An A330 aircraft was taxiing to its departure runway when the flight crew noticed a smell of heated asphalt in the cockpit. The outside air temperature was 38 °C. The flight crew reportedly suspected that the smell was coming from the heated airport ground. There were 2 flight crew members, 10 cabin crew members, and 223 passengers onboard.

The flight crew performed a takeoff with both air conditioning packs set to OFF, and then switched pack 2 back to ON during the initial climb.  Soon after, they detected a smell of "dirty socks". The flight crew switched pack 2 OFF again. This stopped the smell. They waited for 5 minutes and switched pack 2 ON again. The smell did not reappear. Pack 1 was set to ON soon after.

The cabin crew members confirmed the presence of the smell in the cabin during the initial climb but also that the smell quickly disappeared.

When the aircraft reached FL 340, several cabin crew members reported that they felt burning sensation and irritation of the eyes, as well as headaches. The flight crew decided to perform an in-flight turnback. They put on their oxygen masks and initiated the descent.

Several cabin crew members decided to put on their PBE (fig.1). Seven of them faced difficulties using their PBE:

• Several of them found it difficult to open the vacuum bag in which the PBE was packaged. Two of them had to use scissors or a knife to open the bag
• One of the two straps used to initiate the oxygen supply and secure the mask broke off when a cabin crew pulled on it
• One cabin crew member needed three minutes to don their PBE and felt very uncomfortable due to the high temperature and the tightness of the neck seal
• Several cabin crew members felt that inhalation was difficult when using the PBE
• Communication between crew members wearing PBE was challenging.

The aircraft landed safely after two hours of flight with no reported injuries among passengers or crew.

Troubleshooting performed by the maintenance crew did not formally identify the root cause of the smell. 

The CCOM mentions that Protective Breathing Equipment (PBE) protects the user's face and respiratory system from heat, smoke and noxious gases.

Post-flight inspection of the PBE used during the event revealed that, in addition to the broken strap on a PBE, a second PBE showed damage on the visor that could not be a result of incorrect removal from the vacuum bag.

Despite having regular training on the use of PBE, the cabin crew found it difficult to use the PBE in this situation, which highlights the potential need for training improvement.

Two cabin crew members kept their PBE on until after landing, which resulted in the PBE being used for longer than the certified duration of 15 minutes. Although no health issues were reported by PBE users, this incident underscored the importance of increasing cabin crew awareness regarding the limitations of PBE and the potential for hypoxia with prolonged use.

PBE, also called smoke hood, is designed to protect the crew members from smoke, carbon dioxide, and other harmful gases while they are on flight deck duty or while combating fires. PBE is available in several locations in the aircraft cabin, in the cockpit, and crew rest areas.

Several models of PBE are available. Each one has its specificities that are detailed in the PBE manufacturer’s documentation. However, regardless of the PBE type, they are based on a similar concept of a closed-circuit breathing system (fig.2).

(fig.2) Principle of PBE

Each PBE includes a hood to cover the head of the user, providing a protected environment. A neck seal ensures the airtightness of the hood to prevent smoke, gas, or fumes from entering the hood.

The CO2 exhaled by the user is removed by a CO2 absorber cartridge. Additional oxygen supply is obtained via either a gaseous oxygen cylinder or a chemical oxygen generator. Oxygen can be provided directly into the hood or through a facemask depending on the PBE type (fig.3). The user generally activates the oxygen supply by pulling on an activation ring or a lanyard. The activation device may differ depending on the PBE model.

Each PBE is packed in a vacuum/moisture resistance bag to protect it from humidity and contamination (fig.4). Each vacuum bag is stored in a container. Integrity of both the container and the vacuum bag is essential to ensure operational PBE. 

A serviceability or condition indicator is available on the container of some PBE models. On other PBE models, a humidity indicator is available. 

A tamper seal or a tamper latch is available on some containers to indicate if the container was opened.

PBE usually has a 10-year service life (after date of manufacturing). An expiry date is displayed on the container or on the vacuum bag (fig.5). 

(fig.5) Examples of containers equipped with a serviceability and humidity indicator as well as tamper seal or tamper latch

PBE must be replaced as specified in the Maintenance Planning Document (MPD), before reaching its expiry date. 

PBE must be inspected at the interval defined in the MPD. The associated Aircraft Maintenance Manual (AMM) procedure must be followed.
Typical checks that must be performed include:

• Check of the PBE expiry date
• Check the vacuum/moisture resistance bag condition (if visible): The bag must not be inflated
• Check the container’s tamper seal or tamper latch condition (if installed): If damaged, the AMM may request that the container be  opened to verify the integrity of the vacuum bag and replace the damaged tamper seal or tamper latch
• Check that the PBE serviceability/condition indicator (if installed on the container) is green (if red, the vacuum is compromised. The PBE must be replaced)
• Check that the humidity indicator (if installed) is blue (if pink, the PBE must be replaced) 
• Check of the general condition of the container.

