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maneuver margin exists prior to buffet onset. This altitude provides at
least a 0.2g margin (33° bank) for FAA operations or a 0.3g margin (40°
bank) for CAA/JAA operations prior to buffet.
Although each of these limits are checked by the FMC, available thrust may limit
the ability to accomplish anything other than relatively minor maneuvering. The
amber band limits do not provide an indication of maneuver capability as limited
by available thrust.
The minimum maneuver speed indication on the speed tape (as installed) does not
guarantee the ability to maintain level flight at that speed. Decelerating the
airplane to the amber band may create a situation where it is impossible to
maintain speed and/or altitude because as speed decreases airplane drag may
exceed available thrust, especially while turning. Operators may wish to reduce
exposure to this situation by changing the FMC parameters (via maintenance
action) to suit individual operator needs. Flight crews intending to operate at or
near the maximum operation altitude should be familiar with the performance
characteristics of the airplane in these conditions.
To get the most accurate altitude limits from the FMC, ensure the following entries
are accurate:
• airplane weight
• cruise CG
• temperature deviation at the cruise altitude.
October 31, 2004
767 Flight Crew Training Manual
Climb, Cruise, Descent and
Holding
Copyright © The Boeing Company. See title page for details.
4.6 FCT 767 (TM)
For LNAV operation, the FMC provides a real-time bank angle limiting function.
This function will protect the commanded bank angle from exceeding the current
available thrust limit. This bank angle limiting protection is only available when
in LNAV.
For operations other than LNAV, fly at least 10 knots above the lower amber band
and use bank angles of 10° or less when operating at or near maximum altitude. If
speed drops below the lower amber band, immediately increase speed by doing
one or more of the following:
• reduce angle of bank
• increase thrust up to maximum continuous
• descend.
Turbulence at or near maximum altitude can momentarily increase the airplanes
angle-of attack and activate the stick shaker. When flying at speeds near the lower
amber band, any maneuvering will increase the load factor and reduce the margin
to buffet onset and stick shaker.
FMC fuel predictions are not available above the FMC maximum altitude and are
not displayed on the CDU. VNAV is not available above FMC maximum altitude.
Fuel burn at or above maximum altitude increases. Flight above this altitude is not
recommended.
Optimum Altitude
Optimum altitude is the cruise altitude for minimum cost when operating in the
ECON mode, and for minimum fuel burn when in the LRC or pilot-selected speed
modes. In ECON mode, optimum altitude increases as either airplane weight or
cost index decreases. In LRC or selected speed modes, optimum altitude increases
as either airplane weight or speed decreases. On each flight, optimum altitude
continues to increase as weight decreases during the flight.
For shorter trips, optimum altitude as defined above may not be achievable since
the TOD (top of descent) point occurs prior to completing the climb to optimum
altitude.
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) 4.7
Flight plans not constrained by short trip distance are typically based on
conducting the cruise portion of the flight within plus or minus 2000 feet of
optimum altitude. Since the optimum altitude increases as fuel is consumed during
the flight, it is necessary to climb to a higher cruise altitude every few hours to
achieve the flight plan fuel burn. This technique, referred to as Step Climb Cruise,
is typically accomplished by initially climbing 2000 feet above optimum altitude
and then cruising at that flight level until 2000 feet below optimum. For most
flights, one or more step climbs may be required before reaching TOD. It may be
especially advantageous to request an initial cruise altitude above optimum if
altitude changes are difficult to obtain on specific routes. This minimizes the
possibility of being held at a low altitude/high fuel consumption condition for long
periods of time. The requested/accepted initial cruise altitude should be compared
to the thrust limited or the maneuver margin limited altitudes. Remember, a cruise
thrust limited altitude is dependent upon the cruise level temperature. If the cruise
level temperature increases above the chart value for gross weight, maximum
　
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