The U.S. Air Mobility Command (AMC) has released the
findings of three detailed accident investigation boards (AIBs) concerning
incidents involving its next-generation KC-46A Pegasus aerial refueling
tankers. The reports shed light on the complex operational challenges and system limitations encountered during critical refueling missions, resulting in millions of dollars in damage, but fortunately, no fatalities or injuries.“These investigations underscore the inherent complexities
of integrating a new, sophisticated aircraft into a vital operational fleet and
highlight the Air Force's proactive measures to enhance safety and
effectiveness,” AMC said in a press release.
The incidents under scrutiny occurred on Oct. 15, 2022, and
Nov. 7, 2022, involving KC-46A aircraft assigned to the 305th Air Mobility Wing
at Joint Base McGuire-Dix-Lakehurst, N.J., and a more recent event on Aug. 21,
2024, involving an aircraft assigned to the 22nd Air Refueling Wing at
McConnell Air Force Base, Kan.
Air Force Lt Gen Rebecca Sonkiss, AMC Deputy Commander,
emphasized the strategic importance of the fleet and the Air Force's commitment
to continuous improvement.
"The KC-46 tanker fleet will sustain our air refueling
mission capabilities for decades to come," Sonkiss said. "Challenges
with adding a new aircraft to the fleet are not uncommon, but we do not take
these incidents lightly. We have used the lessons learned to refine our KC-46
operations, including focused training and guidance while partnering with the
contractor to implement long-term solutions."
Early indicators and insights gleaned from these and other
events have already prompted AMC to implement significant precautionary
measures. These include specified training protocols for aerial refueling
involving fighter aircraft and a crucial adjustment to the refueling envelope,
increasing it from six feet to ten feet. This expanded envelope provides boom
operators with additional time to react during critical situations and offers
improved visual cues of receiver aircraft, mitigating risks associated with the
KC-46A's unique boom characteristics.
October 15, 2022: Boom Strikes Tanker Tail Amid Nozzle
Binding
The first incident detailed in the released reports occurred
on Oct. 15, 2022, during routine air refueling operations off the U.S. East
Coast. A KC-46A Pegasus, operated by the 2nd Air Refueling Squadron from Joint
Base McGuire-Dix-Lakehurst, was attempting to refuel an F-15E Strike Eagle from
the 335th Fighting Squadron, Seymour Johnson AFB, N.C.
During a breakaway maneuver, a nozzle binding accident took
place, where the refueling nozzle became stuck within the F-15E's receptacle.
This led to the air-refueling boom (ARB) striking the tail section of the
KC-46A, causing substantial damage. While there were no fatalities, injuries,
or damage to civilian property, the estimated damage to the KC-46A was
significant, totaling $8.3 million.
The accident investigation board, led by Col Chad Cisewski,
concluded that multiple factors substantially contributed to the mishap. A
primary cause was identified as a limitation of the ARB control system itself.
The boom operator inadvertently applied a radial force on the ARB, causing the
nozzle to bind. This system limitation subsequently led the ARB into an
uncontrollable upward motion, striking the tanker’s tail. Further, the AIB
found that the F-15E pilot did not adequately consider KC-46A’s
"stiff-boom" characteristics. The KC-46A's boom requires
significantly more fore-aft thrust input from the receiver aircraft to move the
boom telescope in and out while in contact, a characteristic that the F-15E
pilot's actions did not fully account for, thus exacerbating the binding issue.
November 7, 2022: Damaged Nozzle During Training Exercise
Less than a month later, on Nov. 7, 2022, another KC-46A
from the 305th Air Mobility Wing, operated by the 2nd Air Refueling Squadron,
encountered a similar issue. The tanker had departed Naval Air Station Cecil
Field, Fla., to refuel an F-22A Raptor from the 94th Fighter Squadron, Joint
Base Langley-Eustis, Va., as part of a joint-force training exercise
originating from Tyndall Air Force Base, Fla.
During the second air refueling attempt of the sortie, the
KC-46A again experienced a nozzle binding event during a breakaway with the
F-22A. While the boom did not strike the tanker in this instance, the bound
forces exceeded the structural limitations of the ARB nozzle, causing it to be damaged beyond repair. The estimated damages for this incident were $103,295.12, with
no fatalities, injuries, or collateral damage.
Col Justin Ballinger led this investigation board, which
also determined that multiple factors were substantial contributors. The board
highlighted the boom operator’s failure to verify that the ARB nozzle was
completely clear of the F-22A’s air refueling receptacle before making further
ARB control inputs. Manual control inputs by the boom operator created a radial
force, causing the nozzle to bind within the F-22A’s receptacle. Like the
previous incident, the F-22A pilot’s actions were also cited. The pilot did not
adequately consider the KC-46A's stiff-boom characteristics, which resulted in
a rapid forward movement of their aircraft relative to the KC-46A, contributing
significantly to the binding and subsequent damage.
August 21, 2024: Critical Boom Failure Mid-Flight
The most recent incident covered by the released reports
occurred on Aug. 21, 2024. A KC-46A Pegasus assigned to the 22nd Air Refueling
Wing, operated by the 931st Air Refueling Wing, departed Travis Air Force Base,
Calif., to refuel an F-15E assigned to the 366th Fighter Wing in support of Operation
Noble Eagle, a critical homeland defense mission.
During the fourth air refueling attempt, the KC-46A again
experienced nozzle binding in the F-15E receptacle. Upon release, the boom
rapidly flew upward, striking the bottom aft portion of the KC-46A. The impact
and subsequent violent oscillations of the boom—left and right—resulted in a
critical failure of the boom shaft structure, with portions detaching from the
KC-46A in flight. The KC-46A crew declared an in-flight emergency and safely
returned to Travis AFB, where emergency response personnel met them.
The estimated damages from this severe incident were the
highest of the three, at $14 million. Again, no fatalities, injuries, or damage
to civilian property were reported. The accident investigation board,
spearheaded by Col Diane Patton, concluded that the mishap was primarily caused
by the boom operator's control inputs, coupled with the receiver aircraft’s
excessive closure rate and instability, which collectively led to the boom
striking the tanker aircraft with catastrophic results.
Moving Forward: Continuous Improvement and Contractor
Partnership
The common threads in these incidents—nozzle binding,
challenging boom characteristics, boom operator input, and receiver aircraft
flight dynamics—paint a picture of the learning curve associated with a new air
refueling platform. The Air Force's prompt response, including specialized
training and expanding the refueling envelope, demonstrates a commitment to
minimizing future occurrences.
"We are continually refining our tactics, techniques,
and procedures," Sonkiss added, emphasizing the collaborative approach.
"Our partnership with the contractor, Boeing, is crucial in addressing
both immediate operational solutions and long-term system enhancements to
ensure the KC-46A's reliability and safety."
While these three significant incidents have now been
thoroughly investigated, the Air Mobility Command noted that another
nozzle-binding incident occurred on July 8, 2025. The circumstances of this
event remain under investigation, and upon its completion, AMC will determine
if further mitigation efforts are required.
