What this relates to
Vapours or odours can arise in an aircraft for a variety of reasons. Depending on the source, concentration and chemical composition of the odor, the health or capabilities of the aircraft occupants may be endangered. To avoid potential risks, the crew may decide to land or use oxygen masks as a precaution. Airlines use established procedures to investigate such incidents and rectify their causes.
An uncontrolled fire in an aircraft is one of the hazards with the greatest potential impact and can result in loss of control due to damage to the structure and/or control systems. Fires can also lead to crew and passenger injuries.
Example
During the cruise phase of a flight, the cockpit crew of a passenger aircraft detects an unusual odour and follows the relevant procedures for such a scenario. After landing the crew reports the observation to the maintenance organisation, and the latter determines the cause.