Preventing Aircraft Stalls
Recently, a Beech 18 twin-engine airplane that was flying a load of jumpers crashed into the yard of a residence, killing the pilot. Luckily, nobody was killed on the ground, and the jumpers had all been able to exit the airplane before it crashed, landing safely. While the National Transportation Safety Board will not release its report for quite a while, the preliminary information points to the aircraft’s entering a stall as the jumpers were positioning in the door to exit.
You learned (or should have learned) about aircraft weight-and-balance issues as a student in Category E of the Integrated Student Program, and it is usually a topic of discussion during Safety Day presentations. But we must consider weight and balance on every flight, not just during discussions a couple of times a year. Although the pilot is in command of the airplane, the jumpers and pilot share the responsibility of keeping the plane right side up and in controlled flight during skydiving operations. Just because you are not a pilot does not mean that you don’t need to understand what the pilot needs from you to help him stay in control of the airplane.
Whether the airplane is a Cessna 182 flying one jumper or a Twin Otter flying 23, the principles are pretty much the same, although the procedures themselves will vary based on the aircraft. A pilot must ensure the aircraft is airworthy for each flight, which includes loading and flying the aircraft within its weight-and-balance limits. After climbing to altitude, the pilot will configure the aircraft for jump run, which includes leveling the aircraft, reducing power, adding flaps (if required) and maintaining the correct airspeed. Once the airplane approaches the jumpers’ exit point, the pilot will signal that the airplane is ready for the door to be opened and that the jumpers may start their climbouts and exits. By this time, the pilot should have the airplane stabilized in level flight and flying at the correct airspeed. The pilot will then continue to work to control the airplane as the jumpers set up and exit the aircraft, which includes maintaining pitch, heading and airspeed as the center of gravity shifts toward the rear of the aircraft while the jumpers move to position in the door. But the pilot faces challenges in addition to the weight-and-balance shift. Increased drag from the bodies hanging on the outside of the airplane, as well as reduced airflow across the tail (which makes the elevator and rudder less effective), come into play as the jumpers move into position in the door. It is at this point in the jump run that the chances of a stall are greatest.
Not only does the pilot need to do his job correctly, but the jumpers also need to work together during the climbout and exit to help ensure the airplane keeps flying. In a larger airplane with a side door, such as a Twin Otter, King Air or Caravan, the load needs to stay forward as much as possible while the first groups climb out and prepare to exit. Even if you are part of a big-way that includes most or all of the jumpers on the plane, this is still the case. The biggest reason a pilot loses control of an airplane on jump run is because too many jumpers move toward the rear of the airplane at the same time. Make sure your pilot knows that you have a large group exiting and that he is OK with the number of jumpers and their exit plan. The base and outside floaters need to set up in the door quickly and exit as soon as possible. The late divers should stay as near the front of the plane as possible until the base has let go of the plane. If the load consists of several smaller groups, each group should set up in the door and exit while the remaining groups stay as far forward in the fuselage as possible.
Although it is not exactly rocket science, keeping the plane right side up during jump operations is a combined effort that requires planning, common sense and training for both the jump pilot and the jumpers. If we all work together, we can help ensure we never lose another jumper, pilot or airplane because of a stalled aircraft.
—Jim Crouch | D-16979
USPA Director of Safety & Training