Appendix A to Part 91 - Category II Operations:
Manual, Instruments, Equipment, and Maintenance
1. Category II Manual
(a) Application for approval. An applicant for approval of a
Category II manual or an amendment to an approved Category II manual must
submit the proposed manual or amendment to the Flight Standards District
Office having jurisdiction of the area in which the applicant is located.
If the application requests an evaluation program, it must include the
(1) The location of the aircraft and the place where the demonstrations
are to be conducted; and
(2) The date the demonstrations are to commence (at least 10 days after
filing the application).
(b) Contents. Each Category II manual must contain:
(1) The registration number, make, and model of the aircraft to which
(2) A maintenance program as specified in section 4 of this appendix;
(3) The procedures and instructions related to recognition of decision
height, use of runway visual range information, approach monitoring, the
decision region (the region between the middle marker and the decision
height), the maximum permissible deviations of the basic ILS indicator
within the decision region, a missed approach, use of airborne low
approach equipment, minimum altitude for the use of the autopilot,
instrument and equipment failure warning systems, instrument failure, and
other procedures, instructions, and limitations that may be found
necessary by the Administrator.
2. Required Instruments and Equipment
The instruments and equipment listed in this section must be installed
in each aircraft operated in a Category II operation. This section does
not require duplication of instruments and equipment required by §91.205
or any other provisions of this chapter.
(a) Group I. (1) Two localizer and glide slope receiving
systems. Each system must provide a basic ILS display and each side of the
instrument panel must have a basic ILS display. However, a single
localizer antenna and a single glide slope antenna may be used.
(2) A communications system that does not affect the operation of at
least one of the ILS systems.
(3) A marker beacon receiver that provides distinctive aural and visual
indications of the outer and the middle markers.
(4) Two gyroscopic pitch and bank indicating systems.
(5) Two gyroscopic direction indicating systems.
(6) Two airspeed indicators.
(7) Two sensitive altimeters adjustable for barometric pressure, each
having a placarded correction for altimeter scale error and for the wheel
height of the aircraft. After June 26, 1979, two sensitive altimeters
adjustable for barometric pressure, having markings at 20-foot intervals
and each having a placarded correction for altimeter scale error and for
the wheel height of the aircraft.
(8) Two vertical speed indicators.
(9) A flight control guidance system that consists of either an
automatic approach coupler or a flight director system. A flight director
system must display computed information as steering command in relation
to an ILS localizer and, on the same instrument, either computed
information as pitch command in relation to an ILS glide slope or basic
ILS glide slope information. An automatic approach coupler must provide at
least automatic steering in relation to an ILS localizer. The flight
control guidance system may be operated from one of the receiving systems
required by subparagraph (1) of this paragraph.
(10) For Category II operations with decision heights below 150 feet
either a marker beacon receiver providing aural and visual indications of
the inner marker or a radio altimeter.
(b) Group II. (1) Warning systems for immediate detection by the
pilot of system faults in items (1), (4), (5), and (9) of Group I and, if
installed for use in Category III operations, the radio altimeter and
(2) Dual controls.
(3) An externally vented static pressure system with an alternate
static pressure source.
(4) A windshield wiper or equivalent means of providing adequate
cockpit visibility for a safe visual transition by either pilot to
touchdown and rollout.
(5) A heat source for each airspeed system pitot tube installed or an
equivalent means of preventing malfunctioning due to icing of the pitot
3. Instruments and Equipment Approval
(a) General. The instruments and equipment required by section 2
of this appendix must be approved as provided in this section before being
used in Category II operations. Before presenting an aircraft for approval
of the instruments and equipment, it must be shown that since the
beginning of the 12th calendar month before the date of submission --
(1) The ILS localizer and glide slope equipment were bench checked
according to the manufacturer's instructions and found to meet those
standards specified in RTCA Paper 23-63/DO-117 dated March 14, 1963,
"Standard Adjustment Criteria for Airborne Localizer and Glide Slope
Receivers," which may be obtained from the RTCA Secretariat, 1425 K St.,
NW., Washington, DC 20005.
(2) The altimeters and the static pressure systems were tested and
inspected in accordance with appendix E to
part 43 of this chapter; and
(3) All other instruments and items of equipment specified in section
2(a) of this appendix that are listed in the proposed maintenance program
were bench checked and found to meet the manufacturer's specifications.
(b) Flight control guidance system. All components of the flight
control guidance system must be approved as installed by the evaluation
program specified in paragraph (e) of this section if they have not been
approved for Category III operations under applicable type or supplemental
type certification procedures. In addition, subsequent changes to make,
model, or design of the components must be approved under this paragraph.
Related systems or devices, such as the autothrottle and computed missed
approach guidance system, must be approved in the same manner if they are
to be used for Category II operations.
(c) Radio altimeter. A radio altimeter must meet the performance
criteria of this paragraph for original approval and after each subsequent
(1) It must display to the flight crew clearly and positively the wheel
height of the main landing gear above the terrain.
(2) It must display wheel height above the terrain to an accuracy of
plus or minus 5 feet or 5 percent, whichever is greater, under the
(i) Pitch angles of zero to plus or minus 5 degrees about the mean
(ii) Roll angles of zero to 20 degrees in either direction.
(iii) Forward velocities from minimum approach speed up to 200 knots.
(iv) Sink rates from zero to 15 feet per second at altitudes from 100
to 200 feet.
(3) Over level ground, it must track the actual altitude of the
aircraft without significant lag or oscillation.
