Tethered-Aviation ConOps (TACO)

Focus on Experimental Airborne Wind Energy (AWE)

Proposed FAA Advisory Circular

Proposal for Action- ICAO Standards And Recommended Practices (SARPs)

Note to the TACO 7th Draft-
At the second Airborne Wind Energy (AWE) Conference (AWEC2010), the attending FAA official publicly called for the early industry to define the emerging aircraft types into the FAA's Category & Class system. For its part NASA informally tasked industry players with developing ConOps frameworks for AWE in the US National Airspace (NAS). The Airborne Wind Energy Industry Association (AWEIA) responded by initiating this report addressing requirements. KiteLab Group, an AWE R & D pioneer, volunteered to compile a master Tethered Aviation ConOps (TACO), in an open collaborative process. TACO is intended as an FAA Advisory Circular to inform aviation stakeholders of the issues. While AWE is the priority application of this ConOps, the full scope is TA as a whole. Not only are there exciting new kinds of TA, bit there is a vast pool of historic TA precedent & working models to apply to AWE operations.  T ethered or not, persistent acceptance-barriers exist to autonomous aviation in the US NAS (National AirSpace). The current FAA requirement for piloted systems will hold for some years.  Thus this early-stage TAConOps Draft is "pilot-centric", embracing the pilot's key stakeholder status, but also is forward-looking toward eventual flight autonomy (Appendix). As a major future energy technology, AWE has the potential to subsidize many of the dreams of aviation planners & general aviation. This document is intended to evolve & merge into the NextGen Airspace ConOps. The US (FAA) regulatory standard is expected to drive the international picture (ICAO, etc). Send corrections, additions, & comments to santos137@yahoo.com
Executive Summary
Tethered Aviation is an old & important branch of Aeronautics, with aerostats, aerotowing , & kites as well-known examples. New tether-based flight systems under development will enhance conventional aviation capabilities, host infrastructure (i.e., communications), spin-off industries, create recreation, & generate clean energy. This "New Aviation" requires the primary stakeholders, pilots, developers, regulatory bodies, & populations, to come together to resolve technical & social challenges & realize the great potential. For the immediate purpose of private R&D, the current system is not broke; change by small increments grows over time into major mature sectors.
Pilots are a key stakeholder, as primary users of airspace most exposed to flight risk. Following aviation norms & traditions, pilots will lead safe effective Tethered Aviation R&D, fill jobs in the new aviation industries  & ensure safe operations consistent with shared airspace. The aerospace industry tasked with designing systems that pilots accept & the FAA can certify as airworthy. Policy developers & decision makers, from the national to the local level, are another key stakeholder group. These aviation interests must reach concensus to convince extended stakeholders that TA enhances society as a "good neighbor". The TACO lays out a basis for them to help reach a public consensus regarding the best use of TA in the NAS.
Aviation Self-Regulation Principle
By tradition the FAA relies on all sectors of aviation, via its user & industry associations, to refine & promote best practice of members. Safe operations & responsible leadership by each sector allows the FAA to maximize resources & perform oversight with a light touch. 
The Airborne Wind Energy Industry Association (AWEIA) undertakes, as part of its formal mission, to perform the leadership role of self-regulation for AWE in particular, but also to serve specialized TA as a whole. This TACO is AWEIA's first step in coordinating member standards for safety & acting as the industry liason with the FAA & ICAO. AWEIA will petition the FAA for new Rulemaking following the example of the Experimental Aircraft Association (EAA) & FAA together creating the regulatory package for a new category of Light Sport Aviation. Similarly AWEIA will work within the ICAO framework to develop a core SARPs.
There are already urgent R&D safety issues AWEIA is addressing, such as obligatory sharing of safety-critical failure modes & mishap reporting. AWEIA is just one of several associations with overlapping interest in TA. AOPA & EAA have strong interests within the new sectors. The American Kiters Association (AKA) governs recreational & professional kite operations. The American Modelers Association (AMA) is responsible for safe hobbyist aviation. User associations in soaring & other sectors that commonly perform tethered operations also have stakeholder oversight roles. Key wind energy industry standards promoted by AWEA also apply to AWE operations.
TA Excise Taxes & User Fees
The new AWE  technology taps airspace as a source of vast energy. M ajor energy sources all pay excise taxes, with 5% of producer's selling price typical. Unlike excise taxes on extractive non-renewable energy sources which eventually run out, renewables generate revenue in perpetuity. Barriers to broad AWE societal stakeholder acceptance, like NIMBY (not-in-my-back-yard) forces, will tend to melt away before a rich new tax base that more than offsets any negatives.  Energy excise taxes often directly offset environmental downsides with mitigation measures. The average citizen who does not fly or own aircraft still shares a birthright to the airspace commons. An equitable AWE Excise Tax can make a huge contribution to basic social welfare & a new era of sustainable prosperity for all.
Airspace access is by tradition a Public Commons based on Freedom-of-the-Seas. There is already resistance by existing aviation stakeholders to allowing privatization of AirSpace as some venture-capital AWE stakeholders have proposed. Utility-scale AWE operations can contribute to shared airspace by paying Excise Taxes on energy extracted & maybe even special Airspace User Fees. Airspace User Fees is a toxic idea to existing aviation but makes sense for some of the new types of aviation.
The AWE industry can thus earn aviation stakeholder acceptance by subsidizing common airspace infrastructure benefiting all. AWE tax revenue can offset existing FAA costs, relieving the overall Federal budget, pay for NextGen infrastructure, guarantee liability performance, & fund publicly-shared AWE R & D. The early industry requires a phase-in period for taxes, so as to not choke off early investment & to promote initial growth. As significant mature AWE revenue-base develops, & airspace becomes widely impacted, the tax base can be tapped. Small-scale personal AWE operating at low altitudes should be exempted commercial taxes.
Like all aviation, TA operations must carry Liability Insurance proportional to risk. Such insurance is currently unavailable from traditional providers & a special TA Liability Fund is needed to jumpstart liability coverage. Secondary coverage, like Hull Insurance, does not fall under this recommnedation. A wrongful death these days can cost some ten million USD. The insurability guaranteed by an excise endowed fund can ensure that a financially weak AWE player in a freak-accident (even an unknown failure-mode) event does not leave victims or families uncompensated.


