Concept of Operations (TACO)
Case Focus on Experimental
Airborne Wind Energy Systems (AWES)
AWE AirborneWind Energy
AWECS AirborneWindEnergyConversionSystem (old usage)
ConOps Concept of Operations
FF FreeFlight XC
FAA US FederalAviationAdministration
FARs US FederalAviationRegulations
FBO FixedBaseOperator, a small airport admin
LSA LightSportAviation/Aircraft Category
LLJ LowLevelJet Stream
METAR METeorologicalAviationReporting data format
NextGen NextGeneration aviation plan/standards
NIMBY NotInMyBackYard population
SARPs ICAO Standards&RecommendedPractices
VO Visual Observer
Preface to this Draft
In 2010 FAA and NASA staffers informally called on the early AWES industry
define its new "energy aircraft" types into the FAA's Category/Class system
and develop a ConOps for AWES in US NAS. In response, AWEIA undertook
this document, TACO, to formally
address these requirements. The work aims
toward a consensus FAA Advisory Circular and ICAO Proposal-For-Action,
informing aviation stakeholders about AWE issues and operations. TACO covers
the full scope of TA, not just AWES, building on solid existing models wherever
possible, and is intended to merge smoothly with NextGen Airspace ConOps.
This is an open living document; AWEIA member, KiteLab Group, builds and
maintains it on a volunteer basis. Send corrections, additions, & comments to:
Aviation Self-Regulation Principle
Regulatory Standards, Exceptions, and Exemptions
FAA AWES Temporary Rules
Category, Class, & Type Certifications for TA
Pilot Categories & Training
Tethered Aviation is an aeronautical class and set of methods to transfer
force over distance via cables between aircraft, payloads, and anchors or vehicles.
Well-known instances include kites, aerotowing, and aerostats (moored balloons).
New tethered flight concepts
are expanding aviation capabilities to create new
applications, jobs, industries and novel recreations. TA even promises to generate
abundant wind energy, as AWES, also known as "Kite Energy".
This clean energy technology may someday subsidize, by airspace usage
fees and excise taxes, the needs and dreams of populations and general aviation.
Stakeholders such as pilots, developers, regulatory bodies, and government are
working together to resolve technical and social challenges. The current aviation
regulatory framework is not broken, but daily
protects public saftey at reasonable
cost, and is a sound foundation to build on.
Pilots are primary workers in airspace
most exposed to flight risk, and the FAA
itself is pilot-led. The standing FAA requirement for direct pilot supervision of
UAS systems will hold for years yet. This ConOps is thus "pilot-centric",
embracing the pilot as a key stakeholder, but also forward-looking to eventual
validated autonomous flight. Upholding aviation norms and traditions, pilots
already lead R&D of safe effective TA and will ensure safe operations in
shared airspace. New pilots will be needed to fill the many flying jobs created.
aerospace industry will create
large-scale systems that pilots accept and
FAA inspectors certify as airworthy. Policy developers and decision makers,
from the national to local scale, are a key
stakeholder group to properly inform.
Knowledgable stakeholders must
strive to honestly convince extended stakeholders
(populations) that TA enhances society as a "good neighbor". TACO best-practice
standards lay the basis for wide public acceptance.
Aviation Self-Regulation Principle
The FAA relies on all aviation sectors, via user agencies, associations, and
industries, to help define, promote, and even enforce best practice of members.
Safe aviation operations presided over by responsible
FAA to maximize its limited resources and regulate with a light
touch. Failure of any sector to ensure safety brings down the full weight of
Accordingly, the Airborne Wind Energy Industry Association (AWEIA)
has, as part of its formal mission. a global leadership role in self-regulation
of AWE and related TA. TACO is AWEIA's project to coordinate Consencus
Standards for safety and to act as industry liason with regulators like the FAA
and ICAO. AWEIA intends to enforce on
standards in its field, even exceeding and anticipating government regulations.
AWEIA will petition the FAA for new Rulemaking as needed, following
the successful example of the Experimental Aircraft Association and
FAA together creating a regulatory framework for the new LSA category.
