# DEPARTMENT OF TRANSPORTATION

# Federal Aviation Administration

## 

## Large Agricultural Restricted Category Airplane Certification Topics 

#### 

#### AGENCY: Federal Aviation Administration (FAA), DOT

**ACTION**: Notice, request for comment.

The FAA is seeking public comment on this proposal. The FAA has
published in the [Federal Register]{.underline} a notice of availability
and request for public comments on this subject. Please include the
words "Large Agricultural Restricted Category Airplane Certification
Topics" in the subject line of your comments on this proposal. To help
us to assemble and collectively respond to public comments, if you
submit comments electronically, please include a text message version of
your comments if you submit a PDF file. You may electronically submit
your comments on this proposal to the following e-mail address:
**[9-awa-avr-air-policycomments@faa.gov]{.underline}** .

**SUMMARY**: This notice requests comments on, three particular topics
concerning certification criteria for three different large airplane
design proposals for restricted category aircraft to be used for
agricultural and firefighting missions.

(1) The manufacturer requests FAA approval to certify the airplane to
    all appropriate airworthiness requirements at a baseline weight that
    is a fraction of the maximum certificated takeoff weight of the
    airplane. The manufacturer proposes to certify the airplane to Part
    23 requirements, and to operate at reduced speed and load factors
    when operating heavier than the baseline weight. The FAA is not
    accepting the proposal to permit operational limits for routine use
    of overweight approvals. However, the FAA believes the applicant's
    proposed limit maneuver load factor at the maximum certificated
    takeoff weight is acceptable for the large airplane agricultural
    special purpose operation, when the airplane is certificated to
    damage tolerance evaluation criteria with an appropriately severe
    usage spectrum.

(2) The manufacturer proposes that a single engine airplane is safer
    than multiple engines for a large restricted category agricultural
    and firefighting airplane. Considering the nature of agricultural
    aircraft operations, we at the FAA request data and comments from
    the agricultural aircraft industry on airplane operating practices
    as they might affect the consequences of a propulsion system
    failure. Since the proposed aircraft will be used for forest
    firefighting, we also request comments from that group.

(3) The manufacturer is proposing a 36,000 pound twin engine airplane
    design for the agricultural and firefighting missions. The FAA and
    the manufacturer have worked to develop a certification basis that
    primarily consists of part 23 airworthiness standards, with many
    part 25 requirements primarily for the certification of the aircraft
    structures. The FAA believes that this is appropriate for a large
    airplane that will not be used for carrying passengers or cargo.
    This notice states how you may find the proposed certification
    basis, and gives all interested persons an opportunity to comment on
    the proposal.

**DATES**: Submit comments on or before \[INSERT DATE 60 DAYS AFTER DATE
OF PUBLICATION IN THE FEDERAL REGISTER\]

**ADDRESS**: Send all comments on this proposal to: Federal Aviation
Administration, Aircraft Certification Service, Aircraft Engineering
Division, Room 815, 800 Independence Avenue, SW., Washington, DC 20591,
ATTN: Steve Flanagan, AIR-110. Or, deliver comments to: Federal Aviation
Administration, Room 815, 800 Independence Ave, SW, Washington, DC
20591. You may also send comments electronically to the following
Internet address: 9-awa-avr-air-policycomments@faa.gov.

**FOR FURTHER INFORMATION CONTACT**: Mr. Steve Flanagan, Certification
Procedures Branch, AIR-110, Aircraft Engineering Division, Aircraft
Certification Service, Federal Aviation Administration, 800 Independence
Avenue, SW., Room 815 Washington, DC 20591, telephone (202) 267-3549;
fax (202) 267-5340; E-mail: steve.flanagan@faa.gov.

# SUPPLEMENTARY INFORMATION:

# Comments Invited

You are invited to comment on the proposal by submitting written data,
views, or arguments to the address above. You may examine comments
received on the proposal before and after the closing date, in Room 815,
FAA Headquarters Building (FOB-10A), 800 Independence Avenue, SW.,
Washington, DC 20591, weekdays except Federal holidays, between 8:30
a.m. and 4:30 p.m. The Director of Aircraft Certification Service will
consider all communications received on or before the closing date.

