https://crsreports.congress.gov
December 2, 2022
F-35 Joint Strike Fighter (JSF) Engine Options
The Department of Defense (DOD) is considering whether
to upgrade the F-35 Joint Strike Fighter’s (JSF’s) existing
F135 engine—the Engine Enhancement Package (EEP)—or
to develop and procure a new engine for the aircraft—the
Adaptive Engine Technology Program (AETP). Congress
has long expressed interest in issues relating to the F-35’s
engine. Section 242 of the FY2022 National Defense
Authorization Act (P.L. 117-81) required DOD to develop
an acquisition strategy for transitioning the engine of the
Air Force version of the JSF (the F-35A) to the AETP.
Section 243 required DOD to develop a separate acquisition
strategy for transitioning the Marine Corps and Navy
versions (the F-35B and F-35C, respectively) to some form
of advanced propulsion.
History of F135 Engine
The F135 (see Figure 1)—designed and built by Pratt &
Whitney (P&W) of Middletown, CT—is the only engine
that currently powers the F-35. (For more on the F-35
program, see CRS Report RL30563, F-35 Joint Strike
Fighter (JSF) Program, by John R. Hoehn.) DOD awarded
P&W the F135 contract in 2001. P&W decided to derive
the F135 from the F119 engine, which powers the Air
Force’s F-22 fighter, to speed up the F135’s development.
Figure 1. Diagram of F135 Engine
Source: CRS adapted graphic from GAO report GAO-22-104678,
July 2022, p. 6, at https://www.gao.gov/assets/730/721771.pdf.
General Electric (GE) and Rolls Royce (RR), alternatively,
collaborated to develop an engine for the JSF called the
F136, and the F-35 program initially planned to use both
engines. The Navy ended its participation in the F136
program. Following DOD’s F135 contract award in 2001,
GE and RR continued to develop the F136. In FY2011,
Congress ended development funding for the F136, and GE
and RR announced in December 2011 that they would no
longer continue developing the F136.
P&W has experienced design challenges with the F135
engine, such as bleed air requirements and sustainability
issues. Air Force Lieutenant General Eric Fick, the Program
Executive Officer for the JSF program, testified in April
2022 that DOD originally defined the F135’s requirements
for bleed air (compressed air taken from within the engine)
during early development. However, engine capability
design modifications and new requirements emerged during
the F-35 Continuous Capability Development Delivery
(C2D2) program. The F-35 C2D2 program provides
“incremental ... improvements to maintain joint air
dominance against evolving threats.” He stated that “[t]o
provide the necessary bleed air, the engine was required to
run hotter, and early engineering assessments suggest that
this increase in operating temperature could decrease
engine life, driving earlier depot inductions and an increase
in life cycle cost.”
A July 2021 Government Accountability Office (GAO)
report (GAO-21-39) stated that “[a]ccording to multiple
service and program officials, challenges related to F-35
engine sustainment are currently affecting the program and
may pose its greatest sustainment risk over the next 10
years.” The report described two issues affecting the
engine:
The need to “[remove] engines for unscheduled
maintenance more often than expected, primarily to
repair the power module—a key component of the
engine that generates thrust for the aircraft to fly”; and
DOD’s ability “to repair only 43 percent of removed
power modules in 2020, thereby resulting in a backlog
of power modules needing repair.”
The report stated that these issues resulted in not meeting
goals for engine repair turnaround times, and that “DOD
recognizes that it lacks the capacity to make both
unscheduled and scheduled engine power module repairs at
the levels needed to support the F-35 program.”
An updated July 2022 report (GAO-22-104678) stated that
the “number of power modules needing repair was largely
due to coating distress of the high-pressure turbine blades.
F-35 aircraft operations in dusty or sandy environments, as
well as the higher running temperatures, have caused
accelerated coating distress on the blades.” The report
further stated:
Annual engine sustainment costs, a portion of total
sustainment costs, have increased from $79 million
in fiscal year 2016 to $315 million in fiscal year
2020.... By fiscal year 2028, maintenance costs for
the F-35 aircraft engine are projected to be over $1
billion annually. According to Pratt & Whitney
officials, scheduled maintenance has the potential
to be over 70 percent of total engine maintenance
costs by 2030.
