Fatal DC-4 Crash in Alaska Triggered by an Incorrectly Installed B-Nut

Timeline

Event 1 —

The DC-4 began its flight after the aircraft had been prepared for departure.

1.

Event 2 —

The aircraft carried a large fuel load for the planned operation.

2.

Event 3 —

A component in the propeller-feathering system had been incorrectly installed before the flight.

3.

Event 4 —

During flight, an explosion damaged the aircraft and its flight-control system.

4.

Event 5 —

The resulting damage left the aircraft difficult or impossible to control.

5.

Event 6 —

The aircraft crashed in Alaska and the crew were killed.

6.

Tragic DC-4 Crash in Alaska: How an Incorrectly Installed B-Nut Triggered a Fatal Chain Reaction

The Douglas DC-4 had been airborne for only a few minutes when a small plume of white smoke began trailing from its left outboard engine.

Then flames appeared.

The four-engine aircraft was carrying thousands of gallons of fuel and propane on a routine cargo run from Fairbanks to the remote community of Kobuk, Alaska. At first, the problem appeared to involve one engine.

But the emergency was about to become far more serious.

The pilots reported a fire and began turning back toward Fairbanks. Surveillance video captured the smoke and flames around the No. 1 engine. Seconds later, a bright explosion erupted behind the engine.

The aircraft suddenly entered an uncontrolled left turn.

The pilots could no longer control it.

The No. 1 engine separated from the wing just before the aircraft struck terrain near the Tanana River.

The main wreckage was followed by another major explosion several minutes later.

Both pilots died.

The subsequent investigation revealed an extraordinary maintenance chain: the No. 1 engine had lost power for a reason investigators could not determine, but when the pilots attempted to feather its propeller, an incorrectly installed B-nut in the propeller-feathering system allowed high-pressure engine oil to spray directly onto the hot exhaust system. At the same time, an improperly repaired fuel leak had allowed gasoline to accumulate in the wing structure behind the engine.

The resulting fire ignited that fuel.

The explosion damaged the aircraft's aileron control system.

And a relatively small maintenance error became one of the links in a fatal chain of events. (NTSB Data)

A 1945 Aircraft Still Flying Cargo in Alaska

The accident aircraft was Douglas C-54D-DC N3054V, the military-derived transport aircraft commonly known in civilian service as the DC-4.

Built in 1945, the aircraft had accumulated approximately 24,726.6 flight hours by the time of the accident. It was operated by Alaska Air Fuel Corporation, which used the aircraft for transporting fuel to remote Alaskan communities. (NTSB Data)

On April 23, 2024, N3054V was scheduled to fly from Fairbanks International Airport (FAI) to Kobuk Airport (OBU).

This was not a passenger flight.

The aircraft was carrying approximately 3,400 gallons of unleaded fuel along with two 100-gallon propane tanks.

There were two people aboard: the captain and the copilot.

Both were highly experienced.

The captain, age 68, had accumulated approximately 35,547 hours of total flight time, including nearly 21,000 hours as pilot in command.

The 63-year-old copilot had approximately 10,769 hours, including more than 4,000 hours as pilot in command. (NTSB Data)

This was therefore not an accident involving inexperienced pilots attempting to operate an unfamiliar aircraft.

The crew knew the DC-4.

They knew multi-engine operations.

They knew how to handle engine failures.

The problem was that the aircraft's maintenance history had created a combination of hazards that went far beyond an ordinary engine failure.

The No. 1 Engine Had Recently Been Replaced

One of the first things investigators examined was the history of the left outboard engine.

The No. 1 engine had been replaced twice in the weeks immediately before the accident.

A serviceable engine was installed approximately two weeks before the crash.

It was then replaced again with an overhauled engine approximately one week before the accident.

The overhauled engine had been completed by Anderson Aeromotive in November 2023. (NTSB Data)

That history would become significant.

The engine that eventually lost power was not simply an old component that had been operating unchanged for years.

It had recently undergone major maintenance and had been installed on the aircraft shortly before the accident.

The wreckage was too badly damaged by the subsequent fire, explosion and impact.

This distinction is critical.

The NTSB determined that the engine almost certainly lost power shortly after takeoff.

But the reason for that initial power loss remains undetermined.

The B-nut was not identified as the cause of the engine failure.

Instead, it became critical after the engine lost power, when the crew attempted to feather the propeller.

That sequence is at the heart of the accident.