# Background

## **Restricted Category Background**

Restricted category approvals date back to 1945 as an option to normal
category approvals for small airplanes and small rotorcraft. When Part 8
of the Civil Aeronautics Regulations (CARs) was adopted on August 12,
1950, references to restricted category certification procedural rules
were removed from the airworthiness standards in CARs part 03 (small
aircraft) and part 06 (rotorcraft). The rules, and the advisory and
guidance material for restricted category were combined in the single
document Civil Aeronautics Manual (CAM) 8 "Aircraft Airworthiness --
Restricted Category". CAM documents provided in a single place both the
rules and the advisory material for compliance with those rules. CAM 8
provided mostly advisory material that was judged consistent with the
minimal procedural regulations for obtaining a restricted category type
certificate. CAM 8 policy was the first identification of the special
purpose operations that are now listed in 14 CFR § 21.25(b). These
special purpose operations included several different agricultural
missions, plus forest and wildlife conservation. The aerial firefighting
mission is one that is considered as forest and wildlife conservation.

CAM 8 advisory material in Appendix A described acceptable simplified
modifications for small aircraft conducting agricultural special purpose
operations. Appendix B of CAM 8 provided advisory material for
certification criteria for type certificates or changes to type
certificates for small aircraft in the restricted category.

The restricted category approval process was intended to justify a
different level of certitude and of safety when modifying aircraft for
special purpose operations, as contrasted to aircraft intended to carry
passengers or cargo. This flexibility worked in two ways. "A different
level of certitude" permitted the applicant to use simplified methods of
compliance to demonstrate the integrity of the proposed modification. "A
different level of safety" permitted the applicant to work with the FAA
to identify certain airworthiness standards appropriate for the small
aircraft as inappropriate for the special purpose operation. When
restricted category was originally in the airworthiness standards for
small airplanes and rotorcraft, an airworthiness standard would be
judged inappropriate if it made the aircraft incapable of conducting the
intended special purpose operation. With the adoption of CAR part 8, the
criteria for determining an inappropriate airworthiness standard was
broadened. It now included economic burden and unduly restrictive
requirements for aircraft that neither carried passengers nor operated
outside of rural, sparsely populated areas.

## **Current Restricted Category Policy**

Much of our current policy on restricted category aircraft type
certification procedures is published in paragraph 6-1 of FAA Order
8110.4B, [Type Certification]{.underline}, dated April 24, 2000. Over
time, this order has consolidated policy from a number of different
sources and dates. For example, Order 8110.4B paragraph 6-1.b includes
procedural information from FAA Action Notice A8110.22, dated August 16,
1990. Also, paragraph 6-1.b.(4) of Order 8110.4B states the limitation
of CAM 8 advisory material to previously certificated small agricultural
airplanes with a certification basis of CAR part 8. This policy was
originally published in Advisory Circular (AC) 20-33B on May 1, 1975.

The procedure to determine airworthiness requirements that are
inappropriate for the restricted category special purpose operation is
stated in paragraph 6-1.b.(2) of Order 8110.4B. Paragraph 6-1.b.(3)
gives the different reasons for a restricted category type certificate's
variance from the airworthiness standards which are the basis for a
standard airworthiness certificate. These two paragraphs were the
guidance for the procedures the FAA and the applicant used to develop
these proposals.

### 

### **Current Agricultural Airplane Policy**

Our most recent review of agricultural aircraft certification and
operations was a joint government and agricultural aviation industry
study team from 1993 - 1998. The team developed guidance material that
standardized methods of compliance for small airplanes with restricted
category type certificates that are used for agricultural aviation
operations. This effort gave us significant agricultural aviation
experience in the Small Airplane Directorate. This team's effort was
unsuccessful in resolving the issue of permitting agricultural aircraft
operations at weights in excess of 12,500 pounds. The team's work
resulted in AC 21.25-1, [Issuance of Type Certificate: Restricted
Category Airplanes]{.underline}, dated December 1, 1997. At the same
time the Small Airplane Directorate issued to FAA offices a policy
memorandum dated December 1, 1997, that clarified for these aircraft
acceptable methods of compliance for certain airworthiness standards in
14 CFR part 23 as they might be used for small agricultural airplane
restricted category type certification programs.

