Passenger airlines in the U.S. have recorded a remarkable period of safety over the past 10 years. Not so the nation’s cargo planes. 

Five domestically registered aircraft have crashed since 2009 — killing 16 people — including Saturday’s violent plunge into a bay near Houston of a plane carrying Amazon.com Inc. packages.

While no cause has been identified for that crash, which killed all three people aboard, it has revived concerns that safety standards for such things as mandatory sleep breaks for pilots or fire safety regulations are more lax on the cargo airlines than their passenger counterparts.

The Federal Aviation Administration, as part of its ongoing efforts to monitor safety issues, had been “taking a focused look at cargo operations” before the accident, the agency said in a statement on Monday night. The FAA also said it was looking at “any additional measure that may be warranted.”

John Cox, president of consulting company Safety Operating Systems and a former airline pilot, said “there have been a higher number of cargo accidents than passenger accidents almost as far back as I can remember.” And, he said, “That still continues today.”

There’s been just a single death on U.S.-registered passenger airlines since Feb. 12, 2009.

“We do have some safety concerns that remain,” said Captain Robert Travis, president of the Independent Pilots Association, which represents about 3,000 United Parcel Service Inc. pilots.

Equalizing Regulations

The Air Line Pilots Association, which represents flight crews at FedEx Corp., has called for equalizing the safety and security regulations for passenger and cargo flights. “Lesser requirements are placed on all-cargo operations in several crucial areas, which results in unnecessary safety risk,” the union said in a position paper posted on its website.

Little is known about what caused the Atlas Air wide body Boeing Co. 767-300, operating on behalf of Amazon, to suddenly dive from about 5,800 feet (1,768 meters) into a bay as it approached Houston. A video captured from a nearby jail showed the plane didn’t turn or try to pull out of the plunge in its final seconds, according to National Transportation Safety Board Chairman Robert Sumwalt.

Atlas Air Worldwide Holdings Inc. fell 5.76 percent Monday to $55.51. The company said in a statement that it was “deeply saddened” by the crash and was assisting the victims’ families.

The accident drew attention to the safety records of passenger compared to cargo airlines.

Cox said safety in the cargo arena has improved along with passenger airlines and that he wouldn’t characterize the industry as unsafe. However, cargo operations sometimes occur in more hazardous conditions, such as during the middle of the night or at airports that aren’t as well equipped, he said.

In some areas, the regulations aren’t as rigorous for cargo flights, he said.

Cargo carriers follow older regulations that require pilots get at least eight hours of rest each day. The newer rules for passenger airlines, which went into effect in 2014, call for at least 10 hours off between shifts to ensure crew members can reach a hotel room and still get close to eight hours of sleep.

The new rules also added requirements designed to reduce fatigue, including cutting the amount of hours crews can work per day if they fly late at night.

The cargo industry has a good safety record and any differences in how it’s regulated are the result of its unique operating requirements, said George Novak, president of the National Air Carrier Association, a trade group representing freight haulers, including Atlas.

“If the FAA felt there was a serious safety lapse or a gap, action would have been taken some time ago,” Novak said.

The association has been participating the FAA’s review of cargo safety, he said.

The difference in the safety record of passenger and cargo carriers is even more stark when comparing the number of flights they make: In 2017, the most recent year for which complete data is available, passenger flights totaled 9 million compared to 603,000 for cargo, almost 15 times higher, according to U.S. Transportation Department data.

The NTSB objected to cargo carriers being excluded from the 2014 rules designed to give airline pilots more rest, particularly when they fly late at night.

“The NTSB disagrees with this exclusion, as many of the fatigue-related accidents that we have investigated over the years involved cargo operators,” the safety board wrote to the FAA in a 2013 letter.

One factor that has led to accidents is the higher likelihood of hazardous or flammable material being carried on cargo flights, according to accident reports.

Dubai Crash

A UPS Boeing 747 crashed in Dubai on Sept. 3, 2010, after a fire erupted on the plane and pilots couldn’t reach the airport. The plane was carrying more than 81,000 lithium-based batteries, which can burn at high temperatures or explode, according to a report by the General Civil Aviation Authority of the United Arab Emirates.

While guidelines adopted by the United Nations International Civil Aviation Organization and followed by airlines prohibit bulk shipments of such batteries on passenger flights, there are no such restrictions on cargo airlines.

Both UPS and FedEx have taken numerous steps to ensure manufacturers package batteries properly and are exploring better equipment to contain fires.

“Although the companies have been very proactive, there’s always the opportunity for some undeclared hazmat to get through and that’s a concern,” Travis said.

One accident illustrating the hazards of carrying cargo occurred April 29, 2013, at Bagram Air Base in Afghanistan.

A National Air Cargo Inc. 747 under contract to the U.S. military crashed shortly after takeoff when heavy vehicles in the cargo hold broke loose and slid backward, damaging flight controls. All seven people aboard died.

The NTSB identified issues with the airline’s procedures for restraining large loads and said the FAA didn’t adequately oversee safety at the carrier.