Reduced Vertical Separation Minimum for Aircraft

Abstract

Because of the dramatic increase in air traffic over the past decade, aviation organizations in the United States and other internationally based counterparts find ways to prevent congestion on routes with high traffic incidents. In order to do this, RVSM is proposed. RVSM or Reduced Vertical Separation Minimum is the reduction of the vertical separation from current 2,000-ft. minimum to 1,000-ft. minimum of the FL 290. After a thorough study, the ICAO Review of General Concept of Separation Panel (RGCSP) concluded that it is technically feasible to implement the 1,000-ft. separation standard safely (Federal Aviation Administration [FAA], 2005).
Since its implementation, there is a remarkable 28% decline on operational errors in the airspace in which RVSM is applied. Also, fuel costs are decreasing significantly due to more efficient altitudes at which the planes are flying. Not only that, there is a reduction in the number of conflicts; situations wherein a plane has to move laterally or vertically as ordered by the controller (Federal Aviation Administration [FAA], 2008).
These results suggest that the new separation standard of 1,000-ft. minimum besides being as safe is more effective than that of the previous vertical separation of 2,000-ft. minimum.

Reduced Vertical Separation Minimum for Aircraft

In 1988, ICAO completed a study that concluded the feasibility of the safe implementation of the 1000-ft. separation standard. The study was conducted due to the arising problem of flight- level congestion in airspaces with high traffic incidents. Before the RSVM implementation, the standard vertical separation for altitudes between 29,000 and 41,000 is 2,000-ft (FAA, 2008). The pressure altimeter’s accuracy decreases with height and this instrument is used in aircrafts to determine their level, so that is why the standard vertical separation implemented before was 2,000-ft. But over the years, when altimeters were combined with air data computers (ADC), they become more accurate. Maintaining a set level using autopilots is also more easier nowadays. These developments led to question the 2,000-ft. separation for many modern aircrafts. Given the technology nowadays, it became apparent that the existing separation standard is too cautious. Therefore the proposal to reduce it to 1,000-ft. was made by ICAO.

Reduced Vertical Separation Minimum (RVSM) between FL 290 FI 410 has already been implemented in European Airspace since January 24, 2002. The purpose of this is to prevent flight-level congestions, thus optimizing flight profiles (Jeppesen Sanderson, Incorporated [JSI], 2000). In North America, RSVM airspace has only been implemented recently (ARINC Incorporated, 2008).

Approval for RVSM Operations

Before an aircraft can have the permission to operate within the EUR RVSM Airspace, it would have to pass the standards of the RVSM first. In order to have the approval of the responsible authority, the aircraft operators need to achieve two things. First is that granted all types of aircraft have received airworthiness approval. Meaning each one of them has complied with Minimum Aircraft System Performance Specification (MASPS). Second is the state’s approval regarding the operations manual together with the maintenance procedures, which are specific to the operations of RVSM (JSI, 2000).

There are exclusions from the RVSM MASPS such as state aircraft. But they can still be accommodated within the EUR RVSM Airspace with the provision that the 2000-ft. minimum vertical separation between such aircraft and all other IFR aircraft is maintained by ATC. STS/NONRVSM is filled by state aircraft for special handling request in Field 18 of the ICAO FPL (JSI, 2000).

Height Monitoring Principles

There are two types of equipments used to monitor the height – keeping performance of aircraft in the EUR RVSM Airspace. These two are the Height Monitoring Units (HMUs), with a coverage of 45 NM and GPS Monitoring Units (GPUs). HMUs are fixed ground based height-monitoring facilities at Linz (N48 12 E014 18), Nattenheim (N49 57 E006 28) and Geneva (N46 22 E005 56). Without action from aircraft operators, these equipments can monitor passing aircraft by themselves. On the other hand, GMUs are portable monitoring units. They are carried onboard the aircraft to supplement HMUs. Also, they monitor aircraft which are not normally flying over HMUs (JSI, 2000).

Participation in the monitoring program is a requirement to all RVSM compliant aircraft. For their height to be monitored, aircraft can request a re – routing in some instances.

RVSM Procedures in Transition Areas

The task of handling the transition of aircraft from an RVSM to a non-RVSM environment and vice-versa has been designated to a number of FIR/UIRs in the EUR RVSM Airspace. Under special procedures, ATC is allowed to transition both RVSM and non – RVSM Civil and State aircraft within this “EUR RVSM Transition Airspace”. So a change from Conventional Flight Levels to RVSM Flight Levels And vice – versa should be expected by the flight crews. For those non-RVSM aircraft and any other aircraft, the ATC will continue to provide a 2,000-ft vertical separation minimum (VSM) (JSI, 2000).

