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weather. For example, airports with only a global positioning system (GPS) approach procedure cannot be used as an
alternate by TSO-C129/129A users even though the N/A
has been removed from the approach chart. For select
RNAV (GPS) and GPS approach procedures the N/A is
being removed so they may be used as an alternate by aircraft equipped with an approach approved WAAS receiver.
Because GPS is not authorized as a substitute means of navigation guidance when conducting a conventional approach
at an alternate airport, if the approach procedure requires
either DME or ADF, the aircraft must be equipped with the
appropriate DME or ADF avionics in order to use the
approach as an alternate.
For airplane Part 91 requirements, an alternate airport must
be listed on IFR flight plans if the forecast weather at the
destination airport, from a time period of plus or minus one
hour from the estimated time of arrival (ETA), includes ceil-
2-11
Figure 2-14. IFR Alternate Minimums.
2-12
ALTERNATE MINIMUMS FOR
COMMERCIAL OPERATORS
IFR alternate minimums for Part 121 and 135 operators
are very specific and have more stringent requirements
than Part 91 operators.
Part 121 operators are required by their OpsSpecs and
Parts 121.617 and 121.625 to have a takeoff alternate
airport for their departure airport in addition to their airport of intended landing if the weather at the departure
airport is below the landing minimums in the certificate
holder’s OpsSpecs for that airport. The alternate must be
within two hours flying time for an aircraft with three or
more engines with an engine out in normal cruise in still
air. For two engine aircraft, the alternate must be within
one hour. The airport of intended landing may be used
in lieu of an alternate providing it meets all the requirements. Part 121 operators must also file for alternate
airports when the weather at their destination airport,
from one hour before to one hour after their ETA, is
forecast to be below a 2,000-foot ceiling and/or less
than 3 miles visibility.
For airports with at least one operational navigational
facility that provides a straight-in non-precision
approach, a straight-in precision approach, or a circling
maneuver from an instrument approach procedure determine the ceiling and visibility by:
• Adding 400 feet to the authorized CAT I
HAA/HAT for ceiling.
• Adding one mile to the authorized CAT I visibility
for visibility minimums.
This is but one example of the criteria required for Part
121 operators when calculating minimums. Part 135
operators are also subject to their own specific rules
regarding the selection and use of alternate minimums
as outlined in their OpsSpecs and Part 135.219 through
Part 135.225, and they differ widely from those used by
Part 121 operators.
Typically, dispatchers who plan flights for these operators are responsible for planning alternate airports. The
dispatcher considers aircraft performance, aircraft
equipment and its condition, and route of flight when
choosing alternates. In the event changes need to be
made to the flight plan en route due to deteriorating
weather, the dispatcher will maintain contact with the
flight crew and will reroute their flight as necessary.
Therefore, it is the pilot’s responsibility to execute the
flight as planned by the dispatcher; this is especially true
for Part 121 pilots. To aid in the planning of alternates,
dispatchers have a list of airports that are approved as
alternates so they can quickly determine which airports
should be used for a particular flight. Dispatchers also
use flight-planning software that plans routes including
alternates for the flight. This type of software is tailored
for individual operators and includes their normal flight
paths and approved airports. Flight planning software
and services are provided through private sources.
Though the pilot is the final authority for the flight and
ultimately has full responsibility, the dispatcher is
responsible for creating flight plans that are accurate and
comply with the CFRs. Alternate minimum criteria are
only used as planning tools to ensure the pilot-in-command and dispatcher are thinking ahead to the approach
phase of flight. In the event the flight would actually
need to divert to an alternate, the published approach
minimums or lower-than-standard minimums must be
used as addressed in OpsSpecs documents.
DEPARTURE PROCEDURES
Departure procedures are preplanned routes that provide
transitions from the departure airport to the en route
structure. Primarily, these procedures are designed to
　
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