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waypoint-related altitude constraint below cruise altitude on a LEGS page
generates a descent guidance path. The path is built from the lowest constraint
upward, assuming idle thrust, or approach idle below the anti-ice altitude entered
on the DESCENT FORECAST page.
The path is based on the descent speed schedule, any entered speed/altitude
constraints or forecast use of anti-ice. The path reflects descent wind values
entered on the DESCENT FORECAST page.
Descent Constraints
Descent constraints may be automatically entered in the route when selecting an
arrival procedure, or manually entered through the CDU.
Set all mandatory altitude restrictions and at or above constraints in the Mode
Control Panel (MCP) altitude window. The next altitude may be set when the
restriction has been assured, and further clearance has been received.
Shallow vertical path segments may result in the autothrottle supplying partial
power to maintain the target speed. Vertical path segments steeper than an idle
descent may require the use of speedbrakes for speed control. Deceleration
requirements below cruise altitude (such as at 10,000 MSL) are accomplished
based on a rate of descent of approximately 500 fpm. When a deceleration is
required at top of descent, it is performed in level flight.
Speed Intervention
VNAV speed intervention can be used to respond to ATC speed change
requirements. VNAV SPD pitch mode responds to speed intervention by changing
airplane pitch while the thrust remains at idle. VNAV PTH pitch mode may require
the use of speedbrakes or increased thrust to maintain the desired airspeed.
October 31, 2004
767 Flight Crew Training Manual
Climb, Cruise, Descent and
Holding
Copyright © The Boeing Company. See title page for details.
4.18 FCT 767 (TM)
Offpath Descent (as installed)
The LEGS pages should reflect the planned arrival procedure. If a published
arrival procedure is required for reference while being radar vectored, or the
arrival is momentarily interrupted by a heading vector from ATC, the offpath
descent circles provide a good planning tool to determine drag and thrust
requirements for the descent.
The outer circle is referenced to the end of descent point, using a clean
configuration and a direct path from the airplane position to the end of descent
waypoint constraint. The inner circle is referenced to the end of descent point
using speedbrakes. A separate waypoint may be entered on the OFFPATH DES
page as a reference for the descent circles.
Both circles assume normal descent speed schedules, including deceleration at
transition altitude, but do not include waypoint speed and altitude constraints.
Descent Planning
Flight deck workload typically increases as the airplane descends into the terminal
area. Distractions must be minimized and administrative and nonessential duties
completed before descent or postponed until after landing. The earlier that
essential duties can be performed, the more time will be available for the critical
approach and landing phases.
Operational factors and/or terminal area procedures may not permit following the
optimum descent schedule. Terminal area requirements can be incorporated into
basic flight planning but ATC, weather, icing and other traffic may require
adjustments to meet the requirements.
Proper descent planning is necessary to arrive at the desired altitude at the proper
speed and configuration. The distance required for the descent is approximately
3.5 NM/1000 feet altitude loss for no wind conditions using ECON speed. Rate of
descent is dependent upon thrust, drag, airspeed schedule and gross weight.
Descent Rates
Descent Rates tables provide typical rates of descent below 20,000 feet with idle
thrust and speedbrakes extended or retracted.
Target Speed
Rate of Descent (Typical)
Clean With Speedbrake
All 767-200/300 767-400
M 0.78 / 290 knots 1800 fpm 2700 fpm 3700 fpm
250 knots 1500 fpm 2000 fpm 2600 fpm
VREF 30 + 80 1200 fpm 1600 fpm 2200 fpm
October 31, 2004
767 Flight Crew Training Manual
Climb, Cruise, Descent and
Holding
Copyright © The Boeing Company. See title page for details.
FCT 767 (TM) 4.19
Normally, descend with idle thrust and in clean configuration (no speedbrakes).
Maintain cruise altitude until the proper distance or time out for the planned
descent and then hold the selected airspeed schedule during descent. Deviations
from this schedule may result in arriving too high at destination and require
circling to descend, or arriving too low and far out requiring extra time and fuel to
reach destination.
The speedbrake may be used to correct the descent profile if arriving too high or
　
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