Perform CAT II/III approaches (A320)[PDF]

INTRODUCTION

The purpose of this article is to provide general and standard operating concepts applicable to CAT II/III approaches, the main goal of which is to provide a higher level of safety when landing in low visibility conditions.

It is recommended to perform these types of approaches in CAT I or better weather conditions, before flying in actual LVO (Low Visibility Operations)
As a general rule, Low Visibility Procedures (LVP) are those applicable to an aerodrome in order to achieve a safe operation during weather conditions lower than those required for CAT I, other than CAT II, in CAT II/III approaches and low visibility take-offs.

Despite the slight differences that may be found among ICAO, FAA or EASA regulations, all refer to the same principles for CAT II/III operations.

REVIEW OF IMPORTANT CONCEPTS

ILS

Refer to Instrument Landing System - ILS (Beacon)

MARKER BEACON

Refer to Marker Beacon (Beacon)

AIRPORT LIGHTING

Refer to Aerodrome Lighting System

AIRPORT MARKING

Refer to Aerodrome Marking Signs

RUNWAY VISUAL RANGE

Runway Visual Range (RVR) is the range over which a pilot of an aircraft on the centreline of the runway can see the runway surface markings or the lights delineating the runway or identifying its centreline (ICAO). RVR values are given for the three basic portions of the runway: TOUCH DOWN ZONE (TDZ), MID-RUNWAY PORTION (MID) and ROLL OUT PORTION.

RVR makes part of the ground equipment necessary for CAT II/III operations. This value is measured by a system of calibrated automatic visibility meters (previously known as transmissometer for earlier versions of this equipment), which consists of a transmitter and a receiver used to obtain a measurement of the visibility in terms of extinction coefficient of transmitted light. In other words, this will basically determine how far the light beam can go in space.

For CAT II operations, the TDZ measurement is required, but for CAT III, both the TDZ and MID are mandatory.

DECISION HEIGHT(DH)

The Decision Height (DH) is a specified vertical point in the Precision Approach or approach with vertical guidance at which a Missed Approach must be initiated if the required visual reference to continue the approach has not been established (ICAO ANNEX 6).

Bear in mind that DH, unlike the DA, is a radio altimeter based reference point.
DH.jpg

Refer to IFR precision approach and minima for more information.

AIRBUS 320 RELATED CONCEPTS

FMGS

The Flight Management Guidance System (F.M.G.S) contains the following:

  • 2 Flight Augmentation Computers (FAC)
  • 2 Flight Management Guidance Computers (FMGC)
  • 2 Multipurpose Control and Display Units (MCDU)
  • 1 Flight Control Unit (FCU) with two independent channels.
FMGS Units
Each FMGS is divided into two main parts: Flight Management (FM) and Flight Guidance (FG).

The Flight Management (FM) part controls the following functions:

  • Navigation and management of navigation radios
  • Management of flight planning
  • Prediction and optimization of performance
  • Display management
The Flight Guidance (FG) part performs the following functions:
  • Autopilot (AP) command
  • Flight Director (FD) command
  • Autothrust (A/THR) command

Each FMGS computes its own landing category : CAT1, CAT2, CAT3 Single and CAT3 Dual, which will be displayed on the FMA. Each category depends upon the availability of aircraft systems and functions. When the capability downgrades, a triple click aural warning will be triggered with the respective change on the FMA indication.

Understand the FMA (Flight Mode Annunciator) at all times.
It is essential to understand that, in case of failure of any of the FMGS components, there will be a direct impact on the CAT II/III aircraft capability (See 'Handling of Abnormals' for more info).

ALERT HEIGHT

An Alert Height is a height above the runway, based on the characteristics of the aircraft and its fail-operational automatic landing system, above which a CATIII approach would be discontinued and a missed approach initiated if a failure occurred in one of the redundant parts of the automatic landing system, or in the relevant ground equipment (ICAO).

In other words, it’s stated that if a failure occurred below the Alert Height, it would be ignored and the approach continued.
AH2.jpg
Typically, Alert Height is set at 100ft for A320 family aircraft and it may be set to a lower value depending on the operator’s requirements. However, it can never be set at a value higher than 100ft for this type.

FAIL OPERATIONAL

An automatic landing system is Fail Operational if, in case of a failure occurred below alert height, the approach, flare and landing could be completed by the remaining part of the automatic system.
A Fail Operational landings system is displayed on the FMA as CAT III DUAL
CAT III DUAL.jpg
In the event of a failure, the Automatic Landing System will operate as a Fail Passive System.

