在空客的烟雾程序中，执行完立即动作部分之后，如果烟源不是立即可见、可接近、可扑灭的，且能够被立即隔离，则需要开始备降和下降至 FL100 / MEA-MORA。
那么这个下降高度的要求对不同的机型有没有不同的考虑呢？因为之前有一种说法是 A320/A330 下降是为了可能需要开窗排烟，而 A350 并不需要也不能开窗，那 A350 为什么也需要下降呢？保持较大的压差不是更有利于排烟么？
空客在回复中确认了 A320/A330/A340 确实有开窗的考虑，而 A350 由于通风系统设计不一样，没有单独的排烟程序（参考 A350 烟雾程序介绍），考虑主要是另外的因素：
- 如果后续出现情况不可控，需要立即着陆，那么一开始的下降能够节省时间，大约 15 分钟。
- 保持程序统一，尤其是对跨机型的飞行员。
这两个理由我觉得还是可以接受的。
原文
Q
In SMOKE procedure for all Airbus aircrafts, after IMMEDIATELY ACTIONS, if smoke/fumes source is not immediately obvious, accessible, extinguishable, and isolated, we need DIVERSION and DESCENT TO FL 100 / MEA-MORA.
What is the reason of DESCENT? Is there any different consideration between A320 and A350?
A
Airbus would like to indicate that the DESCENT TO FL 100 / MEA-MORA in the SMOKE procedure was initially introduced on A320/A330/A340 programs to prepare the cockpit windows opening performed during the [QRH] REMOVAL OF SMOKE / FUMES procedure.
As CSC knows, contrary to the other Airbus programs, there is no sliding windows on the A350 and there is no [QRH] REMOVAL OF SMOKE / FUMES procedure.
In fact, the A350 ventilation system differs from the other Airbus aircraft and has been designed and certified to cope with smoke scenario with the need to quickly remove smoke.
On the A350, the SMOKE REMOVAL actions are addressed by the selection of the VENT AVNCS EXTRACT to OVRD position which is part of the immediate actions of the [QRH] SMOKE/FUMES procedure and the SMOKE L(R) AVNCS SMOKE ECAM procedure.
However, as CSC mentions, although the cockpit windows cannot be opened on A350, the DESCENT TO FL 100 / MEA-MORA is still introduced in the A350 [QRH] SMOKE / FUMES procedure for the following reasons:
- In the case of a situation that requests to consider an immediate landing (if the situation becomes UNMANAGEABLE), the aircraft has to land within a delay of 15 minutes. The objective is to gain time in this case.
- This ensures commonality between all Airbus programs, especially for the crews having a cross qualification.
