Eddie Sez:

It is becoming next to impossible to fly just about anywhere in the world without RVSM. You need to know more than just where it is in effect, the rules for getting you and your aircraft RVSM qualified, and how to keep your aircraft eligible to fly through regularly performance checks. You also need to know the country-specific rules that may not be what you are expecting in terms of flight level selection and contingency procedures.

What follows are quotes from the relevant regulatory documents, listed below, as well as my comments in blue.


General

[AC 91-85]


Location

Most of the world. The exceptions are becoming rarer and you will have to check the Jeppesen State pages prior to every trip to be sure. Implementation varies by country:


Accuracy / Performance Standards

[AC 91-85 ¶6.b.] Altimetry System Error (ASE). The difference between the pressure altitude displayed to the flight crew when referenced to International System of Units (SI) standard ground pressure setting (29.92 in. Hg/1013.25 hPa) and free stream pressure altitude.

[AC 91-85 ¶8.c.(3)] The requirements in the basic RVSM envelope are as follows:

(a) At the point in the basic RVSM envelope where ASE mean reaches its largest absolute value, the absolute value should not exceed 80 ft (25 m).

(b) At the point in the basic RVSM envelope where ASE mean plus ASE3 SD reaches its largest absolute value, the absolute value should not exceed 200 ft (60 m).

[AC 91-85 ¶8.c.(4) The requirements in the full RVSM envelope are as follows:

(a) At the point in the full RVSM envelope where ASE mean reaches its largest absolute value, the absolute value should not exceed 120 ft (37 m).

(b) At the point in the full RVSM envelope where ASE mean plus of ASE3 SD reaches its largest absolute value, the absolute value should not exceed 245 ft (75 m).

The RVSM tolerance seems to be specified as tight as 80 feet but then gets confused with additives of standard deviation that bring that number as high as 245 feet.

[AC 91-85 ¶8.d.] Altitude Keeping. An automatic altitude control system should be required, and it should be capable of controlling altitude within ±65 ft (±20 m) about the acquired altitude when operated in straight and level flight under non turbulent, non gust conditions.

So how accurate does your aircraft altitude have to be? The regulations are filled with formulas based on large fleets of aircraft and do not give a cut and dried answer. For our purposes you need to keep the following two numbers in mind:


Documentation / Certification

[AC 91-85 ¶12.g.]

(1) Authorization for parts 121, 125, 129, and 135 operators to operate in RVSM airspace should be granted through the issuance of an OpSpec paragraph from Part B (En Route Authorizations, Limitations, and Procedures) and Part D (Aircraft Maintenance). Each aircraft type group for which the operator is granted authority should be listed in OpSpecs. Authorization to conduct RVSM operations in an RVSM area of operations that is new to the operator should be granted by adding the part B RVSM OpSpecs paragraph number to the appropriate area of operations in the Part B paragraph: Authorized Areas of En Route Operation Limitations and Procedures.

(2) Part 91K operators’ authorization to operate in RVSM airspace should be granted through the issuance of a management specifications (MSpecs) paragraph from Part B and Part D. Each aircraft type group for which the operator is granted authority should be listed in MSpecs. Authorization to conduct RVSM operations in an RVSM area of operations that is new to the operator should be granted by adding the Part B RVSM MSpecs paragraph number to the appropriate area of operations in the Part B paragraph.

(3) Part 91 operators and part 125 operators holding a LODA should be issued an initial letter of authorization (LOA) when the initial authorization process has been completed. Part 91 operators are not required to obtain a new or amended LOA to operate in individual areas of operation where RVSM is implemented. For example, an operator that has obtained an LOA and is conducting RVSM operations in the North Atlantic is not required to obtain another LOA to conduct RVSM operations in the domestic United States.

(4) Operators issued OpSpecs are not required to also obtain an LOA for those operations when they are conducted under part 91, provided that:

(a) The aircraft is operated under the operator name listed on the OpSpecs.

(b) The flight is conducted in an area of operations listed in the OpSpecs.

(c) The aircraft is operated under the conditions under which the OpSpecs were granted (e.g., if the operator holds part 135 OpSpecs, then the pilots used for the part 91 operation must have received part 135 training. If this is not the case, then an LOA would be required).

If you want to fly just about anywhere in the world between FL290 and FL410, you are going to need an LOA or OpSpecs issued by your country of registration.


Aircraft Monitoring

[AC 91-85 ¶12.d.(8)] The operator should provide a plan for participation in the RVSM monitoring program. This program should normally entail a check of at least a portion of the operator’s aircraft by an independent height-monitoring system. The FAA RVSM Documentation Web site at http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/enroute/rvsm/ contains guidance on monitoring programs for specific areas of operation.

