理论上来说，在飞机静止的时候，TAT 应该等于 OAT。
参考 A350 FCOM LIM-AG-OPS A ENVIRONMENTAL ENVELOPE 部分，最小 TAT 是-52 ℃。而气压高度为 0 的最小 OAT 是略小于-54℃的。为什么两者不一致呢？
空客解释：
- 从目的来说，最小 TAT 是为了保证飞机在长时间暴露在低温情况下，结构还能恢复的温度限制。而最小 OAT 是为了保证飞机的各种系统能正常运行的温度限制。
- 从测量来说，OAT 是机场气象部门报告的，TAT 是飞机探头测量的，测量位置不同。
所以，两种温度的目的、测量方式和位置，以及认证标准都不同，所以限制会有所不同。
TechRequest 原文：
Q:
In FCOM LIM-AG-OPS A ENVIRONMENTAL ENVELOPE, minimum TAT is -52℃. And in the chart above, the minimum OAT on 0 pressure altitude is even below -54℃。If aircraft stay still on ground without wind, TAT should be same with OAT. So why the minimum values are different?
A:
The purpose of the minimum TAT limitation is to ensure that the recovery temperature (approximating the structure temperature in cruise) is high enough to avoid a prolonged exposure of the aircraft equipment below their qualification temperature. The limitation on the TAT ensure that the recovery temperature remains within its limits.
The minimum OAT is related to the ensure that the aircraft and its system can be operated at this minimum OAT.
On ground, the OAT is provided by the weather station of the airport, whereas the TAT is measured by the aircraft probes. As the location of these sensors are different, the TAT and the OAT measurement may be different, even without aircraft speed.
To conclude, the OAT and TAT limitations are needed for different certifications criteria and are checked on ground against different means of measurement. CSC must comply with both.