US F-18 Hornet fighter jet
A US Marine Corps F/A-18 Hornet fighter jet crashed in the Pacific Ocean off the coast of Japan on Dec. 7, 2016, killing the pilot Capt. Jake Frederick. It was the sixth crash of a US military F/A-18 in just six months. The Canadian and Swiss air forces each also lost a Hornet during the same period.

That's a lot of crashes. And there's a good chance the recent incidents are just the beginning of a dangerous new era for the dozens of American and allied squadrons flying the aged, overworked twin-engine fighters.

The Pentagon still possesses hundreds of the 1980s- and '90s-vintage "legacy" F/A-18s -- not to be confused with newer and more modern, second-generation Super Hornets. Besides Canada and Switzerland, US allies including Australia, Kuwait, Finland, Malaysia and Spain also operate old, first-gen F/A-18s.

The nimble Hornet helped to modernize US Navy and Marine Corps fighter ops when it debuted in the early 1980s. It can dogfight and attack targets on the ground with equal aplomb. It's rugged enough to launch from and land on an aircraft carrier as well as fly from austere land bases.

The original F/A-18 was never meant to fly for 30 years

But the original F/A-18 was never meant to fly for 30 years. Successive rounds of budget cuts and decades of poor planning have delayed the Hornet's replacement -- and stuck some of the free world's finest fighter pilots with planes that are quickly becoming unsafe to fly.

At the same time, cuts in flying time -- an expedient way for the military to save cash -- have eroded pilots' skills in recent years, increasing their chances of making a fatal mistake in mid-air.

The current spate of crashes began on June 2, 2016, when an F/A-18 belonging to the US Navy's Blue Angels aerobatic team crashed in Tennessee. The pilot, Marine captain Jeffery Kuss, died in the accident.

A Marine Hornet struck the ground at a military training range in California on July 27, 2016, killing flier Maj. Richard Norton.

On Aug. 2, a Navy F/A-18 crashed in Nevada. The pilot managed to safely eject. A Swiss pilot died when his Hornet fell from the sky on Aug. 29.

A Marine Hornet crashed in California on Oct. 25. The pilot survived.

On Nov. 9, two Marine F/A-18s collided in mid-air -- again over California. One pilot managed to land his damaged jet. The other ejected before his plane tumbled to Earth.

Canadian Air Force captain Thomas McQueen perished when his F/A-18 crashed on Nov. 28.

Six months. Eight accidents. Eight destroyed Hornets and one damaged one. Five dead aviators. Owing in large part to the F/A-18 accidents, the US Marine Corps' aircraft accident rate has spiked to a 12-year high. In the fiscal year between October 2015 and September 2016, Marine jets crashed at a rate of 3.39 every 100,000 flight hours -- the highest since 2004.

Owing in large part to the F/A-18 accidents, the US Marine Corps' aircraft accident rate has spiked to a 12-year high

The Marines, in particular, saw this coming. "I am concerned with our current readiness rates, both in equipment and personnel," Lt. Gen. Jon Davis, the Marines' top aviation officer, wrote in the Corps' most recent annual report on its aviation capabilities, released in February 2016.

In April 2016, Davis told the US Senate that just 87 of the Marine Corps' 276 Hornets were flightworthy — a mere 32 percent. In its aviation report, the Corps claimed it needed 58 percent of the F/A-18s to be ready for flight in order to have enough planes for combat operations, basic flight instruction and day-to-day training at the squadron level.

After assigning 40 Hornets to combat deployments and 30 to the dedicated training squadron, the Corps discovered it had just 17 F/A-18s available for squadron-level training at eight units. Two planes apiece for squadrons that might have as many as 20 pilots.

The US Navy's own F/A-18 squadrons are in only slightly better shape. In late 2013, one reserve unit flying out of New Orleans reported that just eight of its dozen Hornets were flightworthy.

Foreign air forces face similar maintenance and training challenges.

As originally built by McDonnell Douglas, F/A-18s were good for 6,000 flight hours. With the end of the Cold War, the Navy and Marines delayed plans for replacement fighters -- and extended the old Hornets to 8,000 hours in order to bridge the gap. Now the military expects some F/A-18s to last a staggering 10,000 flight hours.

There just aren't enough new planes to replace the old Hornets. The Navy ended up buying Super Hornets from Boeing starting in the late 1990s to replace some of its legacy F/A-18s, but the Marines opted to wait until Lockheed Martin's F-35 stealth fighter was ready. The Marines got their last legacy Hornet in 2000 -- and their first combat-ready F-35 in 2015. Never before had the Marine Corps gone so long without new fighter planes.

F-35s are finally entering service, but slowly. After all, they're expensive -- as much as $250 million per fighter, nearly eight times what the last legacy F/A-18 cost.

The Marines estimate the last F/A-18s will finally leave the inventory in 2030. To afford the F-35 and other pricey weapons programs while still remaining under Congressionally-mandated spending caps, the Pentagon cut training and maintenance budgets. The result -- inadequately-trained pilots flying poorly-maintained planes that are past their expiration dates.

"I am concerned with our current readiness rates, both in equipment and personnel."

Retired Navy commander Chris Harmer, a former helicopter pilot, spelled out the deadly arithmetic in an interview with Marine Corps Times in early 2016. "For a given population of pilots -- aviators -- the less they fly, the less training missions they get, the less training the aviation maintenance personnel get, the less money we have for spare parts, the less money we have for training exercises, the higher the mishap rate will be if everything else is held constant," Harmer warned.

The Pentagon asked for -- and Congress mostly agreed to -- hundreds of millions of dollars for extra training and plane-repairs in 2017. But the money will have come too late to stop Harmer's prediction from coming true.

Too late to prevent eight old F/A-18s from crashing...and five pilots from dying.