Originally Posted by
airchina981
Can someone please verify this for me. There is no restriction/ company policy or regs that say you cannot shoot a CAT II/III Autoland into an airfield where the minima are about CAT I. Lets say im going into Chicago and the ceiling is reported 300 feet. Vis 6 miles. They are only advertising ILS approaches in use. I would still do a CAT III autoland to guarentee a landing ( pending no automation fails etc).
The tower at any field does not have to be advertising CATII/III specific approaches for you to shoot them legally? The ILS critical area is protected when Cig is below 800 or 2 correct?
To answer your question directly, yes, you can legally shoot a Cat II/III approach even if the airport is not using low visibility procedures. Per the AIM, 1-1-9:
3. In order to ensure that pilot and controller expectations match with respect to critical area protection for a given approach and landing operation, a flight crew should advise the tower any time it intends to conduct any autoland operation or use an SA CAT I, any CAT II, or any CAT III line of minima anytime the official weather observation is at or above a ceiling of 800 feet and 2 miles visibility. If ATC is unable to protect the critical area, they will advise the flight crew.
EXAMPLE−Denver Tower, United 1153, Request Autoland (runway)
ATC replies with "United 1153, Denver Tower, Roger, Critical Areas not protected."
However, that doesn't necessarily completely guarantee ILS signal protection. From the AIM, next paragraph:
4. Pilots are cautioned that even when the critical areas are considered to be protected, unless the official weather observation including controller observations indicates a ceiling less than 200 feet or RVR less than 2000 feet, ATC may still authorize a preceding arriving, departing, or missed approach aircraft to pass through or over the localizer critical area and that this may cause signal disturbances that could result in an undesired aircraft state during the final stages of the approach, landing, and rollout.
This is likely what happened with the aforementioned KORD incident.
Further, a Cat II/III approach doesn't necessarily guarantee a landing. Though unlikely, airplane or ground equipment failures could cause a missed approach depending on the approach flown, Cat III Fail Operational, Cat III Fail Passive, Cat II, or Cat I. In general, loss of autothrottles would preclude a Cat III FO. Loss of the TDZ RVR would preclude all but a Cat III FO. A Flaps Drive or Flaps Disagree message when configuring would preclude an autoland for most Boeing airplanes, thereby being unable to do a Cat III. Cat II may be possible if the operator allows a manual landing.
As with all flying, some judgment may be required.