CAT II/III Autoland: Minima, Fail-Passive vs Fail-Operational

CAT II/III Autoland: Minima, Fail-Passive vs Fail-Operational

CAT II and CAT III autoland let an airliner complete an ILS approach and landing in visibility too low for a normal approach. They depend on four things working together: a certified aircraft, an equipped runway, an approved operator and a current, trained crew. The difference between categories comes down to decision height and runway visual range (RVR). The difference between system types comes down to what happens when something fails. This guide covers both, then walks through the crew procedures, the A320 specifics and the training behind them.

TL;DR

• CAT IIIa has no decision height (or one below 100 feet) and RVR of at least 700 feet. CAT IIIb goes lower, and CAT IIIc has no RVR limit on paper.
• Fail-passive systems leave the pilot to take over after a failure. Fail-operational systems can finish the landing after a single failure below alert height.
• Autoland is a crew-monitored operation, not a hands-off one. The pilot still watches the flight path and decides whether to continue or go around.
• On the A320 family, the PFD shows “CAT 3 SINGLE” for fail-passive and “CAT 3 DUAL” for fail-operational.
• Airport low visibility procedures, ILS protection and operator approval matter as much as the aircraft.

Table of Contents

• What CAT II and CAT III autoland actually mean
• CAT III minima by sub-category
• Fail-passive vs fail-operational
• What has to be in place before the approach
• Crew procedures and decision points
• A320 autoland procedures
• What happens when something fails
• Perspective
• Practice it before an airline does it for you
• How to prepare for CAT II/III work
• FAQ
• Sources

What CAT II and CAT III autoland actually mean

An autoland system flies the aircraft down the ILS using the localizer and glideslope signals, along with a radar altimeter for height. At the right height it brings the thrust to idle, flares the aircraft and, in the more capable versions, steers it along the runway after touchdown. SKYbrary’s autoland overview describes this as an operation the crew monitors throughout.

The “category” tells you how low the weather minima can go. CAT I is a standard ILS approach. CAT II and CAT III step down from there, with lower decision heights and smaller visibility requirements. Each step demands more from the aircraft, the ground equipment and the crew. Autoland is the usual way to fly the lower CAT III minima, because at those values the pilot may have little or no useful visual reference before touchdown.

Two terms come up constantly:

• Decision height (DH): the height at which the pilot must have the required visual reference to continue, or else go around.
• Runway visual range (RVR): the distance along the runway a pilot can see, measured by sensors beside it and reported to the crew.

CAT III operations sometimes have no decision height at all. The crew’s decision point then becomes an alert height or a system-status check rather than a visual call.

CAT III minima by sub-category

The FAA defines the CAT III sub-categories by decision height and RVR. The figures below come from FAA material.

CAT IIIc exists in the definitions, but a landing with no visibility at all also requires taxi guidance in the same conditions. Most operators plan around IIIa and IIIb. Your own operations specifications and approvals set the limits you can actually use, not the table.

Note the regional difference in CAT IIIb: the FAA and EASA floors are not identical. A pilot flying for a carrier that operates across both systems needs to know which one applies to the airport and approval in use.

Fail-passive vs fail-operational

This is the distinction pilots search for most, and it decides what the crew does when a system drops out low on the approach.

Fail-passive. If a failure occurs, the aircraft does not deviate significantly from its flight path, but it cannot complete the landing by itself. The pilot has to take control. FAA AC 120-28D describes this in its definitions.

Fail-operational. The system has enough redundancy to continue. It can finish the approach, flare and touchdown, or rollout, after the failure of any single component, using the elements that remain. The same advisory circular covers this, citing the point below alert height.

The practical consequences:

The fail-passive response comes from the same FAA guidance on failures during CAT III. In plain terms: fail-passive generally means go around if something fails below the decision height, unless the pilot decides continuing is safer. Fail-operational means the aircraft is designed to carry on.

The A320 annunciations are covered in Airbus’s Getting to Grips with CAT 2 / CAT 3 guide, which is worth reading in full if you fly the type.

What has to be in place before the approach

Autoland is not only an aircraft feature. Four layers all have to line up.

