In this case, "did" is a way of avoiding repetition. Some simpler examples will make it clearer: "Did you bring your coat?" "Yes, I did." (= "Yes, I did bring my coat." / "Yes, I brought my coat.") "Did the plane head south?" "Yes, it did." (= "Yes, the plane did head south." / "Yes, the plane headed south.") Now we can look at your sentence: ...when a plane leaves the airport heading to the south, as the plane that crashed did... = when a plane leaves the airport heading to the south, as the plane that crashed headed to the south,... But that sounds pretty awkward because of the repetition. Anyway, the phrase "as the plane that crashed did" refers to the fact that "the plane that crashed" left the airport heading to the south.

The sentence suggests that all planes heading south should "quickly turn the aircraft after passing the Chuo Expressway." The "did" indicates that the crashed plane headed south (so it should have quickly turned). To put it another way, "According to the pilot, because the plane left the airport heading south, the pilot should have quickly turned the aircraft after passing the Chuo Expressway." I hope that helps.

All the above explanations are very helpful. For a simple mind (like mine), I help myself by writing this out: "did" = left the airport heading to the south. The word "did" replaces the seven words "left the airport heading to the south" to avoid repetition.

'Did', is the past tense of 'do'. Here it is talking about the completed action of the plane crashing. "as it did"

Interesting... overall the sentence is a little awkward and might only make sense in a specific context. If you want to use the expression "as the plane that crashed did" then here's how I would write the sentence... "As the plane that crashed did, the second plane also made the mistake of veering off the runway and hitting a wall" Basically "As the plane that crashed HAD DONE, the second plane that came after did the exact same thing and hit the wall" The sentence you have has the context that there were two planes. The first plane crashed, but correctly turned the air craft after passing the Chuo Expressway. Then I guess later it had a problem and crashed. Then there was a second plane, and it did the right thing like the first plane, which was turn after the Chuo.