The wood had dense undergrowth which retarded Hindering movement , made it difficult to keep Preventing_or_letting direction and during the battle the trees were brought Bringing down by shellfire , becoming entangled Hindering with barbed-wire and strewn Filling with German and British dead .

The subsequent investigation found Coming_to_believe that the flight crew had inadvertently retarded Cause_change_of_position_on_a_scale the power levers below the lowest position allowable in flight ( known as `` flight idle '' ) , causing Causation both propellers to overspeed Motion and leading to Causation a complete loss Earnings_and_losses of engine power .