WASHINGTON ― America’s aging C-135 reconnaissance planes keep breaking down, and alarmed lawmakers want the U.S. Air Force to tell them why.

Based at Offutt Air Force Base, Nebraska, the 55th Wing’s Boeing-made reconnaissance and intelligence-gathering aircraft, all more than 50 years old, are meant to carry out critical missions from operating bases in England, Greece, Japan and Qatar.

But an Omaha World-Herald investigative series has found that mechanical problems plague the jets, cutting short 500 of their flights since 2016 and one of every 12 missions since 2015. That’s prompted Nebraska lawmakers to write to Air Force Secretary Heather Wilson, urging her to probe and report on the health of the 55th Wing’s worn-out fleet.

Meanwhile, the Nebraska delegation is trying to fend off an effort within Congress to strip funding to recapitalize the OC-135, which conducts overflights of Russia under the 34-nation Open Skies Treaty. Some lawmakers and Pentagon officials have grown skeptical of the treaty, which allows reciprocal surveillance flights, amid alleged Russian violations, but the administration has requested funds for two new airliners to take over the mission.

“It has one of the worst maintenance rates in the United States Air Force,” Rep. Don Bacon, R-Neb., said of the OC-135 on the House floor last week. “It frequently breaks down in Russia, putting us in very hostile, awkward situations with Russians at their bases.”

The chair of the Senate Armed Services Committee’s Strategic Forces Subcommittee, Deb Fischer, led the letter with Sen. Ben Sasse, a SASC member; Bacon (a retired brigadier general and former 55th Wing commander who sits on the House Armed Services Committee), as well as Reps. Jeff Fortenberry and Adrian Smith.

The letter asked Wilson to report on the 55th Wing’s safety, security and continued mission effectiveness as well as the Air Force’s long-term plans to sustain and recapitalize the wing’s capabilities.

It referenced the RC-135V/W Rivet Joint, RC-135S Cobra Ball, RC-135U Combat Sent, WC-135 Constant Phoenix, TC-135 Rivet Joint Trainer and the OC-135 Open Skies aircraft.

In the current budget season, House and Senate lawmakers have taken divergent approaches to the Trump administration’s $222 million request for the two new aircraft.

House appropriators and authorizers stripped the funding from their 2019 bills. The authorization bill withholds the funding until Russia adheres to the treaty and agrees to extradite Russians indicted for meddling in U.S. elections in 2016.

Fischer helped ensure the Senate-passed 2019 authorization bill did include funding for OC-135 recapitalization, and the bill will have to be reconciled with its House counterpart.

Defense Secretary Jim Mattis directed the Air Force to recapitalize the aircraft. He wrote to Fischer in May to acknowledge that unplanned maintenance issues meant the U.S. completed only 64 percent of its scheduled overflights in 2017, while Russia typically completes all of its scheduled overflights.

The White House Office of Management and Budget has also issued letters objecting to the absence of OC-135 recapitalization funding in the House bills.