Etihad B773 near Adelaide on Oct 14th 2017, cargo smoke indication

Last Update: August 22, 2018 / 14:05:57 GMT/Zulu time

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Incident Facts

Date of incident
Oct 14, 2017

Classification
Incident

Flight number
EY-450

Aircraft Registration
A6-ETR

Aircraft Type
Boeing 777-300

ICAO Type Designator
B773

An Etihad Boeing 777-300, registration A6-ETR performing flight EY-450 (dep Oct 13th) from Abu Dhabi (United Arab Emirates) to Sydney,NS (Australia) with 349 people on board, was enroute at FL370 about 290nm northnorthwest of Adelaide,SA (Australia) when the crew received a cargo smoke indication and diverted the aircraft to Adelaide. Cabin crew were just serving breakfast when they terminated the service and rapidly prepared the cabin for landing. The aircraft landed on Adelaide's runway 23 about 50 minutes later. The aircraft vacated the runway and stopped on a taxiway, where passengers disembarked via stairs.

The passengers were rebooked onto other domestic flights from Adelaide to Sydney.

The occurrence aircraft is still on the ground in Adelaide about 25 hours after landing.

The airline reported a recirculation fan in the cargo hold caused the smoke indication.

On Aug 22nd 2018 the ATSB released their final report concluding the probable causes of the serious incident were:

- During cruise, a burning smell was detected in the flight deck and the forward cargo compartment fire warning activated. The flight crew armed and set the forward cargo fire suppression system and diverted the aircraft to the nearest airport for a safe landing.

- A wiring loom situated above the forward cargo compartment about body station 508 was incorrectly routed, likely during manufacture of the aircraft. Over several years, wires in that loom chafed against the support structure and short circuited. Electrical arcing created smoke that activated the forward cargo smoke detector.

The ATSB summarized the sequence of events:

On 14 October 2017, a Boeing 777-300 aircraft, registered A6-ETR and operated by Etihad Airways, was on a scheduled passenger service from Abu Dhabi, United Arab Emirates (UAE) to Sydney, New South Wales. An augmented flight crew, consisting of two pilots in each crew (crew A and crew B) conducted the flight.

At about 0407 Central Daylight-saving Time, while in the cruise and with flight crew B flying the aircraft, the flight crew noticed a burning smell coming from an air vent. In an attempt to establish the source of the smell, they requested that cabin crewmembers check the forward galley. The cabin crew confirmed that the forward galley was clear of any burning smells or smoke. The flight crew then requested two other cabin crewmembers enter the flight deck, who confirmed the burning smell. Around this time, the aural fire bell activated, a master warning light illuminated and a warning message ‘FIRE CARGO FWD’ was displayed on the engine-indicating and crew-alerting system.

In response, the flight crew actioned the non-normal checklist, which included arming the forward cargo fire switches located in the flight compartment overhead panel. This action resulted in numerous mechanical and electrical actions, including de-energising the recirculation fan3 and closing the air vents in the forward cargo compartment. The flight crew then selected the cargo fire discharge switch, which discharged the two fire extinguisher bottles located in the forward cargo compartment.4 The flight crew declared a MAYDAY5 to air traffic control and advised of their intention to divert to Adelaide Airport, South Australia, as it was the nearest suitable airport for the aircraft type.

Flight crew A had just completed their scheduled rest period and entered the flight deck where they were briefed by flight crew B of the situation. Flight crew A assumed control of the aircraft as they were the designated crew for landing. Flight crew B remained on the flight deck to provide assistance. A rapid descent to flight level (FL)6 125 was conducted and the aircraft was diverted to Adelaide.

During the remainder of the flight, the cabin crew, operator and passengers were informed of the situation a
nd the diversion. The flight crew also advised air traffic control that, if smoke or fire from the forward cargo compartment was confirmed by emergency services upon landing, they would evacuate the aircraft on the runway.

