A row of U.S. Air Force KC-135 tails from the Iowa Air National Guard on the ramp at the Iowa Air National Guard’s 185th Air Refueling Wing in Sioux City in 2019. (Vincent De Groot/U.S. Air National Guard)
WASHINGTON — The Air Force has grounded hundreds of utility aircraft, including KC-135 aerial refueling planes, until they are inspected and found not to have a faulty part in the tail section that helps keep them in the air, service officials said Wednesday.
The Air Force Materiel Command said inspectors are looking for “non-conforming” pins in the vertical tail assemblies of the aircraft. Inspectors are checking the pins in the service’s fleet of KC-135 Stratotankers and two variants — the RC-135 reconnaissance plane and WC-135 radiation-detection aircraft.
If a vertical terminal fitting pin failed, the tail section could break off the plane.
"We're taking this action out of an abundance of caution, after consulting with our engineering experts," said Col. Michael Kovalchek, a senior materiel leader. “We are working closely with Air Mobility Command and all operational users and anticipate all potentially affected aircraft will be inspected.”
Each aircraft has two fitting pins in its tail section, one on each side, that attach the tail fin to the main fuselage. The tail section is critical to flight because it provides stability and helps the pilots steer the plane. There are hundreds of KC-135s, RC-135s and WC-135s in the Air Force fleet.
Wednesday’s order accelerates a previous directive to inspect the planes. The original order, given last week, called for the planes to be checked within 15 days. The new order states they now must be inspected before they can fly again.
“Although no mishaps have resulted, leaders elected to accelerate the inspection due to a lack of information to assess the risk of materiel failure in non-conforming parts,” according to an Air Force statement. “Planes that have already been inspected and found with proper pins have already returned to flying status.”
The Air Force said nearly 100 planes had been inspected by the start of this week, and 24 faulty pins were found. The defects include whether the pins are too small, made of the wrong material, have “insufficient plating,” or lack a stress layer that makes them stronger.
The Boeing-made KC-135 is a mid-air refueling aircraft that’s been in service since the late 1950s. The RC-135 was introduced in the 1960s and the WC-135 “Constant Phoenix” in 1965. The main function of the WC-135 is to conduct atmospheric tests to detect nuclear explosions. The Air Force said the inspections take about 30 minutes and most will be conducted at the Oklahoma City Air Logistics Complex. Officials said planes discovered to have faulty pins will get a one-time flight authorization to fly to the repair location.
In 1985, more than 500 people were killed when a Japan Air Lines 737 lost its tail assembly in mid-flight and crashed into a mountain 60 miles northwest of Tokyo. It remains one of the deadliest plane crashes in history. It was later determined that a stress fracture caused an explosive decompression that took off the tail section.
Last September, an Air Force KC-135 was forced to make an emergency landing in Japan after its retractable nozzle, called a boom, broke as it was attempting to refuel a B-1 bomber over the Pacific Ocean. Both planes landed safely.
This isn’t the first time the Air Force has grounded the KC-135 due to a possible issue in the tail section. It temporarily grounded a third of its KC-135s in 2000 due to a manufacturing defect with another part of the tail assembly, the stabilizer trim actuator.
