aim-94

AIM

11/3/22

[a]

During domestic operations for com-

merce or for hire, operators must have a second
navigation system capable of reversion or contin-
gency operations.

[b]

Operators must have two independ-

ent navigation systems appropriate to the route to be
flown, or one system that is suitable and a second,
independent backup capability that allows the
operator to proceed safely and land at a different
airport, and the aircraft must have sufficient fuel
(reference 14 CFR 121.349, 125.203, 129.17, and
135.165). These rules ensure the safety of the
operation by preventing a single point of failure.

NOTE

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An aircraft approved for multi-sensor navigation and
equipped with a single navigation system must maintain an
ability to navigate or proceed safely in the event that any
one component of the navigation system fails, including the
flight management system (FMS). Retaining a FMS-inde-
pendent VOR capability would satisfy this requirement.

[c]

The requirements for a second

system apply to the entire set of equipment needed to
achieve the navigation capability, not just the
individual components of the system such as the radio
navigation receiver. For example, to use two RNAV
systems (e.g., GPS and DME/DME/IRU) to comply
with the requirements, the aircraft must be equipped
with two independent radio navigation receivers and
two independent navigation computers (e.g., flight
management systems (FMS)). Alternatively, to
comply with the requirements using a single RNAV
system with an installed and operable VOR
capability, the VOR capability must be independent
of the FMS.

[d]

To satisfy the requirement for two

independent navigation systems, if the primary
navigation system is GPS

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based, the second system

must be independent of GPS (for example, VOR or
DME/DME/IRU). This allows continued navigation
in case of failure of the GPS or WAAS services.
Recognizing that GPS interference and test events
resulting in the loss of GPS services have become
more common, the FAA requires operators conduct-
ing IFR operations under 14 CFR 121.349, 125.203,
129.17 and 135.65 to retain a non-GPS navigation
capability consisting of either DME/DME, IRU, or
VOR for en route and terminal operations, and VOR
and ILS for final approach. Since this system is to be
used as a reversionary capability, single equipage is
sufficient.

3. O c e a n i c, D o m e s t i c , En Route, and

Terminal Area Operations

(a)

Conduct GPS IFR operations in oceanic

areas only when approved avionics systems are
installed. TSO

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C196() users and TSO

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C129() GPS

users authorized for Class A1, A2, B1, B2, C1, or C2
operations may use GPS in place of another approved
means of long

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range navigation, such as dual INS.

(See TBL 1

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5 and TBL 1

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6.) Aircraft with a

single installation GPS, meeting the above specifica-
tions, are authorized to operate on short oceanic
routes requiring one means of long

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range navigation

(reference AC 20-138, Appendix 1).

(b)

Conduct GPS domestic, en route, and

terminal IFR operations only when approved
avionics systems are installed. Pilots may use GPS
via TSO

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C129() authorized for Class A1, B1, B3,

C1, or C3 operations GPS via TSO-C196(); or
GPS/WAAS with either TSO-C145() or
TSO-C146(). When using TSO-C129() or
TSO-C196() receivers, the avionics necessary to
receive all of the ground

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based facilities appropriate

for the route to the destination airport and any
required alternate airport must be installed and
operational. Ground

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based facilities necessary for

these routes must be operational.

(1)

GPS en route IFR operations may be

conducted in Alaska outside the operational service
volume of ground

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based navigation aids when a

TSO

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C145() or TSO

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C146() GPS/wide area aug-

mentation system (WAAS) system is installed and
operating. WAAS is the U.S. version of a
satellite-based augmentation system (SBAS).

[a]

In Alaska, aircraft may operate on

GNSS Q-routes with GPS (TSO-C129 () or
TSO-C196 ()) equipment while the aircraft remains
in Air Traffic Control (ATC) radar surveillance or
with GPS/WAAS (TSO-C145 () or TSO-C146 ())
which does not require ATC radar surveillance.

[b]

In Alaska, aircraft may only operate

on GNSS T-routes with GPS/WAAS (TSO-C145 () or
TSO-C146 ()) equipment.

(2)

Ground

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based navigation equipment

is not required to be installed and operating for en
route IFR operations when using GPS/WAAS
navigation systems. All operators should ensure that
an alternate means of navigation is available in the
unlikely event the GPS/WAAS navigation system
becomes inoperative.

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Navigation Aids