WASHINGTON (CNN) -- The Federal Aviation Administration is proposing a $689,800 fine against FedEx for violating federal rules governing the shipment of hazardous materials on cargo planes.

An inspector who conducted an audit in 2009 found a FedEx cargo facility in Connecticut violated regulations 93 times in a three-month period that year, the FAA said.

In 89 of those instances, FedEx failed to notify pilots about the nature, quantity or weight of hazardous materials on their aircraft. In the remaining four cases, FedEx accepted packages that shippers had not accurately described or certified in documents, the FAA said.

The alleged violations occurred at the company's facility at Bradley International Airport in Windsor Locks, Connecticut.

"Pilots must know they are carrying dangerous goods so they can take all necessary safety precautions," FAA Administrator Randy Babbitt said in a statement. "Shippers and airlines must follow the rules so they are able to move these materials safely."

A FedEx spokeswoman told CNN all of the cases involved "errors in documentation" -- paperwork errors that did not endanger the aircraft.

"All of these packages traveled through the FedEx system safely and never posed any danger to our aircraft or crew members," said spokeswoman Sally Davenport.

Davenport said FedEx is asking the FAA for an informal conference to discuss the proposal, and will ask the agency to reconsider the fine.

FedEx currently has 688 aircraft, ranging from Boeing 777s to Cessna turbo-props, and has 10 hubs and a network of smaller facilities, including the Bradley Airport facility. The company handles about 3.5 million packages a day.

Davenport said shippers of dangerous goods are responsible for identifying the goods, and trained specialists at FedEx review the shipments and enter 30 different elements of information into an internal system.

FedEx does not know if some errors cited by the FAA resulted from a lack of information or misinformation on the paperwork, or whether a FedEx employee make a mistake, she said.

Hazardous materials incidents aboard cargo planes, while infrequent, have occurred in recent years. In 2004, a fire broke out in a container being loaded on a FedEx MD-11 in Memphis, Tennessee, causing $20,000 in damage. Investigators blamed the incident on unapproved packaging used by the company that shipped the product -- lithium-ion batteries.

In 2006, the pilot of a UPS DC-8 landed at Philadelphia International Airport after a fire broke out on board. The crew sustained minor injuries, but the airplane and most of the cargo were destroyed by the blaze after landing. The source of the fire was not determined.

In perhaps the most famous incident involving hazardous materials, a ValuJet Airlines passenger plane crashed in the Florida Everglades in 1996, killing 110 people. The National Transportation Safety Board blamed the crash on the actuation of oxygen-generating canisters being improperly carried as cargo, and the failure of the manufacturer to properly package the chemical-filled generators.