Landing a helicopter in trees is not a purpose but a survival tactic used by pilots during an emergency to absorb the impact and increase the chances of survival. The crash-landing is typically performed using a procedure called "autorotation," which allows the helicopter to descend in a controlled manner.
How trees increase survivability
Energy absorption: Trees and branches can absorb a significant amount of the helicopter's kinetic energy during a crash. This can be less hazardous than crashing on hard, flat ground.
Deceleration: Flying through a dense canopy of trees allows for more gradual deceleration compared to an abrupt stop.
Directional control: By maintaining a level attitude, a pilot can use the tree canopy as a guide to ensure a vertical descent, reducing the risk of an uncontrolled spin or a direct, head-on impact.
Reduced vertical impact: For helicopters, the main rotor can act as an "umbrella," with the blades and rotor system helping to cushion the vertical impact and absorb some of the excessive descent rate.
Avoiding fire: In the case of a plane crash, some pilots are taught to aim between trees to shear off the wings and dissipate energy, but this increases the risk of fire. Helicopters, however, do not have wings and landing in trees can help avoid fire by preventing ruptured fuel tanks.
Pilot technique during a forced landing
Maintain control: Pilots are trained to "fly the aircraft all the way to a stop" by maintaining as much control as possible. Fatalities are often the result of a loss of control.
Minimize speed: Pilots will try to slow down the helicopter to a controllable speed just above the stall speed for the softest possible impact.
Autorotation: If the engine fails, the pilot enters an autorotation, a state where air flowing up through the rotor system keeps the blades spinning. This allows the pilot to use the stored energy in the rotor blades to cushion the final moments of the landing.
This emergency technique is a last resort when no suitable clearing or body of water is available.
