Every time you step into an aircraft, you are entering an environment that is highly controlled to be as safe as possible. From the design of the doors and the seats to the safety briefing, everything is highly regulated. However many of these regulations are sometimes considered to be “written in blood”.

What this means is that aviation, cabin safety has evolved from what it used to be decades ago. Unfortunately, a lot of what was learned has been done so when things go wrong, ie when aircraft end up in an accident.

Many times, it is the accidents where not all passengers survive that give a lot of information to investigators and designers. This is logical. When all passengers survive, that means everything went right while many accidents where all passengers perish, the “container” or fuselage has catastrophic damage.

This article will shortly step through how an investigation works in accordance with ICAO Annex 13; then, what a recommendation is; finally, it will look at case studies on how investigations have shaped modern cabin safety.

This specific article is not meant to go especially in-depth, but there is a conference paper in the works on this topic that includes items such as doors and seats.

ICAO Annex 13 Investigation Process. Image: sassofia.com

What Exactly Is an Investigation?


When reading about aviation accident investigations, the term ICAO Annex 13 gets thrown around a lot. That is due to the fact that Annex 13 is a guideline for all countries on how an aviation accident should be investigated.

There are different parts of the Annex 13 guidelines, from how the accident should be registered, who should take part, up to how to write the final report.

When an accident or incident occurs, the first step is that it needs to be officially reported. This starts a whole chain of events based on the severity of the accident or incident.

For the actual investigation, the country of occurrence in most cases will run the investigation, and they will invite the countries where the aircraft and engines are manufactured. Other parties invited are usually the operator and its country plus the country of the citizens on board.

The first steps will be to collect facts and data from the site, as well as to secure the black boxes.  This is a priority to be done in the first hours and days, as depending on external factors such as weather or the need to reopen an airport. The site will not be able to be preserved.

Beyond the traditional wreckage gathering and interviews, there are also novel investigation methods being used. One common one is to use drones to map the site; another is to use a laser scanner device for the same purpose.

Fire damage can give a lot of clues to the investigators, but is can also hide evidence and require in depth analysis.

Out of every accident investigation, there are always recommendations to the aviation industry, or to specific players, on how to improve safety for the traveling public.

Photo: Jonathan Borba on Pexels

What Is a Recommendation?


At the end of every accident report, there is a section titled “Recommendations.” These recommendations can be for any part of aviation, and are based off of what the findings were in the investigation.

Investigators have looked at the whole sequence of events and usually have identified areas where practices can be changed to make aviation safer.

The regulatory authorities accept some of these recommendations before the final report is even released. Others, like the flight desk video recorder, appear repeatedly in many different reports.

As the goal of the investigation is only about safety and not about blame or financial reasoning, sometimes there is a lot of pushback on some recommendations. The most current example is the flight deck video recorder, which while being invaluable to the investigators, has massive privacy concerns for the Pilots themselves.

It will be highly unlikely therefore, that video recording will ever make it into the flight deck.

gray air vehicle with yellow coated cable around docking wheels
Photo by Joël Super on Pexels.com

How Did We Get Here?


Aviation cabin safety is a special sector of safety due to the fact that the normal traveling passenger is not in any way trained regarding aircraft. Beyond that, the cabin needs to be designed for people of all sizes, from the seat sizes to the seat pitch and the size of the doors.

What does this mean in a practical sense? It means that things are designed for an “average” size person, trying to take into account the averages for both females and male builds. So people who are on the lower or higher end of the sizes might have trouble using parts of the cabin.

There is also a lack of accessible design for disabled passengers, even with the strides made in parts such as the toilets.

The regulation of cabin design is something that has come up in the last years, as some of the regulations are quite old. However, changing these older regulations can be challenging as it usually requires testing and research, which can be expensive and extensive.

What this can mean is, as stated above, that changes to regulations usually only happen after something occurs that has gone wrong. Unfortunately, that means usually for cabin safety that people might be injured or even die before a regulation comes under scrutiny.

Case Studies


These next sections will cover some specific case studies and their impact on current day cabin safety. All information related to the accidents themselves will be taken from their respective accident reports, written and released by the corresponding accident investigation organization.

Evacuation


Evacuation has become more of a hot topic in the last years, as there is only a limited amount of time that the people on board can safely exit. The current regulation is listed at 90 seconds for a full aircraft of people to exit with only half of the doors in use.

