Reduced Vertical Separation Minima (RVSM) was introduced to allow aircrafts in designated airspace to operate with a reduced separation of 1000 feet from FL290 through FL410 instead of the previous 2000 ft that has been around since 1960. Technical advancements have led to significant improvements in the accuracies if the altimeter systems in aircraft and makes RVSM implementation possible.
Equipment Requirements for RVSM system
RVSM requires the following equipment to meet its performance requirements:
1. Two independent altitude measurement systems consisting of:
- A cross-coupled static source/system, with ice protection if required
- Equipment to measure static pressure sensed by the static source
- Equipment to provide a digitally encoded signal corresponding to the displayed pressure altitude, for automatic altitude reporting purposes
- Static source error correction (SSEC), if needed to meet the performance criteria for RVSM flight envelopes
- Reference signals for automatic control and alerting at selected altitude, derived from an altitude measurement system that meets the performance criteria for RVSM flight envelopes.
2. Secondary Surveillance Radar (SSR) altitude reporting transponder with the capability for switching to operate from either altitude measurement system; Mode C and Mode S systems are permissible.
3. An altitude alert system
4. An automatic altitude control system (certified autopilot)
The equipment installed for the monitoring of the aircraft altitude should have the capability to demonstrate continued accuracy and integrity to the parameters established for RVSM approval and should be maintained in accordance with the manufacturer’s performance requirements. Airframe and other dependent systems should be maintained in accordance with the airframe manufacturers inspection standards and procedures.
Calibration and Maintenance Program Requirements
Once an aircraft is certified to be in RVSM compliance, a calibration and maintenance program needs to be implemented to ensure continued operation to RVSM standards. This typically includes calibration of the altitude reporting and indicating systems and operational tests of the autopilot, transponder and altitude alert system. These checks need to be accomplished every 24 months.
RVSM certified aircraft also need to ensure that the static ports and the areas around the static ports has not been damaged or distorted in any way. Slight waviness in the aircraft skin or any other surface irregularities can cause pressure fluctuations across the static ports at higher altitudes and airspeeds. Surface measurements or skin mapping checks should be made to ensure adherence to the airframe manufacturer’s RVSM tolerances. These tests and inspections should also be performed every 24 months or following unscheduled repairs, or alterations having an effect of airframe performance.
The approved RSVM calibration and maintenance program should be a part of an effective quality control system. The quality control system should include regular calibrations of test equipment traceable to national standards, annual audits of calibration and maintenance activities and compliance with established facility maintenance practices.
RVSM maintenance can be contracted out to an FAA approved repair station, if authorized within the calibration and maintenance program. Proper documentation will be required to ensure that the repair station is capable to perform the required aircraft calibration and maintenance requirements for the aircraft and equipment.