H1 Why Are Flight Levels Measured in Feet and Not Meters?

Flight levels are predominantly measured in feet, which might seem paradoxical given the widespread adoption of the metric system globally. This practice is rooted in a combination of historical, practical, and safety considerations. In this article, we explore why feet continue to be the standard unit for flight levels in aviation.

H2 Historical Precedence

The aviation industry in the United States established its measurement standards early in the 20th century, a time when feet were the de facto standard unit of measurement. The U.S. has long been a global leader in aviation, and its standards have significantly influenced international norms. This historical precedent has persisted, even as many countries have embraced the metric system for general measurements.

H2 Pressure Altitude and Simplified Communication

H3 Pressure Altitude

Flight levels are based on pressure altitude, which is measured in feet. This measurement is closely tied to the altimeter settings used in aircraft, which are calibrated in inches of mercury (inHg) in the U.S. This alignment further strengthens the use of feet in aviation. Simplifying communication and coordination between pilots and air traffic controllers from different countries is crucial, and the use of the same unit of measurement helps achieve this.

H3 International Standards and Flexibility

The International Civil Aviation Organization (ICAO) allows for the use of feet for flight levels, partly due to the need for consistency in international flights. This flexibility ensures that pilots and controllers maintain a common understanding, even when working in diverse and multilingual environments. While many countries use the metric system, the standardization around feet provides a unifying language in the aviation industry.

H2 Operational Consistency and Safety

H3 Consistency in Aircraft Systems and Instruments

Many aircraft systems and instruments are designed to operate with feet as the unit of measure. A shift to the metric system would necessitate extensive re-engineering of equipment, retraining of pilots and air traffic controllers, and significant changes in operational procedures. Such changes could be costly and complex, leading to potential safety risks.

H3 Maintaining Safety Through Familiarity

Maintaining a consistent measurement system is critical for safety in aviation. Many pilots and air traffic controllers are accustomed to using feet, and any sudden change to meters could lead to confusion and an increased risk of errors. The familiarity with feet allows for quicker and more accurate readings, thereby enhancing overall safety.

H2 Why Not Speed?

Interestingly, while altitude is measured in feet, speed in aviation can also be measured in both feet per minute (fpm) and meters per second (m/s). However, pilots and air traffic controllers often prefer feet per minute due to its direct relation to vertical motion and the natural human inclination to think in terms of vertical progress.

H3 Radio Altitude in Final Stages

During the final stages of landing, radio altitudes are reported in increments of feet, such as 100 feet, 90 feet, 80 feet, 70 feet, 60 feet, and 50 feet. Converting these values to meters can be cumbersome and may lead to confusion, especially in critical landing scenarios where precision is paramount.

While Russia may not predominantly use feet for flight levels, this practice aligns with the broader international standards and ensures seamless communication among a diverse global aviation community.

In conclusion, the continued use of feet for flight levels in aviation is a result of historical precedence, practical operational needs, and a commitment to safety. Despite the global trend towards the metric system, the measurement of flight levels in feet remains a crucial and well-established practice in the aviation industry.