Which of the following is NOT a common medical emergency encountered on flights?

In the context of common medical emergencies encountered on flights, broken bones are less frequently reported compared to cardiac events, allergic reactions, and respiratory issues. This is largely due to the nature of how injuries occur in aviation environments. Most common medical emergencies on flights arise from existing health conditions exacerbated by the conditions of flying, such as reduced oxygen levels and anxiety, rather than from trauma like broken bones, which typically result from accidents or falls.

Cardiac events can occur suddenly, and the confined space of an aircraft makes it essential for crew members to be prepared to respond. Allergic reactions, often related to food or environmental allergens, can also happen on flights, necessitating immediate attention. Respiratory problems might arise due to altitude changes or pre-existing conditions, making them relevant in an in-flight setting. Broken bones, while serious, are less likely to be a direct outcome of flight-specific circumstances, thus categorizing them as a less common emergency in this environment.