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FCT 777/787 Preliminary (TM) 4.11
Fuel temperature should be maintained within AFM limitations as specified in the
Limitations chapter of the FCOM.
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 one hour to stabilize the fuel temperature. In most
cases, the required descent would be 3,000 to 5,000 feet below optimum altitude.
In more severe cases, 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.
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, enroute winds, and cruise speed.
Actual fuel burn should be compared to 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
October 31, 2006
777/787 Flight Crew Training Manual
Climb, Cruise, Descent and
Holding
Copyright © The Boeing Company. See title page for details.
4.12 FCT 777/787 Preliminary (TM)
• stronger headwind component
• fuel imbalance
• improperly trimmed airplane
• excessive thrust lever adjustments.
Cruise fuel penalties include:
• ISA + 10° C: 1% increase in trip fuel
777-200 - 777-300ER
• 2,000 feet above optimum altitude: 1% to 2% increase in trip fuel
787-8
• 2,000 feet above optimum altitude: TBD% to TBD% increase in trip fuel
777-200 - 777-300ER
• 4,000 feet below optimum altitude: 4% to 5% increase in trip fuel
787-8
• 4,000 feet below optimum altitude: TBD% to TBD% increase in trip fuel
777-200 - 777-300ER
• 8,000 feet below optimum altitude: 12% to 14% increase in trip fuel
787-8
• 8,000 feet below optimum altitude: TBD% to TBD% increase in trip fuel
777-200 - 777-300ER
• cruise speed 0.01M above scheduled: 1% to 2% increase in trip fuel.
787-8
• cruise speed 0.01M above scheduled: TBD to TBD increase in trip fuel.
For cruise within 2,000 feet of optimum, long range cruise speed can be
approximated by using 0.84M. Long range cruise also provides the 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, 2006
777/787 Flight Crew Training Manual
Climb, Cruise, Descent and
Holding
Copyright © The Boeing Company. See title page for details.
FCT 777/787 Preliminary (TM) 4.13
Engine Inoperative Cruise/Driftdown
Performance of a non-normal checklist or sudden engine failure may lead to the
requirement to perform a single engine driftdown.
Engine inoperative cruise information is available from the FMC.
If an engine failure occurs while at cruise altitude, it may be necessary to descend.
On the FMC ACT CRZ page, select ENG OUT. This displays MOD CRZ
calculated on engine out MCT and maintaining the airspeed displayed on the EO
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787机组训练手册Flight Crew Training Manual 787(54)