(4) With the aircraft at an altitude of 200 feet or less, any abrupt
change in terrain representing no more than 10 percent of the aircraft's
altitude must not cause the altimeter to unlock, and indicator response to
such changes must not exceed 0.1 seconds and, in addition, if the system
unlocks for greater changes, it must reacquire the signal in less than 1
(5) Systems that contain a push-to-test feature must test the entire
system (with or without an antenna) at a simulated altitude of less than
(6) The system must provide to the flight crew a positive failure
warning display any time there is a loss of power or an absence of ground
return signals within the designed range of operating altitudes.
(d) Other instruments and equipment. All other instruments and
items of equipment required by §2 of this appendix must be capable of
performing as necessary for Category II operations. Approval is also
required after each subsequent alteration to these instruments and items
(e) Evaluation program -- (1) Application. Approval by
evaluation is requested as a part of the application for approval of the
Category II manual.
(2) Demonstrations. Unless otherwise authorized by the
Administrator, the evaluation program for each aircraft requires the
demonstrations specified in this paragraph. At least 50 ILS approaches
must be flown with at least five approaches on each of three different ILS
facilities and no more than one half of the total approaches on any one
ILS facility. All approaches shall be flown under simulated instrument
conditions to a 100-foot decision height and 90 percent of the total
approaches made must be successful. A successful approach is one in which
(i) At the 100-foot decision height, the indicated airspeed and heading
are satisfactory for a normal flare and landing (speed must be plus or
minus 5 knots of programmed airspeed, but may not be less than computed
threshold speed if autothrottles are used);
(ii) The aircraft at the 100-foot decision height, is positioned so
that the cockpit is within, and tracking so as to remain within, the
lateral confines of the runway extended;
(iii) Deviation from glide slope after leaving the outer marker does
not exceed 50 percent of full-scale deflection as displayed on the ILS
(iv) No unusual roughness or excessive attitude changes occur after
leaving the middle marker; and
(v) In the case of an aircraft equipped with an approach coupler, the
aircraft is sufficiently in trim when the approach coupler is disconnected
at the decision height to allow for the continuation of a normal approach
(3) Records. During the evaluation program the following
information must be maintained by the applicant for the aircraft with
respect to each approach and made available to the Adninistrator upon
(i) Each deficiency in airborne instruments and equipment that
prevented the initiation of an approach.
(ii) The reasons for discontinuing an approach, including the altitude
above the runway at which it was discontinued.
(iii) Speed control at the 100-foot decision height if auto throttles
(iv) Trim condition of the aircraft upon disconnecting the auto coupler
with respect to continuation to flare and landing.
(v) Position of the aircraft at the middle marker and at the decision
height indicated both on a diagram of the basic ILS display and a diagram
of the runway extended to the middle marker. Estimated touchdown point
must be indicated on the runway diagram.
(vi) Compatibility of flight director with the auto coupler, if
(vii) Quality of overall system performance.
(4) Evaluation. A final evaluation of the flight control
guidance system is made upon successful completion of the demonstrations.
If no hazardous tendencies have been displayed or are otherwise known to
exist, the system is approved as installed.
4. Maintenance program
(a) Each maintenance program must contain the following:
(1) A list of each instrument and item of equipment specified in §2 of
this appendix that is installed in the aircraft and approved for Category
II operations, including the make and model of those specified in §2(a).
(2) A schedule that provides for the performance of inspections under
subparagraph (5) of this paragraph within 3 calendar months after the date
of the previous inspection. The inspection must be performed by a person
authorized by part 43 of this chapter, except that each alternate
inspection may be replaced by a functional flight check. This functional
flight check must be performed by a pilot holding a Category II pilot
authorization for the type aircraft checked.
(3) A schedule that provides for the performance of bench checks for
each listed instrument and item of equipment that is specified in section
2(a) within 12 calendar months after the date of the previous bench check.
(4) A schedule that provides for the performance of a test and
inspection of each static pressure system in accordance with appendix E to
part 43 of this chapter within 12 calendar months after the date of
the previous test and inspection.
(5) The procedures for the performance of the periodic inspections and
functional flight checks to determine the ability of each listed
instrument and item of equipment specified in section 2(a) of this
appendix to perform as approved for Category II operations including a
procedure for recording functional flight checks.
(6) A procedure for assuring that the pilot is informed of all defects
in listed instruments and items of equipment.
(7) A procedure for assuring that the condition of each listed
instrument and item of equipment upon which maintenance is performed is at
least equal to its Category II approval condition before it is returned to
service for Category II operations.
(8) A procedure for an entry in the maintenance records required by
§43.9 of this chapter that shows the date, airport, and reasons for each
discontinued Category II operation because of a malfunction of a listed
instrument or item of equipment.
(b) Bench check. A bench check required by this section must
comply with this paragraph.
(1) It must be performed by a certificated repair station holding one
of the following ratings as appropriate to the equipment checked:
(i) An instrument rating.
(ii) A radio rating.
(iii) A rating issued under subpart D of part 145 of this chapter.
(2) It must consist of removal of an instrument or item of equipment
and performance of the following:
(i) A visual inspection for cleanliness, impending failure, and the
need for lubrication, repair, or replacement of parts;
(ii) Correction of items found by that visual inspection; and
(iii) Calibration to at least the manufacturer's specifications unless
otherwise specified in the approved Category II manual for the aircraft in
which the instrument or item of equipment is installed.
(c) Extensions. After the completion of one maintenance cycle of
12 calendar months, a request to extend the period for checks, tests, and
inspections is approved if it is shown that the performance of particular
equipment justifies the requested extension.
[Doc. No. 18334, 54 FR 34325, Aug. 18, 1989]
Effective Date Note: At 66 FR 41116, Aug. 6, 2001, appendix A to
part 91 was amended by removing paragraph 4(b)(1)(iii), effective Apr. 6,