CEN11LA585 · Aero Commander CALLAIR A-9B

The accident occurred during a glider tow operation. The glider pilot reported experiencing some turbulence during initial climb, followed by a high intensity thermal. The glider pilot lost sight of the airplane (towplane) briefly then relocated it below and to the right of the glider. He released from the towplane and landed without further incident. The glider pilot noted that the towplane appeared to be in stable flight at the time of the release. A witness stated that the takeoff appeared to be normal, but the towplane and glider encountered some turbulence near the end of the runway. He commented that the glider pilot appeared to be having some difficulty staying in position behind the towplane. At one point, the glider was subjected to a tugging motion, which appeared to be due to slack being taken out of the tow rope. The glider subsequently separated from the towplane. The towplane turned right, while the glider continued straight ahead briefly. The towplane was about 350 feet above ground level when the right wing dropped and it entered a 60- to 70-degree nose-down attitude. The towplane completed about one-half of a rotation before the witness lost sight of it behind trees. The towplane impacted an open field about 1/2 mile west of the departure end of the runway. A postaccident examination of the towplane did not reveal any anomalies consistent with a preimpact failure or malfunction. It is likely that, when the glider pilot allowed the glider to climb above the towplane to the extent that he lost sight of the towplane, the resulting tension on the tow rope reduced the towplane pilot's control authority. The resulting loss of airspeed subsequently induced an aerodynamic stall. Although the glider and the towplane separated, there was not enough altitude for the towplane pilot to recover from the upset before the towplane impacted the ground.

Verbatim NTSB analysis and probable cause from the NTSB dataset