I was in the middle of a situation at my former employer (non-aviation industry, but a major company) that showed me the truth of how companies handle these situations. Hint, HR is for the company, not the employees.
We had a co-worker promoted to manager of our team. Another co-worker was a mate of his for some time and according to him had covered up for a number of this new managers "romantic indiscretions" in the past. I had no direct knowledge of this, but seeing his behaviour when on the drink it seemed plausible, he went for anything female like a bull at a gate despite being in a relationship. The story I was told was one time the mate was non the wiser that he was being used as an alibi, and innocently said "he's not here" when the managers wife called one time. She caught on which then went into divorce proceedings. The manager then blamed this on my co-worker, believing he was dobbed in for some reason (despite the co-worker having no motivation to do so nor any evidence that this was the case).
From there things went down hill. The manager pulled his overtime, starting taking projects from him, hired a new worker with the specific skills to replace the targeted co-worker. When ordered to train someone else on his work, he tried but the trainee was thrown in too early and when the co-worker helped save the day he was given a dressing down for getting involved. The manager was caught trying to prove the co-worker was not working his claimed hours by checking his login times. At annual review he was suddenly dropped from several years of second top level to an unsatisfactory level. The co-worker clearly knew he was getting retribution for the perceived grievance so he escalated it.
Here is where it went wrong, HR did not get involved, but the next level of management did. All they did was back up the new manager. I am not really sure why it was handled this way, but there was some claims of vested interest in this middle manager getting involved. With little progress and more and more aggression on both sides (both the co-worker and new manager were hot heads) things escalated up the chain.
By the time HR did get involved their position was to cover up for management and not actually resolve anything. Their stupid solution was to slightly change reporting lines into a non-working arrangement. There was nothing done to address the bullying by the manager, they just tried to find ways to justify managements positions in the matter or ways to shunt the worker to another team. By this point the co-worker was a wreck - he was stressed, angry, upset that his real work effort was being overridden by this and on the verge of a breakdown. I knew him as a pretty tough nut, but I saw this actually reduce him to tears. Myself and two co-workers had witnessed most of this from the sidelines, and admittedly had most of the information from the co-worker, but knew the manager enough to know who was telling the truth. We went to a separate part of HR together to try and back him up and get it resolved - again nothing happened.
Eventually the guy went on stress leave under workcover and consulted a lawyer. They were so confident in the bullying case they were prepared to go pro-bono, and that was before the worker was accidentally copied on an email that showed 4 levels of management and HR collaborating in an illegal performance management exercise about him (I was there when I saw the manager who sent it desperately trying to recall the email). Once they found out he was consulting a lawyer they pulled his company access, I am talking in minutes here, and put him on some strange sick leave setup (they knew firing him at this point was legal suicide).
In the end the only resolution was for him to leave, but that was also part of his legal support getting a 6 figure settlement for him. The manager stayed on and one by one isolated his entire team with the same psychotic crap - tantrums, abuse, openly blaming failures on specific team members to other managers. Even the one guy who backed him up through the original bullying issue ended up turning his back and seeing the truth eventually.
I later got a better offer and openly told some of the managers involved that the companies handling of the bullying issue reinforced my decision to leave. The whole episode taught me a few things:
1. Document everything, and keep it away from work.
2. Don't forget HR work for the company - their interest is to ensure the company does not get in trouble, not that everyone is happy.
3. Legal advice can be invaluable - it can put a lot of power in your corner if necessary, but don't wave it as a threat, that just forces them to react.
4. While it may feel wrong , walking away may give you your life back.
5. Your work record means nothing under a vindictive asshat.