Swiss A333 enroute on Jul 11th 2023, unusual odour in cockpit and cabin

Last Update: June 4, 2025 / 14:00:16 GMT/Zulu time

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Incident Facts

Date of incident
Jul 11, 2023

Classification
Incident

Airline
Swiss International Airlines

Flight number
LX-18

Departure
Zurich, Switzerland

Destination
Newark, United States

Aircraft Registration
HB-JHL

Aircraft Type
Airbus A330-300

ICAO Type Designator
A333

A Swiss International Airlines Airbus A330-300, registration HB-JHL performing flight LX-18 from Zurich (Switzerland) to Newark,NJ (USA), was enroute at FL340 about 70nm southeast of London Heathrow,EN (UK) when the crew decided descend the aircraft to FL100 and turn around due to unusual odour in cockpit and cabin. The aircraft levelled off at FL100 about 15 minutes later and subsequently diverted to Paris Charles de Gaulle, where the aircraft landed without further incident about 50 minutes after leaving FL340.

The airline reported the aircraft diverted due to an unusual odour in cockpit and cabin.

The aircraft is currently still on the ground in Paris about 3 hours after landing.

On Oct 11th 2023 Switzerland's SUST reported they opened an investigation into the occurrence rated a serious incident stating: "During an inflight emergency due to a smell event of unknown nature, the cabin crew had to wear protective breathing equipment (PBE) as a precautionary measure. Some of the respirators were damaged after difficult removal from the vacuum packaging and could no longer fulfill their protective function."

On Jun 4th 2025 the SUST released their final report concluding the probable causes of the serious incident were:

In the serious incident, an unusual smell developed in the aircraft cabin during the cruise flight, the cause of which could not be determined. This prompted the cockpit crew to put on their oxygen masks and several cabin crew members to use Protective Breathing Equipment (PBE). Several cabin crew members reported significant difficulties in using the PBE, both in unpacking, unfolding, putting on and activating the units and in their subsequent use. In addition, several PBE units exhibited technical defects and were therefore not or only partially functional. This represents a significant safety risk.

The following factors contributed to the serious incident:

- The recurring maintenance measures were inadequate, which is why the existing defects in the PBE units remained undetected.

- The crew members were trained exclusively with dummy PBE provided for training purposes, which differs considerably from the real PBE used in an emergency. As a result, the crew members were unaware of various difficulties when using the PBE.

- The technical design of the PBE was such that trained cabin crew members were unable to activate the PBE within a reasonable amount of time. The time required was several times longer than that specified in the certification criteria. In addition, communication was severely impaired when the PBE was in use.

The SUST analysed human and operational factors:

Smell perceptions

The cockpit crew noticed an unusual smell for the first time during taxiing to the runway. The conclusion that it was odours from the heated taxiway surface due to the high summer air temperature on that day is obvious and conclusive. The decision to continue the flight and takeoff is therefore comprehensible.

During the initial climb, the smell was strong but dissipated shortly thereafter. During the flight, the smell intensified again, prompting several cabin crew members to complain of physical discomfort. The cockpit crew then decided to make a diversion to a suitable airport. They put on their oxygen masks, as the origin of the smell remained unknown, and carried out the correct emergency procedures. This procedure was appropriate to the situation.

This case, as well as many other incidents involving fumes or smell, is an example of how difficult it is to make a conclusive assessment of the situation, as it is generally not possible to determine the cause of the fumes and smell. For this reason, a crew must a priori assume the worst plausible case, for example, that a fire could develop undetected and of unknown origin. Subtle warning signals, such as the perception of physical symptoms in individual crew members or passengers, must therefore always be taken seriously, even if no obvious causes for these symptoms can be identified.

Protective Breathing Equipment

The initial and recurring training of crew members, who must be able to use PBE, takes place with dummy PBE. The dummy PBE is not packaged and is ready to be placed on the head.

Under these conditions, the important first part of the application, namely the removal of the PBE from the vacuum-sealed packaging and the unfolding of the PBE before putting it on the head, cannot be practised. However, the functional demonstrations carried out during the safety investigation showed that unpacking the PBE from the vacuum-sealed packaging and the subsequent unfolding of the PBE in particular caused considerable difficulties. In addition, the dummy PBE does not simulate the strong heat development after activation or the difficult breathing with the PBE put on.

As trainers do not usually gain experience with real PBE at any point in their professional careers, they cannot draw on their own experiences with any difficulties in dealing with PBE. Accordingly, they are unable to raise the trainees' awareness of difficulties in a targeted manner.

In an emergency situation, crew members are exposed to increased stress. For example, crew members who experienced a real emergency situation reported a "startle moment" at the point when they had to use PBE. Appropriate training can counteract these effects.

For all the reasons mentioned above, training with PBE should be designed to be as realistic as possible so that crew members can draw on this training experience in an emergency. The Swiss Transportation Safety Investigation Board issues a safety notice in this regard.

During the serious incident, some PBE was worn for significantly longer than the 15 minutes specified in the approval criteria. However, the supply of breathing air is only guaranteed for this period by design. At some point after 15 minutes, the KO2 container is depleted, and the chemical process no longer generates oxygen. The wearer should be able to recognize this expiration by the temperature and humidity in the smoke hood rising and by breathing becoming more difficult. If the PBE is not removed during this phase, oxygen deficiency may occur.
Aircraft Registration Data
Registration mark
HB-JHL
Country of Registration
Switzerland
Date of Registration
QAfqlljpcAfceccmn Subscribe to unlock
Certification Basis
EAgclm Subscribe to unlock
Airworthyness Category
CAgbh mhemjbqbhl Subscribe to unlock
Legal Basis
Mhli Subscribe to unlock
TCDS Ident. No.
qfk jqjkb Subscribe to unlock
Manufacturer
AIRBUS S.A.S.
Aircraft Model / Type
A330-343
ICAO Aircraft Type
A333
Year of Manufacture
Lddp Subscribe to unlock
Serial Number
Gbmf Subscribe to unlock
Aircraft Address / Mode S Code (HEX)
N l dl Subscribe to unlock
Max. Operational Passenger Seating Capacity (MOPSC), indicative
Mhb Subscribe to unlock
Minimum Crew
P Subscribe to unlock
Maximum Take off Mass (MTOM) [kg]
Pqplef Subscribe to unlock
Engine Count
H Subscribe to unlock
Engine
KAcjfjlmikjeA hAimed pnieAbipqqi cA Subscribe to unlock
Main Owner
F Subscribe to unlock
Main Operator
A gilfdmcmgd lkqpqldqkid cecdbfqijdqnfdcbpfnjqpdeecclebgnfcelAdjhmdlAAibdgnl igilc Subscribe to unlock
Incident Facts

Date of incident
Jul 11, 2023

Classification
Incident

Airline
Swiss International Airlines

Flight number
LX-18

Departure
Zurich, Switzerland

Destination
Newark, United States

Aircraft Registration
HB-JHL

Aircraft Type
Airbus A330-300

ICAO Type Designator
A333

This article is published under license from Avherald.com. © of text by Avherald.com.
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