Date: 22 January 2002
Time: 1528 hours
Location: Ohau Range
Aircraft Type: Alexander Schleicher Segelflugzeugbau ASW 20
While on a cross-country flight with three other gliders in company, ZK-GVW was soaring the eastern slopes of the Ohau Range in conditions of weak lift. Passing approximately 4500ft, the aircraft was seen to impact the terrain in a near vertical attitude. The wreckage was first reached by ground parties approximately ten minutes later and the pilot was confirmed as deceased.
|An Alexander Schleicher Segelflugzeubau ASW 20 similar to ZK-GVW||Location of ZK-GVW accident, 22 January 2002|
|image embedded from Wikipedia on 29 August 2010||map embedded from Google Maps on 29 August 2010|
After departing Omarama at approximately 1400 hours, the accident aircraft proceeded to circumnavigate the Omarama valley in an anticlockwise direction, using orographic lift to sustain the flight. Immediately prior to the accident, ZK-GVW was the lowest of the group of four gliders flying left-hand circuits close to the Ohau ridge. As ZK-GVW turned towards the ridge, pilots of the other aircraft observed ZK-GVW complete what appeared to be a wing-over to the left into a near vertical dive, from which the pilot did not recover and the aircraft impacted the terrain.
At the time of the accident, a light easterly flow prevailed with overcast cloud cover at 5500ft. Visibility was good with no precipitation and the other pilots reported observing no wind shear or other adverse conditions.
Wreckage and Impact
Analysis of impact marks at the crash site confirmed that the aircraft contacted the terrain in a wings level and near vertical attitude. The aircraft was on an easterly heading at 4400ft when it struck the 40 degree scree slope.
CAA Analysis and Conclusions
The CAA (Civil Aviation Authority) investigation1 concluded that it was likely that the grey overcast combined with a similarly uniform grey scree slope resulted in pilot disorientation due to lack of visual cues. These conditions would have made assessment of distance from the slope and bank angle difficult. The pilot of ZK-GVW, due to distraction or inability to correctly recognise the size of objects on the slope may have misjudged the turn radius of the glider. Recognising this error, likely resulted in the pilot increasing bank and g-loading in an attempt to maintain terrain clearance, which consequently resulted in an incipient spin. Such a spin would have been difficult to recover from in the little altitude available considering the very low nose attitude and featureless terrain for reference. The high forces involved in the rapid deceleration of the aircraft on impact were not survivable.
A brief HFACS Analysis of this accident reveals a number of causal factors which can be classified as unsafe acts.
|HFACS Category||Causal Factor|
|Perceptual Errors||The visual illusion created by the uniform grey overcast and the scree slope likely resulted in a “grey out” condition, which resulted in pilot disorientation and loss of control.|
|Skill-based Errors||Inadvertent stall and incipient spin entry are obvious skill-based errors even given poor visual references.|
|Decision Errors||Although not explicitly mentioned in the accident report, the pilot’s decision to turn towards rising terrain in conditions of poor terrain definition may be questionable.|
The accident report does not identify any particular causal factors which may be categorised as preconditions for unsafe acts.
Want to know more?
- CAA Accident Report 02/99: ZK-GVW
- The published Civil Aviation Authority of New Zealand report into this accident.
- AviationKnowledge - Human Factors Analysis and Classification Systems (HFACS)
- Visit here to find out more about the Human Factors Analysis and Classification System.
- AviationKnowledge - Fatal Gliding Accidents in New Zealand
- Visit here to find out more about other fatal gliding accidents in New Zealand.