCA Document specification names for compliant ADS-B Out systems.
To enter the surveillance code for your aircraft into an ICAO flight plan, please do the following:
- Go to More > Aircraft and tap on the Aircraft Profile > Scroll down to the FILING section and tap Other Information > Enter the ADS-B code (260B or 282B) for the ADS-B type in the SUR field.
- Now, when you file a flight plan using that aircraft profile, the SUR code will be included.
Examples of Transponder and ADS-B codes
Non-ADS-B out compliant transponders
GTX330/33 - S
GTX327 - C
GTX328 - S
Honeywell Bendix King Transponders
KT 73 - S
KT 76A - C
KT 76C - C
ADS-B Out Transponder (1090ES)
B1 or B2
Other Information: SUR/260B CODE/A00000
GTX330ES/33ES - E, B1, and SUR/260B
GTX335 - E, B1, and SUR/260B
GTX345 - E, B2, and SUR/260B
GTX345/R - E, B2, and SUR/260B
G375 GPS/Transponder - E, B2, and SUR/260B
GTX-3000 - L, B1, and SUR/260B
Lynx NGT-9000 - E, B2, and SUR/260B
Stratus ESG - E, B1, and SUR/260B
TT31 - E, B1, and SUR/260B
Honeywell Bendix King Transponders:
KT 74 - E, B1, and SUR/260B
AXP340 - E, B1, and SUR/260B
AXP322 - E, B1, and SUR/260B
TDR-94-94D (501 and 502 only) - E, B1, and SUR/260B
ADS-B Out UAT Systems:
U1 or U2
Other Information: SUR/282B CODE/A00000
Garmin UAT Systems:
GDL82 with Mode A/C - C, U1, and SUR/282B
GDL88/84 wMode S - S, U2, and SUR/282B
GDL88/84 with Mode A/C - C, U2, and SUR/282B
FreeFlight UAT Systems
Ranger 978 XVR with mode A/C - C, U2, and SUR/282B
Ranger Lite with mode A/C - C, U1, and SUR/282B
L3 UAT Systems
Lynx NGT 1000 - C, U1, and SUR/282B
Lynx NGT- 2000/2500 - C, U2, and SUR/282B
uAvionix UAT Systems:
SkyBeacon - C, U1, and SUR/282B
Tail Beacon - C, U1, and SUR/282B
Echo UAT - - C, U2, and SUR/282B