AIM 4-1-20

General Pilots should be aware that proper application of transponder and ADS-B operating procedures will provide both VFR and IFR aircraft with a higher degree of safety while operating on the ground and airborne. Transponder/ADS-B panel designs differ; therefore, a pilot should be thoroughly familiar with the operation of their particular equipment to maximize its full potential. ADS-B Out, and transponders with altitude reporting mode turned ON (Mode C or S), substantially increase the capability of surveillance systems to see an aircraft. This provides air traffic controllers, as well as pilots of suitably equipped aircraft (TCAS and ADS-B In), increased situational awareness and the ability to identify potential traffic conflicts. Even VFR pilots who are not in contact with ATC will be afforded greater protection from IFR aircraft and VFR aircraft that are receiving traffic advisories. Nevertheless, pilots should never relax their visual scanning for other aircraft, and should include the ADS-B In display (if equipped) in their normal traffic scan.

Air Traffic Control Radar Beacon System (ATCRBS) is similar to and compatible with military coded radar beacon equipment. Civil Mode A is identical to military Mode 3.

Transponder and ADS-B operations on the ground . Civil and military aircraft should operate with the transponder in the altitude reporting mode (consult the aircraft's flight manual to determine the specific transponder position to enable altitude reporting) and ADS-B Out transmissions enabled at all airports, any time the aircraft is positioned on any portion of the airport movement area. This includes all defined taxiways and runways. Pilots must pay particular attention to ATIS and airport diagram notations, General Notes (included on airport charts), and comply with directions pertaining to transponder and ADS-B usage. Generally, these directions are: Departures. Select the transponder mode which allows altitude reporting and enable ADS-B during pushback or taxi-out from parking spot. Select TA or TA/RA (if equipped with TCAS) when taking the active runway.

Arrivals. If TCAS equipped, deselect TA or TA/RA upon leaving the active runway, but continue transponder and ADS-B transmissions in the altitude reporting mode. Select STBY or OFF for transponder and ADS-B upon arriving at the aircraft's parking spot or gate.

Transponder and ADS-B Operations While Airborne. Unless otherwise requested by ATC, aircraft equipped with an ATC transponder maintained in accordance with 14 CFR section 91.413 MUST operate with this equipment on the appropriate Mode 3/A code, or other code as assigned by ATC, and with altitude reporting enabled whenever in controlled airspace. If practicable, aircraft SHOULD operate with the transponder enabled in uncontrolled airspace.

Aircraft equipped with ADS-B Out MUST operate with this equipment in the transmit mode at all times, unless otherwise requested by ATC.

Transponder and ADS-B Operation Under Visual Flight Rules (VFR). Unless otherwise instructed by an ATC facility, adjust transponder/ADS-B to reply on Mode 3/A Code 1200 regardless of altitude.

When required to operate their transponder/ADS-B, pilots must always operate that equipment with altitude reporting enabled unless otherwise instructed by ATC or unless the installed equipment has not been tested and calibrated as required by 14 CFR section 91.217. If deactivation is required, turn off altitude reporting.

When participating in a VFR standard formation flight that is not receiving ATC services, only the lead aircraft should operate its transponder and ADS-B Out and squawk code 1203. Once established in formation, all other aircraft should squawk standby and disable ADS-B transmissions. NOTE-

If the formation flight is receiving ATC services, pilots can expect ATC to direct all non-lead aircraft to STOP Squawk, and should not do so until instructed.

Firefighting aircraft not in contact with ATC may squawk 1255 in lieu of 1200 while en route to, from, or within the designated firefighting area(s).

VFR aircraft flying authorized SAR missions for the USAF or USCG may be advised to squawk 1277 in lieu of 1200 while en route to, from, or within the designated search area.

VFR gliders should squawk 1202 in lieu of 1200.

REFERENCE-

FAA Order JO 7110.66, National Beacon Code Allocation Plan (NBCAP).

A pilot on an IFR flight who elects to cancel the IFR flight plan prior to reaching their destination, should adjust the transponder/ADS-B according to VFR operations.

