ANA B788 near Takamatsu on Jan 16th 2013, battery problem and burning smell on board (including JAL Boston, Ethiopian London and JAL Tokyo events)

Last Update: August 19, 2015 / 16:56:16 GMT/Zulu time

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Incident Facts

Date of incident
Jan 16, 2013

Classification
Incident

Aircraft Registration
JA804A

Aircraft Type
Boeing 787-8 Dreamliner

ICAO Type Designator
B788

On Aug 19th 2015 the AAIB released their final report into ET-AOP concluding:

The following causal factors were identified in the ground fire:

- A thermal runaway failure of the lithium manganese dioxide battery in the ELT resulted in the uncontrolled release of stored energy within the battery cells.

- The location and orientation of the ELT, and the compromised seal on the battery cover-plate, allowed the resulting hot gas, flames and battery decomposition products to impinge directly on the aircraft’s composite fuselage structure, providing sufficient thermal energy to initiate a fire in the rear fuselage crown.

- The resin in the composite material provided fuel for the fire, allowing a slow-burning fire to become established in the fuselage crown, which continued to propagate from the ELT location even after the energy from the battery thermal runaway was exhausted.

- The Navigation Radio System safety assessment conducted in support of the ELT certification did not identify any ELT battery failure modes which could represent a hazard to the aircraft and therefore these failure modes were not mitigated in the ELT design or the B787 ELT installation.

The following factors most likely contributed to the thermal runaway of the ELT battery:

- The trapped ELT battery wires created a short-circuit condition, providing a current path for an unplanned discharge of the ELT battery.

- The ELT battery may have exhibited an unbalanced discharge response, resulting in the early depletion of a single cell which experienced a voltage reversal, leading to a thermal runaway failure.

- The Positive Temperature Coefficient protective device in the battery did not provide the level of external short-circuit protection intended in the design.

- There was no evidence that the reset behaviour and the implications of the variable switching point of the PTC, had been fully taken into account during the design of the ELT battery.

- The absence of cell segregation features in the battery or ELT design meant the single-cell thermal runaway failure was able to propagate rapidly to the remaining cells.

The AAIB analysed: "Examination of the ELT identified that a high-energy thermal event had occurred within its battery, consistent with a cascading thermal runaway. The trapped wires indicated the likelihood of an external short-circuit having contributed to the battery failure. The nature and intensity of the battery failure resulted in the cell electrode windings being destroyed or completely consumed. Therefore there was little evidence available which could provide an indication of the pre‑incident cell condition and it was not possible to determine whether any other failure mechanism may have contributed to the thermal runaway."

And continued: "Examination of the ELT confirmed that the battery wires were crossed and trapped between the battery cover-plate and the ELT case. Forensic analysis confirmed that there was evidence of metal-to-metal contact between the conductor of the positive wire and the underside of the battery cover-plate. ... Direct contact between the positive conductor and the cover-plate could have provided a path for current to flow through the battery circuit and ELT case, creating a short-circuit condition."

The AAIB analysed: "Sufficient slack existed in the ELT wires to allow them to become trapped under the cover-plate. The investigation concluded that the wires were probably trapped during ELT production, or when the battery was last accessed, and this condition remained undetected until the incident."

The AAIB summarized analysis: "Neither the cell-level nor battery-level safety features were able to prevent this single-cell failure, which then propagated to adjacent cells, resulting in a cascading thermal runaway, rupture of the cells and consequent release of smoke, fire and flammable electrolyte."
Incident Facts

Date of incident
Jan 16, 2013

Classification
Incident

Aircraft Registration
JA804A

Aircraft Type
Boeing 787-8 Dreamliner

ICAO Type Designator
B788

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