A camouflaged former military jet shocked two boatloads of parasailors Wednesday afternoon off Kewalo Basin when it appeared to develop trouble and slowed like it was going into a stall before the pilot ejected and the aircraft crashed and rapidly sank.

“Everybody started pointing at it, and the next thing you know, he went from that stall and then he started going into a sideways spin and before you know it, he hit the eject button and shot out of the aircraft. We made a U-turn and went to go rescue the pilot,” said Dan Westphal, the captain of the X-treme Parasail boat, which had about 10 passengers on board.

Another boat nearby belonging to Hawaiian Parasail had two people in the air in a parachute.

The crew “thought the plane was going to hit our customers in the parachute at first,” said Mark Neumann, the owner of Hawaiian Parasail. “It went by them and it didn’t hit it. But it went into the water very close to our boat.”

City Emergency Medical Services officials said the 47-year-old male pilot in the single-seat jet was taken in serious condition to a hospital after a “controlled fall from aircraft.”

Ian Gregor, a Federal Aviation Administration spokesman, said that the Hawker Hunter went down around 2:25 p.m. after taking off. Accounts varied as to whether the plane went down one or several miles from shore.

Joint Base Pearl Harbor- Hickam officials said in a statement that the jet was being operated by a civilian contractor flying in conjunction with the Hawaii Air National Guard’s “Sentry Aloha” exercises, which are scheduled through Dec. 19. The exercise was suspended for the rest of the day but will resume this morning.

FLIGHTS WERE NOT allowed to depart Daniel K. Inouye International Airport for less than a half-hour after the crash as a precaution, state Department of Transportation spokesman Tim Sakahara said.

The Coast Guard said the plane belonged to the Virginia-based Airborne Tactical Advantage Co. The company said on its website that for the past 20 years, ATAC has trained Navy, Marine, Air Force and Army crews.

ATAC flies the Mk-58 Hawker Hunter, the F-21 KFIR and L-39 Albatros. Hawker Hunters, a British single-seat fighter that first flew in 1951, are used to replicate enemy aircraft in training exercises.

John Zentner, designated a spokesman for ATAC, said the company was “making sure we’re taking care of our pilot and his family.”

“We can’t comment on anything specific, but I will say that he successfully ejected from the aircraft and was picked up by the Coast Guard. So he’s being treated right now,” Zentner said.

He said the pilot has been flying with ATAC “for quite a while” and is “well known through the local area.” The Hawker Hunter was one of two aircraft based in Hawaii, he said.

“We’re in the very beginning stages of our investigation and we’ll be working with relevant authorities to make sure we go through this in a very deliberate and methodical way to get to the bottom of it,” Zentner said.

SENTRY ALOHA, a large-scale fighter exercise, started Dec. 5, and the Hawaii National Guard had warned that Oahu residents, particularly along the island’s southern coast, might see an increase in military aircraft.

The exercise is hosted by the Air Guard’s 154th Wing to provide realistic combat training for Air National Guard, Air Force and other Department of Defense services, officials said.

Maj. Jeff Hickman, a Hawaii Guard spokesman, said the Air Guard will conduct an interim safety board investigation into the crash and pass the results to the National Transportation Safety Board, which will conduct a full investigation.

Visiting units include KC-135 Stratotanker air refueling support from the Iowa and Wisconsin Air National Guard, F-15 Eagles from the Oregon Air National Guard and U.S. Navy F-18 Hornets based in California.

Westphal, the captain of the X-treme Parasail boat, said crew member Mack Ladner jumped out of the boat and helped rescue the pilot.

“The pilot looked like he had a little bit of blood coming from his mouth, maybe,” Westphal said. “… But he had a big life jacket inflated around him. He was getting all tangled in the parachute, so my crew member swam over and got him untangled and got him over to the Coast Guard boat as they pulled up.”

“I said, ‘You OK?’ He said he was in a little bit of pain,” Ladner said. The pilot’s back was hurting a little, the 21-year-old crewman said.

“I’m glad he was all right,” he added.

“We’ve watched thousands and thousands of planes every day,” he said. “We take pictures of them with the parachute in the air, but I never imagined one crash in front of us like this.”

Westphal said another jet circled around after the Hawker Hunter crashed.

Jamey Regelbrugge was captaining the Hawaiian Parasail boat when he saw the jet fly over the parachute he was pulling behind his boat. He saw the pilot eject and the plane crash into the water.

“The jet sunk immediately,” Regelbrugge said. “Just a big huge splash and then just went down.

“It was almost like surreal,” he said. “It was almost fake. I couldn’t believe what I was seeing.”

Neumann, the company’s owner, said, “It scared the heck out of my guys, my crew. They didn’t know if there was somebody else in the plane that went down.”

During last summer’s Rim of the Pacific exercises, ATAC “aggressor” aircraft flew nearly 100 hours in support of training with the aircraft carrier USS Carl Vinson, as well as the multinational naval force participating in the exercise, the company said. ATAC said it has participated in every RIMPAC exercise since 2006.