Reduced vertical separation minimums

Reduced Vertical Separation Minimums

Change is coming

By Jim Sparks

July / August 1998

It has been forecast that by the year 2015, there will be twice the number of aircraft flying as today. This will have a dramatic effect on the way these machines are operated. We will need to accommodate twice the number of flights in the same amount of airspace. There will of course be the need to develop additional airports, and therefore a need for additional radio channels to enable precision navigational capabilities.

Many European aircraft operators, as well as US aircraft traveling internationally, have already had first-hand exposure to some of the operational changes. In time, every corner of the globe will be affected.

These new programs include RVSM, B RNAV, FM Immunity and 8.33 kHz spacing. As with most operational changes, maintenance procedures will also be amended. Reduced Vertical Separation Minimums (RSVM) provide a means of increasing air traffic on some existing routes.

The FAA, in conjunction with the International Civil Aviation Organization (ICAO), undertook a study to increase enroute airspace capacity in the heavily traveled North Atlantic and determined that RVSM would be technically feasible without imposing unreasonable demands. It would now allow air traffic control to maintain 1000' vertical separation between aircraft where 2000' used to be required. This would double the number of aircraft in some of the high density air routes in any given time period.

The North Atlantic Minimum Navigation Performance Specifications (NATMNPS) includes the procedures for RVSM operations in the altitude range between 42,000 feet and 28,500 feet. No one is allowed to enter this airspace unless RVSM approval is granted by the country of aircraft registration. Any aircraft not approved can still cross the North Atlantic, but must either fly above FL 420 or below FL 285.

To become eligible for RVSM operations, the aircraft will have some system requirements including:
• Two independent altitude indicating systems
• A transponder with altitude reporting capability - if only one transponder is installed, it will need to be able to obtain altitude data from either altimeter system • An altitude alert system.
• An automatic altitude control system

The approval process begins with the airframe manufacturer developing a data package including the definition of the aircraft group; i.e. aircraft that are identical in design and have identical static systems and like-avionic systems. The data package will also include a definition of the flight envelope, as well as required information to show compliance with RVSM. There is also a procedure to ensure all aircraft submitted for airworthiness approval meets RVSM requirements along with the information to be used to maintain RVSM integrity while in service.

Once the manufacturer has compiled the data package, it is then up to the individual operator to ensure the specific aircraft meets the requirements. Often this includes a detailed inspection of the area around and in front of the static ports. The object of this inspection is to check for skin waviness or deformation, as well as rivet condition and evaluation of any previous damage or repair. In some cases, specialized jigs are used to detect any skin surface anomalies. Some aircraft types will require repeat inspections at predetermined intervals. Static defects need to be determined in varying flight regimes and may require correction.