NASA has released a sweeping investigation report into the propulsion system failures that plagued Boeing’s CST-100 Starliner during its Crewed Flight Test (CFT) last year. The report finds a cascade of hardware failures, qualification gaps, organizational breakdowns, and a culture that prioritized schedule and provider success over engineering rigor in the program.

“We returned the crew safely, but the path we took did not reflect NASA at our best.”
NASA Administrator Jared Isaacman on the Boeing CFT-1 flight in 2024.

The report, compiled by a Program Investigation Team (PIT) chartered in February 2025 and completed in November 2025, spans 311 pages and issues 61 formal recommendations spanning technical, organizational, and cultural areas. It concludes that the events during the June 2024 mission meet the criteria for a Type A mishap — NASA’s most serious classification — and recommends the agency retroactively designate it as such.

NASA Administrator Jared Isaacman said today in a press conference that, “OFT and OFT-2 investigations did not drive to or take sufficient action on the actual root cause of the anomalies that we observed. The investigations often stopped short of the proximate or the direct cause, treated it with a fix, or accepted the issue as an unexplained anomaly. In some cases, the proximate cause diagnosis itself was incorrect due to insufficient rigor in following the data to its logical conclusion.”

He added, “We still stepped into the crewed flight test.”

Synopsis Of A Near Miss

Starliner CFT-1 launched on June 5, 2024, from SLC-40 at The Cape, carrying NASA astronauts Butch Wilmore and Suni Williams to the International Space Station. What was planned as an 8-to-14-day certification mission stretched to 93 days as engineers grappled with four distinct hardware anomalies in the spacecraft’s propulsion system.

Ultimately, NASA determined that the risk to the crew posed by using Starliner’s service module RCS for departure from the ISS could not be closed out within agreed-upon margins. The capsule returned uncrewed on September 7, 2024, landing at White Sands Space Harbor.

Wilmore and Williams remained aboard the ISS as part of Expedition 71/72 and returned to Earth on March 18, 2025, aboard SpaceX’s Crew-9 Dragon, landing safely offshore in the Gulf of Mexico. Both astronauts have since retired from NASA.

What Went Wrong?

During approach to the ISS, five service module reaction control system (RCS) thrusters triggered their fail-off fault detection, resulting in a temporary loss of six-degrees-of-freedom control on the docking axis. Through in-situ troubleshooting, four of the five thrusters were recovered, allowing Starliner to dock. Simultaneously, seven of the spacecraft’s eight helium manifolds developed leaks during the mission, attributed to material incompatibility between seals and the oxidizer (nitrogen tetroxide), compounded by inadequate O-ring sizing.

A separate failure struck during descent when a crew module RCS thruster failed to fire, reducing that system to zero fault tolerance. The leading theory points to corrosion from carbazic acid — formed when residual propellant reacted with carbon dioxide — blocking the thruster valve. With only a single redundant thruster remaining for that control axis, loss of that thruster would have been catastrophic.

The propulsion system also lacked the required two-fault tolerance for deorbit burns, a design flaw that had existed since early development but went unidentified until CFT pre-launch preparations.

CFT-1: Four Key Anomalies
Anomaly	Description	Most Probable Cause
SM RCS Thruster Failures	Five thrusters failed off during ISS rendezvous, resulting in a temporary loss of 6-degrees-of-freedom control on the docking axis	Two-phase oxidizer flow (vaporization and cavitation) and Teflon poppet extrusion in oxidizer valves restricting flow
CM RCS Jet Failure	A descent thruster failed to fire, reducing the system to zero fault tolerance — loss of the single remaining redundant thruster would have resulted in loss of crew	Corrosion from carbazic acid formed by residual propellant reacting with CO₂, blocking the thruster valve
Helium Manifold Leaks	Seven of eight SM helium manifolds leaked during the mission, compromising propulsion system pressurization	Material incompatibility of seals with NTO oxidizer, compounded by inadequate O-ring sizing and poor gland fill/squeeze tolerances
Deorbit Fault Tolerance Gap	The propulsion system lacked required two-fault tolerance for deorbit burns — a design flaw present since early development but not identified until CFT pre-launch	Longstanding design deficiency undetected through multiple review cycles due to gaps in systems engineering and hazard analysis

Boeing And NASA Had Mutual Distrust Of Each Other

The report pulled no punches in assigning blame for the issues. NASA and Boeing were both identified as having some responsibility for the issues that arose before and during the Crewed Flight Test.

Perhaps the most striking portions of the 311-page report detail the cultural dysfunction that defined the CFT-1 mission. The PIT conducted 66 interviews with NASA and Boeing personnel in technical, management, and leadership roles, revealing a workforce fractured by mistrust, adversarial attitudes, and communication breakdowns between the two organizations.

The report stated that Boeing team members described feeling trapped in an environment where they were constantly bringing NASA the “wrong rock” and getting stuck in “gotcha” moments. One interviewee described NASA’s approach as adversarial rather than collaborative, with teams breaking Boeing’s work rather than bringing solutions. By the time the decision came to return Starliner uncrewed, Boeing felt the decision had been made without them.

Isaacman added some color to that end, saying, “Disagreements over crew return options deteriorated into unprofessional conduct while the crew remained on orbit. Witness statements describe an environment where advocacy tied to the Starliner program viability persisted, alongside insufficient senior NASA leadership engagement to refocus teams on safety and mission outcomes.”

On the NASA side, engineers reported being told their questions were “too detailed” or “out of scope,” with no follow-up mechanisms to address those concerns. Multiple interviewees noted a perception that Boeing selectively presented only favorable data, withheld dissenting views, or minimized risks. Personal relationships between CCP program management and Boeing management blurred professional boundaries, leading to perceptions of favoritism and lack of objectivity.

What’s Next For Starliner?

It’s hard to tell, but clearly, there is a lot of work remaining to be completed prior to the next Starliner flight.

“NASA will continue to work with Boeing, as we do all of our partners that are undertaking test flights,” said NASA Administrator Jared Isaacman.

“Sustained crew and cargo access to low Earth orbit will remain essential, and America benefits from competition and redundancy. But to be clear, NASA will not fly another crew on Starliner until technical causes are understood and corrected, the propulsion system is fully qualified, and appropriate investigation recommendations are implemented.”

Boeing was not present at today’s press conference, and has not made any statement on the report as of yet.