#### (1) Overweight Operations At Weights Exceeding Small Airplane Weight Limit of 12,500 Pounds 

A manufacturer had proposed to the FAA on October 29, 2002 that his
restricted category agricultural airplane design satisfy part 23
structure certification requirements at a baseline weight of 12,500
pounds, and be approved for operation at a weight not to exceed 19,000
pounds, provided that the airplane shows positive static strength
margins at an airplane limit load factor of no less than 2.5g. This
proposal was consistent with FAA criteria developed for a previous
agricultural airplane design in 1992. The manufacturer contends that the
engineering principles that were the basis for the advisory material in
Appendix A of CAM 8 are valid for permitting operation at weights in
excess of the weight limit for which the airplane is originally
certificated.

In considering the manufacturer's proposal, the FAA has reiterated its
position as stated in AC 20-33B that CAM 8 advisory and regulatory
material are limited to aircraft that were originally certificated to
CAR part 8. Also, FAA believes that the advisory material in Appendix A
and Appendix B of CAM 8 was based on an assumption that the aircraft was
designed to utility category requirements. Evidence of this is seen in
the discussion in CAM 8 paragraph 7.1 "General Effects of Gross Weight
Changes" in Appendix A "Restricted Category Aircraft Modifications" of
CAM 8 (+4.4g limit load factor), and in paragraph .211 "Flight Load
Factors" in Appendix B "Airworthiness Criteria for Agricultural and
Similar Special Purpose Aircraft" of CAM 8 (+4.2g limit load factor).
The FAA also believes the maneuvers that characterize the definition of
utility category in §23.3(b)(1) and (2) can be considered as appropriate
for the aerial application mission. Finally, FAA has expressed its
concern that structural failures resulting from aircraft fatigue are
evidence that the maneuver loads of restricted category operations
require additional static strength structural margins (compared to
normal air transportation operations) to provide stress levels that do
not cause fast fatigue crack growth following initiation of a crack.

#### 

#### Review of Agricultural Aircraft Accident Data

FAA reviewed the National Transportation Safety Board (NTSB) online
aircraft accident database for fatal agricultural (part 137 operations)
airplane accidents occurring from 1988 to summer 2003. The review found
seven airplane inflight structural failures. One of the seven accidents
was not attributed to fatigue, but to a tensile overload failure of the
wing. One of the accidents was attributed to a fatigue failure initiated
by a modification made to the airplane in service. The other five
accidents were attributed to inflight wing failure from fatigue. The
seven accidents were among six different agricultural airplane models.

Appropriate Limit Maneuver Load Factor Criteria for Type Certificated
Large Airplane Restricted Category Airplanes

The manufacturer responded to FAA with data showing that for
agricultural airplane operations, internal strains do not develop
simultaneously with the occurrence of peak load factors. The FAA's
original intention by imposing the utility category limit maneuver load
factor of +4.4g for this large airplane was to address potential
airplane fatigue problems by reducing the internal structural stress
levels. This was intended to provide a static strength margin thought to
be appropriate for simplified fatigue analyses for restricted category
type certificated airplanes. The manufacturer has agreed that +2.5g as a
limit maneuver load factor does not adequately represent the severity of
the agricultural airplane special purpose operation. Instead, the
manufacturer has proposed to certify the airplane to all the
requirements in its certification basis at a baseline weight of 75% of
the maximum certificated takeoff weight, with certification to limit
maneuver load factors of +4.4g at the baseline weight, or +3.3g at the
maximum certificated takeoff weight. Also, the manufacturer has proposed
that the airplane fatigue analysis will be based on damage tolerance
analysis rather than the safe life approach used for previous small
agricultural airplanes. The damage tolerance analysis will reflect
actual airplane usage and internal stress levels. FAA also may compare
this with existing gust and maneuver acceleration data for agricultural
airplane operations (*DOT/FAA/CT-91/20, "General Aviation Aircraft --
Normal Acceleration Data Analysis and Collection Project", February
1993*). The FAA will require that the damage tolerance analysis be
supported by test evidence, as called for in §23.572(a)(3) and
§23.573(b). In this way, the FAA's concerns about fatigue will be more
directly addressed.