The airport and runway

The ILS must be certified for the category, and the runway needs the lighting and markings that go with it. Visual aids for CAT III do not have to match the scale of the non-visual aids. Their selection depends on the conditions in which operations are meant to take place, according to ICAO EUR guidance material.

Airports also run low visibility procedures (LVP). These protect the ILS critical and sensitive areas from large moving objects such as vehicles and other aircraft, which can distort the signal. FAA AC 120-28D lists LVP as a requirement for CAT II/III operations. If the airport has not activated LVP, you plan on the basis that the lower minima are not available.

The aircraft

The autopilot, autothrust, radar altimeters, displays and warnings must be certified and serviceable for the category. Dispatch rules, including which items may be inoperative, come from the minimum equipment list and the operator’s approval. Check the aircraft’s status before departure and again on the approach, because a degraded system can drop the aircraft to a lower capability.

The operator

The operator needs authorization for the minima it intends to use. That covers procedures, maintenance programs and crew training.

The crew

Both pilots need to be current and trained in the procedure, including the briefing, the monitoring tasks and the failure responses. This is the layer you control directly, and it is mostly trained in a simulator.

Crew procedures and decision points

Autoland does not remove the pilots from the loop. Their jobs change from hand-flying to monitoring and deciding.

According to the Airbus guidance on CAT 2 and CAT 3 operations, pilots monitor the performance of the autoland system and make sure the aircraft stays within lateral and vertical limits. If a failure occurs, they either take manual control, when visual cues allow it, or start a missed approach, when they do not.

A sensible sequence on the approach:

1. Brief it. Confirm the category, the minima, the alert height or DH, the failure responses and who calls what.
2. Check status early. Confirm the system annunciation, the ILS and the reported RVR before reaching the approach phase where a change becomes hard to manage.
3. Monitor the track. Watch the localizer and glideslope deviations, the autopilot modes and the radar altimeter callouts.
4. Reach the decision point. With a DH, establish the visual reference and check lateral and longitudinal progress. EASA’s guidance says a missed approach is required for CAT III operations with a DH if the aircraft is not within limits at that point.
5. Land and roll out. Monitor the flare, touchdown and rollout, and be ready to take over.

The point of the briefing is that nobody decides on the fly what a failure means. If you have already agreed the response, a warning at 40 feet is a procedure, not a surprise.

For a deeper look at how operators set up and approve this work, our guide to low visibility operations, minima and training covers the approval and training side.

A320 autoland procedures

The A320 family is where many pilots meet CAT III for the first time, so a few type-specific points are worth knowing.

Capability annunciations. The PFD shows “CAT 3 SINGLE” when the aircraft is fail-passive and “CAT 3 DUAL” when it is fail-operational, per Airbus’s CAT 2/CAT 3 guide. Read the annunciation as the statement of what the aircraft can do if something fails. It tells you what your response will be before the failure happens.

Thrust at touchdown. Pilots must make sure thrust is at idle by touchdown. On A320 family aircraft the crew monitors the landing, and the “RETARD” auto-callout at 10 feet radio altitude reminds the pilot to move the thrust levers to idle, although autothrust usually brings thrust to idle before that, as SKYbrary notes.

Go-around. If a go-around becomes necessary, specific rules govern how modes engage. The Airbus guide covers them, and they are exactly the kind of detail to rehearse in the simulator rather than read once.

Monitoring. The same discipline applies as on any type: call out deviations, keep the approach stabilized and keep your hand ready to take the controls if the aircraft stops doing what the annunciation promised.

If you are preparing for an A320 type rating or want to rehearse low visibility approaches on a Level D device, see our A320 simulator training and the A320 type rating (CEO/NEO) pages.

What happens when something fails

The response depends on the system type and on where in the approach the failure happens.

• Fail-operational system: the design lets the landing continue after a single failure below alert height.
• Fail-passive system: a failure below the decision height generally means a missed approach, unless the pilot judges that continuing is the safest course. This is the position in the FAA’s criteria.
• Failure above the decision point: the crew reassesses the category and minima they can now use, and goes around or diverts if the approach no longer qualifies.
• Loss of required ground conditions: if the LVP are cancelled or the ILS status changes, treat the approach as no longer meeting the category.

