Plane that struck glider in fatal mid-air crash had faulty collision avoidance system, TSB report finds

An investigation into a mid-air collision last summer between a glider and its tow-plane that killed two people has found that the collision avoidance system on one of the aircraft wasn’t working.

Gliding instructor and his student died in July 2019 collision

Experienced pilot Allan Wood, 68, and his student, Adam Leinweber, 18, died in the collision. (Allan Wood/Facebook)

An investigation into a mid-air collision that killed two men in southern Alberta in 2019 has found that a glider didn't release from its tow plane in the typical fashion and the plane's collision avoidance system wasn't working.

The crash on July 26, 2019, killed an experienced gliding instructor Allan Wood, 68, and his student, Adam Leinweber, 18, both of Calgary.

The aircraft were flying out of the Cu Nim Gliding Club just outside of the town of Black Diamond, about 40 kilometres south of Calgary. 

A Schleicher ASK 21 glider carrying Wood and Leinweber hit the Cessna 182 Skylane tow plane shortly after detaching.

After the crash, Alberta Soaring Council president Jason Acker said Wood was an "amazing" and "passionate" instructor with two decades of teaching experience at Cu Nim, who had taken up gliding as a birthday present for his 50th birthday.

Leinweber was an air cadet with 604 Moose Squadron in Calgary and was learning to fly gliders on his own time because he was passionately interested in aviation, Acker said. He was only a few flights away from getting his licence and had been due to begin a physics degree program at the University of Calgary that September.

The crash took place on July 26, 2019, across Range Road 22 from the Cu Nim Gliding Club, just outside of Black Diamond, Alta. (Justin Pennell/CBC)

The council president said he believed Leinweber would have been in the front seat of the glider, with Wood in the back seat as the instructor.

Improvised practice turn might have contributed

According to a report by the Transportation Safety Board released on Monday, the glider did not release from the tow plane in the typical fashion — that is, when both aircraft are in a straight and level flight.

Instead, the glider uncoupled itself from the tow plane halfway through the second of two practice turns.

The practice turns had not been agreed to ahead of time. Rather, the glider crew radioed the tow pilot just after taking off to request the exercise, the report noted.

"By releasing in a right turn, the glider was not in a position where the tow pilot would normally expect to see it, i.e., behind and to the right of the tow plane," the report said.

"When the tow plane reached the anticipated release point, the glider had already released; however, the tow plane pilot was not aware. Shortly after, the glider flight crew called the tow plane pilot on the radio to thank him for the tow."

The tow plane's propeller struck the glider's empennage (rear stabilizers) 34 seconds after the glider had released.

"The glider entered a dive from which it was unable to recover and struck terrain in a near-vertical attitude," the report said.

The pilot of the single-engine tow plane was able to safely land the plane. 

Faulty equipment's warning signs weren't heeded

The report also found that both aircraft were equipped with Flarm airborne collision avoidance systems (ACAS), something that was not required by the regulations.

But on the day of the crash, the PowerFlarm Core installed on the tow aircraft was not working, the TSB report said.

In addition, investigators determined that throughout the 2019 flying season, the plane's airborne collision avoidance system had been showing warning signs, such as "Flarm intermittent — keeps resetting" and "Power Flarm display not working."

"These defects were not recorded in the aircraft's journey log, although it was required by the regulations," the TSB report said.

"Airborne collision avoidance systems offer the potential to significantly reduce the risk of mid-air collisions. If an aircraft is equipped with an ACAS, it is important that the system be maintained in a serviceable condition," the TSB report said in its conclusion.

The airborne collision avoidance system on the glider was found to be in working condition.

No procedure when plane loses sight of glider

The report determined that weather and sun position didn't factor into the crash.

The report also noted that the club does not have a standard procedure in place for tow plane pilots to follow if they lose sight of the glider, or if they are unsure of the glider's position relative to their own.

The Cu Nim Gliding Club said in a statement its received the report and will study it.

"The Club will be carefully studying the report and will be taking the safety messages of the CTSB extremely seriously," the emailed statement read.

"Throughout its 60-plus years of operation, the Cu Nim Gliding Club has prided itself on the safety and well-being of its members. The Executive and membership continue to collectively grieve the loss of our friends and remain committed to advancing the passion of soaring safely above the skies of Southern Alberta."

The Soaring Association of Canada (SAC) manual also does not give formal guidance for the tow pilot to follow under these circumstances, the TSB said.