Both the time and the limited exits are based on what could be expected in actual crash conditions. The time is also based on what could be expected due to fire and smoke, the usual primary hazards after a crash has occurred.

There have been many cases in recent years where evacuation was successful, even if the plane was subsequently destroyed by fire. Speed is of the essence before the fuselage is penetrated by fire or the smoke overtakes the people on board.

Such as in the case of Pacific Western Airlines (PWA) 501, delays can occur due to confusion and not enough information. While everyone on board survived, minutes were lost due to miscommunication.

These delays mean as well that there might not be 90 seconds anymore for the people on board to evacuate. In the case of PWA 501, the investigators stated that the last passengers evacuated at the last possible moments.

A big point that has been at the forefront of evacuation safety is the fact that passengers are taking their cabin baggage with them when they evacuate. Combined with airlines charging money for checked bags, the amount of luggage carried in the cabin is ever increasing.

The luggage being taken on board is not just the small personal item, but also large rolling bags which are more of a concern. Since passengers have been taking photos and videos of evacuations, there is evidence that around 50% of passengers are taking bags with them when evacuating the aircraft. While so far there have been no injuries or deaths related to baggage taking by passengers during the evacuation, it might become an issue in the future.

Taking bags cuts into the 90-second window and makes it harder to maneuver within the aircraft. In addition, the bags themselves can puncture or damage slides.

The RAeS states in its Emergency Evacuation of Commercial Passenger Aeroplanes, 2nd Ed. 2020, that it believes that certification of evacuation for aircraft does not take these larger pieces into account. The baggage used in the certification runs is usually light-weight and not representative of bags people are really bringing on.

Lockable overhead bins are perhaps an option, but the hazards might outweigh the benefits. If it is the case that passengers try to break into the overhead bins, it could use up valuable time.

At best, an aircraft evacuation is a highly stressful and fearful experience. With a lack of clear communication between flight deck and cabin, as well as hazardous conditions such as engines still running and fuel spills, an evacuation can become a hazard within itself.

Laudamotion had an incident in 2019 where an evacuation was initiated by the cabin Crew without the Flight Crew being aware. The passengers exited the aircraft in the path of the running engine, and if they had moved into the danger area, they could have been seriously injured.

Dynamic International Airways had a similar event where a passenger was seriously injured by passing behind the running engine.

EgyptAir Flight 667 fuselage fire damage. Photo: Wiki COmmons

Fire


Fire could be considered one of the biggest hazards to commercial aviation. In an accident, the fire might be one of the starting hazards, or it might be a hazard once the aircraft has reached the ground.

For a fire to exist, it requires three things, Fuel, Oxygen, and Heat. Fuel can be anything from cabin materials, cargo, to the aircraft fuel itself.

The addition of oxygen can be hazardous when opening doors during evacuation, as the addition of fresh air can cause a flashover within the cabin. Or, in the case of ValuJet 592, the oxygen can be from a different source.

In this accident, a shipment of expired oxygen generators were packed improperly in the cargo hold.

Oxygen generators create oxygen through an exothermic reaction, meaning that the canisters themselves become very hot. This heat plus the oxygen emitted, and further fuel within the cargo hold allowed the fire to quickly get out of control.

The investigation into ValuJet 592 led to the recommendation to have smoke detection and fire suppression systems in cargo holds.

Heat sources can be due to the engines and electric shorts within the aircraft wiring system. The engines are important when there are fuel spills. While aviation fuel is very stable in its liquid form, once it is heated past flashpoint, it will explode.

According to the final report for the TWA 800 accident, the heated fuel vapors were ignited from a wiring short that caused catastrophic damage.

While TWA 800 was a catastrophic accident, this aviation fuel-heat source interaction is one of the big reasons why evacuation is conducted as fast as possible.  Beyond just exiting the aircraft, it is important for passengers to get away from the plane itself, especially if fire fighting services are not present and spraying foam. 

For the cabin, Swissair 111 is an example of flammable and non-flame resistant materials being used in aircraft with catastrophic results. The Transportation Safety Board of Canada found that the oxygen system in the aircraft could fail in a fire, thereby releasing oxygen to further feed the blaze.

