Yes, you can do it but only in SD mode. You will need 3 female to female RCA connectors from the local "video" shack store to connect your video & left and right audio signals from your hemet cam to the composite cord on your A1. Then just follow the instructions for recording an analog line-in signal on page 106 of the manual.
The A1 also uses a 3.5mm for output/input. it's a 3 ring connector to 3 rca's. Does the helmet cam have a 3.5mm to rca? if so, just get some female-female rca connectors and connect together.