A Fuel Leak Was Already Present

The aircraft had another problem before the accident flight.

The outboard fuel tank on the left wing, located near the No. 1 engine, had been leaking.

The operator had discovered that the tank leaked when it was full.

A repair was made the day before the accident flight to Fairbanks.

But the repair did not stop the leak.

According to the NTSB's final report, the tank continued leaking at approximately 5 to 10 drops of fuel per minute when full. The fuel did not simply fall harmlessly outside the aircraft.

From there, it dripped out of the wing structure behind the engine. (NTSB Data)

The airplane then sat for several days with its fuel tanks full.

Fuel continued to drip into the enclosed wing area.

That meant the aircraft already contained a potentially dangerous accumulation of combustible fuel near the engine and exhaust system before it ever departed Fairbanks.

This is one of the most troubling aspects of the accident.

At the time of takeoff, there was therefore both a recently installed No. 1 engine and an unresolved fuel leak in the same general area.

The Flight Begins Normally

N3054V powered up at approximately 9:25 a.m. Alaska daylight time.

It departed Fairbanks at approximately 9:55 a.m.

The flight was conducted under a company VFR flight plan.

The weather was not particularly challenging.

Visibility was approximately 10 miles.

There was no precipitation or significant obscuration.

The lowest reported clouds were at approximately 11,000 feet above ground level.

In other words, there was no obvious weather emergency forcing the aircraft toward the ground. (NTSB Data)

The aircraft was heading west after departure.

Then something went wrong with the left outboard engine.

Witnesses See Smoke

An eyewitness observed the aircraft shortly after takeoff.

The far-left engine—the No. 1 engine—did not appear to be running.

Then the situation escalated.

The witness saw flames coming from the engine.

The sequence was also captured by surveillance video.

Flames followed.

That visual evidence was crucial.

Investigators did not have to rely solely on witness descriptions of what happened.

The surveillance recording showed the progression from smoke to fire to explosion.

It also provided a timeline that could be compared with ATC communications, aircraft tracking data and the physical evidence recovered from the crash site.

"Fire on Board"

Approximately three minutes after takeoff, the pilots contacted air traffic control.

They reported that there was a fire onboard.

The crew's response was logical.

Now they had a fire.

They needed to return to the airport.

But they were operating a four-engine aircraft in which the No. 1 engine was already producing smoke and flames.

The pilots would also have been expected to feather the failed engine's propeller to reduce drag.

That is where the incorrectly installed B-nut became critical.

When the system was activated, oil was supposed to travel through the appropriate plumbing toward the propeller.

But the plumbing connection near the firewall had been incorrectly assembled.

The result was catastrophic.

What Is a B-Nut?

A B-nut is a type of aerospace tube fitting nut used with flared tubing connections.

The name sounds insignificant.

The component is small.

But in an aircraft system, a small fitting can have a very large consequence if it is installed incorrectly.

In the DC-4's propeller-feathering system, a B-nut was supposed to secure a connection at a bulkhead fitting.

Investigators found that the fitting had a B-nut and metal hard line installed on one side.

The opposing side, however, had no B-nut and no hose attached.

The fitting's threads were intact and showed no apparent mechanical damage.

This meant that when the feathering pump was activated, oil could escape from the improperly configured connection.

And it would not simply leak harmlessly.

It would be sprayed under pressure into the engine compartment.

The exhaust system was extremely hot.

The Feathering System Turns the Problem Into a Fire

The NTSB reconstructed the sequence from the physical evidence.

High-pressure oil was then released through the incorrectly installed fitting.

Investigators found oil residue across the external area of the exhaust system. (NTSB Data)

The white smoke seen in the surveillance video was consistent with the oil reaching the hot exhaust.

Then the oil ignited.

Flames appeared.

But the aircraft already had another problem waiting nearby.

Once the fire reached it, the situation changed from an engine fire into a much larger event.

The fuel-air mixture ignited.

An explosion followed.

The Explosion Damages the Flight Controls

It damaged the aircraft's structure and flight-control system.

The NTSB determined that the explosion separated the aileron bell housing.

That detail is central to understanding why the aircraft suddenly became uncontrollable.

Ailerons control roll.

They allow the pilots to raise one wing and lower the other.

If the mechanical linkage connecting the cockpit controls to the ailerons is destroyed, the pilots can lose their ability to control the aircraft's bank.

That appears to be what happened.

After the explosion, the aircraft entered an uncontrolled descending left turn.

