Virgin Australia AT72 at Canberra on Dec 13th 2018, both engines rolled back temporarily one after the other

Last Update: May 5, 2020 / 13:20:20 GMT/Zulu time

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Incident Facts

Date of incident
Dec 13, 2018

Classification
Incident

Airline
Virgin Australia

Flight number
VA-660

Departure
Sydney, Australia

Destination
Canberra, Australia

Aircraft Registration
VH-FVN

Aircraft Type
ATR ATR-72-200

ICAO Type Designator
AT72

A Virgin Australia Avions de Transport Regional ATR-72-212A, registration VH-FVN performing flight VA-660 from Sydney,NS to Canberra,AC (Australia), was descending through 11,000 feet towards Canberra when the right hand engine (PW127) rolled back and flamed out. The engine automatically restarted about 5 seconds later. The crew continued the descent, descending through 10,000 feet now the left hand engine rolled back and flamed out, also automatically re-lighting. The crew selected manual ignition for the remainder of the flight and landed safely in Canberra.

Australia's TSB (ATSB) rated the occurrence a serious incident and opened an investigation. The flight data recorders have been downloaded.

The occurrence aircraft returned to service about 84 hours after landing Canberra.

On May 5th 2020 the ATSB released their final report concluding the probable causes of the serious incident were:

Contributing factors

- The two engine flameouts were probably the result of the environmental conditions (likely icing and/or heavy/moderate rain) during the flight.

Other factors that increased risk

- The crew selected manual ignition as a preventative measure against further flameout. While ATR recommend that manual ignition should not be selected unless directed by checklist or under minimum equipment list, this was not specifically mentioned in the ATR documentation.

Other key finding

- The aircraft automatic ignition system performed as designed by automatically relighting both engines without pilot input following flameout.

The captain (ATPL, 6,660 hours total, 2,225 hours on type, 204 hours in command) was pilot monitoring, the first officer (6,700 hours total, more than 3000 hours on type) was pilot flying.

The crew was aware of deteriorating weather conditions in Canberra prior to departure and thus had loaded fuel sufficient for an hour hold at Canberra, return to Sydney and hold again one hour at Sydney.

On approach to Canberra, as expected, weather deteriorated, the crew entered a hold to wait for better weather.

The ATSB described the sequence of events that followed:

Shortly after, ATC advised that an approach was now viable (a previous aircraft had landed) but the crew continued to POLLI and assessed the weather for themselves.

The crew elected to hold at POLLI and held there until about 1849 when ATC vectored them to the north to commence the STAR. At 1853, the aircraft was cleared by ATC to resume its own navigation direct to waypoint HUNNI, descend to 9,000 ft to commence the STAR.

At about 1854, shortly after descent had commenced, the aircraft passed FL110 with both power levers close to flight idle when No.2 engine lost power and flamed out. The master warning and ENG 2 OUT annunciators displayed, and No.2 engine torque reduced to zero. In the time it took the crew to acknowledge the warning and confirm what it was, No.2 engine self-recovered, torque returned to normal and the warnings ceased. The crew discussed that they likely encountered icing, confirmed engine power had returned to normal and confirmed that anti-icing and de-icing systems were on. Due to the automatic recovery, the crew were not required to action any checklist or procedures associated with an engine flameout in flight.

At about 1855, both power levers were at flight idle when No.1 engine lost power and flamed out. The master warning and ENG 1 OUT annunciators displayed, and No.1 engine torque reduced to zero. In the same way that No.2 engine had recovered, No.1 engine self-recovered by the time the crew had acknowledged and confirmed the flameout. Again, no checklist or associated procedures were required to be actioned.

The captain immediately identified the de-ice mode selector switch in order to ensure the de-ice cycle was in ‘fast’; however, the captain inadvertently selected the slow cycle. The captain then selected ignition to ‘manual’, in order to provide continuous ignition in an attempt to prevent any further flameouts.

