TAIC report - glider on student trial flight crashed while ridge soaring

9 Nov 2023
Figure 6 from the final report. The glider wreckage is shown in an aerial photo of the accident site. The wings are embedded in trees and bushes on the mountainside. The tail section has broken off. The cockpit structure is also broken off and in numerous pieces.
Fig 6 from the final report. the wreckage in situ. TAIC photo

AO-2020-002 Glider, Schleicher ASK21, ZK-GTG, Impact with Terrain, Mount Tauhara, Taupō, 31 May 2020 

 

Key points: This report is particularly important for gliding clubs, glider pilots, instructors and personnel involved with glider flying activities and aviation regulation in New Zealand.
 

What happened

A gliding club instructor was conducting a trial flight with a short-term club member over Mount Tauhara. Witnesses on the walking track near the mountain summit watched as the glider flew past, left wing down; and then as its left wingtip struck the scrub on the downwind side of the mountain. It disappeared from view and they heard sounds of impact.

The left wingtip had struck first and then the aircraft crashed through the bush until it lodged in a tree and the tail section broke off. Neither the instructor nor the student survived.

 

Why it happened

The instructor was likely trying to manoeuvre away from rising terrain where the glider was low above the mountain and downwind from the ridge face. Despite the instructor's efforts, collision with terrain became unavoidable.

Figure 9 from the report. An aerial view of Mt Tauhara depicting the ridge line, the wind direction towards the mountain flank on one side of the ridge, and the figure-or-eight flight path that gliders use to take advantage of the wind updraft as it hits the mountain flank and is driven upward.
 

Safety issues and recommendations 

Pilot competency associated with ridge soaring

The risk of an accident occurring was increased by Taupō Gliding Club’s lack of systems to ensure that pilots had appropriate competency to ridge soar on Mount Tauhara and safely conduct training flights there.

  • Safety action since this accident: the club developed a training presentation to provide for some formal training and an approval process for pilots to ridge soar on Mount Tauhara. More broadly, Gliding NZ published a document, "Ten vicious traps in ridge and mountain flying" in its newsletter (Nov 2022) and its website. 
     
  • Recommendation: To address a residual safety risk over Mount Tauhara, the Commission recommended that Taupō Gliding Club have a system to … verify that pilots have an appropriate level of competency to ridge soar on Mount Tauhara and safely conduct training flights on the ridge. (Recommendation 010/23)

 

Instructor training at Taupō

There was an increased risk that instructors were not fully competent because audits by Gliding NZ didn’t detect that Taupō Gliding Club had not fully implemented Gliding NZ instructor training procedures.

  • Recommendation: The Commission recommended that Gliding NZ review how gliding club instructors are trained and clubs audited, and then ensure all new instructors are consistently trained to the standards set out in its Manual of Approved Procedures. (Recommendation 011/23)

 

Lessons

  • Pilots must be competent in the correct techniques to manage risks associated with ridge soaring, such as turbulent wind conditions, unpredictable updrafts and proximity to terrain.
     
  • Trial flights should meet the intent of the flight without introducing unnecessary risk.

 

He mihi

The Commission acknowledges Tauhara Maunga, its people, and the people of Ngāti Tūwharetoa for their partnership in responding to this tragic event. The Commissioners thank the Tauhara Mountain Trust, the kaitiaki for Tauhara Maunga which it recognises as an ancestor for ngā hapū o Tauhara. The Commission extends its appreciation for assistance in access to the site and support to conduct its investigation in a culturally appropriate way.