Why Aren't Aircraft Altitudes Given in Metres?
The use of feet for reporting aircraft altitudes is deeply rooted in the history and technical standards of aviation. Despite the widespread adoption of the metric system in many countries, aviation primarily adheres to the imperial system, leading to confusion and inefficiencies in some contexts. This article explores the reasons behind this choice and its implications.
The Dominance of the Imperial System
The primary reason for the continued use of feet in aviation is historical and cultural. Early aviation was dominated by the United States and the United Kingdom, both of which used the imperial system. This standardization has been maintained due to the dominance of these nations in the aviation industry. The metric system, while widely used in most other industries, has not been adopted in aviation for various reasons.
Transition Altitudes: A Complication
A significant challenge in changing the altimeter to metric measurements is the transition altitude. This level is where pilots switch from reporting in feet to reporting in metres. For example, during the flight from Yerevan, Armenia, to Sochi, Russia, the pilots had to switch their altimeter to report in metres. However, this process is fraught with potential errors, as illustrated by the Yerevan-Sochi incident where the confusion led to a critical issue.
Aviation Measurements and Standards
In aviation, the language is US English, and most measurements are given in both feet and metres. This duality ensures compatibility and avoids confusion in international operations. For instance, when flying into or out of a particular airport, the air pressure reading is given in millibars or hectopascals, which are metric units. However, in the United States, this reading is still reported in inches of mercury, maintaining the imperial system's dominance in this area.
Practical Considerations: Separation Standards
Aircraft use a separation standard known as IFR (Instrument Flight Rules) altitudes, which are 1000 feet apart. Odd altitudes are used for eastbound flights and even altitudes for westbound flights. While switching to metres could make sense in theory, it would lead to a series of oddball numbers that are difficult to remember, such as 12500 and 14950. Using 500-meter separation would lose several usable altitudes, and a separation of less than 300 meters would not be safe.
The use of feet in aviation is also linked to the need for clear and precise communication. The standard of using 1000 foot increments allows for easy and straightforward communication between pilots and air traffic control. Any change could complicate this process and introduce further risks.
Conclusion
The use of feet for reporting aircraft altitudes in aviation is a matter of historical inertia and technical standardization. While the metric system is adopted in many other areas, the aviation industry has maintained the use of feet due to its long-standing tradition and practical benefits. Changing this standard would require a significant adjustment in training, communication, and operational procedures, making it a complex and potentially risky endeavor.