Jetstar B788 near Osaka on Mar 29th 2019, both engines temporarily rolled back

Last Update: June 26, 2020 / 18:27:34 GMT/Zulu time

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Photo of Jetstar Airways VH-VKJ, Boeing 787-8 Dreamliner — Jetstar Airways VH-VKJ, Boeing 787-8 Dreamliner (Photo credit: airlines470 / Flickr / License: CC by-sa)

Incident Facts

Date of incident
Mar 29, 2019

Classification
Incident

Airline
Jetstar Airways

Flight number
JQ-15

Departure
Cairns, Australia

Destination
Osaka Kansai, Japan

Aircraft Registration
VH-VKJ

Aircraft Type
Boeing 787-8 Dreamliner

ICAO Type Designator
B788

A Jetstar Boeing 787-8, registration VH-VKJ performing flight JQ-15 from Cairns,QL (Australia) to Osaka Kansai (Japan) with 301 passengers and 11 crew, was descending towards Osaka when the leftt hand engine (GEnx) rolled back for a couple of seconds before recovering. Shortly afterwards the right hand engine rolled back for several tens of seconds and recovered, too. The aircraft continued for a safe landing on Kansai's runway 24R.

The aircraft is still on the ground in Osaka on Apr 4th 2019, about 148 hours after landing.

On Apr 2nd 2019 Japan's Ministry of Transport reported the occurrence was rated a serious incident and is going to be investigated. Both engines temporarily lost thrust about 90km/50nm south of Osaka. The JTSB have dispatched three investigators on site and opened an investigation (editorial note: however, the JTSB has not yet published such information on their website, standing Apr 2nd 2019).

According to ADS-B data the aircraft was descending through FL200 about 50nm south of Kansai Airport.

On Apr 4th 2019 Japan's TSB (JTSB) reported the aircraft was descending through 4900 meters (FL160) when the right hand engine's indications became unstable. Shortly afterwards the left engine's thrust decreased temporarily, the right hand engine's thrust decreased, too. The occurrence was rated a serious incident with the type "A situation similar to the continuous loss of thrust of multiple engines in flight" and is being investigated by the JTSB.

On Apr 4th 2019 Australia's TSB (ATSB) reported they have appointed an accredited representative to join the investigaion led by the JTSB. The ATSB described the occurrence: "At approximately 15,000 feet during descent into Kansai International Airport, Osaka, Japan, the flight crew received an engine thrust warning on the number 2 engine, which subsequently started to surge. The crew then received an engine fail indication on the number 1 engine, without any shift in parameters indicating any engine power loss. That warning was followed by an engine fail warning on the number 2 engine. The number 2 engine auto relight activated and the engine continued to surge during the descent."

On Apr 18th 2019 the US NTSB reported they have assigned an accredited representative representing the state of manufacture of aircraft and engines to join the investigation led by the JTSB. The NTSB described the sequence of events: "On March 29, 2019, a Boeing 787, powered by two General Electric GEnx 1B64P2 turbofan engines and operated by Jetstar Airways, experienced a dual engine event while descending to land at the Kansai International Airport (RJBB), Osaka, Japan. During descent, the No. 2 (right) engine indications were reported to be unstable. Subsequently, the No. 1 (left) engine was reported to have lower thrust than commanded followed by the No. 2 engine having lower than commanded thrust."

On Jun 26th 2020 Japan's TSB released their final report concluding the probable causes of the serious incident were:

In this serious incident, it is highly probable that, when the Aircraft was descending for landing, there occurred oscillation in rpm of each engine causing both engines to temporarily fall below idle at separate times because Residue primarily composed of magnesium salts accumulated in spools impeded movement of spools that involved in fuel metering of both engines.

As for the higher accumulation of Residue primarily composed magnesium salts in spools, it is somewhat likely that the fuel with a higher concentration ratio of biocide, which was loaded in the biocide treatment two days before the serious incident, did not mixed evenly with the remaining fuel in wing tanks, and was fed to the engines.

The JTSB described the sequence of events:

At 18:53 JST (unless otherwise noted, all times are indicated in JST in this report on a 24-hour clock), during the descent at an altitude of about 4,900 m (about 16,000 ft) to Kansai International Airport, the right engine instrument display became unstable with “ENG THRUST R” and “ENG CONTROL R” EICAS*2 messages appeared.

At 18:54, “ENG FUEL SPLIT VALVE R” EICAS message appeared.

