LOW VISIBILITY OPERATIONS Flashcards
The main objective of CAT II/III operations is
to provide a level of safety when landing in low visibility conditions equivalent to that of ‘normal operating conditions.
The main difference between CAT II and CAT III operations is
CAT II provides sufficient visual reference to permit a manual landing at DH, where CAT III does not provide sufficient visual references and requires an automatic landing system, pilots see the runway lights only for a few seconds (say about 5 seconds) before touch down; therefore there is no margin for error.
The minima only permit the pilot to decide if
the aircraft will land in the touch down zone (basically CAT III A) and ensure safety during roll out (CAT III B)
The basis for Low Visibility operations, such as aircraft certification or airline operational demonstration, ensures a high level of safety necessitating, authorization for Low Visibility operations which in turn depends on the following four elements:
The Aircraft
The Flight Crew
The Airport
The Operator
These elements must comply with the regulations established by DGCA. Aircraft on Indigo strength must be approved for Low Visibility operations with an automatic landing system
The main part of AWO (All Weather Operations ) includes taxiing in low
visibility, Category I, Category II, Category III and LVTO operations. Whereas, LVO includes
Low visibility taxi
Low visibility take off
CAT III landing
The ILS installed at various airports in India meet the CAT I level requirement that permits landing up to RVR of
550 m and above.
When RVR is below 550 m, the operations fall into CATII or CAT III depending upon minima and aircraft is not allowed to land or take off unless aircraft, Flight Crew, Airport and operator is appropriately approved– In order to maintain required level of safety.
Definitions and Explanation: CAT I operation
CAT I operation is a precision instrument approach and landing using ILS. The associated company operating minima for CAT I are given below:
DH not lower than 200 feet.
Either a visibility not less than 800 m or RVR not less than 550 m.
Definitions and Explanation: CAT II operation
CAT II operation is a precision instrument approach and landing using ILS with:
Decision Height below 200 ft but not lower than 100 feet and
RVR of not less than 300 m.
CAT II weather minima has been established to provide sufficient visual references at DH to permit a manual landing (or a missed approach) to be executed; it does not mean that
the landing must be made manually
Definitions and Explanation: CAT III operation
CAT III operation is a precision approach at lower than CAT II minima.
CAT III Operation is divided in three sub-categories: CAT IIIA, CAT IIIB, CAT IIIC associated with three minima levels.
CAT III A operation: A precision instrument approach and landing using ILS with…….
DH lower than 100 feet or no DH; and
RVR not less than 175 m.
CAT III B operation: A precision instrument approach and landing using ILS with……..
A DH lower than 50 feet or no DH; and
RVR less than175 m but not less than 50 m.
Note: A320 AFM limits to 75m
CAT III C operation: A precision instrument approach and landing with no DH and no RVR
limitations.
A320 aircraft is approved for ‘Automatic Approach & Automatic Landing’ operations under all weather conditions if
CAT 3 DUAL / CAT 3 SINGLE or CAT2 is displayed on FMA.
A320 is not approved for Auto-Land if
CAT1 is displayed on the FMA.
The automatic landing is required in CAT III operations including ___ in CAT III B.
roll out
The automatic landing is the preferred landing technique in ___ conditions.
CAT II
Automatic Landing pertains to the capability of the aircraft to perform:
(i) Automatic Approach &
(ii) Automatic Landing / Touchdown & subsequently
(iii) Automatic Roll-Out, with or without auto-braking to a full stop
The FMA Second & Third Column displays the
AP guidance modes during the automatic approach / landing. When established on the ILS, this FMA display is GS / LOC initially, and subsequently changes to LAND, FLARE, and ROLLOUT towards the final stages.
The FMA Fourth Column displays the
aircraft’s “Capability” in regard to its automatic approach & automatic landing at a particular moment during the progress of the approach.
The display is of either CAT3 DUAL or CAT3 SINGLE or CAT2 or CAT1.
The changes in approach & landing capability is decided by the FMGC which takes into account the availability of various aircraft technical systems integrated to the aircraft’s Auto - Flight at a particular stage.
If an associated system fails the capability downgrades and if the system is restored, the capability automatically upgrades back.
Whenever a downgrade in capability occurs, a triple click is generated.
The FMA FIFTH COLUMN indicates the
engagement of the number of autopilots, FDs, & A/THR. Whenever there is a change in the fifth column, a triple click is also generated but NOT for any change in regard to FDs since FD is not mandatory for Automatic Approach / Landing.