FARs Category, Class, & Type Certifications for TA

The FAA tasks the AWE Industry (AWEC2010) with defining the profusion of TA designs & new Types into the FAA's Aircraft/Airman/Operations Category, Class, & Type System. As categories naturally grow by adding Classes, so special TA Classes are proposed to be defined within current Categories. Note that FARs are sometimes vague, confused,  & contradictory; no totally clean classification scheme is workable, only patchwork progress. NextGen FARs will improve classification by a major overhaul. There is traditional wiggle-room in the existing system, with many exceptions & options at the discretion of authorities, including classification under multiple categories & classes. Aviation is increasingly diverse & some new branches may become wholly new Categories. 

Just like any other aircraft, TA platforms can be classified by gross-weight & airspeed, by the same physics of "consequence". Weight & Speed (mass & velocity) are primary determinants of Class within a Category. In general higher mass/velocity Classes have Higher Consequence Failure-Modes & so require proportionally higher standards for equivalent safety (mortality to flight hours). Stall Speed is a key safety consideration, the lower the better, with the widest possible range of operation between max airspeed & stall speed.
Some  major Aircraft Categories- aircraft, rotorcraft, normal, utility, acrobatic, commuter, transport,  manned free balloon, glider, special, restricted, etc. As an example of how TA Class can apply across Categories, many given Types can be modified for aerotowing, with special restrictions accruing. Single/Multi-Engine Classes- Many TA applications have powered modes that naturally assign them to an Engine Class within a Category. The trade-off of getting improved reliability from multi engines is a higher standard of Pilot training & engineering design required.

Examples of new Classes created- Tethered-Aerobatic, Tethered-Single-Engine, Tethered-Multi-Engine, Tethered-Normal, Utility, Sport, Ultralight, Moored-Balloon, Aero-Towed Glider, Tethered Rotorcraft.

The tether is a significant flying object in itself. Far-flung tether geometry is a unique TA feature to account for, but has useful similarity to standard geometry flight trajectories & operations like skydiving. Electrically Conductive Tethers require special standards addressing all safety issues. Aircraft joined by tethers into arrays is an operational configuration to validate. The proposal is that this method might greatly enhance safety & reliability.

