A body of law–and that includes Federal law–is typically big and complicated, and may contain surprises. I’ve been wrong about lots of things in my life, even recently. However, based on what I’ve seen so far, I can hardly help but express some degree of uncertainty as to whether 49 USC § 46504 applies to this situation.
To quote that section again, with some boldface for emphasis:
An individual on an aircraft in the special aircraft jurisdiction of the United States who, by assaulting or intimidating a flight crew member or flight attendant of the aircraft, interferes with the performance of the duties of the member or attendant or lessens the ability of the member or attendant to perform those duties, or attempts or conspires to do such an act, shall be fined under title 18, imprisoned for not more than 20 years, or both. However, if a dangerous weapon is used in assaulting or intimidating the member or attendant, the individual shall be imprisoned for any term of years or for life.
https://www.law.cornell.edu/uscode/text/49/46504
It seems to me that the first question to ask would be, “What is ‘the special aircraft jurisdiction of the United States’?”
49 U.S. Code § 46501(2) says, in part:
(2) “special aircraft jurisdiction of the United States” includes any of the following aircraft in flight:
(A) a civil aircraft of the United States.
https://www.law.cornell.edu/uscode/text/49/46501
I guess Dr. Dao’s situation meets part of that definition, because he was on board a civil aircraft.
But after that, at least for me, a second question arises, namely, “What is ‘an aircraft in flight’?”
The part of 49 U.S. Code § 46501(1) that I think is pertinent here says this (again I’ve added boldface):
(1) “aircraft in flight” means an aircraft from the moment all external doors are closed following boarding—
(A) through the moment when one external door is opened to allow passengers to leave the aircraft. . . .
https://www.law.cornell.edu/uscode/text/49/46501
The online magazine Market Watch recently interviewed a man named Joseph Lorusso, who it says is “a Colorado-based aviation attorney and airline-rated pilot.”
Edit 1: The paragraph below is in error:
I can’t find a Joseph Lorusso in the Colorado Bar Association online lawyer database, but from looking at ads, there appears to be a Florida lawyer by that name (the Florida Bar database won’t even give me access, I guess because of my foreign IP address, or else because my reputation precedes me).
Edit 2: I botched my Colorado Bar Association search for Joseph Lorusso. He is in fact in that database. You can just type “Lorusso” in the “Last Name” box and “Joseph” in the “First Name” box, and click the “Search” button. Here is the search page of the database:
http://www.cobar.org/Find-A-Lawyer
Edit 3: Here is the About page for the site of the law partnership of Lorusso & Lorusso:
http://www.lorussolegal.com/about-us/
Edit 4: This is a different Joseph Lorusso from the one in Florida. Apologies for any confusion I may have caused.
The article about the interview of Mr. Lorusso says the following, in part (boldface added by me):
Because the plane’s door was open, Lorusso said the crew followed proper federal protocol by calling local police, as they were still under state jurisdiction. Once the door is closed, the plane falls under federal jurisdiction, and passengers legally must comply with uniformed crew members — including flight attendants.
http://www.marketwatch.com/story/how-to-not-get-bumped-from-a-flight-and-how-to-make-the-most-money-if-you-do-2017-04-11
Mr. Lorusso seems to say about as much as what the law quoted above says.
I think it should be noted that Mr. Lorusso goes on to say that one should comply with instructions, and that one should get off the plane if asked to do so (but he does say so in the context of a discussion of whether the door is open or shut).
The third question that occurs to me would be, “Did Dr. Dao interfere with a crew member or attendant by ‘assaulting or intimidating’ them?”
I’ll let other people form their own conclusions about that question, but it seems to me that that question will lack relevance with regard to 49 USC § 46504 if it is shown that the plane was not in “the special aircraft jurisdiction of the United States.”