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altitude reporting feature of your transponder/ADS

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B. An instruction by ATC to "STOP ALTITUDE SQUAWK,

ALTITUDE DIFFERS BY (number of feet) FEET," may be an indication that t
he 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

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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.

d.  IDENT Feature

Transponder/ADS

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B Out equipment must be operated only as specified by ATC. Activate the
"IDENT" feature

only when requested by ATC.

e.  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

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7677, 7700

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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.

f.  Mode C Transponder and ADS

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B Out Requirements

Specific details concerning requirements to carry and operate Mode C
transponders and ADS

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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

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Out when operating:

(a)

In Class A, Class B, or Class C airspace areas;

(b)

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

MSL;

(c)

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;

(d)

Within 30 miles of a Class B airspace primary airport, below 10,000
feet MSL (commonly referred

to as the "Mode C Veil");

(e)

For ADS

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B Out: Class E airspace at and above 3,000 feet MSL over the Gulf of
Mexico from the

coastline of the United States out to 12 nautical miles.

NOTE

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The airspace described in (e) above is specified in 14 CFR  91.225 for
ADS

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B Out requirements. However, 14 CFR  91.215

does not include this airspace for ATC transponder requirements.

Services Available to Pilots

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