The Fire That Started in 2019: Kommandor Susan, MAIB Report 10/2026, and What the Industry Still Gets Wrong About Assumptions

The Incident Didn’t Start on the 25th of January 2025

It didn’t start when smoke began filling the engine room of the Kommandor Susan in the Firth of Forth. It didn’t start when the alarms sounded, when the power went black, or when the crew mustered and scrambled to extinguish a fire that had no business being there.

It started in 2019 — in a shipyard, during a routine overhaul, when someone installed the wrong bearings and nobody noticed.

That’s the uncomfortable truth buried inside MAIB Report 10/2026. The Kommandor Susan didn’t suffer a sudden mechanical failure. She suffered the delayed consequences of a decision made six years earlier, compounded by inadequate oversight, unchallenged assumptions, and extended service intervals applied to components they were never designed for.

No one was hurt. The crew performed well. The fire was extinguished. The vessel made it back to Leith.

But the lesson here is not about what the crew did. It’s about what the organisation failed to do — for six years before anyone struck a match.

What Happened: The Factual Record

At 13:05 on 25 January 2025, the Kommandor Susan — a site investigation vessel operating in the Firth of Forth, Scotland — experienced a catastrophic failure of diesel generator engine number one (DG1) during sea trials.

The failure was violent and immediate. It triggered an engine room fire and a complete power blackout across the vessel.

The crew responded with discipline: the fire was extinguished, all personnel mustered safely, and no injuries were recorded. There was no pollution. But with total electrical power gone, the vessel lost propulsion and began drifting eastward. Attempts to deploy anchors failed — the anchor winches ran on electrical power and were inoperable. Two tugs were called. Limited propulsion was eventually restored. Kommandor Susan was brought back to Leith harbour under tow and her own partial power.

The MAIB investigation, culminating in Report 10/2026, traced the root cause to a 2019 major engine overhaul in which non-genuine components were installed in the Caterpillar 3516B-TA diesel generator engines. Specifically, the big-end and main bearings fitted were not OEM Caterpillar parts. They had a copper backing layer where genuine Caterpillar bearings use aluminium. The bonding between layers was weaker. The durability was inferior. And the extended service intervals that had been approved for these engines — intervals valid only for genuine OEM components — meant the non-genuine parts ran far past the point at which they should have been replaced.

Six years later, one of them gave way.

Root Causes: Five Points of Failure

1. Counterfeit or Substitute Components Installed Without Detection

The most foundational failure was simple: the wrong parts went into the engines. The non-genuine bearings installed during the 2019 overhaul were materially inferior to the OEM specification — different metallurgy, weaker bonding, shorter service life. Post-incident inspection confirmed that pistons, connecting rods, and bearings in DG1 were all non-OEM.

The MAIB notes the parts were installed without the vessel owner’s knowledge — which, on one reading, sounds like an excuse, but on another reading is a damning indictment of the oversight gap that made such a thing possible in the first place.

2. Extended Service Intervals Applied to the Wrong Parts

Extended service intervals for the Caterpillar engines had been approved — and those approvals were legitimate. But they were approved on the assumption that genuine Caterpillar components had been installed. They hadn’t been. The moment non-OEM parts went in, the extended interval regime became a mechanism for running already-inferior components long past their effective service life. No one revisited this assumption. No one asked whether the intervals still applied.

3. No Verification of Component Authenticity

Neither the vessel owner nor the management chain implemented any process to verify that the parts being fitted were genuine OEM components. There was no authentication check, no cross-referencing with Caterpillar approval records, no documentation trail requiring the maintenance contractor to confirm part provenance. The parts went in. The paperwork was filed. The assumption was made.

4. Inadequate Owner Oversight During Critical Maintenance

The MAIB identified what it called “a shortfall in oversight and contractor assurance by the vessel owner during the overhaul.” When a vessel undergoes a major engine overhaul, the owner and superintendent carry a duty to supervise critical work — not just to review completed paperwork after the fact, but to verify that the right parts are being installed in real time. That supervision did not happen here to the required standard.

5. No Accountability Framework for Critical Maintenance Monitoring

The Chief Inspector’s letter to Hays Ships following the investigation highlighted the need for “a structured supervision system that provides clear accountability measures” and systematic monitoring of all critical maintenance work. No such system existed. There was no mechanism to ensure that what was ordered, what was delivered, and what was installed were all the same thing.

The Dangerous Nature of Assumptions

There is a concept in accident investigation called a latent failure — a flaw buried within a system that causes no visible harm until the right (or wrong) set of conditions brings it to the surface. Latent failures are the most dangerous kind, precisely because they are invisible. The system appears to work. The engine runs. The paperwork is clean. The service intervals are extended with confidence. Everything looks fine.

Until it isn’t.

The Kommandor Susan case is a textbook example of how latent failures accumulate. In 2019, a contractor installed non-genuine parts. That was failure one. Nobody checked — failure two. Extended service intervals were applied without verifying the component specification — failure three. Six years passed with no owner audit, no parts traceability review, no challenge to the underlying assumptions — failures four through infinity.

Each of those failures, standing alone, might seem minor. A maintenance contractor cuts a corner. An owner trusts a supplier. A superintendent signs off on extended intervals without cross-checking the OEM specification. None of these, individually, sinks a ship or starts a fire. But they compound. They stack. And then, on a cold January afternoon in the Firth of Forth, the accumulated weight of six years of unchallenged assumptions becomes a catastrophic bearing failure, an engine room fire, and a vessel adrift.

The dangerous thing about assumptions is not that we make them. It’s that, over time, we forget we made them.

What If? — Scenario-Based Escalation

The Kommandor Susan incident resulted in no injuries, no fatalities, no pollution. The crew behaved well. The tugs arrived. The vessel came home. Now remove one or two of those favourable variables.

What if the failure had occurred in heavy weather? In developing North Sea conditions, a vessel adrift with no anchor capability and no propulsion is not merely inconvenienced. She is in immediate danger of foundering, striking offshore infrastructure, or broaching. A fire that was controlled in calm water may not be controllable in three-metre swells.

What if the failure occurred near congested waters or offshore infrastructure? The Firth of Forth is not the open ocean. In the southern North Sea, or near a busy port approach, a vessel adrift with no steerage is a hazard not just to herself but to every structure and vessel in her vicinity.