Shortly after takeoff from a remote mountain airstrip, at approximately 40 feet above ground level the airplane lost altitude, and began to sink. The pilot elected to conduct an off airport precautionary landing, during the landing the airplane nosed over sustaining substantial damage to the right wing, empennage and vertical stabilizer. The pilot reported no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation. In the narrative history of flight section of the NTSB Accident/Incident Reporting Form 6120.1, the pilot stated that he was unsure if the loss in altitude was a result of wind shear, or inadvertent movement of the flap selector by the passenger seated in the right front seat. In the recommendation section of the NTSB Accident/Incident Reporting Form 6120.1, the operator stated that the accident may have been prevented if the company had established mandatory policies limiting loads out of short, high altitude, mountain airstrips, where gusting winds and wind shear is common.