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departures and approaches can be constructed with less separation. As tolerances for navigational
deviation decrease, the need to precisely maintain course grows. All aircraft must ensure they have robust
navigational means. Historically, this robustness has been achieved by installation of redundant
navigational systems. The need for dependable, precise navigation reinforces the redundancy
requirements.
While navigation accuracy and reliability pertain to military operations and traffic management, current
systems are achieving the necessary standard without redundancy, and without reliance on ground based
navigation aids. The Federal Radionavigation Plan, signed March 2002, establishes the following
national policies:
􀂾 Unaugmented, properly certified GPS is approved as a primary system for use in oceanic and remote
airspace.
􀂾 Properly certified GPS is approved as a supplemental system for domestic en route and terminal
navigation, and for non-precision approach and landing operations.
􀂾 The FAA’s phase-down plan for ground-based NAVAIDS retains at least a minimum operational
network of ground-based NAVAIDS for the foreseeable future.
􀂾 Sufficient ground-based NAVAIDS will be maintained to provide the FAA and the airspace users
with a safe recovery and sustained operations capability in the event of a disruption in satellite
navigation service.
6 2001 Federal Radionavigation Systems Plan
UAS ROADMAP 2005
APPENDIX F – AIRSPACE
Page F-10
These policies apply, as a minimum, to all aircraft flying in civil airspace. With GPS, the prospect for
relief of some redundancy requirements in manned aviation may be an option in the future. However, UA
have a diminished prospect for relief since, unlike manned aircraft, a UA cannot readily fallback on dead
reckoning, contact navigation, and map reading in the same sense that a manned aircraft can.
Autonomy. Advances in computer and communications technologies have enabled the development of
autonomous unmanned systems. With the increase in computational power available, developmental UA
are able to achieve much more sophisticated subsystem, guidance, navigation and control, sensor and
communications autonomy than previous systems. Global Hawk is capable of Level 2-3 autonomy today.
Its airborne systems are designed to identify, isolate, and compensate for a wide range of possible
system/sub-system failures and autonomously take actions to ensure system safety. Preprogrammed
decision trees are built to address each possible failure during each part of the mission.
One of the most difficult aspects of high levels of autonomy is ensuring that all elements remain
synchronized. Verifying that 1) all messages are received, 2) all aircraft have correctly interpreted the
messages, and 3) the entire squadron has a single set of mission plans to execute will be a key
accomplishment. Once developed, such reliable, highly autonomous UA systems should facilitate
integration into the FAA’s Joint Air Traffic Management Vision.
Lost Link. In the event of lost command and control, military UA are typically programmed to climb to a
pre-defined altitude to attempt to reestablish contact. If contact is not reestablished in a given time, the
UA can be pre-programmed to 1) retrace its outbound route home, 2) fly direct to home, or 3) continue its
mission. With respect to lost communications between the GCSs and the UA, or the UA and ATC,
however, there is no procedure for a communications-out recovery. Examination of a lost link scenario
illustrates that this communications issue can become a critical UA failure mode, if left unaddressed.
NORDO (No Radio) requirements are well documented in 14 CFR 91.185. Remarkably, most lost link
situations bear a striking resemblance to NORDO, and UA would enhance their predictability by
autonomously following the guidance. The one exception to this case is the VFR conditions clause. UA,
even with an adequate S&A system (autonomous), would enhance overall safety by continuing to fly IFR.
Should normal ATC-voice communications fail, the FAA also has the capability to patch airspace users
through to the controlling ATC authority by phone at any time.
FUTURE ENVIRONMENT
The migration of the NAS from ground based traffic control to airborne traffic management, scheduled to
occur over the next decade, will have significant implications for UA. S&A will become an integrated,
automated part of routine position reporting and navigation functions by relying on a combination of
ADS-B and GPS. In effect, it will create a virtual bubble of airspace around each aircraft so that when
bubbles contact, avoidance is initiated. All aircraft will be required to be equipped to the same level,
　
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