Joined: 11 Dec 2005
|Posted: Thu Feb 07, 2008 5:08 am Post subject: B737-300 Low Fuel Temperature
|Fuel temperature changes relative to total air temperature (TAT). For example, extended operation at high cruise altitudes tends to reduce fuel temperature. In some cases the fuel temperature may approach the minimum fuel temperature limit.
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 deg C per hour with a maximum of 12 deg C per hour possible under the most extreme conditions.
Total air temperature can be raised under 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.
In most situations warmer air can be reached by descending but there have been reports of warmer air at higher flights 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 3000 to 5000 feet below optimum altitude. In more severe cases descent to altitudes of 25,000 to 30,000 feet might be required. An increase of 0.01 Mach results in an increase of 0.5 to 0.7 deg C TAT.