Steve 76 has a good point there. As a company training pilot, part of my job to ensure the company emergency check list is followed at all times. The emergency check list is there to keep an average pilot out of trouble within the confines of approved company procedures. However, I would certainly look long at hard for secondary indications of a fire before shutting it down and encourage all to do like wise. Look for smoke by turning in the direction of the fire, fly out of balance a bit (at reduced speed), is there a smoke shadow over land etc etc. You don't always need a mirror. Like Nick said, one of the most important things is "DON'T RUSH!!!"