Okay, so for the sake of those who can't say anything, I feel I have to say something.
Remember how much you hate people talking about things they don't understand? So do I. And let's face it: if you're not on the inside of an organization, you don't know 100% of what's going on there. Oftentimes it's less than 50%. And if it has to do with security, the percentage can drop as low as 10%.
The hysteria around Chris Roberts supposedly hacking a plane and "making it go sideways" has reached an all-time high. Which isn't to say it couldn't go higher, because media. But let's go through the versions here:
There's what he told people he did.
There's what they interpreted from what he said.
There's what he thought he did.
There's what he actually did.
Then there's the usual Telephone game of people misinterpreting, mis-reporting, and deliberately twisting all those things when they hear them second- and third-hand.
But one fact remains: there are people who actually know what's possible to do, and they ain't talking. Nor will they. Even if Roberts was talking complete bullshit, nobody on the inside is going to step forward and say it publicly. So in this case, silence does not equal assent.
We don't know whether the airline manufacturer already has experts doing pentesting, and they don't need any more, thankyouverymuch. Just because they're ignoring your reports doesn't mean they don't already know about what you think you're trying to say. They don't actually owe you an answer: "No, you didn't really get through, but if you had done THIS instead ..." Just because you decide to walk onto the court, it doesn't mean you get to be a player.
We don't know why United decided to come out with a bug bounty program, although it's mighty responsible of them NOT to encourage randoms to try hacking the avionics. Those who are complaining that it's missing from the bug bounty program are completely clueless in that regard, and have probably never been personally responsible for anything more consequential than a runaway shopping cart.
There may be no truth at all to what the FBI claims Roberts did, and they're just prosecuting him because letting him go free would send the wrong message to other juvenile delinquents out there.
The bottom line is, if you're not actively working WITH the company whose technology you're researching, then you're an adversary. So don't be surprised if they treat you like one. United has every right to say to Roberts, "You didn't actually do anything harmful, but you're a dick, so stay off our airplanes."
You can be a security researcher, but in the immortal, wise words of @wilw: Don't be a dick.