At 0455, the aircraft landed uneventfully. The emergency services advised the flight crew that they did not observe any smoke or fire emanating from the aircraft. The aircraft was taxied from the runway to taxiway ‘F6’, where the emergency services inspected the aircraft externally with a thermal imaging camera. They confirmed that there were no identified hot spots indicating an on-going fire in the forward cargo compartment. Based on this information, as a precaution, the crew decided to conduct a rapid deplane of the passengers through passenger door 5L using mobile boarding stairs. All passengers and crew disembarked in a controlled manner and were transported to the passenger terminal. Nil injuries were reported during the disembarkation.

Initial engineering inspection

Once the forward cargo compartment was emptied of cargo, maintenance engineers inspected the cargo hold for evidence of fire. A small quantity of soot was identified in the cargo ceiling area, between the fiberglass ceiling panel and fiberglass joint sealing tape about aircraft body station.

The ATSB described the engineering inspection:

A detailed inspection between the forward cargo ceiling and passenger floor was conducted at the operator’s maintenance facility in the UAE. Wire bundle W5279, located at about BS 508 was found to have been incorrectly routed. Consequently, the wires had come into contact with screws and nutplates used to close out the cargo-ceiling panel to the ceiling standoff clips.

Over a prolonged period of time, the 115V recirculation fan wire located within that bundle chafed through the insulation coating, allowing the wire to short circuit. The electrical wiring and fourteen of the cargo ceiling panel standoff clips manufactured from PEEK were heat damaged. Sections of the carbon fibre beam web and beam flange at BS 508 between the left buttock7 lines 40 to 60 were also found to be heat damaged and delaminated between 6 and 7 percent in three locations where the current tracked.

Boeing determined that the wiring loom W5279 was likely to have been incorrectly positioned during the aircraft build in 2013. Boeing reported that this was the fifth reported incident involving wire chafing and arcing in the cargo area of a Boeing 777 aircraft. However, this was the first event that triggered the cargo fire warning system and that had been detected in flight. In all of these cases, the wiring loom had been installed incorrectly during manufacture, allowing screws to chafe wires and short circuit.

The ATSB analysed:

The flight crew identified a burning smell in the flight deck and completed the appropriate actions to manage the situation. By arming the forward cargo fire suppression system, electrical power was removed from the recirculation fans, which prevented further arcing and damage to the structural carbon fibre beam, support brackets and wiring. Even though there was a significant amount of soot and electrical arcing, de-energising the electrical circuit manually before sufficient current went to ground negated the electrical load control unit from tripping. It was likely that, once the electrical current was deactivated by arming the forward cargo fire switches, the smoke had also stopped. Discharging the fire bottles in the forward cargo space, even though procedurally correct, had nil effect on this occasion as the source of the electrical arcing was in the sealed zone between the cargo ceiling panel and the passenger floor compartment, not in in the cargo compartment.

A post-incident inspection of the aircraft found an electrical wiring harness (W5279) was in an incorrect location. Consequently, one of the forward cargo ceiling liner retainer screws chafed on the wires, which resulted in the electrical current from the chafed wire dispersing through the passenger floor carbon fibre beam about body station 508. That electrical current generated significant heat where 14 of the cargo ceiling polyetheretherketone resin standoff brackets were heat damaged and several areas of the structural carbon fibre beam were chafed and delaminated. The smoke generated from the arcing was of a magnitude that it migrated through the forward cargo ceiling liner into the forward cargo compartment and activated the forward cargo fire detection system.

This incident was the fifth reported case where damage to the wire bundles in the forward (and aft) cargo compartment of a Boeing 777 aircraft has occurred from chafing on a ceiling liner screw and/or nutplate. This was the first event that triggered the cargo fire warning and the only event to have been detected in air. A subsequent investigation conducted by Boeing found that the wire bundle W5279 had been incorrectly routed, likely during aircraft manufacture, and had not been installed as per the design drawings. Slight variations of the wire bundle position allowed it to run directly above the screw and nutplate, which chafed the wire bundle over time.
Incident Facts

Date of incident
Oct 14, 2017

Classification
Incident

Flight number
EY-450

Aircraft Registration
A6-ETR

Aircraft Type
Boeing 777-300

ICAO Type Designator
B773

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