RVSM:  An Introduction to Reduced Vertical Separation Minima

The global aviation marketplace is booming, and air traffic is growing at a prodigious rate; according to IATA, airline traffic alone will double over the next 20 years.  There are projected to be similar increases in business and general aviation operations as the developing world improves their aviation infrastructure to support their economic growth.  One of the primary challenges in this expanding aviation environment is traffic separation; keeping aircraft apart while allowing the maximum number of aircraft to utilize the most efficient operational altitudes is the concern of air navigation service providers (ANSPs) worldwide.

The International Civil Aviation Organization (ICAO) saw the need to find a way to accommodate more aircraft at the most efficient flight levels over thirty years ago.  In 1982, they embarked on an initiative to identify the technology improvements and procedures required to allow less vertical separation between aircraft in cruise flight.  This ICAO initiative resulted in the revision of ICAO Annex 6—Operation of Aircraft—Part 1 to include reduced vertical separation minima (RVSM).  Today, these ICAO standards have been implemented on a nearly global scale and have been adopted by nearly all ANSPs.  RVSM has reduced the vertical separation required between aircraft from the old standard of 2,000 feet to just 1,000 feet in all airspace between FL290 and FL410, inclusive.

Flying in RVSM airspace requires that aircraft and operators be certified for RVSM operations and maintain manuals that contain procedures to ensure compliance.  Additionally, pilots must be trained in RVSM operations and comply with specific operational practices.  This article will provide an introduction to the aircraft, operator and pilot knowledge requirements for operations in RVSM airspace.  RVSM compliance is important for every turbojet operator, regardless of the size of the company or the frequency of operations.  Without RVSM certification, utilizing the airspace between FL290 and FL410 is generally prohibited.

Aircraft Requirements

In order to fly in RVSM airspace, each aircraft must comply with specific equipment requirements.  Not only must the required equipment be installed, but the equipment must be determined to be functional prior to entering RVSM airspace.  RVSM aircraft equipment requirements include:

  • Two independent altitude measurement systems that meets RVSM performance requirements
  • An altitude alerting system
  • An automatic altitude control system (a certified autopilot that is used while in the RVSM environment) that is sufficient to comply with RVSM performance requirements
  • A secondary surveillance radar (SSR) transponder with altitude reporting system that can be connected to the altitude measurement system in use for altitude keeping. Mode C and Mode S systems are permissible.
  • For TCAS II equipped aircraft, the TCAS II system installed must meet the requirements of TSO C–119b (Version 7.0), or a later version.

The good news is that most new and recently produced turbojet aircraft are designed with RVSM in mind; for these aircraft, the date of RVSM compliance is found on the aircraft’s airworthiness certificate.  For older aircraft that require equipment upgrades to comply with RVSM requirements, the RVSM compliance date is recorded in the maintenance logbook as a part of the supplemental type certificate.  Certifying older aircraft for RVSM operations often necessitates changes to the minimum equipment list in order to establish conditions under which flight may be permitted, but not in RVSM airspace.

Operator Requirements

Flying in RVSM airspace is more than just a matter of having an aircraft certified for RVSM operations.  Each operator will have to receive an RVSM Letter of Authorization from their national regulatory authority (such as the FAA, JAA or CAA) before allowing any aircraft under their operational control to operate in RVSM airspace.  Since all certification requirements are based on ICAO Annex 6, once you are certified for RVSM operations by one ICAO recognized national authority you can operate in RVSM airspace anywhere.  The approval process is fairly straight forward if the operator is already flying an RVSM approved aircraft; in this case, the operator needs only to have their RVSM manual and procedures examined for compliance.  If both the aircraft and operator need approval, the process becomes a bit more complex.

The certification requirements for operators include:

  • The operator must have an RVSM Manual detailing the policies, procedures and training required for RVSM operations. The manual will stipulate the methods by which the operator will ensure that the aircraft and their maintenance procedures will comply with RVSM requirements.  Additionally, the manual will detail how the operator will ensure that each pilot is RVSM knowledgeable and the procedures that will be used on the flight deck to mitigate any gross altitude errors in RVSM airspace.
  • The operator will have to assign a “responsible person” for RVSM compliance. This individual will be empowered to sign agreements related to RVSM with the national regulatory authority and will be responsible for the contents of the RVSM manual.  Additionally, the regulator will need to see a configuration list and MEL that reflects RVSM compliance for each aircraft (fleet approvals are often acceptable).

Pilot Knowledge

It is the responsibility of the operator to ensure that each pilot operating their aircraft is knowledgeable about the requirements of and procedures to be used in RVSM airspace.  The specific pilot training requirements will be spelled out in the RVSM manual and letter of authorization, but the training should cover some topics such as:

  • The application of static source correction error/position correction error data.
  • The visual perception of other aircraft at 1,000 feet of separation during night conditions, when encountering local phenomena such as northern lights, for opposite and same direction traffic, and during turns, the characteristics of aircraft altitude capture systems leading to the occurrence of overshoots.
  • Operational procedures and operating characteristics related to TCAS operation in an RVSM operation. The relationship between the altimetry, automatic altitude control, and transponder systems in normal and abnormal situations.

In addition to these training topics, any RVSM manual will stipulate operational procedures for pilots operating in the RVSM environment.  Some examples of required fight deck procedures include:

Preflight action:

  • Ensuring the functionality and accuracy of altitude measuring equipment and verifying aircraft RVSM compliance through a thorough logbook review.
  • Carefully inspecting the fuselage areas around static sources for damage that could adversely affect altimeter readings.
  • Resolving any RVSM equipment related deficiencies prior to departure.
  • Proper altitude setting procedures.

Prior to entering RVSM airspace:

  • Pilots must re-verify the accuracy of the aircraft’s altimeters through a crosscheck. Additionally, the crew must ensure that the altimeters are reset to the appropriate standard setting at the transition altitude and ensure that the transponder and autopilot altitude control function are operating properly.

While flying in RVSM airspace:

  • Hourly cross checks between the primary and standby altimeters must be made. Primary altimeters must agree +/-200 feet at the cleared flight level.
  • The autopilot, especially the altitude capture function, must be used. The aircraft should not be permitted to undershoot or overshoot an assigned altitude by more than 150 feet.
  • The crew must comply with all ATC clearances. Additionally, they must advise ATC anytime a system malfunction renders the aircraft RVSM non-compliant.