The U.S. Air Force’s fleet of B-2 Spirit stealth bombers hasn’t flown in nearly six months. The service placed its 20 remaining nuclear-capable bombers on a safety pause after an incident that damaged one of the bombers in December 2022. The Air Force insists that the bombers are still ready for action, if necessary, and that the pilots are continuing to train to maintain combat-readiness.

Specifically, the bombers were grounded after an emergency landing at Whiteman Air Force Base in Missouri, according to Air & Space Forces Magazine. On December 10, 2022, a B-2 bomber ran off the runway during the course of the landing and caught fire, severely damaging the aircraft. Neither of the two crew members aboard were injured.

The Air Force issued a worldwide B-2 stand down on December 19. Nineteen of the 20 bombers were stationed at Pearl Harbor at the time, while the 20th B-2 was at Daniel K. Inouye International Airport, a frequent stopover area for bombers headed to the Asia-Pacific region. The most recent Google Maps imagery at highest resolution shows three B-2s on the ground at the airport, as well as C-5M Galaxy, C-17 Globemaster III, and C-130 transports; and KC-135 Stratotankers.

The Air Force has not yet disclosed the cause of the December crash, but it was the second incident in just one year. A previous incident in September 2021, also at Whiteman, was later revealed to have involved worn landing gear springs. The aircraft was sent to the Air Force’s secretive Plant 42, the home of the original B-2 production line, for repairs.

Only 21 B-2s were built—far short of the original Cold War requirement for 132 of the bombers. The fleet is small and precious, yet is the only heavy bomber capable of penetrating heavily defended airspace, so the Air Force will repair damaged jets if at all possible. The only B2 ever declared a total loss came in 2008 at Andersen Air Force Base in Guam. Despite the efforts of firefighting crews, the plane burned to the ground.

Regardless of the extended grounding, the Air Force maintains the planes are still ready to carry out nuclear deterrence missions. The B-2, as well as about half the fleet of B-52 Stratofortress bombers, are the only nuclear-capable bombers in the Air Force arsenal. The remaining B-52s and B-1 bombers have been denuclearized, their ability to carry nuclear weapons deleted to fulfill arms-control agreements with Russia.

The Air Force also states that the pilots are still racking up flying hours, either in other aircraft or in simulators. Much like U-2 pilots, B-2 pilots will often take to the skies in T-38 Talon jet trainers to maintain their basic flying proficiency. The T-38 is highly maneuverable and inexpensive to operate—a distinct advantage over the B-2, which costs upward of $150,000 an hour to fly.

The B-2 is expected to fly on through the early 2030s, when the forthcoming B-21 Raider bomber replaces both the stealth bomber and the B-1.