[Reduced Vertical Separation Minimum (RVSM) Monitoring Requirements, page 1.]

Your aircraft needs to be monitored at least once every two years and you should carry documentation attesting to that. More about that: International Operations / Safety Assessment of Foreign Aircraft (SAFA). If you have more than two aircraft of the same type, you might not need to have every aircraft monitored. See the RVSM Minimum Monitoring Requirements chart is available at http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/enroute/rvsm/documentation/#req. Some corporate aircraft, like the G450, qualify for the two aircraft per fleet proviso. Others require at least 60% or even 100% monitoring. If you have more than two aircraft of the same type, it would be worth your trouble to investigate further.


Equipment Requirements

ICAO

[ICAO Doc 9574, ¶5.1.1.(g)] Before entering RVSM airspace, the pilot should review the status of equipment required. The following equipment should be operating normally:

1) two altitude measurement systems, as defined by the RVSM MASPS;

2) automatic altitude-keeping device(s);

Note.—Redundancy requirements for altitude-keeping devices should be established by regional agreement after an evaluation of such criteria as mean time between failures, length of flight segments and availability of direct pilot-controller communications and radar surveillance.

3) at least one altitude-reporting transponder (if required for operation in that specific RVSM airspace) capable of being switched to operate from either of the two altimetry systems required by the RVSM MASPS; and

4) one altitude-alerting device;

Should any of this equipment fail prior to the aircraft entering RVSM airspace, the pilot should request a new clearance so as to avoid flight in this airspace.

U.S. FAA

[AC 91-85 ¶9.a.] The minimum equipment fit should be as follows:

(1) Two Independent Altitude Measurement Systems. Each system should be composed of the following elements:

(a)Cross-coupled static source/system, provided with ice protection if located in areas subject to ice accretion;

(b) Equipment for measuring static pressure sensed by the static source, converting it to pressure altitude and displaying the pressure altitude to the flight crew;

(c) Equipment for providing a digitally coded signal corresponding to the displayed pressure altitude, for automatic altitude reporting purposes;

(d)SSEC, if needed to meet the performance requirements of paragraphs 8c(3) and 8c(4), or 8c(8), as appropriate; and

(e)The equipment fit should provide reference signals for automatic control and alerting at selected altitude. These signals should preferably be derived from an altitude measurement system meeting the full requirements of this document, but must in all cases meet the requirements of paragraphs 9b(6) and 9c. (See Appendix 7 for additional guidance for configurations found on older model “legacy” airplanes for which RVSM approval is sought.)

(2) One Secondary Surveillance Radar (SSR) Altitude Reporting Transponder. If only one is fitted, it should have the capability for switching to obtain input from either altitude measurement system.

(3) An Altitude Alert System. The altitude alert system should be capable of operation from either of the two required independent altitude measurement systems.

(4) An Automatic Altitude Control System. The automatic altitude control system should be capable of operation from either of the two required independent altitude measurement systems.

The altitude alert system is required to activate when altitude deviates more than 300' (aircraft certified before 1997) or 200' (aircraft certified after 1997).


Operating Practices

Flight Planning

[AC 91-85, Appendix 4, ¶2.]

  1. Verifying that the aircraft is approved for RVSM operations.

  2. Annotating the flight plan to be filed with the Air Traffic Service Provider to show that the aircraft and operator are authorized for RVSM operations.

Preflight Procedures

[AC 91-85, Appendix 4, ¶3.]

  1. Review maintenance logs and forms to ascertain the condition of equipment required for flight in the RVSM airspace. Ensure that maintenance action has been taken to correct defects to required equipment.

  2. During the external inspection of aircraft, pay particular attention to the condition of static sources and the condition of the fuselage skin near each static source and any other component that affects altimetry system accuracy.

  3. Before takeoff, the aircraft altimeters should be set to the local altimeter atmospheric pressure at nautical height (QNH) setting and should display a known elevation (e.g., field elevation) within the limits specified in aircraft operating manuals. The difference between the known elevation and the elevation displayed on the altimeters should not exceed 75 ft. The two primary altimeters should also agree within limits specified by the aircraft operating manual. An alternative procedure using atmospheric pressure at field elevation (QFE) may also be used;

  4. Before takeoff, equipment required for flight in RVSM airspace should be operational, and indications of malfunction should be resolved.

In-flight Procedures

[AC 91-85, Appendix 4, ¶5.]

