The US Air Force (USAF) has directed a safety stand-down of the KC-135 fleet to perform inspections for a ‘non-conforming part’ in the aircraft’s vertical tail assembly.

The service issued a Time Compliance Technical Order (TCTO) on 14 February, restricting all the operational activities for the fleet until the completion of a 30-minute-long inspection.

The USAF imposed similar restrictions on 10 February to inspect all KC-135s that required inspections for its non-conforming vertical terminal fitting pins or tail pins.

The initial directive required inspection in the next 15 days, however, the new TCTO requires inspecting aircraft prior to their next flight.

The KC-135 Programme Office discovered that some of the non-conforming tail pins were not able to meet the necessary technical standards and were probably equipped with some of the aircraft, including the KC-135s, WC-135s and RC-135s.

Following this, around 90 aircraft underwent inspection until 12 February. Out of the total, 24 aircraft were reported to have non-conforming pins. The USAF claimed the faulty fleet did not experience any operational issues.

Some of the aircraft with proper pins have already returned to flying status after completing the inspection process while the faulty ones will be allowed for a one-time flight to the repair facility.

Associated work will primarily be performed at Oklahoma City Air Logistics Complex. It is also a depot maintenance centre for the KC-135 fleet.

The Programme Office said that the pin replacement work is expected to complete within a day.

Air Force Life Cycle Management Centre, Legacy Tanker Division senior materiel leader colonel Michael Kovalchek said: “We are taking this action out of an abundance of caution, after consulting with our engineering experts.

“We are working closely with Air Mobility Command and all operational users and anticipate all potentially affected aircraft will be inspected.”