Welcome in H.C.M.
I have gone through your query regarding ear problem of your husband for last 15 years.
As you said that your husband always feels difficulty in air travel as far as his ear is concerned, it gets blocked and start popping. This indicates dysfunction of eustachian tube, it might be associated sinus problem or sore throat
In such cases C.T.scan and M.R.I.of ear may be normal but abnormalities are expected in radio logical examination of sinuses.
To confirm the diagnosis and for treatment point of view you should do-
(pure tone & Impedance audiometry)
2- Clinical and radiological examination of nose, paranasal sinuses
Though confirm diagnosis is made only after thorough examination and relevant investigations but my past experience is favoring possibility of chronic adhesive otitis media
and in such cases grommet insertion on ear drum gives excellent results.