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
AWEIA is just one of several associations with overlapping interest in TA.
TA operators will emerge from enthusiast communities: EAA and AOPA have
strong interest in the new sectors. The AKA recreational & professional kite
operations. The AMA is responsible for safe hobbyist aviation. User associations
in soaring and other sectors that routinely perform tethered operations
have unique stakeholder roles. Wind energy
standards promoted by
AWEA also apply to AWE operations. Local government and poulations will
have a strong voice in shaping AWES, with a NIMBY veto power if imapacts
warrant. AWEIA undertakes to reconcile all the stakeholders.
Regulatory Standards, Exceptions, and Exemptions
These sections present specific concensus standards for regulating TA. Some
of it is legacy FAA "boiler-plate" in process of being adaptation into an
Standard; an operational manufacturing/design/maintenance/quality
practice approved by or acceptable to a civil
aviation authority. An Exception is a case in which a rule, general principle,
etc., does not apply. There are very few justifyable exceptions to apply to TA. An
Exemption is approval to be free from current regulations in 14 CFR. Minimal
need for any exemption of TA from FARs is a TACO priority.
FAA AWES Temporary Rules
Following a large build-up in interest and activity, late in
the FAA released
governing experimental AWES operations. An AWES community
discussion followed and concensus standards were drafted around many key issues.
The "case-by-case" review process was seen as a reasonable standard for
early AWES R&D regulation. Mishap reporting and open Failure-Mode disclosure
by developers was expresses as an essential community need.
Standards for flight parameters, such as altitude, conspicuity, VFR conditions are
explicitly in force by the 2011 FAA circular. Existing airworthyness standards based
aircraft mass and
velocity are additionally proposed for enforcement by AWEIA,
with its members on notice.
The FAA Advisory Circular governing Obstruction Marking and Lighting
AC 70 7460 1K was accepted as the default standard for AWES conspicuity.
New FAA standards for sUAS operations cover key issues common
to AWES. A PIC and VO, with sense-and avoid cabability are particular
priorities to adopt as an AWES standard for those systems with
Multi-tethers are proposed as a basic safety redundancy method, and the
determination of airworthness should account for the lack or presence of
multi-tethers, or equivalent measures, in the AWES design.
Class, & Type Certifications for TA
Existing FARs cover most of the engineering and flight standards
required to properly regulate the new aviation types. FARs can be
vague, confused, and contradictory; the classification scheme is a
historical patchwork. The system allows needed wiggle-room, with
exceptions, exemptions, and options at the discretion of FAA field
authorities. NextGen FARs will overhaul classification, but quirks
A logical step toward proper regulation is to finally define tethered wings
(large kites) as aircraft. Currently only airplanes, rotorcraft, gliders, and
balloons are formally recognized as Aircraft. A tethered wing anchored
in wind and/or associated motor-winch can be classed as an Engine,
rated by power, for motive or output power. Ratings and Operating
Limitations would be certificated just as
and rotary IC
engines are. The notion of an Airframe remains the same, with the tether
structural interface an added technical concern. Exotic new kinds of
tethered aircraft will need to be Type Certified in a suitable new Category
or special Classes.
Most of the profusion of potential TA design Types pre-sorted into the
FAA's Aircraft/Airman/Operations Category, Class, & Type System.
Categories naturally grow by adding Classes. Specific TA Classes are
proposed to suppliment current
Categories. A new TA Category might
emerge and be ordered in detail under the LSA model of classes and sets.
Like any other aircraft, TA platforms should be classified by gross-weight
and airspeed, by the
same physics of safety-critical "consequence". Weight
and Speed (mass & velocity) are primary determinants of Class within a
Category. In general higher mass/velocity Classes have Higher Consequence
Failure-Modes requiring proportionally higher standards for equivalent safety
(mortality to flight hours).
Current classifications include: normal, utility, acrobatic, commuter, transport,
manned free balloon, glider, special, restricted, etc. As an
example of how a TA
Class can apply across Categories, some given
Types are potentially suitable or
routinely modified for aerotowing, with special appilicable standards.
