Air cargo service in America is like a ticking time bomb. One day a cargo plane — with an exhausted pilot or mechanical problem — will crash into a crowded mall or school and kill scores of people. The Federal Aviation Administration mustn't wait for such a tragedy to jump-start it into action.

Given air cargo's track record — one fatal crash per month on average since 2000 — the FAA should tighten the industry's safety rules and oversight now, particularly for small cargo carriers that have the worst accident rates.

A Miami Herald investigative series described the air-cargo industry's troubled history. (To see the series online, go to www.miami.com.) Among the findings:

n Air cargo is the deadliest segment of commercial aviation. Sixty-nine fatal crashes since 2000 have taken 85 lives.

n The industry is hampered by aging planes, tight deadlines and overnight flights. Pilots fly under extreme pressure to meet tough deadlines. Many get paid only after the delivery.

n Pilots often fly in hazardous weather, sometimes without enough sleep. Many fly planes that have mechanical problems, which is unthinkable in passenger flights.

n Despite the problems, fewer FAA safety rules apply to cargo planes than passenger planes. For example, cargo pilots can fly 40 percent more hours per year; they are not required to have eight hours' rest 24 hours prior to a flight, as are passenger pilots. Small cargo planes aren't required to have "black boxes" that help determine the cause of a crash and can lead to safety improvements.

n Lax enforcement only worsens safety concerns for cargo carriers. In many cases, the FAA allows cargo firms to continue flying despite egregious maintenance lapses and crash histories. For example, the FAA has yet to ground one firm with four crashes involving seven deaths since 2002. That Ohio firm, Grand Aire Express, and its affiliate TriCoastal Air Inc. have had three dozen accidents or incidents since the 1980s, according to FAA records.

In 2000, the FAA fined Grand Aire $290,000 for operating a plane for 20 days without repairing a known problem and for other maintenance failures. Yet the companies continue to fly and accidents continue to happen. The latest crash took a pilot's life in February.

The FAA says it has to be cautious before grounding planes because of the threat of lawsuits. Yet the cost of lawsuits, improved safety and more stringent enforcement should be weighed against the potential loss of life in the sky and on the ground.

The 1997 Fine Air cargo crash in Miami should have spurred FAA reforms. The National Transportation Safety Board found Fine Air and its cargo loader at fault. NTSB also blamed the FAA for not adequately monitoring Fine Air or correcting "known cargo-related deficiencies." In a pointed reprimand, the NTSB said that the FAA "contributed to the accident."

By pilot skill or luck, that crash hit a vacant lot and exploded just short of an industrial park west of Miami International Airport. The crash claimed five lives, including one on the ground. The toll could have been much worse. Had the plane come down just a little to the south, the plane could have plunged into the Mall of the Americas. Had the flight gone east, it could have exploded in dense residential neighborhoods or downtown Miami.

Public safety shouldn't have to rely on luck. The FAA says that its resources are limited. Moreover, its mission to promote the aviation industry may conflict with its mission to protect the flying public. Yet there can be no excuse for indifference to the threat of a potentially disastrous air-cargo crash. The FAA should take seriously its obligation to prevent death from raining down from our skies.