Several scientific studies have shown that the SARS-CoV-2 virus can remain viable and infectious on surfaces for up to several days depending on the type of surface and the environmental conditions. Consequently, aircraft operators might be required by authorities to increase the frequency of aircraft cleaning.
Airbus has been working with numerous industry partners and regulatory agencies across the aviation network, and has tested different solutions for the aircraft interior - including the cabin, cockpit and crew rest areas - in regards to cleaning and disinfecting. These solutions are in addition to the methods already described in its Aircraft Maintenance Manual (AMM) and the Aircraft Maintenance Publication (AMP) for the A220.
Cleaning removes visible soil (such as organic and inorganic material) from objects and surfaces and is normally accomplished manually or mechanically using water with detergents or enzymatic products. Thorough cleaning is essential before high-level disinfection and sterilization because inorganic and organic materials that remain on the surfaces can interfere with the effectiveness of these processes. Cleaning does not kill germs, but by removing them, it lowers their numbers and the risk of spreading infection.
Disinfection eliminates many or all pathogenic microorganisms on inanimate objects. This process does not necessarily clean dirty surfaces or remove germs and viruses, but by inactivating germs and viruses on a surface after cleaning, it further reduces the risk of spreading infection.
First of all, testing had to take into consideration a number of factors including the efficacy of the solution, or how well it performed during tests; and its effectiveness, or how well it would actually perform in the real world. The process time to apply the solution would affect resources as well as turnaround time. Aircraft material compatibility needed to be studied in terms of discoloration, flammability, tensile strength and corrosion. And of course, it was key to consider the health and safety of staff handling the solution and of passengers and crew.
On top of what is already described in the Aircraft Maintenance Manual (AMM), and in the Aircraft Maintenance Publication (AMP) for the A220, Airbus investigated several disinfection methods:
These treatments are based on the generation of liquid droplets which will widely disperse the disinfecting liquid into the cabin. The main advantage of fogging and electrostatic spraying is that it enables large areas to be treated, in a short time frame. However, Airbus identified risks of accumulation of disinfecting agents that could be induced by the usage of these methods, as well as a potential effect on cabin material in the mid or long term.
Electrostatic fogging and spraying can be done with handheld units, independently from on-ground equipment.
This quick method of disinfection and its effectiveness is known from other industries. The main interest of chemical fogging is to treat visible surfaces which may be touched by cabin and cockpit occupants, but also to treat non-visible surfaces as the very small particles containing the disinfecting agent are less influenced by gravity, stay in the air, and follow the airflow. Fogging with a smaller droplet size could enable less liquid to be used.
Fogging or large-area spraying may allow disinfectants to accumulate in non-visible aircraft areas. Mid and long-term effects regarding material compatibility in general and corrosion in particular, cannot be excluded when using these methods. Tests on soft materials have shown that the flame retardancy can be reduced depending on the chemical. These methods and associated potential effects would have to be closely assessed and monitored by the operator.
Gaseous hydrogen peroxide
Hydrogen peroxide (H₂O₂) is commonly used as a strong bleaching agent and as a disinfecting agent (for example in medicine, waste water and in the food industry) and is highly efficient against bacteria and viruses.
Note that here we only refer to the gaseous form.
- An airflow at ambient temperature is continuously blown over a high surface material that has soaked up a preheated aqueous solution of hydrogen peroxide.
- An airflow is dehumidified, then preheated above 100 °C; subsequently an aqueous solution of hydrogen peroxide is injected which causes a flash evaporation.
- Photocatalytic generation of hydrogen peroxide from natural humidity and oxygen already in the air is applied at ambient temperature.
There are potential risks of mid and long-term effects regarding material compatibility and for corrosion in particular. Turn Around Time (TAT) could be impacted by the waiting period required before people can enter the aircraft after the treatment process.
UltraViolet Germicidal Irradiation
UltraViolet Germicidal Irradiation (UVGI) uses short-wave ultraviolet (UV-C) energy to inactivate viral, bacterial, and fungal organisms. The effectiveness of this treatment depends on several variables including the applied UV wavelength, radiation intensity, the dwell time on a given surface, the nature of the germs to inhibit and the complexity of the surface geometry.
This quick method of disinfection and its effectiveness is known from other industries. It is semi- automated and could be a faster disinfection process with no residuals or consumables. It is highly efficient as an antiviral. No flammability impact has been noted.
There are potential mid and long-term effects regarding material compatibility (e.g. discoloration, reduction in tensile strength). The broad effectiveness of this method in the cabin environment is questionable due to several reasons, including the shadowing effect and required radiation intensity.
Thermal disinfection - from 37°Celsius (dark purple) to 57°Celsius (light yellow)
Thermal disinfection is a method using temperatures higher than usual ambient temperature. The effectiveness of the treatment lies in three variables: temperature (T), dwell time and relative humidity (RH).
As stated in the World Health Organisation (WHO) guidance on cleaning and disinfection of environmental surfaces, the COVID-19 virus survives in ambient temperatures but is susceptible to heat and standard disinfection methods. Thermal disinfection benefits from the sensitivity of viruses to temperature which, when combined with humidity, can render the virus ineffective.
- Using airport ground support equipment such as Pre-Conditioned Air (PCA) to inject hot air in the aircraft through the low pressure ground connector or directly through the aircraft door.
- Using the aircraft Environment Control System (ECS) or so-called “air conditioning” system.
- Using remote electrical heaters positioned inside the cabin & cockpit and crew rest areas.
- Or a combination of the aforementioned.
Airbus has conducted tests on its single aisle and widebody aircraft to demonstrate the practicality of any thermal disinfection method (e.g. temperature, duration). This was done in cooperation with medical institutes to evaluate the combination of variables which would allow virus inhibition through this method. Current results have not yet reached a satisfactory conclusion.
Disinfectants are approved for use on Airbus aircraft if they have no damaging effects on the aircraft in terms of aircraft structure (i.e. corrosion), electronics and avionics (i.e. insulation of cables), sensors (i.e. smoke detection) or the interiors (i.e. installations, seat covers, curtains, monitors, media devices, windows, galleys, countertops, restrooms, etc.).
Due to the delicate nature of instruments, screens and components installed onboard the aircraft, only approved procedures and products must be used in accordance with Airbus guidance (AMM 12-21-12 and AMP 51-26 and AMP 51-31 for A220).*
On the contrary, some disinfecting substances must not be used on aircraft, such as biocidal substances for general disinfection. Operators should refer to the latest AMM (AMP for the A220).
*AMM: Aircraft Maintenance Manual - *AMP: Aircraft Maintenance Procedure
Cabin disinfection involves aviation partners and regulatory bodies throughout the industry, including the aircraft manufacturer, suppliers, authorities, and of course the operators and ground support teams.
In a collective effort to give a clear picture of possible options, Airbus has worked with other industry partners to test several different solutions for efficiency and feasibility.
Electrostatic spraying or fogging, Ultraviolet (UV) light, gaseous H₂O₂, thermal treatment, and antimicrobial polishes: these are some of the solutions which could be used in the future, independently or combined.
Each method presents benefits and drawbacks. Airbus continues to work actively with partners on alternatives which also include antimicrobial coatings, polishes and touchless features. In the meantime, Airbus recommends all operators to continue using the disinfection method referred to in the AMM and the AMP.