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
improved reliability from multi engines is the higher required standard of
Pilot training & aircraft engineering.
With respect to Certification of aircraft under the FARs, Class means a broad
grouping of aircraft having similar characteristics of propulsion, flight,
landing. Examples include: airplane; rotorcraft;
glider; balloon; landplane;
Structural systems used for airframes also fundamentally categorise aircraft. A
fabric "softwing" has very specific different design and operational parameters
compared to any high speed rigid wing. Best practice is sought in the closest
related avaition specialties, and regulated to those standards, as the ready default.
New sub-classes are proposed for major new configurations like free-flight
cross-linked flying formations.
Experimental and rare aircraft types are flexibly
integrated by ad-hoc classification into multiple categories &
classes. Aviation is
increasingly diverse and a major new branch could merit a wholly new Category.
Any conventional aircraft can in principle be put on a tether, which
does not negate its status as a legal aircraft of a given mass & speed
envelope, but adding a tether adds operational complexity and hazard.
Provisional Sub-Classes- Tethered-Aerobatic, Tethered-Single-Engine
(or turbine), Tethered-Multi-Engine (or turbine), Tethered-Normal, Utility,
Sport, Ultralight, Moored-Balloon, Aero-Towed Glider, Tethered Rotorcraft.
Categories and Classes of aircraft & operations mix, overlap, or otherwise
interrelate. For example, a specific type can be
operated as either a
Commercial or Private Aircraft, with different FARs in play.
Small Aircraft- 12,500 pounds or less, maximum certificated takeoff
weight. This is a default "line-in-the-sand" for developers and regulators
as AWES grow larger, with advantages to staying just small enough.
AWES that operate aerobatically & incur high G-loadings are Acrobatic
Category (limited to 12,500lbs gross). Tether-Weight is to be counted
toward rated gross weight. Tether-Drag should count
L/D. Autonomous Flight of high-consequence platforms (high mass &/or
velocity, especially around populations) require a proportionately more
cautious rigorous path to validation and certification.
AWES are generally high-duty UAS, meriting special 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
400ft for low mass low speed hobbyist model aviation. 500ft as a "floor"
for general VFR aviation. Class G airspace is low altitude and variable,
with higher ceilings in remote areas, 2000ft obstruction limits rule
mast and tower certification, 18,000ft is the defined ceiling to avoid
transport aviation operations. 25,000ft is the defined theshold of
High-Altitude flight, with special applicable standards.
Stall Speed is a key aircraft safety parameter, the lower
the better, with the
widest possible range of operation desirable between max airspeed & stall
speed. Fixed-Wing AWES that land at a fixed point face a
not operate too close to stall on final approach, or land too hard. Sink Rate
or Terminal Velocity might be a partial basis for some AWES regulatory
Pilot Categories & Training
Pilot training and testing is fundamental to aviation. Conventional
pilots in AWES-shared airspace need awareness of new operations and
AWES commercial venture starts lack formal aviation
backgrounds and face acculturation along FAA approved paths. AWES
must master basic
aeronautics, plus specialized knowledge and
operational proficiency. As high-consequence risk emerges by powerful
industrial-scale systems, AWES crews must ultimately meet equivalent
standards of certification to Transport Pilots. See Sec. 61.31 Type rating
requirements, additional training, and authorization requirements.
As used with respect to the certification, ratings, privileges, and limitations of
airmen, Class means a classification of aircraft within a category having similar
operating characteristics. Examples include: single engine; multiengine; land;
water; gyroplane; helicopter; airship; and free balloon; New classes of airman
are proposed for
new TO types that do not clearly fall into existing classes.
Mature TA pilot standards exist within towed gliding (including hang
gliders and paragliders), banner towing, and many approved niche
TA Operational Categories/Classes
Flight operations vary within pilot and aircraft categories. Conditions
and appications often impose specific critical
AWES systems blend operational feaures of usually discrete models, for
example, just as a glider moors or unmoors in and out of free-mode.
