JAKARTA, Indonesia — One Indonesian jetliner plunged to sea from 35,000 feet, killing everyone on board. Another's fuselage split in half after a hard landing. Last week, a Boeing 737 careened off a runway and burst into flames, leaving 21 people dead.

Three accidents in as many months have raised urgent concerns about the safety of Indonesia's booming airline sector, with experts saying poor maintenance, rule-bending and a shortage of trained professionals may be behind the disasters.

Dozens of airlines emerged after Indonesia deregulated its aviation industry in the 1990s, making air travel affordable for many across the sprawling island nation.

Passenger numbers have risen more than 20 percent every year since 2000, putting the system under strain, according to the Indonesia's directorate general of civil aviation.

Last year, a plane crashed, had a near-miss, skipped a runway, made an emergency landing or reported a technical problem every 12 days on average, government statistics show.

"I'm terrified to fly," said Barry Tontey, 50, who lost his daughter in the New Year's Day crash at sea. She was supposed to graduate from medical school in July.

"I don't believe the government or the airlines are committed to safety."

Indonesia's safety record in 2007 was worse than the average African nation, according to Ascend, a London-based global aviation consultancy firm, basing its figures on the rate of passengers killed per million departures.

"Fixing a safety record is a long-term cultural challenge" that requires improving discipline and communication between pilots and crews, said Martin Craigs, president of Hong Kong-based Aerospace Forum Asia. "It's not about quickly ticking boxes in a technical manual. ... It's got to be inbred in the system."

Investigators probing Wednesday's crash-landing of a Garuda Airline jetliner said its front wheels snapped off as it touched down, but would not speculate on the cause of the accident.

Garuda has had nine plane crashes in the past 30 years, killing 330 people, but has made progress recently in improving its safety regulations and training of pilots, experts said. Before Wednesday, its most recent major incident was in 2002, when a plane made an emergency landing on a river, with the loss of one life.

"As a whole, it is one of the best airlines in Indonesia, probably the best," said aviation analyst Dudi Sudibyo.

The flight data recorders of the Adam Air plane that crashed into the sea on New Year's Day, killing all 102 people on board, have not yet been recovered and the wreckage is still lying on the ocean floor. And when another of the airline's planes broke apart on landing weeks later, without causing serious injuries, company spokeswoman Natalia Budihardjo tried to downplay the incident, at one point telling a reporter it was "normal."

The main concern, experts say, is failure by air carriers and aviation officials to comply with Indonesia's regulations, which are considered by the U.S. Federal Aviation Administration to be quite strong.

And when an accident does happen, it is rare that anyone is held accountable, adding to public mistrust. Often, proposals made by senior government officials after a crash fail to address the root problems.