getting to grips with COLD WEATHER OPERATIONS 寒冷天气运行(65)

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As far as the fuel freezing point limitation is concerned and depending on the aircraft type, the following applies:
D3.2 A300/A310
. Fuel can be directly fed into the engines from CTR, INR or OUTR tanks. The OUTR tank being the coldest tank due to its low thermal inertia, a single temperature sensor (when fitted) is located in the left outer tank.
Flight tests showed that in thermally stabilized conditions, the fuel temperature in the
inner tanks is always at least 3°C above the outer tank temperature.
Engine fuel feeding from the OUTR tanks is, therefore, the limiting criteria.
Airworthiness authorities agree that pilots may take benefit of this 3°C difference when fuel is fed from a tank other than the outer tanks.

Therefore, for A300/A310 aircraft, the minimum allowable fuel temperature in flight is:
.
When fuel is fed from OUTR tanks: ACTUAL FUEL FREEZING POINT + ENGINE MARGIN + 2°C

.
When fuel is fed from CTR or INR tanks: ACTUAL FUEL FREEZING POINT + ENGINE MARGIN + 2°C - 3°C

.
For takeoff, it is assumed that the fuel temperature is the same in all tanks and therefore the same limitation as when flying with fuel fed from the OUTR tanks applies (i.e. without taking benefit of the 3°C difference between OUTR and INR in flight).

.
For A300/A310 aircraft without fuel temperature indication, the above limitations also apply; the tank fuel temperature being assessed through a correlation with the Total Air Temperature (TAT). It has been evidenced by development tests and confirmed by additional records obtained in revenue service, that after thermal stabilization, the outer tank fuel temperature is within 2°C of the TAT. (See figure D1)
This offset has the same value (2°C) as the expectable error of the fuel temperature indication system when installed as mentioned above.

Thus the 2°C margin is also requested when TAT is used in place of the actual fuel temperature.
Figure D2,
 illustrates the A300/A310 outer tank fuel temperature response to TAT
variations.

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The following remarks should be highlighted (with respect to the A300 and A310):
-Whatever the initial tank fuel temperature and the magnitude of the TAT change, the tank fuel temperature reaches a complete thermal stabilization (within 2°C of TAT) typically after 2 to 3 hours.
-The outer tank fuel temperature response to any significant change in the TAT typically features a 10-minute time lag.
- Prior to thermal stabilization, the TAT is a conservative indicator of the actual OUTR tank temperature. However in case of TAT increase - warmer air or step descent - the TAT/OUTR tank relationship is reversed. In such a case, reference should be made to the coldest TAT previously observed (i.e. prior to TAT increase) in order to recover a conservative indicator of the actual OUTR tank fuel temperature.
　
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