Altitude- Obstuction Reg altitude (
increase in operational complexity,
by added redundancy, can actually enhance safety.
Categories- Transport, Normal, Utility, Acrobatic, Limited,
Restricted, and Provisional. Provisional uses are defined as needed- STOL,
High Altitude, Marine Environment, Unmanned, IFR, Weight & Speed Cats.,
Obstruction, & so on.
Acrobatic Class- Aerobatic operation is a feature of some AWES, with
issues of conpsicuity, high cycle structural loadings and fast controls.
Novel TA/AWES Categories, Classes, Sets, and Types
The explosion of new configurations defies final classification, but can
be described generally.
AWES with Surface Based Electrical
Many AWES schemes seek to minimise mass aloft by keeping electrical
generation and conductors at the surface. The purest expression of this
philosophy is "rag and string only", with many potential advantages
to aviation safety and economics. Ground-based actuators (winches) can
be massive industrial grade machinery, without the delicate margins of
flyable servos. Radar clutter, comm link dependence, inspectability, high
mass-velocity, and many
other issues are mitigated. There will still be
enormous challenges to safe operations as mechanical power scales grow.
AWES with Electrical Power Systems Aloft
Electrically Conductive AWES Tethers and generators require added
standards to address inherent safety issues. A general suggestion is to
maintain terrestrial electrical code
and fire safety standards as a default
baseline, with aviation standards overlaid.
E-Flight is a fast progressing new category of general aviation. Tethered
E-Flight will share many of the existing and pending standards. E-VTOL
will inherit key standards of existing VTOL.
Case Note: Sky WindPower, Inc, is well regarded for its study of the
electric quadcopter AWES concept space. Makani Power, Inc, leads in
developing large advanced composite
AWES. The Makani models are useful benchmarks for regulation study,
with data being generated via a DOE contract.
Autonomous Flight is slowly maturing as an aviation option. Many teams
are working to automate AWES flight operations to avoid human piloting.
Tethered autonomy has both favorable and adverse aspects. Tether physics
can constrain or add chaos. Flight software must be created to "cleanroom"
standards and formally validated. Sensory and situational uncertainy are
presistent problems. Exception handling is a critical challenge.
relaunch a system after an automatic shutdown is a "tough call" to automate.
Meanwhile, human piloting will rely as necessary on existing avionics, and
supervised autopiloting generally.
Cellular Aerial Arrays
Formations of TA aircraft joined by tethers into dense-arrays is a major AWES
configuration class. A goal of dense-array
methods is to greatly enhance general
aviation safety and reliability by avoiding airspace (and land) sprawl for an
equivalent power capacity. Many functional units can be aggregated to fly as
one well-integrated flight control process, as opposed to many independently
Arrays can incorporate any of the many classes of AWES units. The array can
constrain its units into a high "aggregated stability" whereby the momentary
instabily of any single unit is cancelled by the normal action of its neighbors.
and redundant surface connections are safety advantages,
but given a large arrays, an
unlikely worst-case mishap of a dragging breakaway
could be catastrophic. The highest professionalism and redundant levels of
"killability" are required.
In the long-term, megascale cellular aerial arrays are a megascale geo-engineering
technology with a vast potential impact. Case Note: TUDelft and KiteLab Group are
the R&D leaders in the design-space of cross-linked formations of AWES units.
High Altitude Kite
Even a century ago, kites where shown capable of reaching altitudes in excess
of 30,000ft. Current art and short-term economics favor low-altitude AWE.
Nervertheless, a new round of high-altitude kite aeronautics is is poised
to explore "fuelless aviation" applications even to around 100,000ft. These will
be demanding experiments conducted by top aerospace teams as approved by
the FAA on a case by case basis.
Currently, the stretching of tethers to high altitudes is an unacceptable hazard to
all classes of aviation in shared airspace. The consequences of breakway and
runaway are aggravated. Persistent high Altitude TA must remain in restricted
airspace and await NextGen capabilities to expand operations.