Definitions and Explanation: FREEZING OF FMA
Below 100 ft. ( RA ), the available display on the FMA’s ‘ Fourth Column is frozen. This means that a failure of one AP or a loss of an associated integrated technical / function system would not affect a change in the capability of the aircraft unless LAND mode is disengaged or both auto-pilots are off.
Definitions and Explanation: Fail-Operational automatic landing system
in the event of a failure below AH, the approach, flare and landing can be completed by the remaining part of the automatic system.
CAT 3 Dual is annunciated on FMA as long as the airborne systems are fail-operational. In the event of a failure below the AH, the AP will continue to guide the aircraft on the flight path and automatic landing. The approach, flare and landing can be completed by the remaining part of the automatic system.
In that case no capability degradation is indicated and CAT 3 Dual remains annunciated even after failure.
Definitions and Explanation: Fail-passive automatic landing system
in the event of a failure, there is no significant deviation of aeroplane trim, flight path or altitude but the landing [Landing Roll] will not be completed automatically.
CAT 3 Single is annunciated when the airborne systems become fail passive above AH, which means that a single failure will lead to the AP disconnection without any significant out of trim condition or deviation of the flight path or altitude. Manual flight is then required.
Minimum DH is 50 ft.
Definitions and Explanation: Alert Height
a height above the runway threshold which is based on the characteristics of the aeroplane and its fail operational landing system, above which
a Category III auto-land operation would be discontinued and a missed approach initiated if a failure occurred in one of the redundant parts of the landing system, or in the relevant ground equipment.
If the failure occurs below Alert Height:
FMA indication would remain frozen and FMA continues to indicate CAT 3 DUAL.
The approach can be continued as the aircraft design capability is such that in spite of the failure/ malfunction, the Auto-Pilot would successfully perform an automatic landing using the remaining automatic system.
The flare, touchdown and roll out may be accomplished using the remaining Automatic system.
In other words, if a failure occurred below the Alert Height, it would be ignored by the system and the approach continued. The Alert Height permits the continuing of the approach below RA 100 ft for CAT III B ifCAT 3 DUAL is displayed on the FMA at RA 100 ft.
AH is only linked to the probability of failure (s) of the automatic landing system. The term pertains only to a CAT III ‘Fail Operational’ Automatic Landing.
AH is evaluated during aircraft certification; it is established as 100 ft. for A320. AH concept is relevant only when CAT 3 DUAL is displayed on FMA.
Operators are free to select an AH lower than the 100 ft but not higher than 100 ft.
Alert Height is evaluated during aircraft certification; it is established as
100 ft. for A320
Alert Height concept is relevant only when
CAT 3 DUAL is displayed on FMA
Operators are free to select an AH lower than
the 100 ft but not higher than 100 ft
If the failure occurs above Alert Height
CAT 3 DUAL will downgrade to: CAT 3 SINGLE or
CAT 2 or
CAT 1
on the FMA depending on the failure and you will have to discontinue the CAT III B approach
Definitions and Explanation: DA / DH
A specified altitude or height (A/H) in the precision approach at which a missed approach must be initiated, if the required visual reference to continue the approach has not been established.
If visual references have not been established, a go-around must be executed.
If the visual references have been established, the approach can be continued. However a pilot may always decide to execute a Go around if
sudden degradations in the visual references or a sudden flight path deviation occur
Decision height is the wheel height above
the runway elevation
Visual reference for Category II operations:
a segment of at least 3 consecutive lights being the centre line of the approach lights, or touchdown zone lights, or runway centre line lights, or runway edge lights, or a combination of these is attained and
can be maintained.
This visual reference must include a lateral element of the ground pattern, i.e. an approach lighting crossbar or the landing threshold or a barrette of the touchdown zone lighting.
Visual reference for Category III A operations:
a segment of at least three consecutive lights being the centreline of the approach lights, or touchdown zone lights, or runway centreline lights, or runway edge lights, or a combination of these is
attained and can be maintained.
Visual reference for Category III B operations conducted with fail-operational flight control systems using a decision height:
at least one centreline light is attained and can be maintained.
Visual reference for Category III B operations conducted with fail-operational flight control systems without a decision height:
there are no requirements for a visual verification prior to landing.
