Multiple TAWS Warnings Reveal Safety Reporting Issue
An ATR 72, abruptly flown at a high rate of descent, descended to 440 feet above the ground level, while trying to remain clear of cloud during an impulsively commenced visual approach, triggering multiple Terrain Awareness and Warning System (TAWS) warnings. The Australian Transport Safety Bureau (ATSB), in the first of three investigation reports on incidents with the same individual aircraft, identified ‘significant underreporting…of…TAWS-related occurrences’ by the airline.
On 15 May 2013, Avions de Transport Regional ATR72-212A, VH‑FVR, was conducting a scheduled commercial passenger flight from Brisbane to Moranbah in Queensland. The flight was operated by Virgin Australia Regional Airlines (VARA), formerly Perth, WA based SkyWest.
Corporate Background: Virgin Australia had made an offer to purchase SkyWest in late 2012, which was completed in April 2013, just weeks before this Serious Incident. VARA continues to operate on a separate Air Operators Certificate to Virgin Australia. While the HQ is in Perth, WA most of their ATR operations are in the East of Australia. These ATRs, first introduced in 2011, were primarily flown on behalf of Virgin Australia, even before the purchase. The acquisition signalled a period of growth for Virgin Australia, seen as a move to challenge Qantas, although VARA did delay ATR72 deliveries in January 2014 as part of a move to cool their expansion.
The crew was initially planning to perform an NDB-A approach. After finding out that a Dash 8-300, due to arrive about 2 minutes prior, was to make a visual approach, the ATR crew changed their plans to also conduct a visual approach. The ATSB reported:
…after descending though an overcast cloud layer at about 6,000 ft, they [the crew] became visual with the Moranbah township and the area surrounding the airport. They noted some low cloud and patches of fog around the runway 34 threshold.
The ATSB report that:
During the visual approach to Moranbah, the aircraft descended to a height of 440 ft above ground level as the pilot manoeuvred to avoid cloud. As the pilot levelled the aircraft, a number of terrain awareness warning system (TAWS) ground proximity warning system alerts activated. The aircraft was climbed and the circuit was continued, with the activation of another TAWS alert prior to the aircraft landing. The recorded average vertical speed during the descent from circuit height to 440 ft AGL, the lowest recorded height before the crew initiated a climb, was 1,750 ft/min.
Further warnings were triggered by high bank angles on the base leg turn.
The Captain (ATPL, 4,530 hours total, 1,750 hours on type, 3.5 hours in command) had completed the command upgrade just a few days earlier and was the Pilot Flying. The First Officer (ATPL, 2,880 hours total, 610 hours on type) was Pilot Monitoring. The ATSB say:
According to the operator’s requirements, the FO had sufficient experience to be paired with a captain who had recently been checked to line.
The ATSB Investigation
The ATSB identified the following contributing factors:
1) Approaching the circuit, the captain assessed that a descent below the standard circuit height was necessary to avoid cloud, but did not communicate this to the first officer in a timely manner, thereby preventing identification of a descent limit or appropriate approach alternatives.
2) Due to the crew’s focus on avoiding the cloud, the high rate of descent at a lower than normal altitude was not identified and corrected by the crew in the short time available, resulting in the terrain awareness warning system ‘Terrain Ahead’ and ‘Too Low Terrain’ alerts.
3) Despite briefing the intent to conduct a visual approach, descent in visual conditions was not assured and the crew did not discontinue the approach. This resulted in an undesired aircraft state and subsequent terrain awareness warning system alerts. The ATSB found that the captain’s rapid decision to descend limited the opportunity to discuss alternative approach options, descent limits and go around options should visibility reduce to below that required for visual flight.
To determine if there was an issue with the TAWS fitted on the ATR 72, the ATSB conducted a search of its database to determine the number of alerts reported for the ATR 72 in the previous 12 months. In Australia the Transport Safety Investigation Act 2003 require that activation of TAWS warnings be reported to the ATSB for all air transport operations. The ATSB study identified “significant underreporting” by VARA of ATR72 TAWS-related occurrences to the ATSB, which they identified as a safety issue. The ATSB give no indication on the cause of the underreporting.
Since the accident the ATSB report that:
VARA advised the ATSB of a number of safety actions following this occurrence. This includes the incorporation of the ATR fleet into the company’s cyclic recurrent check programme, the provision of safety promotion briefings to all company pilots, and the production of safety publications that alert crew to the defences that standard operating procedures and threat and error management provide. In addition, VARA directed its flight crew to submit occurrence reports for all ground proximity warning system (TAWS) occurrences and implemented a review process to ensure that all relevant reports are passed to the ATSB. A review of the ATSB database in the period since these initiatives and the production of this investigation report showed that VARA’s reporting of TAWS occurrences was now consistent with other similar operator/operation reporting rates.
The ATSB’s safety message is that:
This occurrence highlights the importance to flight crew of good communication and the inherent risk of spontaneous decision making. In addition, the advantages of following procedural information contained in operational documentation and aeronautical publications, such as the Aeronautical Information Publication Australia, is evident.
Other Serious Incidents with VH-FVR
The very same aircraft, VH-FVR is also the subject of two other ATSB investigations:
- In the first, also at Moranbah, in July 2013 resulted in the aircraft’s right undercarriage leaving the runway surface. That report is also due in March 2015. UPDATE 31 March 2016: ATSB issue their final report: “Consistent with pilot-induced oscillations, the captain’s rudder and nose wheel steering inputs overcorrected heading deviations during the landing roll.”
- The second followed structural damage on a flight from Canberra to Sydney in February 2014 that was not initially identified (previously discussed by Aerossurance). UPDATE 15 June 2016: The ATSB issued their Interim Report which we discuss in detail: ATR 72 In-Flight Pitch Disconnect and Structural Failure UPDATE 24 May 2019: ATSB final report published. UPDATE 12 October: We look at the maintenance aspects ATR72 Missed Damage: Maintenance Lessons
It remains to be seen if ATSB comment on any systemic organisational issues that might arise from these three occurrences or if there are any lessons on the acquisition of airlines and their integration into larger groups.