On 23 June 2015, at about 0638 Western Standard Time (WST), a Bombardier DHC‑8, registered VH‑XFQ, departed from Perth, on a charter passenger flight to Darlot, Western Australia.

Prior to the flight, the captain reviewed the weather information and nominated Leinster, 30 NM west of Darlot, as the alternate aerodrome. Although Leinster was a suitable alternate aerodrome for Darlot, their proximity meant that similar conditions could be expected at both. Accordingly, the captain decided that Wiluna would be suitable if they were unable to land at Darlot or Leinster. In addition, the captain increased the fuel load to the maximum, given the expected payload.

Soon after 0800, as they neared their descent point, the crew could see that a layer of low cloud had formed over the Darlot area. The crew conducted an approach, but were unable to establish the required visual references, due to low cloud, and conducted a missed approach.

The crew commenced a diversion to Leinster. While advice from the ground at Leinster suggest that the weather was deteriorating, it still appeared probable that an approach would be successful. The crew conducted an approach to runway 28, but were unable to establish the required visual references due to low cloud, and conducted a missed approach.

The crew then elected to attempt an approach to the reciprocal runway (runway 10), which appeared to have more favourable conditions. During the later stages of that approach, while still clear of cloud, an enhanced ground proximity warning system (EGPWS) terrain warning triggered. The crew commenced a missed approach in response to the warning.

Low cloud was continuing to move over the area and the captain determined that further attempts to land at Leinster were unlikely to be successful.

The conditions to the north appeared to be clear, and the crew elected to divert to Wiluna. The flight proceeded to Wiluna, and landed uneventfully at about 0925.

The aircraft landed with about 600 lbs of fuel remaining, above the operator’s minimum fixed fuel reserve of 450 lbs.

Following a small number of safety occurrences where unforecast weather events have led to unforeseen diversions or holding, the ATSB commenced a research investigation (Reliability of aviation weather forecasts). This research investigation will examine how often weather events are not forecast in enough time allow pilots to make appropriate decisions (carry additional fuel, make a timely diversion or delay departure).

This incident highlights the importance of lateral thinking during flight planning, particularly where operations to remote areas are planned, and when an alternate aerodrome is close to the planned destination. In this case, the captain assessed the broader weather picture, and added fuel above the minimum requirements on the basis of that assessment. That additional fuel ultimately provided the crew with a safe option, despite encountering unexpected conditions that prevented a landing at the planned alternate aerodrome.


Aviation Short Investigations Bulletin Issue 46

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