( CNN ) -- With no wreckage or flight recorders from Flight 370 to guide them , investigators in Malaysia are poring over information about the backgrounds of the pilots and passengers , radar data , and the transmissions from the cockpit . They also need to pay close attention to another important clue : the cargo manifest . The list of what ends up in the cargo hold of a passenger airplane goes beyond checked luggage . Freight shippers use passenger carriers as well as cargo lines to deliver goods and raw materials . Knowing what was in the cargo hold -- or at least what the official list says was in it -- is important in any accident investigation . It was never more important than it was in the case of the 1996 crash of ValuJet Flight 592 . Opinion : Flight 's resting place is best clue . The ValuJet plane , a DC-9 , crashed into the Florida Everglades shortly after takeoff from Miami . Investigators found the pilots were unable to control the plane after a fire raced through the cargo hold , disabling some of the plane 's systems . The source of the fire was traced to a shipment of oxygen canisters that had been mistakenly labeled and improperly packed . The accident led to a push by the National Transportation Safety Board to put smoke detectors and fire-suppression systems in the cargo bays of all passenger aircraft . The Federal Aviation Administration responded and today , halon fire-suppression systems tucked into the cargo holds are an important safety feature on passenger planes . So far , so good . Since then , a new type of cargo has emerged : lithium batteries . There are two types of lithium batteries . One is the rechargeable batteries like those in your phone and laptop , also called lithium ion batteries . A second type , nonrechargeable batteries , also called lithium metal batteries , are used in everything from toys to medical devices . Lithium metal batteries deliver extremely high densities of energy , and if they are mishandled they can catch fire , a fire that ca n't be extinguished with halon , the most common kind of fire-suppression systems in passenger aircraft . That 's one reason the FAA banned shipments of nonrechargeable lithium metal batteries on passenger planes in 2004 . But that ban only applies in the United States ; international authorities are still considering whether to enact such a rule . Cargo and passenger aircraft are free to carry lithium ion batteries , although they are subject to labeling and packing regulations . So what was on board Flight 370 ? Malaysian officials , after saying the cargo manifest would `` be released in due course , '' later got a little more specific and said the Boeing 777 was carrying 440 pounds of lithium ion batteries . What else ? Nothing that would cause a problem , the Malaysians assure us . An Australian news media report said the Malaysian government refused to release the manifest to the Australian government , which would find such information helpful as it tries to map out a search . Let 's assume little more than luggage and lithium ion batteries were in the plane 's cargo hold . Although lithium ion fires are easier to suppress than lithium metal battery fires , both are susceptible to what 's called `` thermal runaway '' when ignited . That 's when one cell ignites the next cell , creating a fire that 's more difficult to control with traditional fire suppression methods . It 's worth noting that lithium ion batteries were the main suspect in the crash of a UPS Boeing 747 in Dubai in 2010 , killing both pilots as they tried to make an emergency landing . Investigators in the United Arab Emirates studied the cargo records and found that shipments of lithium ion batteries that should have been declared hazardous cargo were not . The reinforced cargo liner was no match for the fire that quickly destroyed the aircraft 's control systems and filled the cockpit with smoke , incapacitating the pilots . Presumably , the Malaysian government is paying close attention to anything on board the aircraft that might have caused a catastrophic fire . They need to be looking beyond the list of transported items , talking to freight shippers who might have had anything on board that was mislabeled , damaged or not handled correctly in transit . That 's just as important as talking to the relatives of the pilots and investigating the flight simulator one had in his home -- which , by the way , is not a crime and in the case of a pilot , often only shows a passion for the job . The opinions expressed in this commentary are solely those of Sylvia Adcock .
Sylvia Adcock : Investigators need to look closely at Flight 370 's cargo manifest . Comment: The plane was carrying a lot of fuel, and the crew hadn't been paying attention when they were filling it up. Malaysian officials said jet was carrying 440 pounds of lithium ion batteries . Adcock : Lithium ion batteries are flammable , can burn in a way that 's difficult to extinguish . Checking this is at least as important as investigating pilot 's flight simulator , she says .