Aviation safety is built on the 'Swiss cheese' model – but the Japan Airlines crash shows the holes sometimes line up

• An aviation safety theory may explain a plane crash in Japan this week. 
• The "Swiss cheese" theory argues that crashes are often caused by a series of small errors. 
• A Japan Airlines plane crashed into a smaller plane while landing at Tokyo Haneda airport Tuesday. 

A Japan Airlines Airbus A350 erupted into a fireball this week after colliding with a Japanese coast guard aircraft on a runway at Tokyo's Haneda Airport.

Five people in the coast guard plane, a smaller Dash-8 turboprop, died. However, in what many people call a miracle, all 379 passengers and crew aboard the A350 jetliner survived.

The aircraft only had three of its eight emergency exit doors available for the evacuation, which took about 18 minutes in total.

An investigation into the cause of the crash is underway. Still, it will likely be months before Japanese regulators release their preliminary findings, and it's impossible to know for sure the root cause before then.

But information is already starting to emerge, with safety experts trying to piece together what happened. Former JAL pilot and aviation safety analyst Hiroyuki Kobayashi told Reuters the cause was likely pilot error.

A published air traffic control transcript said the Dash-8 pilot did not have clearance to enter the active runway. According to the recordings, the instruction was to hold short of the runway, not enter, though the Dash-8 pilot — the one person in the plane who survived the collision — told investigators he believed he had clearance to take off.

While this may look like a straightforward case of pilot error or negligence, a core causation model in aviation safety called the "Swiss cheese model" could tell a different story.

The JAL air crash was likely caused by several smaller errors

Air crashes are rarely caused by a single factor, but rather are a series of individual failures that collectively lead to an incident or accident.

This is commonly illustrated through the "Swiss cheese" model. The "holes" represent the failures, and the slices of cheese represent the layers of protection put in place to prevent those failures from turning into a catastrophe.

Using the method, safety professionals can more easily identify and address safety gaps before an event occurs, whether it be related to human error, technology, procedures, or everything in between.

"Airlines can be accused of cost-cutting in various areas, like putting more seats on airplanes and cutting back on amenities and services," travel analyst Henry Hardevelt told Business Insider. "But one thing airlines don't skimp on is safety."

According to the Swiss cheese model, events like the one in Tokyo can happen when too many safeguards fail — allowing the "holes" to line up and open a window of opportunity for an accident or incident.

"Investigators are going to look at everything like weather, air traffic control, communications, and human factors," Anthony Brickhouse, an aviation safety associate professor at Embry-Riddle Aeronautical University, told Business Insider.

Fatigue, lighting malfunctions and an earthquake may all have played a role

In the case of JAL, the Dash-8 pilots' misunderstood radio call could turn out to be because they were experiencing particularly severe fatigue in the wake of their duties during the earthquake. Fatigue, the hypothetical second hole, is commonly attributed to pilot error.

For the pilots of the A350, it's likely investigators will ask if they saw the Dash-8 on the runway during landing. However, the nighttime conditions — another possible hole — could have made it more difficult for them to spot the turboprop and avoid a collision.

The earthquake may turn out to be a contributing factor in the JAL accident as well. Had the disaster not happened, the Dash-8 likely wouldn't have even been on the runway that night in the first place.

"Something that caught my attention was that this wasn't two commercial airliners colliding, but a commercial airliner and a military aircraft," Brickhouse told BI. "I'd be interested in what role that played in the accident and how the coast guard operates out of Haneda airport."

The string of hazards doesn't stop there, though. Many large global airports have "stop bar" lights that indicates to pilots if a runway is clear. They're intended to stop planes from entering an active runway even if they think they have clearance.

On the day of the accident, however, the lights at the intersection where the Dash-8 entered the runway were malfunctioning, according to a notice to airmen that went into effect on December 27. Pilots are expected to check airport NOTAMs.

"These stop bar lights are a series of red lights at the junction of the taxiway and the runway, and they are a sort of last resort precaution, if you like, to stop pilots from blundering onto an active runway," Geoffrey Thomas, editor in chief of AirlineRatings.com, a source of airline safety ratings and product reviews, said on Thursday.

Airport equipment like the stop bar lighting exists as another redundancy, or layer of Swiss cheese, in an aviation safety system. But the safeguard in place for the Dash-8 failed, too, and could not course-correct the pilot's potential communication error.

Experts have been cautioning for months about the technology gaps in runway detection systems, especially after a string of near-misses gave the US a wake-up call last year.

"Many of the serious incidents could have been avoided through better situational awareness technologies that can help air traffic controllers and pilots detect potential runway conflicts," Flight Safety Foundation CEO Hassan Shahidi told Reuters on Wednesday.

Nevertheless, in every case in the US, at least one layer of Swiss cheese held up to prevent an accident from occurring, from air traffic control's quick corrections to the evasive actions of pilots.

While the investigation will likely uncover even more information as the months go on, it's too early to say what caused the Dash-8 and A350 to collide in Tokyo.

Still, it's a good example of the Swiss cheese model at work in modern aviation and a reminder that even the safest systems are at risk if the right hazards come together at the wrong time.