RVSM REVISION PROPOSAL

Changes for checking Reduced Vertical Separation Minimums

FAA proposes use of ADS-B as a path for high altitude flight level monitoring.


This chart shows the increase in aircraft permitted between FL290 and FL410 through the use of RVSM. Most noteworthy is the economization that aircraft can take advantage of by going to the higher FLs being available to aircraft with RVSM.

Current RVSM approval, Appendix G to Part 91

Section 2 lists the specific tolerances for 2 independent altimetry systems, altitude alert system, altitude hold system, and TCAS II system performance, if so equipped.

Section 3 provides for periodic inspections, functional flight tests, and maintenance and inspection procedures with acceptable maintenance practices for ensuring continued compliance with the RVSM aircraft
requirements.

There must also be a quality assurance program for the accuracy and reliability of equipment used for testing aircraft to determine compliance with the RVSM aircraft requirements. Procedures to return noncompliant aircraft to service are also required. Following sections deal with crew approval, system modification and removal from service as well as other details.

Current final Section 8 initially listed those regions where RVSM was approved. However, all RVSM FIR regions are approved today so Section 8 no longer applies.

RVSM, TCAS II, and ADS-B Out

An FAA memorandum from October 2016 addressed the installation of ADS-B Out systems in aircraft with approved RVSM equipment. Because ADS-B Out in Class A or international airspace may only be 1090ES protocol, the addition of an ADS-B Out system will be affected with a transponder change. Because the transponder does not contribute to the aircraft's altitude-keeping performance, it is not a considered a critical component of the RVSM approval.

Certain RVSM maintenance programs may list specific transponders. However, the FAA states this is simply a matter to modify the approval paperwork. For TCAS II systems, for example, the memorandum stated that a transponder upgrade that only involves software changes or the installation of a follow-on model of a previously approved transponder may not necessarily affect the airworthiness of an installed TCAS II system. Also noted is the fact that TCAS II is not a requirement for RVSM operation.

ADS-B and RVSM

The FAA proposes to add a new Section 9 to Appendix G of Part 91. An aircraft that has an ADS-B Out system operating on 1090ES protocol and meets the standards of FAR 91.227 could qualify for RVSM altitudes. Further stated, the height-keeping performance of the aircraft must be equivalent to the requirement currently given in Section 2 of the Appendix along with the requirement for 2 independent altimetry systems, altitude alert system and altitude hold system standards.

All of this is dependent on the FAA's ability to monitor ADS-B Out performance. The coverage in the CONUS, Guam, Hawaii, and Puerto Rico at RVSM heights is such that this is a non-issue, as full coverage currently exists. Alaska, however, does have some non-coverage areas.

The FAA can make this proposed change, considering the fact that a differentially corrected GPS altitude determination using WAAS is totally independent of pressure gradient.
Transmitting once a second, ADS-B Out provides greater coverage at a higher rate than the current AGHME monitoring sites. While retaining the equipment standards, training, and maintenance, the real advantage for an operator who is appropriately equipped and ADS-B Out compliant is that he need not go through a specific approval process to operate RVSM.

Additionally, this proposed change provides for operation at RVSM altitudes if the aircraft's ADS-B Out system is inoperative per FAR 91.180 (b) and 91.706 (b). This is treated just as inoperative transponders are dealt with today; operators may proceed with ATC approval as long as they do not impose a burden or interfere with other operators.

Interestingly, the FAA states in the NPRM, "For operations outside US airspace, where ADS-B height monitoring may not be available, an aircraft that has recently been monitored by the FAA and found to be operating normally could be safely operated outside of FAA-monitored airspace with a high degree of confidence that the performance requirements would continue to be met."

Certainly any non US airspace manager could determine their own guidelines, but experience has shown that the reliability of height-keeping systems for current RVSM aircraft is high and not likely to change with ADS-B Out installation.

Conclusion

Even though January 2020 is over 2 years away, it's clear that ADS-B Out will change how ATC manages airspace. Capitalizing on the benefits ADS-B offers, operators whose aircraft are optimized for RVSM altitudes could see a simplified means to do so at lower cost while bypassing the current backlog of RVSM applications at some FSDOs.

The capability of the FAA to monitor ADS-B performance on every flight and independently verify height-keeping performance makes the difference. As newer jets enter the market place, having RVSM capability via ADS-B Out will be a significant change in that many aircraft capable of flight level operations already have or certainly will come with the minimum on-board equipment to qualify for RVSM. The FAA will retain the current approval path that is not ADS-B dependent.

Comments to the NPRM are positive; the General Aviation Manufacturers Association (GAMA) and NBAA clearly support this proposed change. One interesting comment from the chief council of a company that specializes in RVSM applications for clients raises the point that a benefit, perhaps unintended, of the existing Section 2 application process is the review of the flight department structure of many smaller Part 91 operators.

Individuals or companies set up structures without realizing that their operation may not meet the FAA operations branch strict definition of a true Part 91 structure. Part of the review process for an RVSM application apparently revealed this and a restructuring can be made.

This NPRM is currently only a proposed change that, if enacted, will provide a significant advantage at an equivalent level of safety. This is best kind of change.

Bill Gunn is former comĀ­pliance manager for the Texas Dept of Transportation, Av Division. He is an ATP, CFII and FAA Safety Team rep. Bill lectures nationally for a private aviation advocacy group and is an aviation compliance mediator.

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