Danu AT42 near Billund on Mar 17th 2016, right engine fire alert, left engine compressor stall on approach

Last Update: February 28, 2019 / 17:46:11 GMT/Zulu time

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Incident Facts

Date of incident
Mar 17, 2016

Classification
Incident

Flight number
DX-26

Destination
Billund, Denmark

Aircraft Registration
LY-DAT

Aircraft Type
ATR ATR-42

ICAO Type Designator
AT42

A Danu Oro Transportas Avions de Transport Regional ATR-42-500 on behalf of DAT Danish Air Transport, registration LY-DAT performing flight DX-26 from Esbjerg to Billund (Denmark) with 7 passengers and 6 crew, was enroute when the crew received a fire indication for the right hand engine (PW127) and shut the engine down. The aircraft continued to Billund and was on final approach to Billund descending through 1000 feet AGL when the left hand engine emitted a loud bang and a large streak of flames. The crew kept the left hand engine running and continued for a safe landing in Billund.

A passenger reported one of the pilots after landing commented in passing that this became a close encounter.

The airline reported that the left hand engine was not on fire and was working at all times, it suffered what is being called a compressor stall. The experienced crew, following the problem of the left hand engine, even attempted to restart the right hand engine. There were 7 passengers and 6 crew on board.

Denmark's HCL have opened an investigation into the occurrence.

On May 9th 2016 the HCL reported in a preliminary report that the aircraft was refueled at Esbjerg and departed Esbjerg's runway 26 and was climbing through 1000 feet MSL when the right hand engine flamed out prompting the crew to perform the memory items of the "engine flameout at takeoff" checklist. The aircraft was subsequently stabilized at 3000 feet MSL, the crew suspected no engine damage and attempted an engine restart in flight, the engine interturbine temperature increased however the engine did not restart. The crew performed the "single engine operation" checklist and other related checklists, then informed Esbjerg AFIS that they had an engine flame out but were continuing to Billund with only the left hand engine operating. The crew captured the localizer of Billund's runway 27, tower informed the crew that the preceding crew had reported getting visual contact with the runway at 200 feet AGL (ILS Cat 1). On short final the commander (who had just been checked out as commander the previous sector on the flight into Esbjerg and thus was acting as commander for the first sector and assuming role as pilot monitoring) noticed that the first officer (pilot flying) had removed the hand from the power levers and was holding the yoke with both hands, noticed that the left hand engine torque had dropped to zero and the autopilot had disconnected, and moved the left power lever forward, at the same time flight and cabin crew heard loud bangs from the left hand engine. Cabin crew reported seeing flames from the rear bottom of the left hand engine. Shortly after the aircraft touched down on runway 27 and vacated the runway via taxiway C and stopped the aircraft on taxiway C due to the fire report by cabin crew, pulled the fire handles and discharged all fire bottles into both engines. No further fire was reported from cabin crew, the passengers were rapidly disembarked through the rear left door. Emergency services also found no fire.

The HCL reported that preliminary investigtion did not detect any trace of fire. A visual inspection of the left hand engine did not reveal any findings, a borescopic inspection found incrustations, deposit and sod on the internal parts of the engine, no internal mechanical faults were found. Both visual and borescopic inspections of the right hand engine did not find any anomaly, the fuel pump and gear box drive train to the high pressure turbine were inspected without findings.

The HCL reported that the right hand fuel tank was found empty. Despite being empty the right hand fuel quantity indicator indicated 510kg of fuel present, the right fuel tank low quantity light did not illuminate despite the quantity dropping below 160kg.

New fuel quantity indicators and low level indicators were installed, but showed the same results, the original indicators were re-installed. A subsequent test of the right hand fuel probe showed the probe was significantly out of tolerances. When the brown wire at the right hand tank probe was manipulated the probe's value changed, the heat shrinkable tubing of the brown wire was removed, during further manipulation the probe's values returned to normal values and could not be deflected anymore regarding of what manipulation was attempted.

The HCL released following preliminary analysis:

The right engine flameout was caused by fuel starvation.

The preliminary AIB investigation revealed that the fuel quantity indication failure was related to the right tank probe No 3 and / or the associated wiring.

The Danish AIB continues the operational and technical safety investigation.

On Feb 28th 2019 the HCL released their final report basically confirming the preliminary analysis by concluding the probable causes of the serious incident were:

Shortly after take off from Esbjerg (EKEB), the right engine flamed out due to fuel starvation.

Despite the fuel quantity indication system indicated more than 500 kg of fuel in the right tank, the right fuel tank was later found to be empty.

During the single engine approach, the left engine suddenly suffered from compressor stall, and flames were seen from the exhaust. The flight crew interpreted the flames as being an engine fire.

Upon landing, the aircraft vacated the runway, the left engine was shut down, and the crew evacuated the aircraft.

The safety investigation found that the fault in the fuel quantity indication system originated from the right tank probe no. 3.

Few months prior to the serious incident, maintenance personnel removed and reinstalled the fuel tank probes. The AIB finds it probable that the fault on probe no. 3 was introduced during this process.

The left engine suffered from high deterioration and damages to the hot section. This made the engine subjectable to compressor stall.

The AIB safety investigation resulted in revisions of maintenance and operator procedures.

The HCL analysed:

Right engine flame out after departure

Shortly after take off from runway 26 at EKEB, the right engine suffered a flame out due to fuel starvation caused by an empty right fuel tank.

The empty right fuel tank was caused by a malfunction in the right part of the fuel quantity indication system.

The malfunction resulted in an incorrectly indicated fuel quantity, which was higher than the actual physical fuel quantity in the right fuel tank. The malfunction was traced to a faulty connector on the right tank probe no. 3.