If entering a U.S. OFFSHORE AIRSPACE AREA from outside the U.S., the pilot should advise on first radio contact with a U.S. radar ATC facility that such equipment is available by adding “transponder” or “ADS-B” (if equipped) to the aircraft identification.

It should be noted by all users of ATC transponders and ADS-B Out systems that the surveillance coverage they can expect is limited to “line of sight” with ground radar and ADS-B radio sites. Low altitude or aircraft antenna shielding by the aircraft itself may result in reduced range or loss of aircraft contact. Though ADS-B often provides superior reception at low altitudes, poor coverage from any surveillance system can be improved by climbing to a higher altitude. NOTE-

Pilots should refer to AIM, paragraph 4-5-7 , Automatic Dependent Surveillance - Broadcast (ADS-B) Services, for a complete description of operating limitations and procedures.

Transponder/ADS-B Code Designation For ATC to utilize one of the 4096 discrete codes, a four-digit code designation will be used; for example, code 2102 will be expressed as “TWO ONE ZERO TWO.” NOTE-

Circumstances may occasionally require ATC to assign a non-discrete code; i.e., a code ending in “00.”

REFERENCE-

FAA Order JO 7110.66, National Beacon Code Allocation Plan (NBCAP).

Automatic Altitude Reporting Most transponders (Modes C and S) and all ADS-B Out systems are capable of automatic altitude reporting. This system converts aircraft altitude in 100-foot increments to coded digital information that is transmitted to the appropriate surveillance facility as well as to ADS-B In and TCAS systems.

Adjust the transponder/ADS-B to reply on the Mode 3/A code specified by ATC and with altitude reporting enabled, unless otherwise directed by ATC or unless the altitude reporting equipment has not been tested and calibrated as required by 14 CFR section 91.217. If deactivation is required by ATC, turn off the altitude reporting feature of your transponder/ADS-B. An instruction by ATC to “STOP ALTITUDE SQUAWK, ALTITUDE DIFFERS BY (number of feet) FEET,” may be an indication that the transmitted altitude information is incorrect, or that the aircraft's altimeter setting is incorrect. While an incorrect altimeter setting has no effect on the transmitted altitude information, it will cause the aircraft to fly at a true altitude different from the assigned altitude. When a controller indicates that an altitude readout is invalid, the pilot should verify that the aircraft altimeter is set correctly. NOTE-

Altitude encoders are preset at standard atmospheric pressure. Local altimeter correction is applied by the surveillance facility before the altitude information is presented to ATC.

Pilots should report exact altitude or flight level to the nearest hundred foot increment when establishing initial contact with an ATC facility. Exact altitude or flight level reports on initial contact provide ATC with information that is required prior to using automatically reported altitude information for separation purposes. This will significantly reduce altitude verification requests.

IDENT Feature Transponder/ADS-B Out equipment must be operated only as specified by ATC. Activate the “IDENT” feature only when requested by ATC.

Code Changes When making routine code changes, pilots should avoid inadvertent selection of Codes 7500, 7600 or 7700 thereby causing momentary false alarms at automated ground facilities. For example, when switching from Code 2700 to Code 7200, switch first to 2200 then to 7200, NOT to 7700 and then 7200. This procedure applies to nondiscrete Code 7500 and all discrete codes in the 7600 and 7700 series (i.e., 7600-7677, 7700-7777) which will trigger special indicators in automated facilities. Only nondiscrete Code 7500 will be decoded as the hijack code.

Under no circumstances should a pilot of a civil aircraft operate the transponder on Code 7777. This code is reserved for military interceptor operations.

Military pilots operating VFR or IFR within restricted/warning areas should adjust their transponders to Code 4000 unless another code has been assigned by ATC.

Mode C Transponder and ADS-B Out Requirements Specific details concerning requirements to carry and operate Mode C transponders and ADS-B Out, as well as exceptions and ATC authorized deviations from those requirements, are found in 14 CFR sections 91.215, 91.225, and 99.13.

