If you must fly with a cold or sinusitis, you might try this remedy:

Benzedrex inhaler

It is available OTC (I get mine at Walgreen's) and has worked like a charm on several occasions. The trick seems to be to use it about 1/2 hour before beginning the descent, when it is harder to equalize the pressure with inflamed eustachian tubes.

Inhale deeply...twice in each nostril while closing off the other nostril. It will burn like the dickens (it is packed with lavender oil as well as a potent decongestant), and you may tear up for a minute, but it really helps to open up the eustachian tubes.

Good luck!