The hazard of Swissair 111 in terms of cabin safety is that the fire was inaccessible and was not able to be accurately analyzed. The investigation from this accident found that even though there were already regulations on materials used within aircraft, items were still found to be flammable.

The outcome of the investigation was a major push to clarify testing methods and to make sure that improperly flammable materials were no longer used within aircraft and cabins.

Air Canada 797 had again a hidden fire somewhere in the rear of the aircraft (the exact location was not determined). The recommendations from this investigation have led to the inclusion of fire detectors in lavatories, automatic fire extinguishing systems in waste bins, and the inclusion of modern halon fire extinguishers.

For Cabin Safety, the goal is to not have a fire start. The fires that are occurring now are also usually different than the ones that happened in the past. Now, we are hearing more and more about personal electronic devices catching fire, many times due to battery puncture. The battery puncture can occur when the device is jammed into an aircraft seat.

This shift in fire cause might mean that the regulations will again need to change. We have already seen it in the flight safety briefing at the beginning of a flight. Furthermore, on some aircraft, safety devices are carried by Crew to isolate these passenger electronic devices if they catch fire.

Photo: Wiki Commons.

Smoke


Where there is fire, there is smoke, and in some cases, the smoke can be more hazardous. In the base forms, many materials used in aircraft are quite flammable, but the materials have been adjusted to fulfill the certification requirements either with self-extinguishing technology, slower than normal burn materials, or other requirements.

However, even with these newer materials, at some point, they will still break down and emit toxic smoke. Ideally, this breakdown occurs once an evacuation has been completed and all passengers and Crew are moved to safety.

The aforementioned Air Canada 797 incident also affected the regulations relating to smoke. The addition of emergency lighting was mandated, as well as the addition of smoke hoods for the Crew.

When the acrid smoke gathers in the cabin, it first fills the upper part. This smoke is impossible to see through, which is why emergency lighting is on the floor and seat areas.  For AC797, the investigators found that passengers had actually gone past the overwing exits and succumbed in the rear of the cabin.

Since smoke is directly related to fire, tacking the fire will also remove the smoke hazard. There have been changes to materials to prevent them from emitting the acrid gasses as long as possible, but that is only a stopgap measure until full material breakdown occurs.

That means that fire prevention, timely landing, and quick evacuation will be the first lines of defense against a smoke hazard. Moving the passengers to less smoke-impacted areas can also help in passenger health as well as evacuation times.

Flight Attendants Spill The Secrets No One Else Knows ...
Brace position. Photo: journeyranger.com

Brace Position


The brace position as we know it is relatively new. British Midlands 92 was the accident that spawned a lot of research on the topic. The reason behind why this accident was the key is relatively morbid, but it was because not all passengers died, and some escaped without serious injury.

I was lucky enough to be present at a lecture by Professor Angus Wallace on this topic while at Cranfield University.

Professor Wallace treated a number of passengers from the accident and then did further research into what a better brace position could be. 

British Midlands 92 occurred in 1989, and in the ’90s, research was conducted into what would be the best passenger brace position. However, this type of research was very expensive, as it needed to be conducted with live testing with dummies.

In the decades following this research, other groups worldwide conducted further research.  However, as it could be expected, the outcomes from the studies did not all agree.

The goal of the brace position is to prevent injury to passengers so that they can subsequently exit from the aircraft in an evacuation under their own power.

As passenger seatbelts are only lap belts, it requires bracing of the lower and upper body to prevent impact with objects around the passenger, such as the seat in front. As seat pitch can vary and passengers are of varying sizes, the testing needs to be exhaustive to determine the most effective brace position.

As of 2016, the IBRACE group was formed, which is supported by the ICAO cabin safety group. The goal of this group is to plan and conduct the research needed to make a final recommendation into what the proper brace position should be.

Photo: Pexels.com

Summary


The research and testing required for cabin safety items can be extremely expensive or have ethical concerns when considering evacuation research. 

This can mean that the investigation into accidents and incidents is perhaps critical to further safety in aviation. At the very least it can help direct what aspects require further research.

“Written in Blood?” Perhaps. But what kind of engineers would we be if we did not intend to learn from events such as these to try and make aviation safer?


Featured image: Cabin Safety. Photo: Sourav Mishra on Pexels.