The Air Force expects to have enough resources—money, spare parts, and maintainers—to keep the B-1B bomber flying safely at least until it can be replaced by the B-21, service officials said, now that Congress will let USAF retire 17 of the most problem-prone Lancers in the inventory. But the Air Force is well behind on a structural fatigue test meant to find life-limiting cracks and stress in B-1 airframes, meaning there could be some surprises ahead.
Congress overrode President Donald J. Trump’s veto of the 2021 National Defense Authorization Act on Jan. 1, clearing the way for the Air Force to reduce the B-1 fleet from 62 aircraft to 45. The B-21 is expected to be delivered in sufficient numbers by 2031 to permit the rest of the B-1s to retire.
Since September 2019, the Air Force has pushed to reduce the B-1 fleet in order to keep a smaller number of the bombers fully potent and ready for action. In recent years, lack of spare parts and a long list of structural and systematic gripes have driven the fleet’s mission capable numbers to as low as just six aircraft ready for combat.
There will now be enough resources for B-1 repairs and structural modifications to “get us as long as we need for the B-1 to fly,” bomber Program Executive Officer Brig. Gen. John P. Newberry told Air Force Magazine in a December interview.
The B-1 was designed to fly between 8,000-10,000 hours, or about 30 years, depending on the rate of usage, but the fleet is 35 years old. To help predict where physical failures are likely to occur, the Air Force has, since 2012, run a structural fatigue test on a B-1 carcass and wing taken out of the boneyard at Davis-Monthan Air Force Base, Ariz. The test apparatus applies forces on the wing and fuselage with a series of bars and pulleys, simulating the effects of multiple flights. The idea is to “age” the test article ahead of the fleet to discover structural problems before they’re encountered in operational aircraft.
The goal, Newberry said, is to achieve 28,000 simulated flight hours on the representative wing, and 27,000 hours on the fuselage; what’s called the “durable life” of the airplane. So far, the service has accumulated 15,875 hours on the wing, but just 7,154 hours on the fuselage. Those hours are actually half of the real numbers, though, because fatigue tests are meant to create a “Certified Structural Life.” The service is only comfortable flying the fleet to half the number of simulated hours applied to the fatigue test article, to leave a generous margin for the unexpected. Consequently, while the wing taken from the boneyard had 3,085 hours already on it, the structural fatigue test could only be credited 1,547 hours at the outset.
“Unfortunately, we’re behind,” Newberry allowed. “The [actual] fleet average is a little over 12,000” hours. The wing test article is ahead of the fleet average, but the fuselage is lagging.
The reason the test is behind has to do with the way structural fatigue tests are run. If a structural failure occurs on the test article, the test must be stopped while the problem is analyzed and a repair is then developed, prototyped, and installed. In this way, a repair is ready to go when actual flying aircraft encounter the problem. The fatigue test then continues with a modification like the one that will be installed on the fleet, so as to be representative of their continued service.
Major problems encountered that required stopping the test included “on the wing … leading and trailing tabs, upper wing splice bolts and drain holes,” Newberry said. On the fuselage, it was “cracks in the longerons, on the dorsal and shoulder longerons.” A repair is now being prototyped on the forward intermediate fuselage. There are also rib cracks, “shearing bolts, and tension clips. So there are various items,” he said.
“We want to get ahead of the fleet,” Newberry said, but he couldn’t predict when that will happen, because it’s impossible to know when the next failure will occur, forcing another halt to the test. Even now, the test is on hold while a fix to a longeron—a main structural piece that carries heavy loads in the structure—is being prototyped.
The B-1 has been used hard, and not in the way intended. Former Chief of Staff Gen. David L. Goldfein explained in September 2019 that the B-1 was used in Afghanistan and Iraq as a high-speed close air support platform, loitering for long periods at high altitudes with its swing wings swept forward, until getting a call to dash to support troops needing air support. However, the aircraft was designed as a strategic penetrator, flying low and fast, with wings swept back. Flying with the wings extended for long periods, while carrying heavy loads, put years of heavy extra stress on the swing mechanism and attach points.
“Now we’re having to pay the piper,” Goldfein said.
