Summary

  • RVSM was implemented to handle increased air traffic by allowing aircraft to fly with only 1,000 feet of vertical separation.
  • Compliance requires an aircraft to feature several specific pieces of equipment.
  • This technology increases efficiency and enhances flight safety.


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It’s pretty standard nowadays to look out the window of an airliner in cruise and see the contrails of another plane that has just passed. If you look out the window for any amount of time, you’re all but guaranteed to see another plane go by, especially if you’re flying through busy airspace. Thanks to technology and innovation, airliners in most countries can safely fly just 1,000 feet vertically separated from each other. This article is about Reduced Vertical Separation Minima or RVSM.


RVSM and its benefits

Reduced Vertical Separation Minima was rolled out between 1997 and 2005, and nearly every ICAO-compliant country is a participating program member. RVSM was implemented as a relief to an increasingly busy international airspace system, and it virtually doubled the amount of participating aircraft that a block of airspace could handle. RVSM airspace ranges from 29,000 feet (FL290) to FL410 inclusive. In a non-RVSM environment, planes are vertically separated in cruise by at least 2,000 feet. RVSM allows aircraft to fly at half this amount of vertical separation, though similar lateral offsets still apply.

A Hawaiian Airlines Airbus A330-200 just after take off.

An additional benefit of RVSM compliance is increased efficiency. With more usable flight levels, RVSM allows controllers to clear pilots to an altitude that most suits their aircraft performance. Jet engines are increasingly efficient at higher altitudes, and flying a multi-hour flight at FL350 rather than FL330 can save thousands of pounds of fuel.

RVSM compliance

Aircraft need specific equipment to be eligible to fly in RVSM airspace. A plane must have at least two air data systems to measure altitude and vertical speed, an autopilot capable of holding the aircraft in level flight, an altitude alerting system, and a particular type of transponder. Suppose just one of the components required for RVSM flight is inoperative. In that case, the controlling agency may be unable to clear the flight into RVSM airspace if a sector is busy since they would have to provide 2,000 feet of vertical separation. A flight will likely be flown below FL290 if a plane has an inoperative autopilot or faulty air data computer since the aircraft is not RVSM-compliant without this equipment.

RVSM critical area

Airliners have pitot tubes, smart probes, static ports, temperature sensors, and ice detectors on both sides of the forward fuselage (and sometimes a bit further aft). The pitot tubes are easily spotted from the terminal as whisker-like installations around the flight deck windows. An up-close look at this part of the plane will reveal boxes or circular markings to outline the boundaries of the “RVSM critical area.”

A closeup of an Airbus A380 cockpit.

Photo: Igor Marx I Shutterstock

Flight through RVSM airspace requires accurate dual-monitoring of altitude, and protecting the tubes and sensors that monitor air data is essential to flight safety. For this reason, the RVSM critical area is outlined so that any dents, scrapes, or other damage can be quickly examined and fixed, if necessary. The pilots pay close attention to this part of the plane during their walk around.

RVSM has been around long enough to be taken for granted. Pilots think of RVSM only when their plane cannot comply with the entry rules. Otherwise, it’s a near certainty that (parts of) most long flights will take place in RVSM airspace unless weather or turbulence dictate otherwise. RVSM is an excellent benefit to efficiency and safety. It also allows for remarkable close-up views of other aircraft as they pass above or below, separated by only 1,000 feet.

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