A LANCAIR ES-P'S DOOR POPPED OFF JUST AFTER LIFT OFF. PLT RETURN TO LAND.

Narrative

I WAS CONDUCTING CREW TRAINING TO AN INDIVIDUAL (CLIENT) WHO HAD JUST COMPLETED HIS LANCAIR ES-P ACFT KIT AND NEEDED 5 HRS OF TRAINING IN AN ES TO BE INSURED. WE WERE IN THE ES FOR THE REQUIRED TRAINING FLTS. WE HAD SPENT APPROX 2 HRS OF GND AND PREFLT PREP BEFORE GETTING INTO THE ACFT. AFTER GETTING INTO THE ACFT; THE CLIENT CLOSED THE DOOR WHICH IS A SINGLE CLAM SHELL TYPE ON THE L SIDE OF ACFT. WE TALKED AT LENGTH ABOUT THE SYS; AND TOOK OUR TIME WITH ALL ASPECTS OF THIS FLT. DURING THE RUN-UP; I REACHED OVER TO PHYSICALLY CHK THAT THE DOOR WAS CLOSED AND LATCHED (WHICH IT WAS); THE CLIENT ENGAGED THE DOOR SEAL AND WE WATCHED IT INFLATE NORMALLY. WE RECEIVED CLRNC TO TAKE OFF AND PROCEEDED WITH A NORMAL TKOF. JUST AFTER LIFTING OFF; THE DOOR DEPARTED THE ACFT. I TOOK CTL OF THE AIRPLANE; DETERMINED THERE WAS NOT ENOUGH RWY TO LAND STRAIGHT AHEAD; CALLED THE TWR AND RECEIVED CLRNC TO LAND ON A DIFFERENT RWY WHICH WAS UNEVENTFUL. THE DOOR WAS RECOVERED AND SUSTAINED SOME MINOR DAMAGE; AND THE ACFT SUSTAINED MINOR DAMAGE AS WELL; NEAR ONE OF THE HINGE ATTACH POINTS. I DON'T THINK I COULD HAVE DONE ANYTHING DIFFERENT TO PREVENT THIS BECAUSE THE CLIENT CLOSED AND LATCHED THE DOOR; AND I PHYSICALLY CHKED THAT IT WAS CLOSED AND LATCHED.