Satisfied that power in both engines had been restored to normal, the crew discussed the situation, but were unable to determine the cause of the flameouts. They confirmed manual ignition ON, icing protection ON and observed that the temperature was 12 degrees, prompting further discussion on the use of icing protection. The crew decided that they would not turn any of the icing protection systems off at that stage and would fly at icing speeds2 if they needed to keep the icing protection on for landing.

The crew stated that the aircraft was in heavy rain at the time of the flameouts but they did not notice any significant icing at the time. Figure 1 depicts the rainfall recorded by radar at about the time of the first flameout.

The crew continued the approach, and at about 1901, the crew confirmed the aircraft was no longer in icing conditions and selected the de-icing OFF but left the anti-icing systems ON.

No further flameouts occurred and the aircraft landed at 1906.

The ATSB wrote, that a post flight inspection did not reveal any mechanical fault or failure and any indication that further detailed inspections were required.

The ATSB analysed:

The ATSB considered internal causes such as a mechanical fault or failure. The engines were running smoothly and producing the required power as commanded with no signs of the impending flameout. Post occurrence maintenance was in conjunction with ATR and PWC guidance and did not identify any mechanical fault or failure. There was no evidence to suggest that a mechanical fault or failure contributed to the flameout.

Of possible external causes, fuel management and fuel quality were not considered contributory to the flameouts. However, evidence indicates that the aircraft encountered significant weather during the flight, including rain, icing and turbulence. Despite this, the ATSB considered that the flight crew managed the weather conditions appropriately and there was no evidence to suggest that the flight should have been cancelled due to those conditions.

The flight crew operating manual (FCOM) listed heavy turbulence as a possible cause of flameout. The crew described the turbulence as moderate and the recorded G load of +1.76 is consistent with crew description of the turbulence. The ATSB did not consider turbulence as contributory to the flameouts.

Icing was also included in the FCOM as a possible cause of flameout. There was no evidence of damage to engine inlets (suggesting no ingestion of large ice accretions) and the crew did not note any significant ice accretion during the flight. Engine de-ice had been on for at least 40 minutes prior to the flameouts which indicates that significant ice accretions would have been very unlikely. The aircraft exited icing conditions approximately 1 minute prior to first flameout (TAT had risen above 7 °C) suggesting that the conditions were suitable for dislodging any ice accretion or that they were not suitable for ice to form. There was insufficient evidence to determine if icing did or did not contribute to the flameouts.

The crew recalled that the aircraft was in heavy rain and Bureau of Metrology (BOM) radar imagery indicates moderate rain at the time. Although the engines passed certification requirements for water ingestion, numerous flameout occurrences have previously been associated with moderate or heavy rain conditions. Testing takes place in a controlled environment but does not account for engine installation and other variables of actual flight conditions. There was insufficient evidence to determine if rain did or did not contribute to the flameouts.

In the absence of evidence to the contrary, it is likely the flameouts were the result of the environmental conditions during the flight. Although the exact environmental influence could not be confirmed, it is likely this was either ice or rain, or some combination of the two.

The automatic ignition function performed as designed, recognising the drop in NH below specified criteria and automatically engaging the ignition system to relight the engines without pilot input.

The known flameout events on ATR aircraft all involved icing or moderate/heavy rain. The auto ignition system has been proven effective and reliable in providing flameout recovery and in all 21 events, as the engines successfully relit without pilot input.

In the absence of specific guidance against the use of manual ignition, the crew selected manual ignition, which operates continuously at one spark per second after the initial 25 seconds. Given the uncommon situation of two engine flameouts, the crew considered that manual ignition was a safety measure to prevent any further flameouts in that a continuous source of ignition may prevent the flame from being extinguished. This is in contrast to automatic ignition, which in the event of a further flameout, would have initially operated at a higher spark rate.
ATR advice to Virgin and other ATR operators is that in the case of a temporary power loss with automatic relight, there is nothing else to do, the system has worked as designed and restored engine power. ATR advice is that selection of manual ignition potentially lowers the flameout protection of the engine and that manual ignition should only be used when directed by a checklist. However, ATR documentation does not contain this guidance.