Autopilot/autoland

[Dick Whittingham]

Need some facts from real operators. When does the autopilot disengage on autoland when the full system drops out? On the 747, how far can you go down the slope with only 2APs engaged? On the A320, which starts with only 2 APs anyway, how far can you go with one? And, finally, how far can you go on an ILS with no autoland available?

Thanks in advance. All my written source info is unclear/confusing

[F/O Junior]

A320:
On CAT I ILS: A/P has to be disengaged at
80 feet with CAT 2 or 3 displayed in FMA
160 feet with CAT 1 displayed in FMA

On CAT II ILS: Minimum DH for autoland is
100 feet with at least one AP engaged in APPR mode and CAT2, CAT3 SINGLE or CAT3 DUAL displayed in FMA

On CAT III ILS: fail passive AL, Minimum is
50 feet with at least one AP engaged in APPR mode and CAT2, CAT3 SINGLE or CAT3 DUAL displayed in FMA

On CAT III ILS: fail operational AL
Alert height 100 feet (200 on A330)
Minimum DH for CAT III with DH : 20 feet (15 on A330)
Minimum DH for CAT III without DH: No DH
2 AP engaged in APPR mode and CAT 3 DUAL is displayed on FMA.

P.S. The CAT display on the FMA has nothing to do with the ground installation. It only reflects the current system capability.

[Dick Whittingham]

Thanks F/O Junior. My query is based on the statement that JAR require fail passive systems to give a reversion to manual with no sudden control input and therefore cannot take the aircraft down into the regime where extra nose up trim is being applied for the flare. What happens with one AP if it disengages at 50RA?

[Pihero]

The first officer calls "Alarm!" and it's a go-around.

[Dick Whittingham]

Thanks P1hero. When you take control, is the aircraft in trim or nose up?
Any 74 or 76 experts out there?

[one.dot.lo]

The F100 I flew was trimmed nose down on AP disconnect, allegedly to prevent stalling if the AP dropped out (personally I think the ground is equally hard either by being trimmed nose down or stalling and spinning in!!)

By contrast the A320 appears to be trimmed completely neutral.

Hope that helps. :)

[Silky]

A320 autopilot stays in till roll out is completed and it will autoland off even a cati approach (not a recomended proc), as for trim absolutly no change in trim after autopilot disengagement, perfectly in trim as always.
Reliability is all down to ground tansmitters as long as AC is servicable.
:) :) :)

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Gravity always wins....

[Dick Whittingham]

Well, back to the drawing board then. I'd still like confirmation from any 3 AP Boeing experts about what happens to trim on AP disengage from LAND 2 very late on finals.

In my day engaging the AP meant calling the nav forward to hold the controls for a while.

[BoxProf]

747:

You can fly in Land 2 mode all the way to touchdown. Doesn't matter when it degrades from Land 3 to Land 2 like some of the earlier 757/767 software issues.

[Dunhovrin]

Dick

In my short time on the 747 I've found that the autopilot is always in trim when you disengage it even on the roll-out at the end of an autoland (but then again the grown-ups only let me do autolands in the sim).

PS Thanks for getting me thru the nav group in 1997.

[Dick Whittingham]

Thanks everybody. I now have the correct facts, which I needed for our JAR stuff. It's amazing the cr** one finds written as gospel truth in some sources.

Thanks again, Dick W.

[scroggs]

Hi Dick,
on the Classic 747, the autopilot/autothrottle is manually disengaged on rollout after an autoland. 2AP, and early 3AP aircraft must be disengaged on touchdown, later 3AP aircraft have full CAT 111 rollout capability. A 2AP (fail passive) aircraft is capable of autoland, but a single autopilot failure limits the aircraft to CAT 1 limits and a manual landing. A 3AP (fail active) aircraft can continue a full autoland after a single autopilot failure. Whether it is then restricted to CAT 11 limits depends on the individual aircraft, and the airline/crew limits (we only work Cat 11 anyway). If the autoland is u/s, the aircraft is limited to CAT 1. On autopilot disconnect, the Boeing manual (and my experience) suggests that the aircraft could 'be significantly out of pitch trim'. The later in the approach the disconnect happens, the more out of trim it will be. Obviously, on the ground the pitch trim is irrelevent. Hope this helps.

[Brenoch]

Well Dick.. I fly the 75/76.. If we have LAND 2 annunciated nose up trim will be applied at 330 RA on the 757 and 767-200 and 100 RA on the 767-300.. We can fly a cat IIIA approach with only LAND 2 annunciated and it is definately not recommended to disengage the A/P after the noseup trim has been applied.. :) From the book "During a LAND2 multi A/P approach and below 330 ft RA an increment of nose up trim is automatically applied for flare. If the A/Ps are subsequently disengaged in the approach, a forward control column force of 20-30 lbs may be required to counter the automatic trim condition. If an automatic multi A/P GA is performed, the increment of automatic trim is removed."