Managing Human Factors – Case Study

In-flight break-up involving Airbus Zephyr unmanned aerial Vehicle Wyndham, WA 28/09/18:

• Wingspan: 25m
• Weight: 65kg

Details:

Following test flights in the northern hemisphere, the Zephyr 8 was positioned to Wyndham, WA for further research and development. Powered by batteries and solar, this 25m wingspan UAV operates in the Stratosphere (up to 74000ft (this is above the Troposphere, which contains all of Earth’s weather)). While the Zephyr had previously completed a 25-day flight, the ultimate goal was to achieve a flight of over 100 days.

As the Zephyr was susceptible to turbulence on its 10-hour climb through the Tropopause, the mission had been abandoned on the previous day due to unsuitable surface winds. Other unsuitable weather for the Zephyr’s climb was identified as layers of air which included both rising and descending air (mixing layer) of greater depth than 1500ft. This was found to be less likely at night.

On the evening of 28 September 2019, the Zephyr was launched at 9:43pm in what was considered, ‘ideal’ conditions. At 1200ft, an uneventful systems check was conducted. The UAV continued to climb in a South Easterly direction. With a climb rate of 5000ft per hour, at 10:40pm it passed 5200ft and experienced an uncommanded roll of 15 degrees to the right, changing track by approximately 180 degrees.

As this was believed to be due to thermal turbulence from a dry salt lake, a northerly track towards smoother air was selected. However, at 11:07pm, passing 8700ft , the UAV again experienced an uncommanded roll of 14 degrees to the right, followed by an uncommanded roll of 17 degrees to the left. Again, the aircraft self corrected however the conditions persisted resulting in a 1000ft descent over 7 mins.

The crew increased power and tried to maneuvre the aircraft to an area they believed had smoother air, however at 1115pm it experienced another uncommanded right roll, from which it was slow to recover. During the recovery it exceeded its maximum airspeed, then with full left rudder applied, the roll angle increased beyond limits and entered an uncontrolled spiral dive. At 11:16pm the airspeed increased beyond Vne and both wings fractured around mid span resulting in an inflight break-up.

Case Study Analysis

Using FDODAR, let’s analyse the accident:

Think about each of the stages: What do the students think happened within the FDODAR model?

• Fly – They continued to maintain control (initially).
• Diagnose – They identified the initial issue was turbulence was created from flying over a hot dry salt lake.
• Options – Changing track was one option, unreported as to whether other options were discussed, although these may have been discussed in preflight brief.
• Decision – They changed track towards potentially smoother air
• Assign Tasks – While PIC changed course in an automatic mode, no other tasks were assigned. (Could have assigned crew members to gather current weather conditions in the area of concern)
• Review – Was this diagnosis and decision correct? Did they try different methods when the problem/s re presented again? Were they potentially mentally fixed with one diagnosis and only one decision?

What other options could this crew have discussed? (Refer to the “Options” slide):

• Options:
  • If Auto => change to a more manual mode, reassess how much control.
  • Return to launch
  • Loiter
  • Communicate
  • Avoid aircraft / birds
  • Safe landing
  • Safe crash / Fire extinguisher / Collect pieces (carbon fibre management)
  • Hand over control to Transmitter / GCS
  • Return to launch low to ground to avoid attacking birds

Were this team too Mission focused in their decisions? (From the “Decision” slide):

• Decision:
  • Based on threats
  • What is the safest option? Manned aircraft and helicopters have pilots and passenger onboard, populous areas have people (including children) on the ground.
  • What are the mission requirements?
  • What is the cost?
  • Company reputation at risk…
  • Always have a contingency plan – Did they have a contingency plan?