Cat III approahes

[schleprock]

Can anyone fill me in on the different types of Cat III approaches? I know what the particulars with regards to ICAO Cat III limitations but I am not sure if these apply to the UK, US and Canada. As well, I would like to know all there is to know about an autoland system. I understand it is a requirement for a Cat III.

Thanks :)

[taraman]

schleprock,

CATIIIA approaches are at no ceiling with 50ft DH

CATIIB have no ceiling and 17ft DH

CATIIIC would have no ceiling and 0 DH, but as far as I know they are not flown until now due to the lack of suitable airborne equipment.

Autoland is not always needed for cat III approaches. The Canadair Ragiional Jet is certified to fly CATIIIA app´s without autothrust and with a head up guidance system. For B & C autoland is mandatory. It consists of Autopilot and autothrust. The Autopilot must be able to perform an automatic flare. As far as I know, for CATIIIB also an auto-rollout feature is needed.

[MFALK]

A CAT IIIC approach is one with 0 DH and 0m RVR. The problem with this is that it would be a problem exiting the runway after landing and finding your way to the parking stand. Even CAT IIIB approaches can have a 0 DH but usually have a minimum touchdown RVR requirement of 75m.

The 17ft DH that Taraman quotes sounds like a MABH. This is the minimum RA value that the aircraft manufacturer has established that the aircraft would not touch the runway in case of a go-around initiated at that height.

17ft is incidentally the MABH for the A320 equipped with CFM56-B engines. The IAE powered A320s may have a different MABH value possibly due to different engine acceleration performance, but I stand to be corrected.

[Tom Cat]

CAT III approaches in the USA:

1) CAT IIIA - DH below 100 feet or no DH and RVR not less than 700 feet

2) CAT IIIB - DH below 50 feet or no DH and RVR not less than 150 feet

3) CAT IIIC - no DH and no RVR limitation

[WOK]

Rollout isn't necessary for CAT IIIB.

Requirements are that the runway is equipped and approved - it needs an ILS with self monitoring and standy power supplies.

The aircraft needs to be equipped and approved - installations vary wildly, esp with older aircaft but basically the system uses two or three autopilots ( or single multi-channel) to couple to the ILS. Below a specific height (not altitude) the a/p uses rad alt (a misnomer) to determine closure rate and effect a flare. The aircraft either has rollout which uses the rudder to steer along the localiser beam or at the point the wheels are down you disconnect and are on your own. Most a/c use autothrottle for autoland, on some it's mandatory some don't need it. The reliabilaty, trustworthiness and ease of use vary wildly from type to type. On 757/767 the system was fairly trap free and a joy to use. On the 747 classics I flew it was a living nightmare, and most people were pleased to pick up a CAT I downgraded a/c so you knew you wouldn't have to try!

The crew need to be trained to CAT II/III standard.

There are subtle differences between the US and Europe as to exact procedures which allow a continued approach.

Once you get out of Europe autoland capable runwys are thin on the ground.

This subject can get awful complex - both technically and wrt the rules. A minefield.

[taraman]

MFALK,

thanks for the correction on the 17ft.
It is actually for an A320 with CFM56 engines, which I fly.
What does the abbreviation MABH stand for? (not the meaning but the full words!)

[Captain Ed]

I retired on the L-1011 in 1987 from TWA. My recollection is that the CAT IIIB in thise days was no DH, but there was a minimum RVR to commence the approach. The figure was 750', I believe.

I flew JFK - Seattle-Portland and back for many years. I put it to use very regularly on those trips.

On touchdown, there was zero forward visibity on many occasions. As the nosewheel lowered to the deck, I could usually see some lights. The plane rolled right down the CL. All you had to do was remember to pop the spoilers, use the brakes, and reverse - being carefull not to get any assymetrical thrust.

[MFALK]

Taraman, if I remember well, MABH is Minimum Approach Break Height.

[CargoRat]

Our -400F
RVR 125M/DH17FT

[CaptA320]

Hate to correct knowlegeable guys like MFALK but I believe it stands for Minimum Approach Break off Hight. It is the minimum hight at which if a missed approach is executed (for the CFM-56 A320) at max landing weight the wheels will not have contact with the runway.

Cheers

MFALK how are you? Long time no contact. Next time your in my neck of the woods drop me a line.

[This message has been edited by CaptA320 (edited 11 April 2000).]

[MFALK]

Hi CaptA320, yes it's been a while! I agree with your definition of MABH... I should be stopping at your Base around the beginning of May but it'll only be a 40 minute stop for some gas... :)

[CaptA320]

Shame you don't get nightstop, anyway I'll keep an eye out for the familiar tail. All the best.

[Royan]

MINIMUM APPROACH BREAK-OFF HEIGHT (MABH)
The lowest height of the wheels above the ground such that if a go-around is initiated without EXTERNAL VISUAL REFERENCES:
· In normal operation, the aircraft does not touch the ground during the procedure.
· With critical engine failure during go- around, it can be demonstrated that taking account of this failure probability, an accident is extremely improbable.

[O\ZON]

Height loss after initation of a go around for the A320-214 is the following:

CONF height AAL height loss
CONF 3 50 42
CONF FULL 50 49

CONF 3 100 42
CONF FULL 100 51

CONF 3 150 42
CONF FULL 150 51

Based on a max landing weight of 64,500 kgs, approach CONFIG 3 or FULL
speed 1,23VSIG + 10kts
Landing gear down
elev 1500 ft
eng anti-ice ON

rgd
O/Z

[Scallywag]

MFALK, We use 17ft on both our CFM & IAE V2500 engined A320's. Same on our CFM A321's. This is only ex-UK though, as in blighty it's DH=0ft, RVR 75m for a Cat3B.

Scally

[HighSpeed]

schleprock,

there are 3 areas of requirements to be covered before one can execute a cat III approach.

1. Aircraft capabilities - Certified, Fail-Operational/Fail-Passive Automatic Landing System.

2. Crew Training & Certification - Training program, type experience, recurrent training and checking.

3. Airfield - ILS facility, ILS maintenance, approach & runway lighting, runway markings, secondary power supply, ATC procedures, etc.

generally, 3 major bodies governs the different limits and requirements. they are :

ICAO, FAA & JAA

Cat IIIA
ICAO & FAA - No DH or DH < 100 ft (30 m), RVR < 700 ft (200 m)
JAA - DH < 100 ft (30 m), RVR < 700 ft (200 m)

Cat IIIB
ICAO & FAA - No DH or DH < 50 ft (15 m), RVR < 700 ft (200 m) > 150 ft (50 m)
JAA - No DH or DH < 50 ft (15 m), RVR < 700 ft (200 m) > 250 ft (75 m)

Cat IIIC
ICAO & FAA - No DH, No RVR
JAA - Not mention in this sub-category

Hope this helps.

HS