Existing missle ranges are proposed as an ideal venue for high-altitude TA testing
on a time-shared basis, as most such restricted airspace is not intensively needed
"Free Flight"- Wind Powered Avaition
Free-Flight is a frontier of aviaton based on
more wings tethered together.
Its been shown with small models that if
each wing flys in its own wind, the tether
stretched across a wind gradient, they can work in opposition and sustain flight in
any direction. Unlike traditional soaring dependent on thermals or terrain, Free-Flight
can be sustained ordinary surface wind gradient or any sort of wind shear, like around
LLJs and inversions.
Case Note: National champion glider pilot and aeroengineer, Dale Kramer, proposes
a cross country demonstration of Free-Flight by tethering his high performance
glider to a large kite farther above. By working glider against kite its predicted he can
fly almost indefinitely without fuel.
The FAA traditionally accomodates such
aviation feats that advance aeronautical knowledge on a case-by-case basis, with only
the highest level of skill and expertise allowed. There will be many unique aeronautical
feats to attempt along these lines.
Many prototype and proposed tethered rotorcraft are proposed for AWES. Some
are E-helicopters whose motors also generate and others autogyros modulated to pull
against loads. General rotorcraft design and.operational factors as currently defined
will apply to the new rotorcraft, with tether factors as added concerns.
AeroTowing, Banner Towing
Traditional TO will persist under existing FARs. A constant exchange of technology
will occur with new types of TO, and many of the old rules will still apply.
Aerotowing continues as a major method of launching gliders and as a design option
for certain situations. An active world record category involoves towing as many
gliders as possible from one tow-plane. Utility towing of cargo
might make a comeback in the future due to economic or
Traditional banner towing operations continue to evolve by incremental hardware
and operational improvements. New types are emerging; for example, the lifitng
of mega-flags by helicopter.
The term Aerostat was first associated with Moored Balloons, but logically extends
to persistent tethered electric aircraft or kite flight. Persistent E-Flight is practical
of a conductive tether. Kites
can keep station in calm by towing in circles
from vehicles or by phased tugs from fixed winch
Once common as wartime Barrage Balloons, Moored Balloons are making a
comeback as radar stations (to 18000AGL) and for low-altitude advertizing.
Many AWES designs employ Moored Balloons for peristence aloft. Moored
balloon regulations are mature and may represent an early regulatory approval
path for AWES.
Norms & Regulations
Key Title 14 Sections of
the Code of US Federal Regulations
(Aeronautics & Space) apply to TA. Part 101 contain the seeds
of many TA regs to come,
but are due for additions and upgrades to
cover holes in safety and to permit enhanced
certificated airworthiness within current regs will prevent AWES
R&D from creating a "menace-to-aviation".
It is widely proposed by the FAA that early AWES might operate under
Obstruction Regs such as govern Antenna Farms, but this model is partial.
For example, an antenna-farm Obstruction is also regulated under mast &
tower structural and electrical codes outside the purview of the FAA. Towers
lack many inherent hazards related to aircraft
crash far afield (runaway). An AWECS is not a tower
& needs to comply
with Airworthiness Standards.
Class G Airspace is a primary realm of current AWES R&D. FSDOs are
the arbiters of allowable experiments, with good decentralized flexibility.
AWE R&D can shop around for a "best-fit" FSDO (generally remote
low-traffic NAS regions). The 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
Obstruction regs, such as
apply to antenna farms, can partly serve
"static" TA operations under 2000ft AGL. Shielded operations
is an option for an AWES operator at suitable 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 be permissible
in a short time-frame of a year or two. The safer bet is that many years must pass
before the required safety and reliability is validated and permitted.
Note: Part 101 sections below edited for brevity,
and Unmanned Free Balloon Regs are partial models for Tethered Free-Flight
PART 101 - MOORED BALLOONS, KITES, UNMANNED ROCKETS
AND UNMANNED FREE BALLOONS
Prt 101 applies to any kite that weighs more than 5 pounds
intended to be
flown at the end of a rope or cable...including a gyroglider attached to a
vehicle on the surface of the earth is considered to be a kite. No person may
conduct operations that require a deviation from this part except under a
certificate of waiver. No person may operate a moored balloon, kite,... in a
restricted area unless he has permission from the using or
controlling agency, as appropriate.
