Boeing didn't keep manufacturing records that might have allowed investigators to determine why the fuselage on an American Airlines 757-200 jetliner tore in flight last year, according to the National Transportation Safety Board.

That issue has also hampered the NTSB's efforts to pinpoint the cause of a larger tear that forced the crew of a Southwest Airlines 737-300 to make an emergency landing April 1, according to two government officials familiar with the investigation. They asked not to be identified as the inquiry is ongoing.

"Records of manufacture for the skin panels on the accident airplane and the other airplanes with fuselage skin cracking were not retained, and were not required to be retained," the NTSB, which investigates U.S. transportation accidents and recommends safety improvements, wrote in a Sept. 19 report on the American incident. "Therefore, a cause for the manufacturing nonconformance could not be identified."

The Federal Aviation Administration, which regulates the aircraft-production industry, may require manufacturers to increase the length of time they keep records, Frank Paskiewicz, acting deputy director of the agency's Aircraft Certification Service, told an NTSB forum Wednesday.

Boeing keeps its records 10 to 11 years, depending on the production date, said Erik Nelson, deputy vice president of manufacturing for the 737 program.

Three other commercial-aircraft makers — Airbus, Bombardier and Embraer — keep their manufacturing records for the life of each airplane, executives of those companies said at the forum.

The American jet's skin was too thin, which led to cracks, the NTSB found. Without records detailing how the plane was built and inspected, the board wrote, it could not determine the source of the manufacturing defect.

In the Southwest incident, a 5-foot section of the jet tore open at 34,000 feet, triggering an explosive decompression and injuring one flight attendant. The plane made an emergency landing in Yuma, Ariz.

The accident has been tied to rivets not being secured properly when the jet was built in 1996, according to the NTSB and Boeing Commercial Airplanes chief Jim Albaugh. Records of how those rivets were installed and inspected don't exist, the officials told Bloomberg News.

The reason records don't exist was detailed in the safety board's report on the American incident, in which an 18- by 7-inch tear opened above the left-side front passenger door at 32,000 feet, about 16 minutes after the jet left Miami on Oct. 26. The jet made an emergency landing in Miami. No one was injured.

During its investigation, the board discovered two other 757s with thin skin and similar patterns of cracking. Manufacturing records for those planes also weren't kept, the board wrote.

The FAA in 2009 revised its rules to require that manufacturers keep records at least five years, according to the Federal Register. In the case of "critical" components, manufacturing records must be kept at least 10 years.

The previous rule, which dated to 1964, required that records be kept two years.

One aviation manufacturer, General Electric, advised the FAA to require that records be kept for 40 years. The agency said in the final rule that it was deferring to the advice of an industry committee. A manufacturer "may maintain records longer if it chooses," the FAA said.

When the agency last considered the issue, manufacturers said it would be too expensive to keep the records for longer periods, Paskiewicz said Wednesday.

"A lot has changed since," he said. "I think it's an opportune time to take a look at that." Many inspection reports and other documents on each aircraft built are now computerized, he said.

The current rule took effect in April, Paskiewicz said. It wouldn't have helped investigators in the American or Southwest investigations, as both jets were built more than 10 years ago.