At 18:57, “ENG FAIL L” EICAS message appeared and disappeared shortly thereafter at an altitude of about 3,600 m (about 12,000 ft). The PIC did not feel malfunction in the left engine parameters at this time. CPL recorded a value below idle lasting for eight seconds in the left engine.

At 18:58, “ENG FAIL R” EICAS message appeared and disappeared after
a while. The PIC disengaged the right auto throttle and set the right engine thrust lever to the idle position in accordance with check list because he confirmed unstable parameters of the right engine. The right engine parameters indicated unstable until landing. CPL recorded a value below idle lasting for 81 seconds in the right engine.

At 19:08, “ENG CONTROL L” EICAS message appeared.

At 19:19, the Aircraft landed at Kansai International Airport.

The JTSB reported the aircraft had received biocide treatment with Kathon FP1.5 in Auckland (New Zealand) on Mar 27th 2019. Tests of the biocide treatment cart as well as analysis following disassembly showed the cart functioned normally.

The JTSB wrote:

Magnesium salts contained in Kathon FP 1.5 are insoluble in fuel. Magnesium salt will dissolve into water if a water phase is present in the fuel. Magnesium salts can precipitate or accumulate in spools through the engine fuel system. It was confirmed that amount of precipitated Magnesium salts increased commensurate with the rise in biocide concentration ratio.

Investigation inside Fuel Tanks of Aircraft

Fuel remained in all tanks was drained after the serious incident, and multiple locations inside each tank were wiped out with cotton swabs for composition investigation, but there was no finding residue of microbial or biocide in all the tanks and sampled fuel.

The JTSB analysed:

(1) From statements of the PIC and the FO and the records of EAFR and CPL, it is highly probable that rpm of each engine, at separate times, temporarily fell below idle during the descent to Kansai International Airport.

(2) From the results of detailed investigation of engine fuel components, accumulation of Residue primarily composed of magnesium salts was observed in multiple locations (fuel filter, FMV spool, FSV spool, VBV spool and HPT ACC spool). It is probable that biocide treatment inside fuel tanks conducted two days before the serious incident was involved in the accumulation of Residue primarily composed of magnesium salts because the composition of the residue were similar to the Kathon FP1.5.

(3) It is highly probable that Residue primarily composed of magnesium salts accumulated in FMV spool and FSV spool, which meter engine combustion fuel, restricted movement of spools, caused inadequate fuel metering, thereby led to engine rpm oscillation that occurred from the first flight after conducting biocide treatment.

(4) It is highly probable from CPL record that engine rpm oscillations was caused by the condition that FMV spool and FSV spool had restricted freedom of movement when fuel pressure was low, and moved more freely when fuel pressure was high. Besides, it is highly probable that engine rpm temporarily fell below idle due to fuel flow that was significantly reduced by movement of FSV spool when engine rpm was reduced to near idle during the descent for landing. It is highly probable that EICAS messages of “ENG FAIL L” and “ENG FAIL R” appeared because the engines temporarily fell below idle.

(5) From the results of the interview with the CS who was in charge of biocide treatment work, it is probably that the CS calculated according to the AMM so that the recommended final concentration ratio in the tanks would be about 100 ppm, and additionally loaded the treated fuel as described in 2.7 (11). According to the AMM calculation formula, the concentration ratio of the additional biocide treated fuel is calculated to be about 250 ppm in the left tank and about 285 ppm in the right tank. However, there was no record of the calculation of the concentration ratio of the biocide and the dosage amount. It is desirable to keep these records because they are considered to be important for traceability of maintenance work.

(6)From the result of investigation on the inside of fuel tanks after the serious incident, it is somewhat likely that the fuel with higher concentration ration of biocide, which was supplied to the engines did not mix evenly inside the fuel tanks because no residue of microbial or biocide was found inside the fuel tanks and in the sampled fuel.

(7) As for the reason why the fuel did not mix evenly inside the fuel tanks, it is somewhat likely that it is affected by the fuel temperature and density of as well as inner structure of fuel tanks; however, it could not be determined how much the fuel was not mixed.

(8) From the biocide test result, it is probable that Magnesium salts contained in biocide did not dissolve in fuel, but dissolved in water contained in fuel and were accumulated in spools as crystals through the engine fuel system.

As resulting safety actions the use of Kathon FP1.5 was suspended by the operator, the engine manufacturer deleted the procedure for biocide treatment with Kathon FP1.5 from their maintenance manuals and issued a service bulletin announcing the suspension of the procedure, the FAA issued a special airworthiness information bulletin, EASA a safety information bulletin and Australia's CASA an airworthiness bulletin in March 2020, all of them recommending the suspension of Kathon FP1.5.