Proposed FAA Advisory Circular
Tethered-Aviation Concept-of-Operations (TACO)
Focus on Experimental Airborne Wind Energy (AWE)
Preface to the 6th Draft-
At the second Airborne Wind Energy (AWE)
Conference (AWEC2010), the FAA 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 written to be suitable as an FAA Advisory
Circular to properly inform all 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 "living document" is intended to evolve
& merge into the NextGen Airspace ConOps. The US
regulatory standard is expected to drive the international picture
(ICAO, etc). Please send corrections or additions to email@example.com
Tethered Aviation is an old & important branch of Aeronautics, with a erostats, aerotowing
, & kites as well-known examples. Tether-based
flight systems under current development will enhance
aviation capabilities, host infrastructure (ie.
communications), spin-off industries, create recreation,
& generate clean energy. This "New Aviation" requires the primary
stakeholders, pilots, developers, regulatory bodies, &
populations, to all come together to resolve the technical & social
challenges & realize the great potential.
are a key stakeholder, as primary users of airspace
& the group most exposed to flight risk. It will be pilots,
following their norms & traditions, who lead safe effective
Tethered Aviation R & D, who take jobs in the new aviation industries &
ensure that operations stay consistent with safe convenient shared
airspace. The aeronautic & aerospace industries are tasked with
designing systems that pilots accept & the FAA, the gatekeeper
stakeholder, can certify as airworthy.While there are new issues
to face in TA, for the purposes of private R & D, the
current system is not broke, & need only change by increments to
transform over time into major mature sectors. All aviation
interests must collectively prove to
extended stakeholder populations that Tethered Aviation
enhances life & is a "good neighbor". General policy
developers & decision makers, from the national to the local
level, are another key early stakeholder group. 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 user & industry associations, to refine
& promote best practice for their 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
prepared under the auspices of AWEIA.
AWEIA will coordinate member standards for safety & act as
liaison between industry & FAA. There are already urgent R
& D safety issues AWEIA is addressing, such as the 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 oversight roles. Key wind energy standards also
apply to AWE operations.
TA Excise Taxes & User Fees
The new AWE technology taps airspace as a source of vast energy. Mature
energy sources all have excise taxes, with 5% of producer's selling
price typical. Unlike excise taxes on extractive non-renewable energy
sources which eventually run out, renewables can generate revenue in
perpetuity. Barriers to
broad AWE societal stakeholder acceptance. like NIMBY
(not-in-my-back-yard) forces, will tend to evaporate before a
rich new tax base that more than offsets any negatives. The average
US 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 & even a
new era of sustainable prosperity for all. Energy excise taxes are also used to offset environmental downsides with mitigation measures.
Airspace is by tradition a Public Commons based on
Freedom-of-the-Seas. There is already resistance on the part of
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 could make sense for the new types of aviation.
The AWE industry can gain ready aviation
stakeholder acceptance by subsidizing common airspace
infrastructure benefiting all. AWE excise charges 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
TA Operations must carry Liability Insurance proportional to risk.
Such insurance is currently unavailable from traditional
providers & a special TA Liability Fund may be needed for
a jumpstart. TA operations can pay premiums into the fund &
Excise Tax funds can help cover special pioneering risks.
wrongful death these days can cost around ten million USD & there
is no AWE liability insurance available. 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
FARs Category, Class, & Type Certifications for TA
The FAA tasked the AWE Industry (AWEC2010) with defining
the profusion of designs & new Types into the FAA's
Aircraft/Airman/Operations Category, Class, & Type
System. Categories naturally grow by added Classes,
so special TA Classes are to be defined within current
Categories. Note that FARs are sometimes vague,
confused, & contradictory; no clean classification ontology
is even possible, only patchwork progress, pending
NextGen. There is traditional wiggle-room in the system,
with many exceptions & options at the discretion of authorities,
including classification under multiple categories & classes.
Aviation is increasingly diverse & its 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".
Far-flung tether geometry is a unique TA feature to account
for, but has useful similarity to standard geometry flight
trajectories & operations like skydiving.
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.
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.
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
Examples of new Classes created- Tethered-Aerobatic,
Tethered-Single-Engine, Tethered-Multi-Engine, Tethered-Normal,
Utility, Sport, Ultralight, Moored-Balloon, Aero-Towed Glider, Tethered
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.
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.
Electrically Conductive Tethers require special standards addressing all safety issues.
Autonomous Flight of high-consequence platforms (high mass &/or
velocity, especially around populations) will require a
proportionately more cautious rigorous path to validation
Aircraft joined by tethers into arrays is an operational
configuration to validate. The proposal is that this method might
greatly enhance safety & reliability.
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 &
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
Pilot Categories & Training
The requirement for proper pilot-training is fundamental in every
branch of aviation. All pilots in TA-shared airspace require awareness.
TA pilots require basic aeronautical training, plus specialized
operational proficiency. As high-consequence risk emerges TA
Pilots will eventually require the same highest-standard
certification as Transport Pilots.
Sec. 61.31 — Type rating requirements, additional training, and authorization requirements.
Some major Operational Categories- Unmanned Aviation System, IFR/VFR, Weight & Speed Cats., Obstruction
Models like the Obstruction regs are only partial. For example, an
antenna-farm Obstruction is regulated under mast &
tower structural codes & does not have the
inherent aviation hazards related to aircraft airworthiness
& potential to crash far afield. Therefore a TAC regulated as an
obstruction also needs to comply with Aircraft regs.
Current norms & Regulations
The FAA's role of maintaining a safe NAS
& especially its job of certificating type airworthiness
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, might serve for persistent "static" TA operations under 2000ft AGL.Shielded operations is a current option for a TA operator able to identify sites.
Draft FAA sUAS regs call for Pilot-in-Command & Visual Observer crews.
Key Title 14 Parts of the Code of US Federal Regulations (Aeronautics & Space)
PART 101 - MOORED BALLOONS, KITES, UNMANNED ROCKETS AND UNMANNED FREE BALLOONS
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).
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
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 keep visual contact to operating in
"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
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.
Special Risks- Mid-Air Collisions, Breakaway, Tether Dragging, Conductive-Tethers, Security,
TACO/Nextgen Transformation Path
The general iterative-spiral validation process toward NextGen Integration-
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-
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 .