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airports, the measured fuel freezing point can yield a lower freezing point than the
specification maximum. The actual delivered freezing temperature can be used if
it is known. Pilots should keep in mind that some airports store fuel above ground
and in extremely low temperature conditions the fuel may already be close to the
minimum allowable temperature before being loaded.
For blends of fuels, use the most conservative freezing point of the fuel on board
as the freezing point of the fuel mixture. This procedure should be used until 3
consecutive refuelings with the lower freezing point fuel have been completed.
Then the lower freezing point may be used. If fuel freezing point is projected to
be critical for the next flight segment, the wing tank fuel should be transferred to
the center wing tank before refueling. The freezing point of the fuel being loaded
can then be used for that flight segment.
Fuel temperature should be maintained within AFM limitations as specified in the
appropriate operations manual.
Maintaining a minimum fuel temperature should not be a concern unless the fuel
temperature approaches the minimum temperature limit. The rate of cooling of the
fuel is approximately 3° C per hour, with a maximum of 12° C per hour possible
under the most extreme conditions.
Total air temperature can be raised in the following three ways, used individually
or in combination:
• climb or descend to a warmer air mass
• deviate to a warmer air mass
• increase Mach number.
Note: In most situations warmer air can be reached by descending but there have
been reports of warmer air at higher flight levels. Air temperature forecasts
should be carefully evaluated when colder than normal temperatures are
anticipated.
It takes from 15 minutes to an hour to stabilize the fuel temperature. In most cases,
the required descent would be 3,000 feet to 5,000 feet below optimum altitude. In
more severe cases a descent to altitudes of 25,000 feet to 30,000 feet might be
required. An increase of 0.01 Mach results in an increase of 0.5° to 0.7° C total air
temperature.
October 31, 2004
767 Flight Crew Training Manual
Climb, Cruise, Descent and
Holding
Copyright © The Boeing Company. See title page for details.
4.10 FCT 767 (TM)
Boeing has developed a Fuel Temperature Prediction Program (FTPP) to assist
operators in addressing fuel freezing point concerns. This program is designed to
be used during the flight planning process and is intended to interface with or be
incorporated in an operator's flight planning system. It has been calibrated by
flight test and operational data. This program enables the crew to determine if fuel
temperature is a concern, helps to determine available options, and may prevent
the need for in-flight crew action to stop the decline in fuel temperature.
Cruise Performance Economy
The flight plan fuel burn from departure to destination is based on certain assumed
conditions. These include takeoff gross weight, cruise altitude, route of flight,
temperature, wind enroute, and cruise speed.
Actual fuel burn should be compared with the flight plan fuel burn throughout the
flight.
The planned fuel burn can increase due to:
• temperature above planned
• a lower cruise altitude than planned
• cruise altitude more than 2,000 feet above optimum altitude
• speed faster than planned or appreciably slower than long range cruise
speed when long-range cruise was planned
• stronger headwind component
• fuel imbalance
• improperly trimmed airplane
• excessive thrust lever adjustments.
Cruise fuel penalties include:
• ISA + 10° C: 1% increase in trip fuel
• 2,000 feet above/below optimum altitude: 1% to 2% increase in trip fuel
• 4,000 feet below optimum altitude: 3% to 5% increase in trip fuel
• 8,000 feet below optimum altitude: 8% to 14% increase in trip fuel
• cruise speed M.01 above LRC: 1% to 2% increase in trip fuel.
For cruise within 2,000 feet of optimum, long range cruise speed can be
approximated by M.80. Long range cruise also provides best buffet margin at all
cruise altitudes.
Note: If a discrepancy is discovered between actual fuel burn and flight plan fuel
burn that cannot be explained by one of the items above, a fuel leak should
be considered. Accomplish the applicable non-normal checklist.
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) 4.11
Engine Inoperative Cruise/Driftdown
　
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