Updated

The cargo of a United Parcel Service plane that caught fire and crashed last year included lithium batteries that should have been declared as hazardous cargo, but weren't, according to an accident report released Sunday by the Dubai government's civil aviation authority.

The report also paints a harrowing picture of two pilots struggling desperately to land their plane while running low on emergency oxygen and fighting smoke so thick they couldn't see their flight instruments or change radio frequencies.

The Boeing 747-400 crashed near the Dubai airport on Sept. 3 as the flight's first officer attempted an emergency landing. Both pilots were killed.

The report, which doesn't identify the cause of the fire, is expected to raise questions about shipments of the batteries. The batteries can short-circuit and cause fires that burn hot enough to melt an airplane.

UPS spokesman Mike Mangeot said the company is evaluating about 40 different safety technologies in response to the accident, including some that would help protect pilots' ability to see in smoke. He said the company is also reevaluating cockpit emergency oxygen systems on their planes.

The UPS plane arrived in Dubai from Hong Kong with cargo identified as "lithium batteries and electronic equipment containing or packed with lithium batteries," which were distributed throughout the cargo compartments, the report said.

There were no hazardous cargo declarations on the flight's manifest, but at least three of the shipments contained rechargeable lithium battery packs that should have been treated as hazardous cargo under international shipping regulations, the report said.

After several hours in Dubai, the plane took off for Germany. Twenty-one minutes into the flight, as the plane was approaching 32,000 feet, a fire alarm sounded. Captain Doug Lampe radioed Bahrain air traffic control that there was a fire on the plane's main deck, which is the same as a passenger cabin on an airliner. He said the plane needed to land as soon as possible.

Even though Doha International Airport was closer, Lampe requested to return to Dubai — a decision that isn't explained in the report. Three minutes after the first alarm, more alarms began to sound. The pilots donned oxygen masks and goggles, which interfered with their ability to talk to each other. About five minutes after first alarm, Lampe reported the cockpit was "full of smoke." He told First Officer Matthew Bell that he was having difficulty seeing his instruments. Bell commented about the heat in the cockpit.

About two minutes later, Lampe "declared a lack of oxygen supply," turned control of the flight over to Bell and left his seat, presumably to find portable oxygen canisters, the report said. There is no indication on either the cockpit voice recorder or the flight data recorder that he ever returned, it said.

Eight minutes after the first fire alarm, Bell radioed, "Mayday, mayday, mayday can you hear me?" He advised that he had to continue using the radio frequency for Bahrain because smoke prevented him from switching to Dubai air traffic control. Bahrain controllers advised they would relay communications to the pilots of another plane who would then relay them to Dubai controllers.

A few minutes later, Bell also said he was leaving the controls to search for oxygen. He returned a short time later, but the report indicates the plane had become difficult to control. While Bell struggled to position the plane to land, it overflew the Dubai airport and crashed.

Lithium batteries are already the focus of an intense lobbying battle underway in Washington. A proposed Transportation Department rule would require that lithium batteries — like those used in watches, cellphones, laptops and countless other products — be treated as hazardous cargo when shipped by air.

Currently, only some larger lithium batteries are required to be treated as hazardous cargo. The proposed rule would require special packaging and handling of battery shipments. Pilots would have to be informed that the batteries are on board and their location. And workers who prepare the batteries for shipment would have to receive special training.

The proposal is opposed by a broad array of foreign and domestic companies, including UPS, as well as several major U.S. trading partners. They say it will cost industry hundreds of millions of dollars and disrupt international shipping.

On Friday, the House passed a Republican-drafted bill that would effectively block the proposal by requiring the U.S. to adhere to weaker international shipping standards.

Unlike other kinds of batteries, some lithium batteries contain metal that will spontaneously ignite if exposed to air. Also, the positive and negative poles in some lithium batteries are close together, leading more easily to short circuiting, which can cause a fire.

Fires involving rechargeable lithium-ion batteries can reach 1,100 degrees, close to the melting point of aluminum, a key material in airplane construction. Lithium-metal battery fires are far hotter, capable of reaching 4,000 degrees.