Always follow the operator’s procedures and the aircraft’s approved flight manual. The above is the general principle, not a substitute for either.

Perspective

We train a lot of pilots who have flown autoland on the line but have rarely had to deal with a real failure on one. In weather you do not usually see the failure coming, and the aircraft does not give you much time. That is why we think this belongs in a Level D full-motion simulator and not just in a classroom.

What we see is that pilots who rehearse the briefing, the status checks and the go-around until they are automatic handle it better than pilots who know the theory. The theory is simple: know what your system is, know what you do if it fails, and decide before you are low. The skill is making that decision calmly.

Our instruction comes from current and former airline pilots and examiners, who have flown these approaches. We would rather you spend your first low-visibility failure in our simulator than in an aircraft.

Jake

Practice it before an airline does it for you

Low visibility approaches are a common part of type rating courses and airline assessments. At Simulator Center we run type rating courses for the A320, A330, B737, B757/767 and ATR 42/72, and Level D simulator sessions that you can book by the hour or in blocks for assessment prep, recurrent and refresher training.

If you are a foreign pilot working toward FAA certification, we also handle FAA license conversion from ICAO, EASA and DGCA licenses, including scheduling, documentation and checkride coordination in a single program. Get in touch through the pages above to ask about the current schedule and pricing.

How to prepare for CAT II/III work

A practical path for a pilot who expects to meet this on the line:

1. Read the manufacturer’s material for your type. The Airbus guide linked above is a good example of the level of detail you want.
2. Learn your operator’s minima and approvals. They set what you can fly, not the generic table.
3. Rehearse failures at different heights. Practice a failure above the alert height, one below, and a go-around from each, with the pilot monitoring calling the right words.
4. Practice the briefing aloud. A briefing you have said ten times is one you will actually use.
5. Review the ground school basics. Our checklist of what to verify before type rating ground school can help you arrive prepared.
6. Rehearse for interviews. Airlines often check how you handle abnormal situations. See how to map ICAO competencies to Level D sim drills.

If you are already on the A320 and need recurrent work, our EBT-aligned A320 recurrent checklist shows what a good session should cover.

FAQ

What is the difference between CAT II and CAT III autoland?

Both are low-visibility ILS operations with lower minima than CAT I. CAT III goes lower still and is divided into IIIa, IIIb and IIIc. CAT IIIa has no DH or one below 100 feet with RVR of at least 700 feet, per FAA material. Your operator’s approval defines the exact CAT II values you can use.

Is fail-passive or fail-operational better?

Fail-operational is more capable, because it can finish the landing after a single failure. Fail-passive is safe, as the aircraft does not deviate significantly after a failure, but the pilot has to take over or go around. Which one you have depends on the aircraft and its approval, as described in FAA AC 120-28D.

Do pilots use autoland on every flight?

No. Autoland needs a certified aircraft, a runway and ILS approved for the category, active low visibility procedures, and an authorized, trained crew. Many landings do not meet those conditions, and most are flown without autoland.

What does the A320 show when autoland is available?

The PFD annunciates “CAT 3 SINGLE” for a fail-passive capability and “CAT 3 DUAL” for fail-operational, according to Airbus guidance. Check the annunciation during the approach briefing so you know your failure response in advance.

Can I practice CAT III approaches in a simulator?

Yes, and it is the safest way to rehearse failures. Our Level D full-motion devices are available for simulator sessions booked by the hour or in blocks.

Sources

• FAA: Runway Visual Range (RVR)
• FAA Advisory Circular 120-28D: Criteria for Approval of Category III Weather Minima
• FAA AIP: Aerodrome Availability and Conditions of Use
• SKYbrary: Autoland
• Airbus: Getting to Grips with CAT 2 / CAT 3
• EASA: Acceptable Means of Compliance and Guidance Material
• ICAO EUR Guidance Material on All Weather Operations at Aerodromes

Recommended

• Low Visibility Operations: Minima, Approvals and Training