MAF is definetly one of the bigger missionary companies out there. Their website is
www.maf.org. I had an informal interview with a recruiter from MAF just last month so feel free to ask me more about it if you want (although I was going through the Canadian version of MAF).
Generally, some large missionary companies (including MAF) want a minimum committment. In the case of MAF, it is 4 years. You are also expected to go through special training, and this also takes time (could be as long as 2 years... fund-raising, language training, missionary lifestyle, culture-adaptation, bible study, etc).
If you are interested in doing this type of work as a time-builder, than I would probably recommend you don't do it. I have spoken with pilots who have done this type of work, and it seems to be extrememly emotionally stressful. On the other hand, people find it very rewarding.
Good luck with your search!
Chris.