Accident Overview
A towplane pilot reported that during a glider tow takeoff, approximately 20 to 30 feet above the ground, the airplane experienced a sudden lurch forward and pitched nose down. The pilot attempted to release the tow line by pushing the release mechanism forward, but did not feel the line release. The aircraft struck the ground in a nose-low attitude, departed the runway, collided with a runway light and a runway sign, and subsequently ground looped.
Glider Pilot Account
The pilot of the glider being towed stated that during takeoff, the glider became airborne and abruptly pitched into a steep nose-high attitude, causing the pilot to lose sight of the towplane. The glider pilot released the tow rope, maintained level flight at approximately 150 feet above ground, and landed on the grass alongside the runway without further incident. In a follow-up telephone conversation, the glider pilot noted that the glider was equipped with a center of gravity (CG) hook setup.
Aircraft Damage
The towplane sustained substantial damage to the right wing.
Mechanical Condition
Both the towplane pilot and the glider pilot reported that there were no preaccident mechanical failures or malfunctions with their respective aircraft that would have precluded normal operation.
Relevant Guidance
The Federal Aviation Administration's Glider Flying Handbook (FAA-H-8083-13A) includes a section on "CG Hooks" stating that compared to a nose hook, a CG hook makes crosswind takeoffs more difficult because the glider can weathervane into the wind more easily. Additionally, a CG hook increases the glider's susceptibility to kiting during takeoff, especially when the CG is near the aft limit, which can present a serious danger to the towplane during aerotow.
The handbook also contains a section titled "Aerotow Takeoff Procedures" which notes that allowing the glider to fly high above and lose sight of the towplane is one of the most dangerous occurrences during aerotow. The tension on the towline from the glider pulls the towplane's tail up, lowering its nose. If the glider continues to rise, pulling the tail higher, the tow pilot may run out of up elevator authority.