during takeoffs or landings. For dynamic rollover to occur,  some factor must first cause the helicopter to roll or pivot  around a skid or landing gear wheel, until its critical rollover  angle is reached. The angle at which dynamic rollover  occurs will vary based on helicopter type. Then, beyond  this point, main rotor thrust continues the roll and recovery  is impossible. After this angle is achieved, the cyclic does  not have sufficient range of control to eliminate the thrust  component and convert it to lift. If the critical rollover angle  is exceeded, the helicopter rolls on its side regardless of the  cyclic corrections made. the chance for recovery. The rate of rolling motion is also  a consideration because, as the roll rate increases, there is  a reduction of the critical rollover angle at which recovery  is still possible. Other critical conditions include operating  at high gross weights with thrust (lift) approximately equal  to the weight. Refer to  Figure 11-5.  The following conditions are most  critical for helicopters with counterclockwise rotor rotation: Dynamic rollover begins when the helicopter starts to pivot  laterally around its skid or wheel. For dynamic rollover to  occur the following three factors must be present: For helicopters with clockwise rotor rotation, the opposite  conditions would be true. When maneuvering with one skid or wheel on the ground,  care must be taken to keep the helicopter cyclic control  carefully adjusted. For example, if a slow takeoff is attempted  and the cyclic is not positioned and adjusted to account for  translating tendency, the critical recovery angle may be  exceeded in less than two seconds. Control can be maintained  if the pilot maintains proper cyclic position and does not  allow the helicopter’s roll and pitch rates to become too  great. Fly the helicopter into the air smoothly while keeping  movements of pitch, roll, and yaw small; do not allow any  abrupt cyclic pressures. This can occur for a variety of reasons, including the failure  to remove a tie down or skid-securing device, or if the skid  or wheel contacts a fixed object while hovering sideward,  or if the gear is stuck in ice, soft asphalt, or mud. Dynamic  rollover may also occur if you use an improper landing or  takeoff technique or while performing slope operations.  Whatever the cause, dynamic rollover is possible if not using  the proper corrective technique. Once started, dynamic rollover cannot be stopped by  application of opposite cyclic control alone. For example,  the right skid contacts an object and becomes the pivot point  while the helicopter starts rolling to the right. Even with full  left cyclic applied, the main rotor thrust vector and its moment  follows the aircraft as it continues rolling to the right. Quickly  reducing collective pitch is the most effective way to stop  dynamic rollover from developing. Dynamic rollover can  occur with any type of landing gear and all types of rotor disks. It is important to remember rotor blades have a limited range  of movement. If the tilt or roll of the helicopter exceeds that  range (5–8°), the controls (cyclic) can no longer command a  vertical lift component and the thrust or lift becomes a lateral  force that rolls the helicopter over. When limited rotor blade  movement is coupled with the fact that most of a helicopter’s  weight is high in the airframe, another element of risk is added  to an already slightly unstable center of gravity. Pilots must  remember that in order to remove thrust, the collective must  be lowered as this is the only recovery technique available. Certain conditions reduce the critical rollover angle, thus  increasing the possibility for dynamic rollover and reducing  Figure 11-5.  Forces acting on a helicopter with right skid on the  ground.  Critical Conditions 11-12 Cyclic Trim 1.  Right side skid or landing wheel down, since  translating tendency adds to the rollover force. 2.  Right lateral center of gravity (CG). 3.  Crosswinds from the left. 4.  Left yaw inputs. 1.  A rolling moment 2.  A pivot point other than the helicopter’s normal CG 3.  Thrust greater than weight Tail rotor thrust Tip-path plane neutral cyclic Tip-path plane full left cyclic Bank  angle Pivot point CG Weight Main rotor thrust