The military contractor whose vintage fighter jet crashed at sea and sank off Kewalo Basin a week ago has been working with local salvage company Parker Marine and might consult with Navy divers in an effort to recover the plane, the Coast Guard said.

The presence of the older military aircraft is expected to increase in Hawaii as the Defense Department seeks more economical training options for its front-line jets — in particular its Oahu- based F-22 Raptor fighters.

A Parker Marine representative said the crashed Hawker Hunter, believed to be in water much deeper than 100 feet, “is deeper than divers can easily go” and will be a challenge to recover.

“We’re still researching what it’s going to take to execute the operation,” John Zentner, a spokesman for the Airborne Tactical Advantage Co., or ATAC, said Tuesday in a phone interview. ATAC owns the downed jet.

“I’ve been telling folks it’s still going to be another couple of days before we know what the plan is, let alone the schedule,” Zentner said.

National Transportation Safety Board spokesman Terry Williams said last week investigators were waiting to talk to pilot Matt Pothier, who ejected and ditched the single-seat fighter about 2 miles from shore shortly after takeoff from Daniel K. Inouye International Airport.

The NTSB said it would look at the pilot’s records and aircraft maintenance. “We want to do an examination of the aircraft once it is recovered,” Williams said.

Pothier, who underwent back surgery at The Queen’s Medical Center, said something went wrong with his aircraft and he couldn’t make it back to the airport.

ATAC was flying two contracted Hawker Hunters in an adversary or “red air” role in the Hawaii Air National Guard’s big Sentry Aloha fighter training exercise.

ATAC’s Hawker Hunters, British-made jets that first flew in 1951, have been participating several times a month with Oahu-based F-22 Raptors, and make regular appearances in Rim of the Pacific exercises every other year. The two camouflage-painted ATAC planes were based at the Kaneohe Bay Marine Corps base, officials said.

According to flight-tracking websites, the crashed Hawker Hunter was number N323AX, which was manufactured in 1958.

“ATAC Hawker Hunter aircraft are used to support U.S. military training requirements by providing realistic adversary aircraft effects in controlled training environments,” the Virginia-based company said in an email.

The aircraft “have been fully refurbished and upgraded with modern avionics to support the highest standard of safety,” ATAC said.

In addition, aircraft are routinely inspected for airworthiness by the Defense Department and have been deemed safe for flight, according to ATAC. The crashed aircraft had been in service with ATAC for over 15 years.

The Air Force plans to increase its contingent of 20 F-22s in Hawaii with fighters being permanently relocated from hurricane-damaged Tyndall Air Force Base in Florida.

The service also wants more “adversary air” of the type offered by ATAC and other contractors to help train F-22 pilots in Hawaii. The contracted jets cost the military far less than using adversary air squadrons of its own.

In July the U.S. Government Accountability Office reported the hourly cost of flying three Air Force jets: an F-22 cost $62,000 per flight hour in 2016, an F-16 cost $19,000 and a T-38 cost $9,000.