.
a published MDA(H) used as a decision altitude.
When either of the above minima are not specifically authorized, use the MDA(H) specified for the instrument procedure.
Airport Surveillance Radar (ASR)
The radar controller is required to discontinue approach guidance when the airplane is at the MAP or one mile from the runway, whichever is greater. Perform the missed approach when instructed by the controller.
Localizer
The MAP for a localizer approach is not the same as for the corresponding ILS approach. For most approaches the MAP distance is to the threshold of the runway. Where authorized, a localizer approach may be flown in VNAV PTH using the missed approach criteria discussed above.
Other Non-ILS Approaches
The MAP for all other non-ILS approaches is depicted on the approach chart. If the procedure has a final approach fix, the MAP may be short of the runway threshold, at the runway threshold, or located over a radio facility on the field. For on airport facilities (VOR or NDB) which do not have a final approach fix, the facility itself is the MAP and in most cases is beyond the runway threshold. Do not assume the airplane will always be in a position to make a normal landing when reaching the MDA(H) prior to reaching the MAP. When the MAP is at or
beyond the runway threshold, the airplane must reach MDA(H) prior to arrival at the MAP if a normal final approach is to be made.
ILS Approach - General
The ILS approach illustrated assumes all preparations for the approach such as review of approach procedure and setting of minima and radios are complete. It focuses on crew actions and avionic systems information. It also includes unique considerations during low weather minima operations. The pattern may be modified to suit local traffic and air traffic requirements.
Decision Altitude/Height - DA(H)
A Decision Altitude/Height is a specified altitude or height in a precision approach where a missed approach must be initiated if the required visual reference to continue the approach has not been established. The “Altitude” value is typically measured by a barometric altimeter and is the determining factor for minima for Category I approaches (e.g. ILS, GLS, or RNAV with VNAV). The “Height” value specified in parenthesis, typically a RA height above the touchdown zone (HAT), is advisory. The RA may not reflect actual height above terrain.
For most Category II and Category III fail passive approaches, the Decision Height is the controlling minima and the altitude value specified is advisory. A Decision Height is usually based on a specified radio altitude above the terrain on the final approach or touchdown zone.
Alert Height - AH
Alert heights are normally used for fail operational Category III operations. Alert height is a height above the runway, above which a Category III approach must be discontinued and a missed approach initiated if a specified failure occurs. For a discussion on specified failures, see the AFDS Faults section, this chapter. Radio altimeters are set in accordance with the airline's policy or at alert height to assist in monitoring autoland status. Most regulatory agencies do not require visual references below alert height.
Fail Operational
Fail operational refers to an AFDS capable of completing an ILS approach, autoland, and rollout following the failure of any single system component after passing alert height.
Fail Passive
Fail passive refers to an AFDS which in the event of a failure, causes no significant deviation of airplane flight path or attitude. A DA(H) is used as approach minimums.
Procedure Turn
The procedure turn size is determined by the ground speed at which the procedure turn is flown. If the procedure turn is flown at an excessively high ground speed, the protected airspace may be exceeded. Cross the procedure turn fix at flaps 5 maneuvering airspeed. The procedure turn should be monitored using the map to assure the airplane remains within protected airspace.
Initial Approach
If a complete arrival procedure to the localizer and glide slope capture point has been selected via the CDU, the initial approach phase may be completed using LNAV and VNAV. Ensure the LEGS page sequence, altitude restrictions and the map display reflect the air traffic clearance. Last minute air traffic changes or constraints may be managed by appropriate use of the MCP heading selector and altitude window. Updating the LEGS sequencing should be accomplished only as time permits.
Approach
Both pilots should not be “heads-down” during the approach. In some cases, such as high density traffic, or when an arrival procedure is used only for reference, revising the FMS flight plan may not be appropriate. Displaying OFF PATH DESCENT circles on the map (if installed) provides vertical flight path guidance which may assist in planning the approach.
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本文链接地址：757 Flight Crew Training Manual 机组训练手册(48)
