REX SF34 near Merimbula on Aug 29th 2019, engine fire indication

Last Update: August 13, 2020 / 15:02:55 GMT/Zulu time

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Photo of REX Regional Express VH-RXX, SAAB 340 — REX Regional Express VH-RXX, SAAB 340 (Photo credit: Simon_sees / Flickr / License: CC by)

Incident Facts

Date of incident
Aug 29, 2019

Classification
Incident

Cause
Engine fire indication

Airline
REX Regional Express

Flight number
ZL-139

Departure
Moruya, Australia

Destination
Merimbula, Australia

Aircraft Registration
VH-RXX

Aircraft Type
SAAB 340

ICAO Type Designator
SF34

A REX Regional Express Saab 340B, registration VH-RXX performing flight ZL-139 from Moruya,NS to Merimbula,NS (Australia) with 19 passengers and 3 crew, was enroute at 9000 feet about 20nm northnortheast of Merimbula (editorial note: distance Moruya to Merimbula about 60nm) at about 20:11L (10:11Z) when the crew received indication of a right hand engine (CT7) fire, shut the engine down, discharged the fire extinguisher and stopped the indication. While emergency services at Merimbula scrambled to assist the aircraft, the aircraft entered a hold and landed safely in Merimbula about 30 minutes later.

There are indeed Australian media claiming, the aircraft entered the hold to dump fuel.

Merimbula emergency services (Fire and Rescue NSW Station 286 Eden FRNSW) reported: "FRNSW EDEN was called to Merimbula airport tonight at 20:17 hours, Rex plane had a emergency landing at Merimbula airport on Thursday night. The emergency response plan for airport emergences was activated and, once emergency agencies were in place at the airport, the aircraft made it successful landing with one engine shut down. Emergency services were told prior to the plane landing, plane had an engine fire which had been extinguished by the pilots. The plane landed safely and landed as normal. None of the passengers or crew were injured, large contingency of emergency services attended the call, FRNSW three appliances, RFS three appliances, NSW police and NSW Ambulance service where at Merimbula airport."

The airline reported the crew received a cockpit indication concerning the right hand engine. On Aug 30th 2019 the airline added that maintenance have not identified any evidence of fire, the engine suffered a mechanical malfunction, sparks may have prompted the impression of a fire to the passengers.

On Aug 30th 2019 Australia's Civil Aviation Safety Agency (CASA) reported the right hand engine suffered a mechanical failure which triggered an engine fire warning. There had been excess heat in the engine causing it to glow red. The engine is currently being stripped down, the cause of the engine failure has not been pinpointed so far.

On Sep 2nd 2019 the ATSB reported the occurrence was rated an incident, a short investigation was opened. The crew received a right hand engine fire warning and shut the engine procedurally down.

On Aug 13th 2020 the ATSB released their final report concluding the probable causes of the incident were:

- Excessive coking in the B-sump oil cavity resulted in oil leaking from the B-sump. This ultimately initiated an internal engine fire and subsequent fracture of the PT shaft and separation of the C-Sump assembly.

- The excessive coking was most likely due to the component not being completely clean when installed at the last major workscope and/or accelerated coking on the component.

The ATSB summarized the sequence of events:

Approximately 8 minutes into the flight, and shortly after levelling off at an altitude of 9,000 ft, the flight crew received an engine fire indication from the right engine. In response, they commenced the memory items for the associated checklist. While conducting the first item on the checklist — reducing the power lever — they heard the engine surge and then produce a loud bang. The cabin crew member reported seeing a brief flash of light from the right side of the aircraft. The flight crew continued the Engine Fire checklist and subsequently shutdown the right engine.

Due to the close proximity to the destination, and with the aircraft already having been set up for the approach, the flight crew decided to continue to Merimbula Airport. A hold was established at a waypoint in order to allow the flight crew to complete all the required checklists, and to ensure the availability of emergency services at the destination.

At about 2040, the aircraft commenced the final approach to Merimbula. It landed without incident 7 minutes later.

A post-flight visual examination of the engine revealed that there were several small burn holes in the power turbine (PT) case and that the C-sump assembly and a section of the PT shaft were missing. The engine had previously undergone unscheduled maintenance for elevated oil consumption.

The ATSB analysed:

The engine failure involving Saab 340B VH-RXX, on 30 August 2019, was initiated by heavy coking in the B-Sump oil cavity, which resulted in oil leaking from the B-Sump and eventually causing an internal oil fire. This over-temperature condition weakened the PT stage 3 disk posts sufficiently to allow some turbine blades to be released, resulting in an imbalance and subsequent fracture of the PT shaft. The engine fire indication received by the flight crew was the result of hot gases being released through the burn holes in the PT case activating the fire-detection system.

The B-sump component had only completed 1,481 flight hours since it was installed on the engine in May 2018. This represented only about 10 per cent of the typical time between major workscopes. The high level of coking found in the B-sump could only have occurred in that timeframe if:

- the component was not completely clean on installation following the major workscope
- there was an accelerated formation of coking within the component
or a combination of both.

Despite the part being cleaned in accordance with the manufacturer’s recommendation, it was not possible to inspect the oil cavity of the B-sump visually to confirm complete removal of coking. In addition, if any coke deposits were remaining within the component, this could have affected the oil flow and cooling within the sump, and contributed to further coking.

The manufacturer advised that there was no evidence that the engine was operated outside their recommendations, and so it is unlikely that there were any operational factors that contributed to the accelerated formation of coking. The exact mechanism which resulted in the level of coking present in the B-sump could not be determined.

A CT7 engine failure or in-flight shutdown due to significant coking in the B-sump is a rare event, with only two known occurrences in the 38 million flight hours accumulated by the engine type.