Q: I travel for business and add up lots of frequent flyer points. However, lately when I try to get the free flights the airlines promise all the time, it seems there are never any FF seats on the flight I want. What can I do about it?

A: Frankly, we wonder about that all the time. Sometimes we’ve been lucky to get the exact flight we want with our FF points for free. Other times, if we had to change our flight schedule on a free flight, we were charge $50 or so to get on another flight that day.

And the most frustrating times were when we were told that FF seats on a flight were a limited number and we couldn’t use our credits for a flight of our choice. Then, when we paid and boarded the flight, it was half full.

The latest info is that FF seats could be even more restricted this season because airlines are caught in a two-way bind. Because of the lousy economy, it’s expected that fewer people will be vacation flying. Anticipating that, fewer flights are scheduled and may be full.

With restrictions getting tighter and airlines struggling for profitability, you may have to do some heavy homework before you try to use your FF credits. Some airlines keep raising the requirements, so make sure you have enough points for the domestic or overseas flight you want.

Decide on the time and day you want to fly, but be very flexible. Sometimes the day of the week makes a difference: a flight on Wednesday may have less passengers than one on Friday, so the airline will allow you to use your FF points. Also, flights departing at 9 a.m. are always much more full than redeye flights that leave at 11 p.m.

If you use a hometown or online travel agency, ask about how to most economically use your FF points. You can also call or check the airline website about its up-to-date FF policy, and decide on your most favorable time and day.