Dynamic Rollover

Another dangerous condition for a helicopter pilot to experience is called dynamic rollover. It is again, where you have a series of conditions that combine to make a dangerous situation. Once again, 3 key elements make up this hazardous condition. They are: A pivot point, a rolling moment, and weight equal to thrust at some time during the manoeuvre. What actually happens is that the helicopter, which is still on the ground, will start to roll over on its side using one skid, or wheel, as the pivot point.



Once the aircraft starts to roll, a downward collective movement is the only thing that will stop the forces in action from flipping the aircraft on its side. By reducing the collective, the thrust to weight ratio decreases, which allows the aircraft to settle back down in a level attitude. If this is done on sideward sloping terrain, a collective reduction performed too quickly can cause the aircraft to roll over on the other side, down the slope. Care must be exercised when performing slope operations, but dynamic roll over can occur on the flattest of surfaces if the pilot becomes complacent.




It is normal practice to tackle a slope from the side and not from the front or back because most helicopters have skid type landing gear with no brakes. Skid gear will most likely slide down a hill if the toes or heels of the skids are pointed up hill once the power is taken away holding the aircraft in place.

Once that force is no longer applied, the weight of the aircraft will get it started sliding and, depending on the slope, could pick up so much speed that it crashes severely at the bottom of the hill. The ones that have wheels and brakes could slide also depending on the degree of slope and condition of the ground.




Other reasons not to attack a slope from the front or back is that the tail boom may strike the hill before the skids do (Again, depending on the degree of the slope) or the rotor system may impact the hill before the skids do. Usually, if the standard 8 degrees of slope are used as a maximum, then a sideward approach to the slope will have the skids touching before the rotor system. Care should be used when passengers depart the aircraft on a slope as they may walk into the rotor if they go up hill. Always brief the passengers to leave the aircraft on the down slope side of the aircraft.