Aircraft Equipment

The Minimum Equipment List (MEL) fulfilling the MASPS has two components. The first one is the two independent altitude measurement systems, each equipped with cross-coupled static/source system with ice protection. This is for instances wherein they will be located in areas which have plenty of ice; display of the computed pressure altitude to the flight crew; digital encoding of the displayed altitude; signals referenced to a pilot selected altitude for automatic altitude control and alerting, and static source error connection. The second is, one SSR transponder with an altitude reporting system in use for altitude keeping. Third is an altitude alerting system and last is an automatic altitude control system (JSI, 2000).

Flight Planning

This step requires greater attention compared to the others. Particular attention should be paid by the flight crew since some conditions may affect operation in RVSM airspace. So the flight crew must first verify that the aircraft is indeed RVSM approved, like it complies with the MEL. Second is that they should analyze the reported and forecast weather that may affect RVSM requirements like turbulence, icing, etc. Finally, they must review the manufacturer and the operator’s restrictions concerning RVSM operations. According to ICAO guidelines, for FPL, if the aircraft is RVSM approved, the letter “W’ should be inserted in Field 10. For RPL on the other hand, if the aircraft is RVSM approved regardless of the requested FL, the letter “W” should be inserted in the Item EQPT, if not, still it should be inserted in the ITEM EQPT for RPL (JSI, 2000).

It should be noted that the insertion of “W” in item 10 of the flight plan does not necessarily mean that an RVSM FL can be planned in European airspace or that an RVSM FL can be requested by the pilot unless this is explicitly promulgated by a State for operation in the airspace of the State, not until January 24, 2002.

Pre-flight Procedures

Before flying, the flight crews should check the condition of the equipment for RVSM operations and make sure that maintenance actions have been taken to correct defects; they should also take note of the condition of static sources and make sure of the accurateness of the altimeter by setting the QNH or the QFE. To check if it is working properly, the reading should agree with the altitude of the apron or the zero height indication within a 75 ft. (23m) tolerance (JSI, 2000).

In – flight Procedures

During the flight, all the required equipments must be monitored to ensure satisfactory operation before and within RVSM airspace. When changing levels, the aircraft should not overshoot or under-shoot the cleared flight level by more than 150 ft. or 45 m. The automatic altitude control system shall be engaged during level cruise by reference to one of the two altimeters. If fitted, the altitude capture feature shall be used whenever possible for the level off. Also, cross checks of the primary altimeters shall be made at intervals of approximately one hour. These primary altimeters shall agree within 200 ft. or 60 m. The failure to meet these conditions will require the altimetry system to be reported as defective and immediately notified to ATC. An initial check shall be recorded just before entering the EUR RVSM Airspace (JSI, 2000).
The intention of RVSM is to allow aircrafts to optimize flight profiles, decrease costs of fuel and avoid congestion in airspace with high traffic incidents (FAA, 2008). Since its implementation, it has enhanced air traffic control flexibility like routing around storms, helped in mitigating conflict points, enhanced volume of aircraft that can be accommodated in a given sector and reduced controller workload like reduced vectoring and flight level changes (FAA, 2005).

Contingency Procedures

In case of failure in equipment, bad weather, too much turbulence, the pilot shall notify the ATC immediately because these can affect the ability of the aircraft to maintain the cleared level or the RVSM requirements. When this happens, the role of the ATC is to make sure that safe separation is maintained which usually means a reversion to the 2,000-ft. minimum. Now, when the pilot was assigned an altitude deviation of 90-ft by the ATC, he should return to the cleared level as soon as possible. For communication trouble, an established procedure is available to the pilot for him to follow (JSI, 2000).
Research tells us that RVSM has helped resolved problems with air traffic, fuel costs and system operations among others, so it is clear to see that this reduction in the vertical separation standard is something that should have been done a long time ago. With groundbreaking developments such as this, flying has never been more wonderful!

References

• ARINC Incorporated. (2008). Reduced Vertical Separation Minimum (RVSM) Services.
• Federal Aviation Administration. (2005). Domestic Reduced Vertical SeparationMinimum (DRVSM). July 10, 2008.
• Federal Aviation Administration. (2008). Reduced Vertical Separation Minimum. July 10, 2008, from http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/enroute/rvsm/
• Jeppesen Sanderson, Incorporated. (2000). Implementation of Reduced Vertical
• Separation Minimum (RVSM) between FL 290 and FI 410 within European Airspace. July 10, 2008.