To stop rapidly grinding down the B-1’s remaining service life, the Air Force has decided to take it out of the close air support mission. Throughout 2020, the Lancer—or “Bone” as crews refer to it—has been limited to bomber task force missions, conducting short-notice, short-duration deployments to Europe, the Pacific, and the Middle East.
Air Force Materiel Command has moved quickly to restore the B-1’s mission capable rates to percentages above 60 percent; still below goal, but far better than the single-digit performance of just a few years ago.
At the B-1 depot maintenance center at Tinker Air Force Base, Okla., a separate “speed line” was set up to repair specific problems crushing the B-1’s readiness, such as the ejection system, cracks in the forward intermediate fuselage, and wing problems. Spare parts also received extra funding.
The reasons the B-1 fell into such low availability rates had to do with the abusive operation of the aircraft coupled by a perfect storm of structural problems that overwhelmed maintainers, according to USAF B-1 program manager William Barnes.
“When we were at very low mission capability rates, … we were behind in analyzing some of the data we were seeing in the full scale fatigue test,” Barnes said. As the data were analyzed, it raised concerns about various areas that needed inspections, which can be invasive and time consuming.
“A lot of that work fell on the backs of the maintainers out in the field,” he said. But, there wasn’t enough capacity at the depot, “nor did we have all the supplies we needed to perform that repair work.”
At the same time—around May 2018—a B-1’s ejection system failed during an inflight emergency. While the crew made a harrowing landing, the incident prompted yet another new wave of fleetwide B-1 inspections, Barnes said, further pressuring the maintainer force.
“Since that time, we got the ejection system all fixed, and got that work off the field maintainers. We brought a lot of the repair work into the depot, …and then in 2019 … [we] stood up the dedicated repair line at Tinker …where we bring in aircraft for nothing but structural repairs. To my knowledge, it’s the only dedicated structural repair line in the Air Force,” Barnes said. Doing it that way allowed the Air Force to hire extra workers to do the surge repairs “and let the maintainers get back to their day-to-day job of launching aircraft and meeting mission needs.”
Doing all that “significatly improved the availability of the fleet,” Barnes said. “It’s put the fleet in a very healthy position as we bring aircraft through depot, perform the structural repairs, and get a healthier aircraft back out to the field.” The fact that the aircraft are “healthier” also reduces the load of necessary inspections, allowing maintainers to focus on daily readiness.
But some big repairs remain undone. A longeron replacement in the forward intermediate fuselage that will require substantial disassembly of the airplane will be an intensive process.
“We are going to bring an aircraft into Boeing’s Palmdale, [Calif.], facility in April to perform a prototype of that repair,” Barnes said, “Where we will replace the forward intermediate fuselage, and we will repair the ‘shoulder’ longeron,” and this will be the prototype for a fleet-wide fix. The repair apparatus will be brought to the depot to be performed, “but that’s not going to happen until the ’23-’24 timeframe,” he said. “So, we’re still a few years away from where we have to be.”
Lt. Col. Joseph Lay, Barnes’ uniformed counterpart, said the longeron is “a huge section of the backbone of the aircraft.” Doing the forward fuselage and the longeron at the same time “facilitate each other” because they require access to the same areas.
The prototype will be done on a B-1 already headed into depot, and it will have “an extended stay” in that status, Newberry noted.
“It’ll go to Tinker for a little bit, and then it’ll go to Palmdale with Boeing, …and then go back to depot and finish out its normal depot. It was picked because it was ready for the depot and it was … needing a forward intermediate fuselage replace as well.”
He added, “It is extensive. This is not a minor repair.”
With a fleet of 45 B-1s, the aircraft will flow through the depot at about nine per year, or the whole fleet every five years, Newberry said, meaning there are likely two more depot cycles for every airplane before the B-1’s putative wholesale retirement. Alongside that, Barnes said, there will typically be “two to four” B-1s in the structural repair line, meaning “five to eight” B-1s at Tinker “at any given time.”
“As we continue with the full scale fatigue test article, we learn more about the fleet, we find other, very small or very significant, structural repairs that need to happen across the fleet,” Barnes said. “So there will be some structures [repair] happening on this fleet, … my guess, probably for the remaining life of the aircraft.”
The Air Force does not expect to initiate a Service Life Extension Program on the B-1 fleet, Newberry said.
Editor’s Note: An expanded version of this story will appear in the January-February 2020 edition of Air Force Magazine.