"C J Campbell" wrote:

Anything that can stand their barking is not
likely to suffer hearing loss from a mere airplane.

That's debatable. You likely wouldn't suffer hearing loss from your own yelling
either! But as a teenager, I remember reading about studies showing how
listening to our music at the volume and for the duration we listened to it
would eventually cause hearing loss, so doesn't it follow that prolonged
exposure to the noise of an airplane engine from inside the cockpit could do
the same? ... and God knows dog's ears are more sensitive than human ears. Some
veterinarians say it wouldn't be a problem; others say they should have
protection just like we do. Guess it boils down to what you and your dog are
comfortable with.

--Shirley