The Air Force has remained tight-lipped about an in-air emergency experienced by a B-1B Lancer bomber in May, but issues recognized during its emergency landing have prompted the branch to ground its entire fleet of the aircraft.

The B-1B Lancer is among America’s most capable bombers — with a top speed that exceeds Mach 1 and a payload capacity of over 75,000 pounds of ordnance, the Lancer (or Bone as it’s occasionally called) provides the United States with unparalleled speed and firepower. Although the aircraft is slated for retirement once the forthcoming B-21 Raider takes to the skies, the Air Force recently announced plans to upgrade the aircraft to keep them operational for decades to come, as production of the Raider reaches numbers sufficient to replace both the bone and another legendary bomber, the stealth B-2 Spirit.

In May, a B-1B out of the 7th Bomb Wing at Dyess Air Force Base was forced to make an emergency landing at Midland International Air and Space Port in Midland, Texas. A fire in one of the aircraft’s engines led to an emergency hatch being blown off the aircraft midflight. Once the aircraft was safely on the ground, an investigation into what went wrong brought an issue with the plane’s ejection seats to light.

The Air Force Global Strike Command issued this statement regarding the stand down:

During the safety investigation process following an emergency landing of a B-1B in Midland, Texas, an issue with ejection seat components was discovered that necessitated the stand-down. As issues are resolved aircraft will return to flight.

The Safety Investigation Board is ongoing. The SIB’s purpose is to prevent future mishaps or losses and is comprised of experts who investigate the incident and recommend corrective actions. The safety of Airmen is the command’s top priority. The Air Force takes safety incidents seriously and works diligently to identify and correct potential causes.”

None of the four-man crew in the bomber during the incident in May were injured, and the Air Force has declined to provide any further information into the nature of the mishap to date. Unconfirmed reports have suggested that the hatch was blown off by the crew as the Offensive Weapon Systems officer attempted to eject from the aircraft, but the ejections seat itself failed to function. SOFREP has not been able to confirm the validity of these reports and the Air Force has declined to respond to questions regarding this possibility, but evidence seems to suggest that this may be the case, as it’s unlikely that an engine fire would result in an emergency hatch being blown unintentionally.

A source that requested anonymity was quoted by The Aviationist as saying that the aircraft commander called for a manual ejection as a result of the engine fire, but the ejection failure forced them to execute an emergency landing. SOFREP has been unable to independently confirm this report.