GPS Use in Non-WGS-84 Reference Datum Airspace
In non-WGS-84 airspace, the local datum (position basis) used to survey the navigation data base position information may result in significant position errors from a survey done using the WGS-84 datum. To the pilot, this means that the position of runways, airports, waypoints, navaids, etc., may not be as accurate as depicted on the map display and may not agree with the GPS position. Operators should consult appropriate sources to determine the current status of airspace in which they operate.
A worldwide survey has been conducted which determined that using the FMC while receiving GPS position updating during SIDS, STARS and enroute navigation meets the required navigation accuracy in non-WGS-84 airspace. This navigation position accuracy may not be adequate for approaches, therefore the airplane flight manual requires the crew to inhibit GPS position updating while flying approaches in non-WGS-84 airspace “unless other appropriate procedures are used.”
Boeing's recommendations for operators are as follows:
.
Provided operational approval has been received and measures to ensure
their accuracy have been taken, RNAV approaches may be flown with
GPS updating enabled. Options available to operators may include
surveys of the published approaches to determine if significant
differences or position errors exist, developing special RNAV procedures
complying with WGS-84 or equivalent, or inhibiting GPS updating.
.
For approaches based upon ground-based navigation aids such as ILS,
VOR, LOC, NDB, etc., the GPS updating need not be inhibited provided
that appropriate raw data is used throughout the approach and missed
approach as the primary navigation reference. LNAV and VNAV may be
used. As always, when a significant difference exists between the airplane
position, raw data course, DME and/or bearing information, discontinue
use of LNAV and VNAV. Provided the FMC is not used as the primary
means of navigation for approaches, this method can be used as the “other
appropriate procedure” in lieu of inhibiting GPS updating.
Operators are encouraged to survey their navigation data bases and have all non-WGS-84 procedures eliminated or modified to WGS-84 standards.
Weather Radar and Terrain Display Policy
Whenever the possibility exists for adverse weather and terrain/obstacles near the intended flight path, one pilot should monitor the weather radar display and the other pilot should monitor the terrain display. The use of the terrain display during night or IMC operations, on departure and approach when in proximity to terrain/obstacles, and at all times in non-radar environments is recommended.
Note: It may be useful to show the terrain display at other times to enhance terrain/situational awareness.
AFDS Procedures
Crewmembers must coordinate their actions so that the airplane is operated safely
and efficiently. Autopilot engagement should only be attempted when the airplane is in trim, F/D commands (if the F/D is on) are essentially satisfied and the airplane flight path is under control. The autopilot is not certified or designed to correct a significant out of trim condition or to recover the airplane from an abnormal flight condition and/or unusual attitude.
Autothrottle Use
To simplify thrust setting procedures, autothrottle use is recommended during takeoff and climb in either automatic or manual flight. During all other phases of flight, autothrottle use is recommended only when the autopilot is engaged.
Manual Flight
The PNF should make AFDS mode selections at the request of the PF. Heading and altitude changes from ATC clearances and speed selections associated with flap position changes may be made without specific directions. However, these selections should be announced, such as, “HEADING 170 SET”. The PF must be aware such changes are being made. This enhances overall safety by requiring that both pilots are aware of all selections, while still allowing one pilot to concentrate on flight path control.
Ensure the proper flight director modes are selected for the desired maneuver. If the flight director commands are not to be followed, it should be turned off.
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本文鏈接地址：757 Flight Crew Training Manual 機組訓練手冊(17)