It is probable that the connector fault was introduced during the heavy maintenance check between 14-12-2015 and 09-02-2016, when the system was last disturbed during performance of AD 2014-0075.

The technical log pages and the MPC reports showed no evidence of problems prior to the heavy maintenance check.

No malfunction in the fuel quantity indication system was revealed during the maintenance check.

At the time of the maintenance check, the test required by the JIC after removal and installation of fuel quantity probes, did not clearly stipulate a requirement for maintenance crew to verify that the uplifted physical fuel quantity corresponded to the indicated fuel quantity.
During operation of the aircraft, the faulty fuel quantity indication remained unrevealed.

The fuel management performed by the flight crews showed significant variations in the fuel calculations.

At the time of the serious incident, the operator did not have procedures on how to manage fuel calculations.

At the time of the serious incident, the operator did not have fuel quantity inaccuracy limitations requiring manual checks of fuel quantity.

Had such procedure been in place, the fuel numbers from the technical log pages would have required a manual check of the fuel quantity by use of magnetic fuel quantity indicators. This would most likely have revealed the faulty FQI system.

Two occasions of fuel caution on CAP were reported in the technical log. The MPC reports indicated that the cautions appeared on other flights as well.

On 14-03-2016, when the fault was first reported in the technical log, the engine fuel filters were replaced.

When reported on the second time on 16-03-2016, the right electrical fuel pump was deemed unserviceable, and the aircraft was MEL released for further flights.

At the time of the serious incident, the TSM did not describe a procedure for illumination of the FUEL light on CAP without associated local alert.
The TSM only described a troubleshooting procedure for FUEL light on CAP with associated low level light on the FQI.

Incorporation of SB ATR-42-28-0033 at the time of the serious incident would have allowed to easier identify the fault in the fuel indication system, by illuminating the low level light on the fuel quantity indicator in relation to the fuel cautions.

Left engine compressor stall during approach

During the single engine approach to EKBI, the left engine suffered three unprovoked compressor stall events. The compressor stall events resulted in flames from the exhaust, which the crew interpreted as being an engine fire.

The compressor stall would only occur when the left engine was running in bleed air off configuration.

The “Engine flame out at take off” and “Single engine operation” checklists required bleed air to be selected off on the engine in operation. Following the right engine flame out, the flight crew performed these checklist items.

The left engine had suffered compressor stall on a previous occasion.
The maintenance records showed that a compressor stall defect had been raised and corrected during the heavy maintenance check. The defect had been rectified by replacement of the IBV and metering plug orifice, and the left engine had been successfully tested on ground.

Even though the compressor stall problem may no longer have been present at the heavy maintenance check, the deterioration of the engine hot section and the NH and NL rotor speed ratio would still make the engine subjectable to compressor stall.

The problem with the ratio between engine NH and NL rotors was only discovered when the engine manufacturer analyzed the performance run data following the serious incident. The ECTM data confirmed the problem.
Contacting the engine manufacturer was part of the fault isolation procedure described in the engine maintenance manual for compressor stall troubleshooting. In case the fault was not rectified, this would be a last step.

Since the left engine was successfully tested after replacement of the IBV, the engine manufacturer was not contacted during the heavy maintenance check.

Flight operation

The safety investigation of the serious incident revealed operational deficiencies.

The management of fuel calculations in the technical logbook was less than adequate.

Operator procedures were not in place to ensure that fuel calculations could determine flaws in the fuel quantity indication system, and ensure that sufficient fuel would be on board the aircraft to complete the flights.

Following the right engine flame out, the flight crew decided not to declare an emergency (mayday) to ATC. This was despite the “Eng flame out at take off” being an emergency checklist, and the suggestion to declare an emergency from the line check pilot.

An emergency declaration to ATC could have allowed prioritized airspace, a dedicated radio channel and rescue services on standby. This would have reduced the disturbances and the flight crew workload, which remained high and stressful during the flight.

When the flight crew performed “Eng flame out at take off” checklist, only the boxed (memory) items were performed. See appendix 7. The flight crew did not consider restarting the engine at this stage.

This resulted in the “Single engine operation” checklist being performed prior to the “Eng restart in flight”, and then again following the unsuccessful attempted engine restart. This increased the flight crew workload unnecessarily.

10 minutes after the flame out the flight crew attempted to restart the right engine. This was prompted by a discussion over the cause of the engine failure, and not as a checklist item.

The restart attempt was performed in accordance with the “Eng restart in flight” checklist. The restart attempt was unsuccessful due to the empty fuel tank.

When the left engine compressor stalled during final approach, the first officer removed his left hand from the power levers and disconnected the autopilot without any callout.

The commander took control of the power levers without any callout.

The flight crew did not know that engine compressor stall was the reason for the loud bangs and the flames reported by the cabin crew and witnessed by themselves.

The uncertainty led the flight crew upon landing to discharge both engine fire extinguisher bottles.

This was in accordance with the “on ground emer evacuation” checklist, and was a fair decision given the circumstances.

The flight crew workload was extraordinary high on short final to runway 27 at EKBI because of:

- Poor weather.
- Single engine operation.
- Engine compressor stalls and loss of engine power.
- Flames from the exhaust.

The extraordinary high flight crew workload most likely caused a lack of flight crew call outs and deviation from standard operating procedures for power lever controls.
Incident Facts

Date of incident
Mar 17, 2016

Classification
Incident

Flight number
DX-26

Destination
Billund, Denmark

Aircraft Registration
LY-DAT

Aircraft Type
ATR ATR-42

ICAO Type Designator
AT42

This article is published under license from Avherald.com. © of text by Avherald.com.
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