Glider disintegrates in mid-air following failed release during aero-tow

Casualties unknown • nahe Flugplatz Jena-Schöngleina, DE

A glider's wing structure failed under extreme loads after the tow rope failed to release, causing the aircraft to break apart during an emergency recovery maneuver.

What happened

On July 10, 2011, a towing operation near Jena-Schöngleina airfield resulted in the destruction of a SZD 30-C „Pirat“ glider and the fatal injury of its pilot. The flight involved a PZL-104 „Wilga 35“ acting as the tug aircraft.

Upon reaching an altitude of approximately 600 meters, the tug pilot signaled for release by waggling the wings. The glider pilot radioed "I am free," indicating the tow rope had been released. However, the rope remained attached. As the glider pilot subsequently maneuvered upward to turn right, the tensioned rope pulled the tail of the PZL-104 „Wilga 35“ upward, forcing the tug into a sudden dive to about 300 meters.

Under the intense tension of the dive, the glider pilot was unable to trigger the release mechanism. The tow rope eventually snapped. Following the separation, the glider pilot attempted an abrupt recovery maneuver to reduce speed and stabilize the aircraft. The extreme aerodynamic loads generated during this recovery caused the glider's wing structure to fail. The aircraft's fuselage plummeted into a wooded area, while the wing segments broke away and drifted across a nearby field. The glider pilot sustained fatal injuries.

The investigation

The BFU examined the wreckage of both aircraft and conducted a specialized wood-structural analysis of the glider's wings via the Fraunhofer Institute. Investigators also performed a destructive pull test on a similar tow rope to determine its breaking strength. The investigation focused on why the rope failed to release and why the glider's structure succumbed to the subsequent loads.

Findings

  • The primary cause was the failure of the tow rope to release from the glider during the release procedure.
  • The glider pilot's report of being "free" was inaccurate, as the release mechanism had not been fully engaged.
  • The use of a tow rope with a high breaking strength, lacking a proper predetermined breaking point (Sollbruchstelle) as required by regulations, contributed to the severity of the event.
  • The sudden, high-G recovery maneuver performed by the glider pilot after the rope snapped placed unsustainable loads on the wooden wing structure.
  • While some minor adhesive gaps were found in the wing construction, these were not considered the cause of the structural failure.

Probable cause

The accident was caused by the tow rope failing to disconnect from the glider, leading to a forced dive of the tug aircraft. The subsequent snapping of the rope and the glider pilot's abrupt recovery maneuver created extreme aerodynamic loads that caused the glider's wings to disintegrate.

Frequently asked questions

What happened in the 2011-07-10 1. Zaklady Szybwcowe „Delta-Bielsko“/ accident near nahe Flugplatz Jena-Schöngleina, DE?

A glider's wing structure failed under extreme loads after the tow rope failed to release, causing the aircraft to break apart during an emergency recovery maneuver.

What aircraft was involved and where did it happen?

The accident on 2011-07-10 involved a 1. Zaklady Szybwcowe „Delta-Bielsko“/, at nahe Flugplatz Jena-Schöngleina, DE.

What was the probable cause of the accident?

The accident was caused by the tow rope failing to disconnect from the glider, leading to a forced dive of the tug aircraft. The subsequent snapping of the rope and the glider pilot's abrupt recovery maneuver created extreme aerodynamic loads that caused the glider's wings to disintegrate.

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