Some Categories & Classes of aircraft & operations are interrelated. For example, UAS Aircraft & Flight Operations are clearly intimately coupled. On the other hand, a UAS might be operated as a Commercial or Private Aircraft.

Tethered Aircraft (TAC) that operate aerobatically & incur high G-loadings are Acrobatic Category (limited to 12,500lbs gross). Tether-Weight counts toward rated gross weight. Tether-Drag counts against rated L/D. Autonomous Flight of high-consequence platforms (high mass &/or velocity, especially around populations) require a proportionately more cautious rigorous path to validation & certification.

AWECS are generally high-duty UAS & so merit Utility designation. According to gross weight they can be sorted into Ultralight, Sport, Normal, Commuter, & Transport Weight & Airspeed Categories.

Operational altitude is a major category criteria. Some relevant ceilings- 400ft for low mass low speed hobbyist model aviation. 500ft as a "floor" for general VFR aviation. Class G airspace, which is  low, but variable, with higher ceilings in remote areas, 2000ft obstruction regulations for mast & tower certification, 18,000ft as an "absolute" ceiling to avoid transport aviation operations.

Note: Many current tethered vehicle platforms are not formally designated as an "aircraft" in the Aircraft Categories under current FARs, but the FAA reserves the right to designate them so. Its now clear that the tethered aircraft must be designated as aircraft so as to be regulated for airworthiness. The irrefutable logic is that any accepted aircraft can in principle be put on a tether, which does not negate its character as an aircraft of a given mass & speed envelope, & even adds to operational hazard. The many large tethered aircraft under development will have to be Type Certified in a suitable Category, a Special Class.

Pilot Categories & Training

Proper pilot training & testing is fundamental to every branch of aviation. All pilots in TA-shared airspace require awareness of the new conditions. All TA pilots require basic aeronautical training, plus specialized operational proficiency. As high-consequence risk emerges, TA Pilots will require the same high standards of certification as Transport Pilots.

Sec. 61.31 — Type rating requirements, additional training, and authorization requirements.

Operational Categories

Given Aircraft Types operate in diverse roles & regulations reflect this. Some major Operational Categories that are explicit or de-facto- , Remoteness, Altitude, Marine Environment, Unmanned Aviation System, IFR/VFR, Weight & Speed Cats., Obstruction, & so on.

Super Density Operations (SDO)

It has been proposed by some developers that AWE can operate under Obstruction Regs such as govern Antenna Farms, but such a model is only partial. For example, an antenna-farm Obstruction is also regulated under mast & tower structural codes not under the purview of the FAA. Towers do not have many inherent aviation hazards related to aircraft airworthiness & a potential to crash far afield. Therefore a TAC partly regulated as an obstruction still needs to comply with Airworthyness regs.

Current Norms & Regulations
The FAA's mandate to maintain a safe NAS already covers TA activity.   Certificating airworthiness within current regs is essential to prevent TA R&D from presenting a "menace-to-aviation". Most AWE venture starts have no formal aviation background & face acculturation along an FAA approved path. Class G Airspace is the primary realm of current TA R & D.FSDOs are the current arbiters of allowable experiments, with decentralized flexibility. AWE R & D can shop around for a "best-fit" FSDO (generally remote low-traffic NAS regions). Special Airworthiness Certificate in the Experimental Category is the certification currently available to civil operators of UAS. NOTAM & COAs allow pioneering AWE R & D to occur.
Obstruction regs, such as apply to antenna farms, can partly serve for persistent "static" TA operations under 2000ft AGL.Shielded operations is an option for a TA operator able to identify sites.
Draft FAA s UAS regs call for Pilot-in-Command & Visual Observer crews. A misconception in the AWE field is that autonomous operations will permissible in a short time-frame of a year or two, but the safer bet is that many years must pass before the required safety & reliability is validated & permitted.
Key Title 14 Parts of the Code of US Federal Regulations (Aeronautics & Space)



The FAA regulates skydiving activity as"Parachute Operations" Part 105 (14 CFR 105). Flight operations for skydiving are conducted under Part 91 "General Operating and Flight Rules" (14 CFR 91).