Cabin crew and flight crew members should check the condition of the PBE devices available in the aircraft before each flight or before the first flight of the day depending on the airline’s policy and local regulations. This includes checking the PBE in the cabin and in the cockpit.

Typical checks that should be performed include:

• Check of the PBE expiry date: If expired, maintenance personnel should be informed
• Check the vacuum bag condition (if visible): The bag must not be inflated
• Check the container’s tamper seal or tamper latch condition (if installed): If damaged, maintenance personnel should be informed
• Check that the PBE serviceability/condition indicator (if installed on the container) is green. If red, the vacuum bag is compromised. Maintenance personnel should be informed: the PBE must be discarded 
• Check that the humidity indicator (if installed) is blue. If pink, maintenance personnel should be informed: the PBE must be discarded 
• Check the general condition of the container.

Adherence to the PBE manufacturer procedure is essential to ensure the safe use of PBE. Here is a recall of some key information to be considered when using the PBE:

As for any oxygen supply, fire risk must be considered for the donning of PBE. 

PBE remains tightly folded in the vacuum/moisture resistant bag for months and may need some effort to be unpacked. It is recommended to have dry hands to open the PBE container and vacuum/moisture resistance bag as it may require some force to do it.

Tear pads also referred to as tear off strips (generally red) must be pulled to open the vacuum bag (fig.6). Arrows may indicate the direction of the pull to ease opening.

Specific unfolding actions may be needed depending on the PBE type.

The neck seal requires widening to don the PBE. This may require some force. 

It is essential to correctly don the PBE and adjust the neck seal so that the airtightness of the device is ensured. Any hair passing through the neck seal can impair the airtightness and create an oxygen leak or allow smoke to enter the hood. Therefore, the user must ensure that all their hair is inside the hood.

It is also essential to correctly adjust the face mask on PBE equipped with this technology so that oxygen supply and CO2 removal is done correctly.

Depending on the type of PBE, the oxygen supply is activated either before, during, or after donning. Oxygen supply activation is done manually (fig.7) or automatically depending on the PBE type. When activated, the oxygen supply produces noise due to the oxygen flowing inside the hood, especially shortly after activation. This indicates that the oxygen supply is activated. The noise may disappear after this initial phase depending on the type of oxygen generation. The user should be aware of the time when the oxygen is activated and check the duration of usage.

Chemical oxygen generators and CO2 absorber cartridges may emit heat due to the chemical reactions that occur. The moisture level of the mask may also increase due to the humidity from the user’s exhalation. Therefore, the user should be prepared for this experience of a closed, relatively hot, and humid environment. However, excessive heat and humidity can be a sign of the device dysfunctioning and requires immediate PBE removal.

The duration of use is limited to 15 minutes. The PBE must be removed as soon as the oxygen supply stops or a dysfunction of the PBE occurs.

The PBE must be removed away from the source of smoke. 
The user must be aware that oxygen may remain in their hair and clothes after the removal of the PBE and that used PBE may still generate oxygen for a period of time.

Depending on the PBE model, the oxygen generator and CO2 absorber cartridge may remain hot after use. The crew members should avoid touching them until they are cooled down. 

When removed, PBE must be considered as unserviceable. It must not be used again.

PBE is used during emergency events and must be donned quickly. The context of an emergency event may create additional stress for the crew when trying to don the PBE.  Therefore, it is essential that appropriate training is provided for the crew in order to mitigate such stress and improve overall performance and decision-making.

During training, crews should be reminded about the physiological signs of hypoxia and hypercapnia. This will enable them to react appropriately by immediately removing their PBE at the first signs of hypoxia or hypercapnia.

Crews must be trained on the specific PBE model(s) installed in the aircraft they are assigned to fly.
Flight and cabin crews should have access to the user guide from the PBE manufacturer. This will enable them to familiarize themselves with the PBE's characteristics, limitations, and signs of oxygen supply stoppage.

As per regulations, cabin crews and flight crews must be regularly trained on the use of PBE. Dummy PBE devices are usually used for training. They may have a similar shape and weight and simulate some features, however, they are not fully representative of the real PBE that the crews may use onboard the aircraft.

Training PBE is usually already removed from the vacuum/moisture resistance bag and container and unfolded. As a result, the trainees do not experience the actual opening of the PBE container and vacuum bag. Real PBE remains tightly folded in the vacuum bag for months and may need some effort to be unpacked and unfolded.

Training PBE is reused many times. Despite having the possibility to replace the neck seal, it may not be as tight as a new unit. 

Training devices do not have an oxygen supply or a CO2 absorber. Therefore, the use of the training PBE does not provide a realistic experience of the sound of the oxygen supply and of the heat that may be generated by the chemical reaction(s) that occur in real PBE. This may create a startle effect and stress when the crew members use the PBE in a real situation, where they experience the sounds, heat, and relative discomfort for the first time.

A training device cannot reproduce the specific signs that would indicate the need to remove the PBE.