. 
2 (or 3) ADIRU's associated with the engaged autopilot(s) in Nav mode

Category II Approach Flight Director
The following equipment must be operative for a Flight Director (FD) approach requiring the use of Category II minima:
. 
2 independent sources of electrical power. (The APU may be a substitute
source of power for the left or right electrical system.)

. 
2 separate flight directors, one of which must be the right FD

. 
2 attitude indicators supplied by different symbol generators including
attitude, radio altitude, ILS deviation, DA(H) indication and AFDS status

757-200
. 
2 (or 3) IRU's in Nav mode
757-300

. 
2 (or 3) ADIRU's in Nav mode

Category III Operations
Category III operations are based on an approach to touchdown using the automatic landing system. Normal operations should not require pilot intervention. However, pilot intervention should be anticipated in the event inadequate airplane performance is suspected, or when an automatic landing cannot be safely accomplished in the touchdown zone. Guard the controls on approach through the landing roll and be prepared to take over manually, if required.
The airplane is certified for Category IIIb operations with two engines operating. The airplane is certified for Category IIIa operations with two engines operating or with one engine inoperative if the engine failure occurs during the final approach.
Note: Some airplanes are also certified for Category IIIa approach and autoland
through rollout, with an engine inoperative prior to selecting landing flaps.
See Engine Out Autoland tables in the ILS - One Engine Inoperative
section.
Category IIIa/Autoland
For Category IIIa operations the following equipment must be operative and LAND 2 or LAND 3 annunciated:
. 
2 independent sources of electrical power. (The APU generator may be a
substitute source of power for the left or right electrical system.)

. 
2 or 3 autopilots

. 
3 hydraulic systems

. 
2 attitude indicators supplied by different symbol generators including
attitude, radio altitude, ILS deviation, DA(H) or AH indications, and
AFDS status

. 
2 (or 3) IRU's (associated with the engaged autopilots) in Nav mode

. 
autoland status annunciator for the pilot conducting the approach

Category IIIb/Autoland
For Category IIIb operations, visual reference is not normally a specific requirement for continuation of the approach to touchdown.
Category IIIb operations require the following equipment to be operative and LAND 3 annunciated:
. 
3 autopilots

. 
3 hydraulic systems

. 
autothrottle

. 
3 independent sources of electrical power. Normally the left generator, the
right generator and the battery bus. (The APU generator may be a
substitute source of power for the left or right engine driven generator.)

. 
2 autoland status annunciators

. 
2 attitude indicators supplied by different symbol generators including
attitude, radio altitude, ILS deviation, AH or DA(H) indications, and
AFDS status

757-200

. 
3 IRU's in Nav mode
757-300

. 
3 ADIRU's in Nav mode

AFDS Faults
Faults leading to non-normal operations can be divided into two categories:
. 
those occurring above AH

. 
those occurring at or below alert height.

Within these categories many non-normal situations or scenarios are possible. The flight deck is designed so that a quick analysis and decision can be made for virtually all non-normal or fault situations using the crew alerting system and autoland status annunciation.
If the flight crew is aware of the airplane equipment requirements for the approach, the following can be used for any AFDS fault indication:
Above Alert Height
Immediately after recognizing the fault from the crew alerting system, instrument flags, or engine indications, check autoland status annunciation.
. 
if the autoland status annunciation has not changed, and the equipment is
not required for the approach or can be switched, (e.g., flight director),
continue the approach

. 
if the autoland status annunciation has changed, or the equipment is
required for the approach, adjust to the appropriate higher minimums or
go-around.

At or Below Alert Height
For any EICAS alert, continue the approach to an automatic landing and rollout unless NO AUTOLAND is displayed. The pilot should not intervene unless it is clearly evident that pilot action is required.
　
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