FAIL PASSIVE

An automatic landing system is Fail Passive if, in the event of a failure, there is no significant out-of-trim condition or flight path or attitude deviation but the landing cannot be completed automatically.
A Fail Passive landing system is displayed on the FMA as CAT III SINGLE
Fail Passive.jpg
In the event of a failure with a Fail Passive system, the pilot assumes control of the aircraft.

Note: Below Alert Height, the FMGS freezes the landing capability until LAND mode is disengaged or both APs are off, thus guaranteeing no degradation in the category of the system should a failure occur below this height (100ft Radio Altimeter).

PREPARATORY WORK

CAT II/III APPROACH PREPARATION

In addition to the applicable standards, pilots should take special measures in preparation for CAT II/III approaches.

Limitations

  • Wind: 30kt HW, 20XW, 10TW (check your manual since it may differ)
  • Elevation: Check your manual for autoland maximum altitude (typically 9200ft as the max value)

Aircraft Capability

As soon as you arm the approach on the FCU, the system will display the Landing Capability (CAT1/2/3 SINGLE or DUAL). However, If any item is inoperative due to, for example, a computer fail during cruise, you should refer to QRH to verify the expected landing capability. Some failures are not monitored by the FMGC, so be prepared in advance.

Note: depending on your simulation features, there might be possible failures randomly activated by your simulation platform.

Airport Facilities and Weather

  • Check current NOTAMs applicable to airport facilities. Those NOTAMs in relation to ground equipment and facilities are often simulated in IVAO. So be prepared for possible CAT II/III restrictions.
  • Check current METAR and TAF on destination and alternate airports (Alternates must be above minima). Be prepared for LVP operations. Visibility is the main character here. However, do not forget about wind components and runway conditions.
    Automatic Rollout has not been demonstrated on contaminated runways.

Crew Qualification

In IVAO, everybody is free to fly, following certain rules. We do not need approval nor a qualification. However, we encourage you to keep reading this article and practice these types of approaches in CAT I or better conditions.

Seating Position

In real life, this is a very important part. Set up your 3D cockpit view so that you can monitor your instruments and look outside. You may loose some visual references if you do not correctly set your cockpit views.

Landing Lights

Normally NOT USED in CAT II/III weather conditions. Using landing lights during low visibility at night may have a negative impact, since the reflection can reduce the visibility even more.

Approach and Go around Strategies

Two important things in regards to this:

  • In CAT II approaches, autoland is recommended
    , whereas
    In CAT III approaches, AUTOLAND is absolutely MANDATORY.

Consider a possible course of actions in case of degradations in the aircraft capability (triple aural click) in order to assess all available options.

  • Be Go-around minded during the approach. Should a failure occur above 1000ft Radio Altimeter, all ECAMs and DH amendments must be completed before reaching 1000ft. Otherwise, perform a missed approach.

Approach Briefing

Briefing should highlight some relevant points necessary for CAT II/III operations such as aircraft capability, airport facilities and weather minima, as well as operational tasks during the approach (task sharing when flying in shared cockpit), call outs and strategies.

Other considerations

  • Make an AUTOLAND system test by depressing the AUTOLAND push button on the glareshield (Check your flight sim features for this).
  • Set Autobreaks to LOW/MED. Assess runway conditions, landing distance and possible taxi-out route.
  • Set DHs according to the charted values. For CATIII approaches with no DH, "NO" should be entered in the DH field of the MCDU to avoid false "HUNDRED ABOVE" or "MINIMUM" auto callouts which would not be applicable.
  • Consider flaps setting accordingly. Most A320s series are approved for autoland in Flaps 3 or Full. Check your manual for limitations.

OPERATIONAL TASKS (TASK SHARING)

According to A320 SOPs, pilots should review in advance all those operational tasks required for CAT II/III approaches. This is well known as Task Sharing, since these tasks are shared between Pilot Flying (PF) and Pilot Monitoring (PM).

Regardless you fly alone or in a shared cockpit, this part of the preparation is mandatory every time an automatic approach and land is attempted.
  • At 350 ft RA: CHECK “LAND” on FMA

- CHECK ILS course.

