Asiana Airlines Flight 991

Asiana Airlines Flight 991 was a cargo flight operated by Asiana Airlines. On 28 July 2011, the Boeing 747-400F flying from Seoul, South Korea, to Shanghai, China, crashed into the sea off Jeju Island after suffering a in-flight cargo fire. Both pilots, the only two people on board, were killed. The accident marked the second loss of a 747 freighter due to a cargo hold fire in less than a year, following the crash of UPS Airlines Flight 6 in Dubai in September 2010.

Accident
Flight 991 was crewed by two pilots: Captain Choi Sang-gi, 52, with 14,100 logged flight hours (including 6,800 on the Boeing 747) and First Officer Lee Jeong-woong, 43, with 5,200 logged flight hours (including 492 on the Boeing 747). The aircraft took off from Incheon International Airport at 03:04 local time on 28 July bound for Shanghai Pudong International Airport.

The aircraft was loaded with 58 tonnes of cargo, the majority of which consisted of semiconductors, mobile phones, liquid crystal displays, and light-emitting diodes. The remaining 400 kg of cargo consisted of lithium batteries, paint and photoresist fluid.

At 03:54, while cruising at 34,000 ft, the crew contacted air traffic control (ATC) reporting a fire on board, requesting an immediate descent and diversion to Jeju Airport, South Korea, for an emergency landing.

The aircraft was observed on radar descending towards 8000 ft at 04:01 and then erratically climbing and descending for the following nine minutes, reaching an altitude of almost 15,000 ft. In their last communications to ATC, the crew reported heavy vibrations and loss of flight controls. After a steep descent to 4,000 ft, radio contact was lost at 04:11, when the aircraft was 130 km west of Jeju Island.

Aircraft
The aircraft involved was a Boeing 747-48EF registered as HL7604, the 1370th 747 built. It first flew on 15 February 2006, and was delivered to Asiana Airlines a week later. At the time of the accident, the aircraft had flown more than 26,300 flight hours and 4799 takeoff/landing cycles. It was equipped with four General Electric CF6-80C2B1F engines and its maintenance history did not reveal anything significant during the accident investigation.

Search
Search-and-rescue operations conducted by the Republic of Korea Coast Guard recovered parts of the aircraft within a day of the crash. The search effort involved a total of 10 ships from the Coast Guard, the Navy, and the Korea Hydrographic and Oceanographic Administration, as well as three helicopters. The South Korean government also requested the assistance of Singapore and the U.S. Navy.

On 17 August, the search team identified the location of 39 parts of the aircraft lying on the sea floor at a depth of around 80 m (250 ft). Among them was the tail section, which was expected to contain the flight data recorder (FDR) and cockpit voice recorder (CVR), but both boxes had broken off their mounting brackets. The bodies of the two crewmembers were recovered on 29 October.

The FDR was finally found in May, but the memory module detached from the FDR chassis, potentially by heavy sea waves, so nothing useful could be used. The CVR was never found.

Investigation
The South Korean Aviation and Railway Accident Investigation Board (ARAIB) conducted the investigation, but due to the loss of both flight recorders, it could not fully determine the causes of the fire nor the exact sequence of events prior to the impact with the sea. From the distribution of fire and heat damage on the recovered debris, a fire was found to have started in or near one of the ULD pallets containing dangerous goods in the rear fuselage, but not enough evidence was found to determine exactly what caused the fire.

The fire was not contained and quickly propagated forward to the rest of the fuselage. Fire damage and soot were found in the air conditioning ducts that run along the fuselage and on ceiling panels near the cockpit area. The cockpit smoke evacuation vent displayed traces of soot, indicating that smoke had entered the cockpit. Some electronic components that were part of the cargo were found embedded in the wing's upper surface, together with traces of paint and photoresist, suggesting that at some point, the flammable liquids transported in one of the pallets ignited, causing an explosion that blew out portions of the fuselage in midair.

It was estimated that only 18 minutes had elapsed from the moment the fire was first detected to the final impact with the sea. The crew likely would not have been able to extinguish the fire or safely land the plane within that time frame.

Aftermath
According to Asiana, the crash of Flight 991 led to damages to the airline of about US$190 million (200.4 billion won). In 2012, the International Civil Aviation Organization considered applying new safety standards to air carriage of lithium batteries as a result of this and the preceding crash of UPS Airlines Flight 6.