In general, the CFRs require aircraft to be equipped with an operable Mode C transponder and ADS-B Out when operating: In Class A, Class B, or Class C airspace areas;

Above the ceiling and within the lateral boundaries of Class B or Class C airspace up to 10,000 feet MSL;

Class E airspace at and above 10,000 feet MSL within the 48 contiguous states and the District of Columbia, excluding the airspace at and below 2,500 feet AGL;

Within 30 miles of a Class B airspace primary airport, below 10,000 feet MSL (commonly referred to as the “Mode C Veil”);

For ADS-B Out: Class E airspace at and above 3,000 feet MSL over the Gulf of America from the coastline of the United States out to 12 nautical miles. NOTE-

The airspace described in (e) above is specified in 14 CFR § 91.225 for ADS-B Out requirements. However, 14 CFR § 91.215 does not include this airspace for ATC transponder requirements.

Transponder and ADS-B Out requirements do not apply to any aircraft that was not originally certificated with an electrical system, or that has not subsequently been certified with such a system installed, including balloons and gliders. These aircraft may conduct operations without a transponder or ADS-B Out when operating: Outside any Class B or Class C airspace area; and

Below the altitude of the ceiling of a Class B or Class C airspace area designated for an airport, or 10,000 feet MSL, whichever is lower.

14 CFR section 99.13 requires all aircraft flying into, within, or across the contiguous U.S. ADIZ be equipped with a Mode C or Mode S transponder. Balloons, gliders and aircraft not equipped with an engine-driven electrical system are excepted from this requirement. REFERENCE-

AIM, Chapter 5 , Section 6 , National Security and Interception Procedures.

Pilots must ensure that their aircraft transponder/ADS-B is operating on an appropriate ATC-assigned VFR/IFR code with altitude reporting enabled when operating in such airspace. If in doubt about the operational status of either feature of your transponder while airborne, contact the nearest ATC facility or FSS and they will advise you what facility you should contact for determining the status of your equipment.

In-flight requests for “immediate” deviation from the transponder requirements may be approved by controllers only for failed equipment, and onlywhen the flight will continue IFR or when weather conditions prevent VFR descent and continued VFR flight in airspace not affected by the CFRs. All other requests for deviation should be made at least 1 hour before the proposed operation by contacting the nearest Flight Service or Air Traffic facility in person or by telephone. The nearest ARTCC will normally be the controlling agency and is responsible for coordinating requests involving deviations in other ARTCC areas.

In-flight requests for “immediate” deviation from the ADS-B Out requirements may be approved by ATC only for failed equipment, and may be accommodated based on workload, alternate surveillance availability, or other factors. All other requests for deviation must be made at least 1 hour before the proposed operation, following the procedures contained in Advisory Circular (AC) 90-114, Automatic Dependent Surveillance-Broadcast Operations.

Cooperative Surveillance Phraseology. Air traffic controllers, both civil and military, will use the following phraseology when referring to operation of cooperative ATC surveillance equipment. Except as noted, the following ATC instructions do not apply to military transponders operating in other than Mode 3/A/C/S. SQUAWK (number). Operate radar beacon transponder/ADS-B on designated code with altitude reporting enabled.

IDENT. Engage the “IDENT” feature (military I/P) of the transponder/ADS-B.

SQUAWK (number) AND IDENT. Operate transponder/ADS-B on specified code with altitude reporting enabled, and engage the “IDENT” (military I/P) feature.

SQUAWK STANDBY. Switch transponder/ADS-B to standby position.

SQUAWK NORMAL. Resume normal transponder/ADS-B operation on previously assigned code. (Used after “SQUAWK STANDBY,” or by military after specific transponder tests).

SQUAWK ALTITUDE. Activate Mode C with automatic altitude reporting.

STOP ALTITUDE SQUAWK. Turn off automatic altitude reporting.

STOP SQUAWK (Mode in use). Stop transponder and ADS-B Out transmissions, or switch off only specified mode of the aircraft transponder (military).

SQUAWK MAYDAY. Operate transponder/ADS-B in the emergency position (Mode A Code 7700 for civil transponder. Mode 3 Code 7700 and emergency feature for military transponder.)

SQUAWK VFR. Operate radar beacon transponder/ADS-B on Code 1200 in the Mode A/3, or other appropriate VFR code, with altitude reporting enabled.