RVR is reported depending upon the RVR value/trend in the increments of
100m, 50m or 25m
RVR is reported up to 3 points along runway whenever normal visibility is detected as being less than
1500m
The minimum RVR value for the mid-point/stop-end is ___ in CAT I, CAT II and CAT III A.
125m
The minimum RVR value for the mid-point/stop-end is ___ in CAT III B.
75m
Definitions and Explanation: Approach Ban Point
The point on a final approach where the reported weather conditions at the runway must meet the applicable minima so as to be able to meet regulatory requirements for continuing an instrument approach to a landing.
If after entering the final approach segment or descending below 1000 ft. above the aerodrome elevation, the reported RVR/visibility falls below the applicable minimum,
the approach may be continued to DA or MDA/H
Definitions and Explanation: Final Approach
That part of an instrument approach procedure which commences at the specified final approach fix or point, or where such a fix or point is not specified,
a) at the end of the last procedure turn, base turn or inbound turn of a racetrack procedure, if specified; or
b) At the point of interception of the last track specified in the approach procedure; and ends at a point in the vicinity of an aerodrome from which:
1) A landing can be made; or
2) A missed approach procedure is initiated.
Definitions and Explanation: Cockpit Cut-off Angle
The angle made by the direction of aircraft nose with fore and aft axis, with pilot’s eye correctly positioned, is called the Cockpit Cut-off Angle.
- This is 20 degrees for A320 Aircraft with a 4 deg. Pitch Angle on final approach; the earliest point visible will be 16 degrees below horizon.
Cockpit Cut-off Angle: As a rule of thumb, an incorrect seating position which reduces the cut off angle by 1 degree reduces the visual segment by
approx. 10m (30 feet)
Definitions and Explanation: Minimum Approach Break-off height (MABH):
MABH is the lowest height above the ground, measured by radio altimeter, such that if a missed approach is initiated without external references in normal operations the aircraft does not touch the ground during the procedure. With an engine failure during missed approach, it can be demonstrated that taking this failure probability, an accident is extremely improbable.
The MABH or the altitude loss during automatic GA can be used to determine the minimum DH in Cat III operation.
AFM MABH is 25 ft. AGL for Cat III with DH.
Minimum Approach Break-off height (MABH) AFM A320 for Cat III with DH is
25 ft. AGL
Criteria for Implementing Low Visibility Procedures (LVP)
Either the Touch down RVR or MID RVR is less than 800m, or,
The cloud ceiling is less than 200 ft. and
SP has been completed and the airport is safeguarded.
Definitions and Explanation: LVTO
A term used in relation to flight operations referring to take-off on a runway where the RVR is less than 400 m.
Whenever any reported RVR (TD/MID/END) goes below 400 m, it will be considered as Low Visibility Take-Off.
All three RVRs are mandatory but if TDZ RVR is not available, pilot assessment is acceptable. But then MID & END RVRs must be reported and not less than 200 M.
200 m and below, all three RVR (TDZ/MID/END) must be reported.
LVTO: Whenever the Runway centreline lights spacing is up to 30 m – minimum
RVR value required (TD/MID/END) for take-off is
150m
VILK (RWY 27), VIAR (RWY 34),
VIDP (RWY 09 and 27), VECC (RWY 19 L)
LVTO: Whenever Centreline lights spacing is 15 m or less – Minimum RVR value
required (TD/MID/END) for take-off is
125m
VIDP on RWA 28 and 10,
29 and 11, OMAA, OMDB all runways
Following items have to be serviceable at the commencement of a low visibility take-off,
Category II or III approach in accordance with the AFM or other approved document.
- Windshield wipers (where fitted) for both PIC and Co-pilot
- Window heat system for all heated cockpit windows
- Anti-skid system
- Thrust reversers for all engines
NOTE: Full thrust take off rating is to be used for LVTO. Supervised take-off and landing is not permitted during CAT II/III operations or LVTO.
CAT II and CAT III autoland are approved in CONF ___
CONF 3 and CONF FULL.
CAT II and CAT III fail passive autoland are only approved in CONF ___
CONF FULL, and if engine-out procedures are completed before reaching 1 000 ft in approach.
Maximum wind limitations for CAT II or CAT III automatic approach or automatic landing and automatic roll out:
Headwind: 30 kt.
Tailwind: 10 kt.
Crosswind: 20 kt.
