What happened
In September 2021, two separate Virgin Australia flights performed unauthorized displaced threshold approaches at Darwin Airport. At the time, construction work at the opposite end of the runway had caused a displaced threshold on runway 29, but runway 11 remained unaffected.
In the first instance, the crew of VH-YIS misread a NOTAM, leading them to believe runway 1 and 11 had a displaced threshold. Despite receiving a flight coordinator (FCON) message that clarified the thresholds were displaced at different times, the crew proceeded with a plan for a VOR-T displaced threshold approach. When Air Traffic Control (ATC) cleared the aircraft for a standard VOR-Z approach, the crew continued with their original, incorrect plan without notifying ATC. The pilot's readback omitted the 'Zulu' suffix, which ATC failed to correct.
In the second instance, the crew of VH-YFC misinterpreted the same NOTAM, incorrectly concluding that both ends of the runway were simultaneously displaced. The crew intended to verify the runway status via the ATIS upon arrival; however, the ATIS only noted a reduced runway length for the active runway 11 and did not explicitly state the threshold was displaced. Consequently, the crew performed the displaced threshold approach without realizing the error until after the aircraft had landed.
The investigation
The investigation focused on how both crews arrived at the same incorrect operational conclusion. Investigators examined the NOTAMs, FCON messages, and ATIS broadcasts used by both flights. It was determined that the crew of VH-YIS relied on a flawed pre-flight interpretation despite receiving updated FCON information. For VH-YFC, the investigation found that the crew failed to identify that the reduced runway length was due to works at the upwind end, and the brevity of the ATIS prevented them from catching the error.
Findings
- The flight crew of VH-YIS misinterpreted airport information during their pre-flight briefing, leading to the planning of a VOR-T approach instead of the standard VOR-Z.
- The crew of VH-YFC also misread the NOTAM, believing both ends of the runway were displaced.
- Misinterpretation of NOTAM information was the primary driver for both incidents.
- Both crews failed to utilize the ATIS effectively to verify runway status.
- A critical safety opportunity was missed when ATC did not request a full readback of the approach clearance for VH-YIS, which could have highlighted the discrepancy.