101.7 covers "Hazardous operations" and has a key catch-all clause-
"No person may operate any moored balloon, kite,... in a manner that creates
a hazard to other persons, or their property." It goes on to assert "No person
operating any moored balloon, kite,... may allow an object to be dropped
therefrom, if such action creates a hazard to other persons or their property."
next subparts apply to
the operation of moored balloons and kites.A person
operating a moored balloon or kite within a restricted area must comply only
with 101.19 and with additionallimitations imposed by the using or controlling
agency, as appropriate.
101.13 Operating limitations. (a) Except as provided in paragraph (b) next, no
person may operate a moored balloon or kite- (1) Less than 500
feet from cloud
base; (2) More than 500 feet above the surface of the earth; (3) From an area
where the ground visibility is less than three miles; or (4) Within five miles of the
boundary of any airport. (b) Paragraph (a) of this section does not apply to the
operation of a balloon or kite below the top of any structure and within 250 feet
of it, if that shielded operation does not obscure any lighting on the structure.
101.15 Notice requirements. No person may operate an unshielded moored balloon
or kite more than150 feet above the surface of the earth unless, at least 24 hours
before beginning the operation, he gives the following information to the FAA ATC
that is nearest to the place of intended operation: (a) The names and addresses
of the owners and operators. (b) The size of the balloon or the size and weight of the
kite. (c) The location of the operation. (d) The height above the surface of the earth at
which the balloon or kite is to be operated. (e) The date, time, and duration of the
101.17 Lighting and marking requirements. (a) No person may operate a moored balloon
or kite, between sunset and
sunrise unless the balloon or kite, and its mooring lines, are
lighted so as to give a visual warning equal to that required for obstructions to air
navigation in the FAA publication "Obstruction Marking and Lighting" . (b) No
may operate a moored balloon or kite between sunrise and sunset unless its mooring lines
have colored pennants or streamers attached at not more than 50 foot intervals beginning
at 150 feet above the surface of the earth and visible for at least one mile.
101.19 Rapid deflation device. No person may operate a moored balloon unless it has
a device that will automatically and rapidly deflate the balloon if it escapes from
its moorings. If the device does not function properly,
the operator shall immediately
notify the nearest ATC facility of the location and time of the escape and the estimated
flight path of the balloon.
Subpart D - Unmanned Free Balloons 101.31 Applicability. This subpart applies
to the operation of unmanned free balloons. However, a person operating an
unmanned free balloon within a restricted area must comply only with 101.33 (d) and
(e) and with any additional
limitations that are imposed by the using or controlling
appropriate. 101.33 Operating limitations. No person may operate an
unmanned free balloon- (a) Unless otherwise authorized by ATC, in a control zone
below 2,000 feet above the surface, or in an airport traffic area; (b) At any altitude
where there are clouds or obscuring phenomena of more than five-tenths coverage;
(c) At any altitude below 60,000 feet standard pressure altitude where the horizontal
visibility is less than five miles; (d) During the first 1,000 feet of ascent, over a
congested area of a city, town, or settlement or an open-air assembly of persons
not associated with the
operation; or (e) In such a manner that impact of the balloon,
or part thereof including its payload, with the surface creates a hazard to persons or
property not associated with the operation. (a) No person may operate an unmanned
free balloon unless- (1) It is equipped with at least two payload cut-down systems or
devices that operate independently of each other; (2) At least two methods, systems,
devices, or combinations thereof, that function independently of each other, are
employed for terminating the flight of the
balloon envelope; and (3) The balloon
envelope is equipped with a radar reflective device(s) or material that will present
an echo to surface radar operating in the 200 MHz to 2700 MHz frequency range.
The operator shall activate the appropriate devices required by paragraphs
(a) (1) and (2) of this section when weather conditions are less than those prescribed
for operation under this subpart, or if a malfunction or any other reason makes
the further operation hazardous to other air traffic or to persons and property on th
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