AIM
4/3/14
4−1−16
Services Available to Pilots
incorrect altimeter setting. While an incorrect
altimeter setting has no effect on the Mode C altitude
information transmitted by your transponder (trans-
ponders are preset at 29.92), it would cause you to fly
at an actual altitude different from your assigned
altitude. When a controller indicates that an altitude
readout is invalid, the pilot should initiate a check to
verify that the aircraft altimeter is set correctly.
3.
Pilots of aircraft with operating Mode C
altitude reporting transponders 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 Mode C altitude information
for separation purposes. This will significantly
reduce altitude verification requests.
d. Transponder IDENT Feature
1.
The transponder must be operated only as
specified by ATC. Activate the “IDENT” feature only
upon request of the ATC controller.
e. Code Changes
1.
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.
2.
Under no circumstances should a pilot of a
civil aircraft operate the transponder on Code 7777.
This code is reserved for military interceptor
operations.
3.
Military pilots operating VFR or IFR within
restricted/warning areas should adjust their trans-
ponders to Code 4000 unless another code has been
assigned by ATC.
f. Mode C Transponder Requirements
1.
Specific details concerning requirements to
carry and operate Mode C transponders, as well as
exceptions and ATC authorized deviations from the
requirements are found in 14 CFR Section 91.215 and
14 CFR Section 99.12.
2.
In general, the CFRs require aircraft to be
equipped with Mode C transponders when operating:
(a)
At or above 10,000 feet MSL over the
48 contiguous states or the District of Columbia,
excluding that airspace below 2,500 feet AGL;
(b)
Within 30 miles of a Class B airspace
primary airport, below 10,000 feet MSL. Balloons,
gliders, and aircraft not equipped with an engine
driven electrical system are excepted from the above
requirements when operating below the floor of
Class A airspace and/or; outside of a Class B airspace
and below the ceiling of the Class B airspace (or
10,000 feet MSL, whichever is lower);
(c)
Within and above all Class C airspace, up
to 10,000 feet MSL;
(d)
Within 10 miles of certain designated
airports, excluding that airspace which is both outside
the Class D surface area and below 1,200 feet AGL.
Balloons, gliders and aircraft not equipped with an
engine driven electrical system are excepted from this
requirement.
3.
14 CFR Section 99.12 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.
4.
Pilots must ensure that their aircraft trans-
ponder is operating on an appropriate ATC assigned
VFR/IFR code and Mode C 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.
5.
In-flight requests for “immediate” deviation
from the transponder requirement may be approved
by controllers only when 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 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.