The manufacturer also provided data showing that requiring a +4.4g limit
maneuver load factor on the proposed 19,000 pound maximum flying weight
airplane would result in such marginal payload performance over its
existing 16,000 pound airplane that the new airplane project would not
be feasible.

The FAA agrees that requiring a +4.4g limit maneuver load factor for a
large airplane imposes a severe and conservative structural design
limit, absent conclusive data that such a high limit load is consistent
with the expected frequency of occurrence of this load level in
agricultural special purpose operations. For small agricultural
airplanes, as stated previously, FAA believes that the +4.4g limit
maneuver load factor is justifiable in light of the difference between
the small airplane "normal category" operations, and what is known about
small airplane agricultural airplane loads. As discussed above
concerning FAA's reasons for consideration of small airplane utility
category limit maneuver load factor requirements, the design of a small
agricultural airplane to a limit maneuver load factor of +4.4g would
permit its certification with a fatigue analysis that is more typical of
current experience and practice for showing compliance with the fatigue
strength or fail-safe strength investigations permitted by §23.572(a)(1)
or (a)(2).

The FAA also reiterates its position that the operational overweight
approval procedures that were published in CAM 8 advisory material are
not appropriate for use in modern agricultural airplanes. The FAA
believes that the controlling variable of "pilot feel" during the
overweight operation is defective, because the pilot senses a vertical
force N~Z~ based on the pilot's own weight, and is not cognizant of the
airplane vertical force N~Z~\*W, which the airplane wing loads apply to
the wing root structure. The inadequacy of this subjective control
system is magnified for a large airplane.

However, the FAA agrees that the combination of a more detailed and
exact fatigue analysis of the large airplane at its proposed operating
weights and usage, combined with a limit maneuver load factor of +3.3g
at the maximum weight, provides adequate structural design criteria for
this large restricted category agricultural airplane. The FAA believes
that this criteria is acceptable based upon service experience and a
review of fatigue spectrum data for other large airplanes used in fire
fighting operations (*NASA Technical Memorandum 84660, "Tabulations of
Recorded Gust and Maneuver Accelerations and Derived Gust Velocities for
Airplanes in the NASA VGH General Aviation Program", September 1983*).
The FAA is not aware of any data concerning service experience of large
airplanes conducting agricultural aviation operations. If the fatigue
design criteria for this airplane forces the airplane weight above
19,000 pounds, the applicant may use the design criteria being
established for the larger twin-engine airplane described in the third
section of this document. If that should happen, the FAA will review
that proposal to adjust for a single-engine airplane.

## 

## **[(2) Considerations for a Large, Single Engine Aircraft]{.underline}**

While the FAA and the manufacturer were developing the certification
basis proposal for the large twin-engine firefighting aircraft in
section (3) of this document, the manufacturer requested that we
consider its position that a safer large agricultural airplane design
would have a single rather than multiple engines. The manufacturer has
requested this for the 19,000 pound airplane design described in the
previous section of this document. When asked for an upper weight limit
for a single engine large restricted category airplane, the manufacturer
considers that current turboprop engine and propeller technology makes a
30,000 pound single engine turboprop agricultural airplane feasible.

The manufacturer contends that the agricultural airplane mission is
almost always at low altitude, and very often at low speed. This differs
from typical air transportation airplanes, where the design criteria for
small airplanes addressing directional and lateral control following an
in-flight engine failure as stated in §23.147(a) and (b) provides a
level of protection from the effects of an engine failure. More
specifically, because of the low altitude of the agricultural airplane
mission, the two-second pilot response delay and 45 degree bank angle
excursion that is permitted by the regulations would likely result in
the loss of the airplane. The requirements for transport category large
airplanes in §25.147(a) are not appropriate for the agricultural
airplane special purpose because the 1.4 V~S1~ criteria is inconsistent
with the slow speed needed for effective aerial application or
dispensing operations. In typical airplane operations, V~MC~ is a
minimum speed intended to assure that the airplane is flying fast enough
during takeoff or landing for the airplane vertical stabilizer/rudder to
overcome asymmetric thrust effects, and to be controllable in event of
the failure of one engine. These requirements are not designed to
address safe low speed flight during the cruise phase of flight. Also,
§23.149(d) requires determination of V~SSE~, a minimum speed to safely
make the critical engine inoperative. For safety, V~MC~ must be greater
V~S~ and V~SSE~. The agricultural special purpose operation requires
slow speeds to remain over the fields being dusted. Slow speeds, low
altitudes, and significant weight changes during the dispensing
operation combine to make the agricultural special purpose operation a
unique situation for the design of engine failure for a twin engine
airplane.

