最近遇到一个中央燃油泵的MEL，在案例分析过程中，大家对MEL里的一个描述产生了争议。MEL要求在起飞后，如果另一个中央燃油泵也不工作后，剩余的燃油能够到达一个合适机场。

问题是这个合适机场要满足什么要求？有三种不同的选择：

1）只要机场满足基本的保障要求（比如长度、道面、消防等级），不考虑天气。
2）在1）的基础上，还要求在放行时天气满足落地标准。
3）在1）的基础上，还要求在放行时天气满足备降标准，空中满足落地标准。

在争执过程中，我去考古了一下“合适机场”这个概念。

《CCAR121R4》
第121.561条 发动机不工作时的着陆和报告
(a)对于所有飞机，在飞机发动机失效，或者为防止可能的损坏而停止发动机运转时，机长均应当按照飞行时间在距离最近的能安全着陆的合适机场着陆。
第121.712条 定义
下列定义适用于本章：
(a)合适机场：是指达到第121.197条规定的着陆限制要求且局方批准合格证持有人使用的机场，它可能是下列两种机场之一：。。。。（不要求天气）

《AC-121-FS-2012-009R1》
1.2 定义
下列定义适用于本咨询通告：
c. 延程运行可选备降机场（Suitable ETOPS Alternate）（CCAR-121部定义的合适机场）：对于特定延程运行航线，不考虑当时的临时状况，列入合格证持有人运行规范的可选的航路备降机场。这些机场必须满足CCAR-121.197条规定的着陆限制要求。它可能是下列两种机场之一：。。。。。。。（不要求天气）

《CCAR121R5》
第121.561条 没变
第121.712条 消失了。。。。。。。。（连定义都没了，怎么办）

可见，这个合适机场的概念和ETOPS运行纠缠不清，以至于我找一下网上的定义，搜索出来的都是ETOPS的东西。其实我的运行并不牵涉到ETOPS，合适机场的概念仍然存在。

再看看FAA的情况：

FAR121
121.565 Engine inoperative: Landing; reporting.
(a) Except as provided in paragraph (b) of this section, whenever an airplane engine fails or whenever an engine is shutdown to prevent possible damage, the pilot in command must land the airplane at the nearest suitable airport, in point of time, at which a safe landing can be made.
121.7 Definitions.
The following definitions apply to those sections of part 121 that apply to ETOPS:
Adequate Airport means an airport that an airplane operator may list with approval from the FAA because that airport meets the landing limitations of §121.197 and is either—

AC 120-42A（已取消）

AC 120-42B
定义不存在。

根据以上对比，121R4中定义的合适机场，应该是Adequate Airport。FAA对于合适机场的定义在AC120-42A当中是有的，更新AC120-42B已经消失了，当前的FAR121也没有定义。
借用网上的一段话：“Officially AC 120-42A was cancelled and replaced by 120-42B, they did not transfer the definition of “suitable” airport. So that is why I asked.”

公司手册中也没有对合适机场有定义。

这个问题的争议重点在于，合适机场的定义是否需要考虑天气？是否应该考虑到备降标准？

后来我偶然看到，在机组训练手册FCTM里有关于合适机场的表述。因为在QRH中常常出现“在最近的合适机场落地”，机组训练手册对此专门做了说明。内容如下：

Landing at the Nearest Suitable Airport
“Plan to land at the nearest suitable airport” is a phrase used in the QRH. This section explains the basis for that statement and how it is applied.In a non-normal situation, the pilot-in-command, having the authority and responsibility for operation and safety of the flight, must make the decision to continue the flight as planned or divert. In an emergency situation, this authority may include necessary deviations from any regulation to meet the emergency. In all cases, the pilot-in-command is expected to take a safe course of action.
The QRH assists flight crews in the decision making process by indicating those situations where “landing at the nearest suitable airport” is required. These situations are described in the Checklist Instructions or the individual NNC. The regulations regarding an engine failure are specific. Most regulatory agencies specify that the pilot-in-command of a twin engine airplane that has an engine failure or engine shutdown should land at the nearest suitable airport at which a safe landing can be made.
A suitable airport is defined by the operating authority for the operator based on guidance material but, in general, must have adequate facilities and meet certain minimum weather and field conditions. If required to divert to the nearest suitable airport (twin engine airplanes with an engine failure), the guidance material also typically specifies that the pilot should select the nearest suitable airport “in point of time” or “in terms of time.” In selecting the nearest suitable airport, the pilot-in-command should consider the suitability of nearby airports in terms of facilities and weather and their proximity to the airplane position. The pilot-in-command may determine, based on the nature of the situation and an examination of the relevant factors, that the safest course of action is to divert to a more distant airport than the nearest air port. For example, there is not necessarily a requirement to spiral down to the airport nearest the airplane’s present position if, in the judgment of the pilot-in-command, it would require equal or less time to continue to another nearby airport.
For persistent smoke or a fire which cannot positively be confirmed to be completely extinguished, the safest course of action typically requires the earliest possible descent, landing and evacuation. This may dictate landing at the nearest airport appropriate for the airplane type, rather than at the nearest suitable airport normally used for the route segment where the incident occurs.

内容有点长。我把它全部贴出来，是因为少了上下文说不清。

文中说明了合适机场考虑的几个要素：必要的设施、天气标准、跑道情况。

是否需要考虑天气标准的问题，已经有了答案。至少波音认为（我也觉得）需要考虑落地标准。所以本文开头的选择1）肯定不对。考虑天气是必要的。

那么，是否需要考虑在放行时，提高到备降标准呢？注意是放行时。

我认为（仅仅是我认为），有这个必要。我来说说我的理由。

想想ETOPS和飘降吧，和正常航班相比较，机长的决策范围变小了很多。比如上海飞北京，是一个正常航班，机长可以毫无忌讳的地选择他认为“就近”的合适机场，这种选择没有被飞机系统或物理条件“限制”。

但是ETOPS和飘降航班，这种选择的范围，被飞机系统或物理条件，限制在某几个机场中间（比如单发后的改航时限，大海和高山）。因此，在放行时，就需要提高为备降标准（ETOPS备降场和航路备降场）。

同样的，依据MEL放行时考虑另一个燃油泵也失效，机场的选择范围一样被限制了。这就是为什么我认为：在放行阶段，如果MEL出现了对合适机场的要求，那么签派员应该把选择的机场，写入放行单，并按备降标准放行，在空中满足落地标准。

==============================================================

题外话1：关于合适机场的定义，局方应该明确一下吧。

题外话2：FCTM中说到了不需要就近合适机场降落的情况，比如着火、烟雾、异味。

题外话3：考虑去最近的合适机场时，考虑的不是距离，而是时间。比如在飞机边上有个合适机场，飞机不可能一头栽向那个机场。只要考虑飞行时间最短的那个机场称为“最近”。