  1. During cleared transition between levels, the aircraft should not be allowed to overshoot or undershoot the cleared flight level by more than 150 ft (45 m);
  2. NOTE: It is recommended that the level off be accomplished using the altitude capture feature of the automatic altitude-control system, if installed.

  3. An automatic altitude-control system should be operative and engaged during level cruise, except when circumstances such as the need to retrim the aircraft or turbulence require disengagement. In any event, adherence to cruise altitude should be done by reference to one of the two primary altimeters;

  4. The altitude-alerting system should be operational;

  5. At intervals of approximately 1 hour, make cross-checks between the primary altimeters and the stand-by altimeter. A minimum of two primary altimeters should agree within 200 ft (60 m) or a lesser value if specified in the aircraft operating manual.

The section goes on to say "The normal pilot scan of cockpit instruments should suffice for altimeter crosschecking on most flights." When oceanic, however, I would recommend recording altimeter performance on the master document.

Hourly Checks

[ICAO Doc 9574, ¶5.1.1.(e)] Regular (hourly) cross-checks between the altimeters should be made, and a minimum of two RVSM MASPS-compliant systems must agree within 60 m (200 ft). Failure to meet this condition will require that the system be reported as defective and notified to ATC.

Standby Altimeter Performance

Table: Standby Altimeter Tolerance, from 14 CFR 43, Appendix E., Table 1.

While there are no in-flight standby altimeter tolerances which would necessitate an in-flight abort, the standby altimeter should be evaluated against 14 CFR 43, Appendix E tolerances for subsequent maintenance action. The tolerances are altitude dependent:


Contingencies

[AC 91-85, ¶4.b.]

(1) Do not interpret guidance for contingency procedures in any way that prejudices the final authority and responsibility of the pilot in command (PIC) for the safe operation of the aircraft.

(2) If the pilot is unsure of the vertical or lateral position of the aircraft or the aircraft deviates from its assigned altitude or track for cause without prior ATC clearance, then the pilot must take action to mitigate the potential for collision with aircraft on adjacent routes or flight levels.

NOTE: In this situation, the pilot should alert adjacent aircraft by making maximum use of aircraft lighting and broadcasting position, flight level (FL), and intentions on 121.5 megahertz (MHz) (as a back-up, the appropriate very high frequency (VHF) inter-pilot air-to-air frequency may be used).

(3) Unless the nature of the contingency dictates otherwise, the pilot should advise ATC as soon as possible of a contingency situation and if possible, request an ATC clearance before deviating from the assigned route or FL.

(4) If a revised ATC clearance cannot be obtained in a timely manner and action is required to avoid potential conflict with other aircraft, then the aircraft should

(a) Acquire and maintain in either direction a track laterally separated by 28 km (15 NM) from the assigned route; and

(b) Once established on the offset track, climb or descend to select a FL which differs from those normally used by 150 m (500 ft);

(c) The pilot may also consider descending below FL 285 or climbing above FL 410. (The vast majority of oceanic traffic operates between FL 290 and 410. Flight above FL 410 or below FL 285 may limit exposure to conflict with other aircraft.)

(5) When executing a contingency maneuver the pilot should:

(a) Watch for conflicting traffic both visually and by reference to Airborne Collision Avoidance System (ACAS) or Traffic Alert and Collision Avoidance System (TCAS), if equipped.

(b) Continue to alert other aircraft using 121.5 MHz (as a back-up, the VHF inter-pilot air-to-air frequency (VHF 123.45) may be used) and aircraft lights.

(c) Continue to fly offset tracks or altitudes until an ATC clearance is obtained.

(d) Obtain an ATC clearance as soon as possible.


Book Notes

Portions of this page can be found in the book International Flight Operations, Part II, Chapter 6.


References

14 CFR 43, Appendix E, Title 14: Altimeter System Test and Inspection, Federal Aviation Administration, Department of Transportation

Advisory Circular 91-85, Authorization of Aircraft and Operators for Flight in Reduced Vertical Separation Minimum Airspace, 8/21/09, U.S. Department of Transportation

ICAO Doc 7030 - Regional Supplementary Procedures, International Civil Aviation Organization, 2 2008

ICAO Doc 9574 - Manual on Implementation of a 300 m (1,000 ft) Vertical Separation Minimum Between FL 290 and FL 410 Inclusive, Second Edition, International Civil Aviation Organization, 2001

Reduced Vertical Separation Minimum (RVSM) Monitoring Requirements, 09/03/2011, available at http://www.faa.gov/about/office_org/headquarters_offices/ato/service_units/enroute/rvsm/.