Quick Question on Ears

[DodgyFlyer]

I was wondering if someone out there could help me with a quick question.

I was talking to someone last week about flying who said they were unable to fly in light aircraft due to excess fluid in the ear. I went and looked through my human performance books to see if there was anything on the subject but found nothing.

I thought that if there was excess fluid then a build up then pressure would build in the ear, but I thought if pressure builds then the passenger could simply swallow and relieve pressure.

Any chance someone could quickly explain why excess fluid in the ear would prevent someone flying in light aircraft as I am none the wiser. Also why do people have excess fluid in the first place?

Thanks