FAA Advisory Circulars provide additional guidance about operations. A TAConOps circular is a logical step.

Banner-Towing & Glider Aero-Towing regulations inform equivalent operations in other applications.

Recreational  NAS use covered by FAA Advisory Circular (AC) 91-57; generally limits operations to below 400 feet ASL well separated from airports & air traffic. This is the appropriate place for virtually all current AWE developers to conduct most experiments without being a "menace to aviation".

Three acceptable means of operating UASs in the NAS: 1) within “restricted” airspace: or under a Special Airworthiness Certificate (2) Experimental Category or (3) Certificate of Waiver or Authorization (COA). A COA authorizes an operator to use defined airspace under specific provisions unique to the operation.  It may require Visual Flight Rules (VFR) & operation only &/or during daylight. COAs are issued for a specified time period; one year typical. COAs require coordination with air traffic control & may require a transponder in certain types of airspace.

A UASs inability to autonomously follow ”sense and avoid” rules means a ground observer (PIC &/or VO) must maintain visual contact operating in unrestricted airspace. The VO must also maintain aural vigilance in a quiet enough setting to detect airplane intrusion before visual spotting.

"Sense & avoid" UASs requirement currently means PIC (Pilot-In-Command) & VO (Visual Observer), plus dive or kite-kill capability.
Possibility of special IFR Rules clearances, especially higher operational ceiling during graveyard shift to help bridge night-time inversion.

TA Operations Notes

Tethered Aviation creates unique operational realities with particular hazards to mitigate.
A tether is a dangerous poorly visible obstacle when extended almost invisibly across large distances. Navigation markers are an existing requirement & will surely  long continue to be a good idea.
Separation, Avoidance, Visibility, & Education (SAVE) is a useful mnemonic for the basic principles of safe TA operations. S is for passive Separation; the relegation of TA operations to remote low-traffic airspace; A is for Avoidance; the effective evasive capability of a TA platform (ie. "kite-killers"). V for Visibility is the standard for obstruction markings, transponders, radar-reflectance, etc.. E for Education is the requirement to appropriately inform & train all pilots operating in proximity to TA, as well as the special Type-Rating knowledge a TA PIC needs.
Turbines on resonant composite wings can be quite noisy making the Visual Observer "deaf" to intruding air traffic (Often an airplane is heard before its seen, helping "sense & avoid".).
Special Risks- Mid-Air Collisions, Breakaway, Tether Dragging, Conductive-Tethers, Security,
TACO/Nextgen Transformation Path
The general iterative-spiral validation process toward NextGen Integration-
Input from all stakeholders
Accommodation of major concerns
Technical Validation
Sign-off by stakeholders
Adoption into NextGen ConOps
EAA & AOPA are key pilot stakeholder representation. ALPA & Carriers are not current stakeholders as commercial aviation is to stay well-separated until NextGen standards apply.
Local governments, where TA operations impact, are key stakeholder representation to proactively include in planning.

Forward-Looking TACO:

The TACO Draft focuses mostly on near-to-mid-term AWE R & D. The forward-looking capabilities referenced below derive from the NGATS Vision Briefing of 2005 toward the NextGen Airspace CONOPS for 2025. Mature Tethered Aviation Operations (TAO) shall conform to these standards-
NextGen Network Integration- Positioning, Navigation, & Timing (PNT) Services; RealTime Community Of Interest (COI) utility;
Layered Adaptive Security (LAS)- TAO will be a fully integrated sector. PIC comm linked.

Service Performance-Based Operations- Load On-Demand; it will be the goal of the AWECS to respond to load demand with LAS.

Weather-Based Decision-Making- An Essential TAO function.
Trajectory-Based Operations (TBO)- Variable geometry kitefarm operations will be certified.
Super-Density Operations (SDO)- Airspace will be treated as a limited resource best maximized by AWE SDO well separated from air traffic.
Supervisory Override of Semi-Automated Flight is a bridge technology
NextGen's Moving Constrained Airspace is a capability needed for Tethered Free-Flight development 
EVFR rules for relaxed visibility will widen the TA flight envelope & be a bridge to Autonomous IFR .

NASA-FAA Research Transition Teams - JPDO Presentation - Master ...

Petition for Exemption or Rulemaking - FAA: Home