The pilots could no longer maintain control. (NTSB Data)

This is why the accident cannot accurately be described simply as "engine failure."

The engine failure initiated the emergency.

The unrepaired fuel leak supplied additional fuel.

The explosion damaged the flight controls.

The loss of control caused the aircraft to descend into terrain.

Each event was connected to the next.

The No. 1 Engine Separates

The aircraft continued its uncontrolled descent.

The separation itself was another indication of the violence of the sequence.

Investigators recovered major portions of the upper left wing and other components near the location of the in-flight explosion.

The debris field contained sections of the aileron bell housing and numerous small pieces of aluminum.

Some of the metal fragments displayed evidence of melting.

This was consistent with the intense thermal event that had occurred before impact. (NTSB Data)

The two pilots were fatally injured.

The Second Explosion

The accident was not over when the aircraft hit the ground.

Approximately three minutes after the impact, another major explosion occurred.

The University of Alaska Fairbanks detected multiple low-frequency signals associated with the accident.

The infrasound datallowed investigators to establish a remarkably detailed timeline:

The first explosion occurred at approximately 10:01.

The aircraft impacted terrain at approximately 10:03.

A second large explosion occurred at approximately 10:06. (NTSB Data)

The post-crash fire destroyed much of the aircraft.

The presence of large quantities of fuel made the recovery operation particularly difficult.

It was the aftermath of an in-flight fire, structural explosion, impact and subsequent fuel-fed fire.

Investigators Reconstruct the Chain

The physical evidence eventually allowed the NTSB to reconstruct the accident in extraordinary detail.

The answer was frustratingly incomplete.

But the engine had suffered extensive thermal and impact damage.

Important components were missing.

The fuel pump, propeller governor and both magnetos had separated from the engine and were not recovered.

The accessory and blower section had also separated from the engine case. (NTSB Data)

The engine's internal components were examined.

Investigators removed two cylinders and used a borescope to inspect internal areas.

But the evidence was not sufficient to establish the original reason for the loss of power.

That finding matters because the accident was not caused by a single maintenance error alone.

The initial engine failure remains unexplained.

The maintenance error determined what happened afterward.

The Maintenance Chain

The NTSB's investigation identified two separate maintenance problems.

1. The incorrectly installed B-nut

When the feathering pump was activated after the engine failed, high-pressure oil sprayed onto the hot exhaust.

2. The incorrectly repaired fuel leak

A repair was performed.

It did not stop the leak.

When the oil-fed fire reached the accumulated fuel, an explosion occurred.

That explosion damaged the aileron control system.

The aircraft became uncontrollable.

These two maintenance issues interacted.

Either problem by itself might not have produced the fatal sequence.

Together, following an engine failure, they created a chain that left the pilots with virtually no chance of recovery.

The Human Element

It is important not to reduce the accident to a mechanic "forgetting a nut."

The NTSB's findings specifically identify maintenance personnel installation as a personnel issue.

That wording reflects the broader safety problem.

It involves procedures, inspections, documentation, independent verification and organizational oversight.

The accident demonstrates why post-maintenance inspections are not paperwork exercises.

The aircraft had also undergone work involving the fuel tank.

Yet two defects remained in the same general area of the aircraft.

The result was an ignition system that the aircraft's designers never intended to create.

A 79-Year-Old Aircraft With a Modern Safety Lesson

It was a product of a different era of aviation.

But the maintenance principles exposed by its crash are timeless.

A hydraulic or oil-pressure fitting does not become less important because the aircraft is old.

A fuel leak does not become acceptable because the aircraft is used for cargo.

A repair is not successful simply because the aircraft can still fly.

And an inspection is not complete until the actual condition of the component has been verified.

The accident therefore provides a powerful reminder that maintenance-induced failures can be more dangerous than the original failure that triggers them.

The No. 1 engine's power loss was serious.

They had an emergency procedure for an engine failure.

The incorrectly installed B-nut changed that manageable emergency into an uncontrolled fire.

And the explosion changed the emergency into an unrecoverable loss of control.

The Crew Had Very Little Time

The flight lasted only minutes.

The aircraft departed at approximately 9:55.

By roughly 9:58, the recorded airspeed began falling from approximately 135 knots toward 117 knots.

At 9:59, the airspeed stabilized.

At 10:00, it began increasing again, reaching approximately 148 knots.

The first explosion occurred around 10:01.

