Flight Redemptions

What is RHSM in Aviation? (Reduced Horizontal Separation Minimal)

Updated: February 27, 2024

What is Reduced Horizontal Separation Minimal (RHSM)?

Reduced Horizontal Separation Minimal (RHSM) is a term used in aviation to describe a set of standards and procedures that allow for reduced separation between aircraft flying at the same altitude. The concept of RHSM was introduced by the International Civil Aviation Organization (ICAO) as a way to increase airspace capacity and improve efficiency in air traffic management.

Under traditional air traffic control procedures, aircraft flying at the same altitude are required to maintain a minimum separation distance of 5 nautical miles laterally. However, with advances in technology and improved communication capabilities, it has become possible to safely reduce this separation distance. RHSM allows for a reduced minimum separation distance of just 3 nautical miles laterally, resulting in more efficient use of airspace.

The Benefits of RHSM

Implementing RHSM has several benefits for both airlines and air traffic control authorities. One of the main advantages is increased airspace capacity. By reducing the separation distance between aircraft, more planes can be safely accommodated within the same airspace, leading to a higher number of flights and improved efficiency.

Another benefit of RHSM is reduced fuel consumption. When aircraft are able to fly closer together, they can take advantage of the aerodynamic benefits of reduced drag, resulting in lower fuel burn. This not only reduces costs for airlines but also has a positive environmental impact by reducing greenhouse gas emissions.

Furthermore, RHSM allows for more flexible routing options. With the reduced separation requirements, aircraft can take more direct routes, avoiding unnecessary detours and saving time. This can result in shorter flight durations and improved passenger experience.

Implementation and Safety Considerations

Implementing RHSM requires a robust system of communication and surveillance to ensure the safety of all aircraft involved. Air traffic control authorities need to have accurate and up-to-date information about the position and trajectory of every aircraft within their airspace. This is achieved through the use of advanced radar and satellite-based surveillance systems.

In addition to surveillance, effective communication between pilots and air traffic controllers is crucial. Pilots must be able to receive clear and timely instructions from controllers and report their position accurately. This is especially important during critical phases of flight, such as takeoff and landing, where close proximity between aircraft can pose a higher risk.

While RHSM has been successfully implemented in many regions around the world, it is important to note that it is not suitable for all airspace environments. Factors such as traffic density, airspace structure, and available technology need to be considered before implementing RHSM. Air traffic control authorities need to conduct thorough risk assessments and ensure that all necessary safety measures are in place before reducing the separation distance between aircraft.


Reduced Horizontal Separation Minimal (RHSM) is a concept that has revolutionized air traffic management by allowing for reduced separation between aircraft flying at the same altitude. This has resulted in increased airspace capacity, reduced fuel consumption, and more flexible routing options. However, the implementation of RHSM requires advanced surveillance and communication systems to ensure the safety of all aircraft involved. With careful planning and risk assessment, RHSM has the potential to further improve efficiency and sustainability in aviation.

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