What should I do if my child has occasional aggressive outbursts?

Keep calm. Try not to react to your child's outburst. Try to soothe him or distract him. If that doesn't work remove him from the situation for a short period of time to help him wind down. The second often forgotten part is to acknowledge good behavior. Remember: "negative attention is better than no attention at all.".
Behavior. Temper tantrums are normal for certain ages. The AAP had a good advice: http://www.healthychildren.org/English/familylife/familydynamics/communication-discipline/Pages/Temper-Tantrums.aspx However, there gets a point when they should outgrow these. Sometime, it's because they haven't been dealt with properly. It can also be more that that, and should be evaluated by your doctor. .