Tethered-Aviation ConOps (TACO)
Focus on Experimental Airborne Wind
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
(add definitions) AKA AOPA AMA AWE AWEIA AWEA ConOps FAA FARs ICAO
NASA R&D SARPs TA TACO sUAS UAV
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
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
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
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
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 &
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
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
Sec. 61.31 — Type rating requirements, additional
training, and authorization requirements.
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
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
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)
PART 101 - MOORED BALLOONS, KITES, UNMANNED ROCKETS AND UNMANNED
Part 77 - OBJECTS AFFECTING NAVIGABLE AIRSPACE
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).
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
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
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,
TACO/Nextgen Transformation Path
The general iterative-spiral validation process
toward NextGen Integration-
Input from all stakeholders
Accommodation of major concerns
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
Local governments, where TA operations impact, are
key stakeholder representation to proactively include in planning.
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
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
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