U.S. Air Force B-1B Lancer bombers by Boeing [BA] began a resumption of flights on May 3rd after a safety stand-down by Gen. Timothy Ray, the head of Air Force Global Strike Command (AFGSC), on Apr. 20th.

“Individual B-1B aircraft will return to flight as inspections and maintenance directed during the stand-down are completed on each aircraft,” AFGSC said on May 6th. The Apr. 20th grounding of the B-1B fleet followed an Apr. 8th “ground emergency” involving one B-1B at Ellsworth AFB, S.D., per AFGSC. While taxiing to the aircraft parking area at 3:45 p.m. that day, maintenance crews saw fuel leaking from the plane and notified the aircrew.

“As to why the standdown took place on April 20, inspections of this issue were on-going following the incident, but after further analysis by engineers, we ordered a safety stand-down of the B-1B Lancer fleet April 20 out of abundance of caution to ensure the further safety of our aircrew members once it was determined a more invasive inspection was required,” AFGSC wrote in a May 6th email.

During the safety stand-down, maintenance depot personnel disassembled the Augmenter Fuel Filter Housing (AFFH) and inspected the parts.  When the mechanics determined the parts to be defect-free, the fuel units were re-assembled, pressure checked, and returned to service, AFGSC said.

New Port Richey, Fla.-based Pall Aeropower Corp., also known as Pall Corp. and Pall Aerospace, builds the AFFH, which filters raw fuel from the B-1B fuel tanks before it enters the augmenter fuel system.

“Clean fuel is critical to reliable engine operation,” AFGSC said. “The housing assembly contains a replaceable filter element and delta pressure indicator (DPI).  When the filter becomes clogged the DPI ‘pops’ and indicates the clogged condition to ground personnel.”

AFGSC said that a B-1B digital twin would likely not have prevented the incident.

“Digital Twin software and computing capacity is still a maturing technology which limits the benefits of having a full up aircraft model,” AFGSC said.

Maj. Gen. Mark Weatherington, the commander of 8th Air Force, said in a statement that the B-1Bs “are still safe to fly and we are confident that this stand-down has resulted in increased safety within the B-1B fleet.”

The latest B-1B grounding marks the third in less than three years. On June 7, 2018, the Air Force grounded the planes for 13 days due to an “issue with ejection seat components.”

The Air Force said it found the ejection seat problem while investigating a B-1B’s emergency landing on May 1, 2018 at Midland International Air and Space Port in Midland, Texas. The bomber, assigned to Dyess AFB, Texas, had four crew members aboard, and no injuries were reported.

On March 28, 2019, AFGSC again ordered a safety stand-down of the B-1B fleet due to ejection seat issues, this time due to improper drogue chute rigging identified during a routine inspection. The Lancers began flying again in late April, 2019 after AFGSC conduced inspections of the pilot egress system.

The drogue chute’s primary function is to right the ejection seat when it leaves the aircraft.

This week, the Air Force Life Cycle Management Center (AFLCMC) at Wright-Patterson AFB, Ohio asked for industry’s input in the possible building of a digital twin for the B-1 to help sustain the aircraft.

“The B-1 is in sustainment with new weapons development work potentially in the future,” AFLCMC said.  “The aircraft has flown five times its certified service life and is experiencing structural issues impacting aircraft availability (AA).  The [B-1] SPO [System Project Office] is looking for ways to predict structural issues and have planned repairs in place to increase AA, decrease periodic depot maintenance (PDM) and field repair times, and enhance structural integrity. We are looking to be cost effective in all implementations and look to create a consortium of industry partners who can participate in the Digital Engineering  transition and access our Product Lifecycle Management (PLM) solution.  All solutions must be sustainable well into the future and adaptable to new situations.  All solutions must include open systems architecture and be non-proprietary government owned.”

Last year’s fiscal 2021 National Defense Authorization Act allowed the Air Force to cut 17 B-1s out of 62 to meet the goal of 45. The service plans to retire the fleet by 2036.