The aircraft impacted terrain around 10:03. (NTSB Data)

That timeline shows how rapidly the accident developed.

The pilots were not dealing with a slow-developing maintenance issue.

They went from a normal departure to engine failure, fire, explosion and loss of control in only a few minutes.

Once the aileron system was destroyed, there was no conventional checklist that could restore control.

Accident Facts

The Aviation Safety Network independently records the accident as the April 23, 2024 crash of Douglas C-54D N3054V near Fairbanks, with two fatalities and no survivors. (Flight Safety Foundation)

The NTSB's Probable Cause

Unlike many recent aviation stories where the investigation remains preliminary, the NTSB has issued a final report for ANC24FA029.

The Board's official probable-cause finding states:

“A loss of power of the No. 1 engine for reasons that could not be determined, and the incorrect installation of a B-nut fitting in the propeller feathering system, which allowed engine oil to spray onto the exhaust system when the propeller was feathered following the loss of engine power.”

The NTSB further determined that an incorrectly repaired fuel leak contributed to the accident, resulting in an explosion that separated the aileron bell housing and led to a loss of control and impact with terrain. (NTSB Data)

Those findings are unusually revealing.

The NTSB did not say that the B-nut caused the initial engine failure.

Why the B-Nut Matters

It can be difficult to understand how such a small component could contribute to the loss of a large four-engine aircraft.

The answer lies in systems interaction.

Normally, that system should operate as intended when a propeller is feathered.

But the incorrect installation left one side of the fitting disconnected.

The exhaust provided an ignition source.

The aircraft lost control.

In other words, the B-nut did not need to be large to be important.

It only needed to be in the wrong configuration at the wrong moment.

That is one of the fundamental realities of aircraft maintenance.

Small components can carry enormous safety consequences.

What Happened to the Two Pilots?

The crew members were both experienced aviation professionals.

The captain had more than 35,000 hours of flight experience.

Neither experience nor aircraft familiarity could overcome the loss of the aircraft's control system following the explosion.

Pilots can respond to engine failures.

They can execute emergency checklists.

They can turn back toward an airport.

But if an explosion destroys the flight-control system, there may be no remaining control authority.

The crew's actions must therefore be evaluated in the context of the information and aircraft capability available to them at the time.

The NTSB did not identify pilot error as the probable cause.

The investigation instead centered on the aircraft's maintenance condition and the chain that followed the No. 1 engine power loss. (NTSB Data)

A Tragedy That Began Before Takeoff

Perhaps the most important lesson from the Fairbanks DC-4 accident is that the accident technically began before the aircraft left the runway.

The attempted repair had already failed.

Nothing visibly catastrophic happened while it was parked.

The defects remained hidden.

The pilots did what pilots are trained to do.

They began the emergency response.

That normal action activated a system containing the incorrectly installed fitting.

The existing fuel leak supplied additional fuel.

The explosion destroyed part of the flight-control system.

The aircraft became uncontrollable.

The pilots had no realistic opportunity to overcome that sequence once it reached its final stages.

The Broader Aviation Safety Lesson

The Alaska Air Fuel DC-4 crash is a powerful reminder that aviation accidents rarely depend on a single broken part.

The initial No. 1 engine failure was never conclusively explained.

Had the aircraft simply lost one engine, the outcome might have been very different.

The aircraft lost control.

The lesson for aviation maintenance is straightforward: every fitting, hose, nut, clamp and repair matters because the safety of the entire aircraft depends on systems working together under abnormal conditions—not merely during normal flight.

A repair that does not actually stop a fuel leak is not a completed repair.

An engine installation requires more than simply mounting an engine and making it operational.

And a post-maintenance inspection must verify the actual configuration of the aircraft.

The DC-4 was almost eight decades old, but the fundamental lesson applies equally to a modern airliner, a business jet, a helicopter or a small piston aircraft.

The accident was not caused by one dramatic mechanical failure.

It was a chain that began with an unexplained engine power loss and was made catastrophic by maintenance defects that allowed oil, heat and fuel to meet in exactly the wrong place.

Two highly experienced pilots were killed.

And a small incorrectly installed fitting became one of the most important pieces of evidence in understanding why.

For the reconstruction's audience, the most important takeaway is perhaps this:

The emergency began in the air, but the conditions that made it fatal were created on the ground.

Primary Source / Investigation Record

Investigation reference: ANC24FA029

Sources

• https://data.ntsb.gov/Docket?NTSBNumber=ANC24FA029