- If LAND is not displayed or if the ILS course is not correct, do not perform an autoland. If visual references are not sufficient for manual landing, GO AROUND.
  • Between 50 and 40 ft RA: CHECK that “FLARE” is displayed on the FMA
  • At approximately 30 ft RA: CHECK that “IDLE” is displayed on the FMA

- Autothrust starts to reduce thrust toward IDLE.

  • At 10 ft: CHECK “RETARD” auto-callout comes up

- MOVE the thrust levers to IDLE. Autothrust disconnects.

  • At touchdown: CHECK “ROLL OUT” on the FMA.

- With the autopilots ON, it should keep the aircraft along the runway centerline.

  • At the end of the Rollout: Disconnect the autopilot.
Task Sharing.jpg

CHART READING

SKBO CAT III.jpg

CAT II/III APPROACH 13R

Final Approach Course: 134o

GS Interception: 5NM from IADO at 10000ft

Glide path: 3.0o

DH: No DH for CAT III, 137ft RA for CAT II

If the aircraft capability is “Fail Passive” (CAT III SINGLE on FMA), set DH to 50ft RA

DESCENT PREPARATION

Use the “TOP HAT” method as per AIRBUS SOP for descent preparation. Follow the flow from left to right. Here you’ll find some of the most important setups.

Prepare the approach at least 80NM before Top of Descent (TOD)
TOP HAT A320.jpg


  1. Pay particular attention to the F-PLN sequence. Select the appropriate ILS approach (CAT II/III). Make a vertical revision and check altitude and speed constraints for each point along the approach. Press key R2:
F-PLN ILS.jpg
Cross check with the charted values
Vertical rev.jpg

2. On RAD NAV page, select the most appropriate radio NAV aids for the procedure.

Check that the ILS frequency pre-selected by the system with the slope value and the approach course according to the procedure are the correct ones.
RADNAV.jpg

3. On PERF, set the approach page with the most current weather data.

Insert the correct DH value based on the category of the approach. In this example, CAT IIIA approach requires NO DH if the automatic landing system is Fail Operational. Insert NO on DH
In case of downgrade in the aircraft capability, amendments on DH values can be done before reaching 1000ft
CATIII DH.jpg

AIRCRAFT GUIDANCE MANAGEMENT

CONDITIONS CAT I CAT II CAT III WITH DH CAT III WITHOUT DH
TECHNIQUE Manual Flight or AP, FD, A/THR AP, FD, A/THR down to DH AP, FD, A/THR AUTOLAND AP, FD, A/THR AUTOLAND
MINIMA AND WEATHER Baro DA and Visibility DH with RA / RVR minima DH with RA / RVR minima RVR minima
AUTOLAND Optional with precautions Recommended Mandatory Mandatory


1. Arm the approach by pressing the APPR push button on the FCU when:
  • Clearance for the approach has been received.
  • Aircraft is on the intercepting trajectory for the final approach course.
  • LOC deviation scale is available on PFD.
This will arm LOC and GS modes.
Attention: Make sure the aircraft is in the correct ILS envelope. Arming the approach too soon may cause a false Glide Slope interception out of the protected area, making the airplane descend outside the normal glide slope capture zone.
Engage both autopilots
APPR PB.jpg

Note: According to ICAO, the normal glide slope envelope is within 10 NM, ±8o off the centerline of the ILS glide path and up to 1.75 θ and down to 0.3 θ (θ = nominal glide path angle)

2. The FMA will show the LOC and GS modes armed in blue, or captured in green (LOC* GS*). It will also show the current capability (CAT 1, CAT 2, CAT 3 SINGLE or CAT 3 DUAL).
FMA.jpg
Bear in mind that if only one autopilot is engaged, the system will be Fail Passive, shown on the FMA as CAT 3 SINGLE.
3. Monitor LOC and GS capture. With GS*, set GO AROUND ALTITUDE.
LOC GS Capture.jpg
4. Check that the aircraft is now Stablished on the LOC and GS.
LOC GS .jpg
5. It is recommended to be early stabilized before reaching 1000ft with landing checklist completed and the aircraft fully configured with all parameters accomplished for the stabilization criteria, since the next tasks are critical and must be prioritized.
Stabilized approach.jpg

COMMON PARAMETERS FOR STABILIZATION DURING THE APPROACH

The stabilization criteria shown here are just a reference. They may vary depending on each operator.
  • Speed: between VAPP -5kt // +10kt
  • V/S: Max -1000ft/min in descent
  • Bank: Max 7o
  • Pitch: Max -2.5o // +10o
  • LOC: deviation not greater than 1/2 dot
  • GS: deviation not greater than 1/2 dot

