The US military has been beset by a series of air accidents and crashes in recent years, and the rise has been shown to correlate with budget cuts introduced in 2013.

The most recent incident occurred May 2, when a Hercules C-130 cargo plane belonging to the Puerto Rico Air National Guard crashed in the southern state of Georgia, killing all nine people on board.

Congressman Adam Smith, the top Democrat on the House Armed Services Committee, introduced a bill to establish an independent commission on military aviation safety.

We need to "understand exactly what causes are contributing to military aviation accidents, how current rates compare to historic averages, and what steps we can take to improve military aviation safety," Smith said.

The commission would review military aviation mishaps between fiscal year 2013 and 2018, compared to historic averages.

2013 was chosen because that was the first year of large congressional budget cuts, known as sequestration.

According to a Military Times review, at least 133 service members were killed from fiscal year 2013-2017 in aviation mishaps.

The budget cuts took hold just as warplanes and their crews were being ordered on near non-stop deployments, such as to Iraq and Syria to fight the Islamic State group.

The cutbacks meant pilots' flight-training hours were reduced, and the Pentagon slashed the numbers of its most experienced plane maintainers, Military Times found.

Fiscal year 2018, which started on October 1, has already seen 12 fatal accidents resulting in 35 deaths of military pilots and crew -- a six-year high, Military Times reported.

"It is essential for our aviators and their families -- as well as for our military's ability to recruit, retain, and perform its mission -- that Congress have an authoritative, objective, apolitical look at the causes of this problem so that we can figure out what is going wrong and what actions need to be taken," Smith said.

Last month, an F-16 crashed near Las Vegas, killing the pilot.

Just a day earlier, four crew members died when a Marine Corps helicopter crashed while on a routine training mission in southern California.

And in Djibouti, two incidents triggered the grounding of US military flights.

According to local news reports in Puerto Rico, one of the pilots of the C-130 that crashed last week had told a friend he was reluctant to board it because it needed serious repairs.

Still, the Pentagon has been reluctant to portray the accidents as indicative of broader systemic failings.

"This is not a crisis," Pentagon spokeswoman Dana White said on Thursday.

"But it is a crisis for each of these families. And we owe them a full investigation, and to understand what's going on."