6 2001 Federal Radionavigation Systems Plan
APPENDIX F – AIRSPACE
Page F-9
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, making the unmanned or manned status of an aircraft transparent to both flyers and to the FAA.
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