TASK SHARING

6. At 350ft RA, LAND mode will engage.
LAND.jpg
If no LAND mode, autoland is not authorized.
7. Between 50ft and 40ft RA, FLARE mode will engage.
FLARE MODE.jpg
8. At approximately 30ft, check IDLE on the FMA. The Autothrust system commands thrust reduction toward idle.
Idle.jpg
9. At 10ft RA, the Auto Callout “RETARD” is triggered. Move thrust levers to idle.
RETARD.jpg
10. At touch down, check “ROLL OUT” on the FMA.
Roll Out.jpg
Apply normal procedures. At the end of the Roll Out, disconnect the autopilots and vacate the runway.
An automatic disconnection of the autopilot will occur if the aircraft heading is 20o or more off the runway centerline when steering the aircraft by the use of the nose wheel steering.
Important Note: bear in mind that perhaps not all flight sim add-ons have the possibility to simulate an AUTOLAND. It will basically depend upon the level of software development.

HANDLING OF ABNORMALS

During some abnormal conditions, the aircraft may experience a downgraded autoland capability.

ECAM actions will guide through the different affected systems to the STATUS page in order for pilots to assess, among other relevant issues, possible degradations of the automatic landing system.

In this example, IR unit #2 has failed.

IR2 FAULT.jpg

The image above shows the current aircraft status, as well as the updates made for the APPR PERF page on the MCDU according to the situation. The CAT II/III approach chart indicates that in case of FAIL PASSIVE (CAT 3 SINGLE) capability, a DH of 50ft RA should be used. (See Chart Reading section).

This DH charted value matches with the minimum DH for CAT 3 SINGLE autoland system as per A320 auto flight limitations.

When the APPR push button is pressed, the approach arms the LOC/GS mode in blue (as when in normal conditions). However, due to the failure affecting the autoland capability, the FMGS shows on the FMA the expected capability CAT 3 SINGLE with both autopilots ON.

CAT3 SINGLE.jpg


There could also be some failures not associated with ECAM actions, like FMGS 2 FAIL for example. This failure triggers a TRIPLE CLICK aural indications if the approach has been armed already, as well as a change on the FMA showing the new autoland capability, and the respective indications on the ECAM STATUS page.
Triple click.jpg

This failure can be also verified by looking at some specific indications on the copilot ND displaying MAP NOT AVAIL and SET OFFSIDE RNG/MODE and the MCDU.

Again, with CAT 3 SINGLE capability, you have to correct the DH to 50ft RA.
FMGC2 FAIL.jpg
After having performed all necessary corrections and assessed the situation, the approach can be continued with the remaining systems.
CAT3 SINGLE 1FMGC.jpg
Note: All ECAM actions and amendments must be done before reaching 1000ft.

SUPPLEMENTARY INFORMATION

According to ICAO Annex 6, there is a very important concept that pilots should be familiar with, and it refers to the “Commencement and Continuation of the Approach”. (Some similar concepts may apply to EASA and FAA regulations)

This is well known as the Approach Ban Policy, and it applies to arriving aircraft when weather conditions are reported to be below minima in order to facilitate the pilot decision making process.

This policy limits aircraft from proceeding beyond a point on an IAP, which is 300 m (1000ft) AFE or the beginning of the final approach segment, unless weather conditions satisfies the required minima for the approach. If weather deteriorates after having passed the approach ban point, the pilot may decide to continue down to DA/H or MDA.

Approach Ban Policy.jpg
The approach can be continued below DH/DA/MDA and landing can be completed if sufficient visual references are established and maintained for the type of approach.

.

The TDZ RVR is always controlling whereas the MID and END portions are controlling if reported and if relevant (EASA Regulations).

Note: “Relevant” in this context refers to that part of the RWY used during the high-speed phase of the landing down to a speed of approximately 60KIAS.)

Reference

  • A320 FCOM/FCTM
  • Getting to grips with CAT II/III
  • All weather operations manual

Author

  • VID 109661 - Creation

DATE OF SUBMISSION

  • 11:38, 23 February 2021

COPYRIGHT

  • This documentation is copyrighted as part of the intellectual property of the International Virtual Aviation Organisation.

DISCLAIMER

  • The content of this documentation is intended for aviation simulation only and must not be used for real aviation operations.