二次监视雷达测距是靠测量（）之间的时间延迟。

An （ ） is established in each （ ） to provide area control service.

When Beijing time is 0801, Zulu time should be （ ） .

“Z” is a common term used by pilots to represent （ ） .

Emergency frequency is （ ） .

“PAN” is the international RTF（ ） signal.

“MAYDAY” is the international RTF （ ） signal.

According to ICAO definition, a condition concerning the safety of an aircraft or other vehicle or of some person on board or within sight but which does not require immediate assistance is （ ） .

There are （ ） VHF channels provided for the aviation voice communications.

Which SSR Code is not right?

The highest VHF frequency of radio communication between air and ground is （ ） .