At least 24 people died in 2008 in five crashes in the USA and around the world on flights operated by U.S.-based non-profit organizations carrying medical patients or foreign development workers, federal records show. That's up from the 16 people who died in crashes on similar flights during the previous eight years, according to the records.

Some charity groups are considering upgrading safety standards, but they oppose new rules that they say could cripple their operations.

Non-profit flights have become an increasingly important means of transporting people. Angel Flight organizations, which fly medical patients to faraway doctors, arrange 20,000 flights a year.

Even though these flights carry passengers, they are treated as private flights that do not have to abide by more rigorous regulations — such as recurring pilot training and government inspections — that govern airlines or charter companies.

"It's just a deadly loophole," says Jim Hall, former chairman of the National Transportation Safety Board (NTSB).

"People blindly assume that whoever they get in an airplane with is going to be careful," NTSB member Robert Sumwalt said. "Unfortunately, we at the NTSB sometimes find out that that is not the case."

Sumwalt — who said he was voicing his own opinions — said the government should consider increasing standards on such flights.

The charity operators say additional regulations are not needed. "If we were to do anything different, it would significantly impact the number of people that we would be able to help," said Christel Gollnick, executive director of Angel Flight Central in Kansas City, Mo.

Federal regulators are trying to promote safety for all private flights, but it would be tough to create new regulations for charity flights without changes in the law, Federal Aviation Administration spokeswoman Laura Brown said. So far, the deaths have not prompted calls for change in Congress or the FAA.

Some recent accidents:

• On Sept. 1, a flight operated by Air Serv International of Warrenton, Va., crashed in the Democratic Republic of the Congo, killing 15 aid workers and two pilots. The non-profit company, which operates like a small airline, flies aid workers in some of the most dangerous places in the world, according to its website. Spokesman Rudolph Joseph said the organization's existing federal oversight is sufficient.

• From June to August, three flights arranged by several charities known as Angel Flight crashed, killing a total of seven people, including the three patients. A 2-year-old girl who died on a June 3 flight in Iowa City was not belted in, the girl's mother, Christina Blanton of Thomasville, Ga., told USA TODAY. Federal regulations require that all passengers age 2 or over wear seat belts.