在航后工作中都会有要求在APU BITE页面里查看滑油量，参照AMM12-13-31-200-801，If you do the APU BITE procedure, you must examine the APU oil level in the no APU operation(APU shutdown) condition or within one hour of starting the APU and before operating the main engines.

此段说明了在CDU上查看APU滑油量的两个条件：1、APU关车；2、APU启动后一小时内，且发动机未运转。

但有些飞机在查看时会出现“UNKNOWN”或者“WAIT”，参照AMM49-61-00-700-801，If the oil level shows UNKNOWN, the APU is operating or it has been longer than one hour since the APU was started. UNKNOWN will also be displayed when the APU and main engines are operating on the ground or during a sensor failure.

此段说明出现“UNKNOWN”的几种情况：1、APU运转超过一小时；2、APU和发动机均在地面运转中；3、传感器失效。

If the oil level shows WAIT, it has been less than two minutes since the APU was shutdown.

此段说明出现“WAIT”是由于检查时距离APU关车还不到2分钟。

航后如果看到的是“UNKNOWN”，可能是因为APU运转已经超过一小时了。那怎么办呢？我们可以先正常完成其他工作，最后断电前，先关闭APU，等待至少两分钟后，在左CDU上（此时只有电瓶供电，右CDU无电）查看即可。