We should wait for the official report, but there is speculation the helicopter altimeter was miscalibrated.
Apparently on the old avionics in the helicopter, the altimeter is calibrated by manual entry of barometric pressure to the nearest 0.1 inch Hg. So a rounding error could cause a 100 ft altitude discrepancy.
Apparently on the old avionics in the helicopter, the altimeter is calibrated by manual entry of barometric pressure to the nearest 0.1 inch Hg. So a rounding error could cause a 100 ft altitude discrepancy.