Re: CSAT III Landing Control

From: (adrian reedy)
Organization: customer of Internet America
Date:         22 Jan 96 04:40:39 
References:   1 2 3 4 5
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On 10 Jan 96 02:01:42 , (Brian A. Reynolds)

|In a discussion on CAT III, we were debating the the actual requirements for
|the various subclasses.  The operational requirements come down to CAT IIIa
|Decision height 50 feet, uncoupled (manual) landing, CAT IIIB, no decision
|height (full automatic landing), disconnect autopilot at a defined speed for
|control, CAT IIIc, automatic landing and roll-out guidance to a full stop.

 The actual CAT III requirements depend on whether the aircraft has a
4 channel, fail operational autopilot (as the L1011 - no decision
height, a 50 ft "alert height"), or a something like the MD88
2 channel "fail passive" autopilot, with a 50 ft decision height.
The individual carriers approved Ops Specs govern precisely
what equipment is required under what conditions.

 Note that no CAT III approaches may be initiated with any required
air or ground component inop.  A failure at any point requires a
missed approach.  Also,  no autopilot disconnects at DH with a manual
landing are permitted underr CAT III.  By definition, they are
autoland only.

 I'm not familiar with the CAT III approval for retrofitted 727s with
the heads-up display.  I don't -think- they have autoland capability.

|Questions -
|At what speed does the nose wheel steering become effective?

  As soon as it touches down.  Nosewheel steering (as it follows the
rudder deflections) tracks the centerline (for rollout mode) as a
function of the localizer signal.

|As a CAT IIIc landing would require a fully controlled nose steering
|mechanism, are there any commercial aircraft certified for this?

 I think IIIc rollout mode capability is predominately dependant on
the localizer not having any kinks in it.  The individual
aircraft/autopilot package has to be approved, along with the runway.
When I was on the L10ll, we did not have rollout mode approved, and
minimum RVR was about 600 feet.  The autopilot was disconnected at
nosewheel touchdown.  This may have changed.  My experience is pretty

|If there is someone knowledgable about the L-1011, what is the
|mecanism for nose wheel steering (i.e. tiller/control wheel or
|controlled through foot pedals?)

 Both.  All transport aircraft I'm familiar with have about a
plus/minus 10 degree nosewheel steering authority through the rudder
pedal steering.  Anything more than that is done with the

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