Very easy two questions about two easy sentence.
1You are not to leave your station without permission.(original)
① . NO leaving your station without permission.
② . NO being to leave to your station without permission.
Question: Are both grammatically correct?
Which is correct ?
2. Tom: It's a wonderful engineer, just listen to it when I start it now. (presses starter. Sound of engine turning over but not starting)
I do know the meaning of the sentence, but want to make clear whether or not the part of the "()" → (presses starter. Sound of engine turning over but not starting) is a complete sentence because I don't think so.
I understand the "presses starter" means the "Tom presses starter", but I don't regard such as " Sound of engine turning over but not starting " is a sentence. tell me how to understand the grammar here.
I guess it means: You hear the sound of engine turning over but the starter does not start.
but why is it written in such way that there is no its different subjects in it?

Question

Very easy two questions about two easy sentence.
1You are not to leave your station without permission.(original)
① . NO leaving your station without permission.
② . NO being to leave to your station without permission.
Question: Are both grammatically correct?
Which is correct ?
2. Tom: It's a wonderful engineer, just listen to it when I start it now. (presses starter. Sound of engine turning over but not starting)
I do know the meaning of the sentence, but want to make clear whether or not the part of the "()"    → (presses starter. Sound of engine turning over but not starting) is a complete sentence because I don't think so.
I understand the "presses starter" means the "Tom presses starter", but  I don't regard such as " Sound of engine turning over but not starting " is a sentence. tell me how to understand the grammar here.
I guess it means: You hear the sound of engine turning over but the starter does not start.
but why is it written in such way that there is no its different subjects in it?

Answer

1) "No leaving your station without permission" is correct.  The other sentence is not correct, and doesn't make sense.

2) You're right that the two sentences in parentheses are not grammatically correct, complete sentences.  It's very common to use this style of writing in movie scripts or plays, when you're describing what the actors do.  The directions for the actors are rarely written in complete sentences.  They simply describe what the actor should do, or what the audience should see or hear.

Sometimes you'll see people use this style even when they're not writing a script.  They're using script format to tell a story.  It might look something like this:

Joe: "I just called him..." *checks watch* "...ten minutes ago."

Instead of writing the whole sentence "Joe checks his watch," the writer just says "checks watch," but the reader knows that the subject of the action is Joe.

Answer

This is a bit like a newspaper headline, only the important words are used.

A newspaper headline might be:
'Hope for holidays overseas' (This is a real headline from The Times)

This is not a full sentence, which would be:
There is hope for holidays overseas to start again.

So you don't need the full sentence to give the idea of what is happening.

Answer

Sorry for my typo, not the "is" but the "as" here  →  
but  I don't regard such as " Sound of engine turning over but not starting " ☆as☆  (not "is" here) a sentence.