After spending a solid 6 years aircrew, I can attest to this. Then again, my plane (the C-5 Galaxy) generated somewhere around 120 dB on takeoff. Super loud inside inflight too. My hearing's taken a big hit because of it. Now I'm Abe Simpson after the THX intro. "Turn it up!"
Seriously, though. As previously stated, the constant drone of a jet, which maintains a solid frequency over long periods of time is not good for your hearing. Ear plugs, noise cancelling headphones, or noise-isolating earphones would go a long way if you're a frequent flier. Take it from me. The VA offered me partial disability for my hearing loss, which I declined since I don't consider that disabled, but still, I don't recommend it if it can be avoided.
That said, it's BECAUSE of my hearing loss that I demand higher quality audio gear now. Counter-intuitive to most people I talk to about it, but the way high end speakers can reproduce everything goes a long way for me, versus lesser speakers which I have a tough time comprehending dialogue and such at times. It's a GREAT excuse to use on my wife.