The manufacturer also contends that the increased reliability of
turboprop compared to piston powerplants is an incremental safety
benefit compared to the service experience that was current when the
demarcation between small and large airplanes was established in 1953 at
12,500 pounds. FAA has noted the increased reliability and safety of
turboprop powered agricultural aircraft in previous safety studies. In
part, we believe that this is a result of our policy requiring type
certificated turbine engines for restricted category aircraft. However,
FAA acknowledges that a large single engine aircraft may expose persons
and property on the ground to a new risk that may not totally be
controlled by the use of restricted category operating limitations. We
believe that, with adequate crashworthiness features, the agricultural
airplane cockpit design can protect the flight crew in event of an
engine failure. The FAA accepts that for en-route flight operations,
aircraft altitude would permit the pilot to avoid persons and property
on the ground in event of failure of the single engine. FAA is concerned
that should the engine failure occur during takeoff or landing, the
pilot would not have enough time or altitude to avoid persons or
property on the ground adjacent to the airport boundary. FAA believes
that the controls provided by operating limitations on restricted
category aircraft in §91.313(e) will minimize this risk to the public.

## 

## **Balancing Levels of Safety for Public and Flight Crew**

We see merit in the manufacturer's argument for the unique features of
the agricultural airplane mission profile. A safety analysis that
assumes an engine failure for a twin engine agricultural aerial
application airplane would conclude that for the flight crew, two
engines would not provide the intended safety benefits of multiple
engines if the engine failure occurred during the dispensing operation.
The safety benefits of neither V~MC~ (minimum control airspeed) nor
V~SSE,~ (in §23.149(d) ) would be effective during the following phases
of flight: low-speed approach to the dispensing operation; dispensing
operation itself; and pull-up from dispensing. If engine failure
occurred during dispensing, there would be little risk to persons and
property on the ground, since the airplane is operating over the
customer's property. So, given an engine failure during these particular
flight phases, a second engine is potentially hazardous to the flight
crew, and is irrelevant to safety of persons and property on the ground,
because the operations are over sparsely populated areas. However, if an
engine fails during the other flight phases (takeoff, climb, enroute
cruise, approach, and landing), a second engine is a safety benefit to
both the flight crew and persons on the ground.

We believe the same potential incremental engine failure hazard
considerations apply for the aerial firefighting mission profile. The
FAA notes from a review of data that there are similar operating speed
and altitude profiles for aerial firefighting conducted as forest
preservation per §21.25(b)(2) or §137.3 as for agricultural aerial
application missions (*NASA Technical Memorandum 89074,"FlightDuration,
Airspeed Practices, and Altitude Management of Airplanes Involved in the
NASA VGH General Aviation Program", August 1987*). FAA notes the concern
expressed for multi-engine reliability and performance in the recent
Blue Ribbon Panel Report to the Chief U.S. Department of Agriculture
Forest Service and Director, U.S. Department of Interior Bureau of Land
Management on firefighting aircraft (*"Federal Aerial Firefighting:
Assessing Safety and Effectiveness"*, *December 2002*). At present, the
FAA believes that this concern is for the on-scene lead plane mission,
rather than the air tanker airplane.

**Request for Comment from Interested Persons Concerning a Large Single
Engine Restricted Category Agricultural/Aerial Firefighting Airplane**

The FAA wants information from interested people concerning this
proposal for large single engine restricted category airplanes. By this
notice, we are also asking for comment from a wider audience. We do not
want to approve a large single engine agricultural airplane design
unless the concept provides a safety benefit to the flight crew at
minimal additional risk to the public on the ground. (For the large
single engine restricted category airplane, we believe that protecting
the public would result from adhering to the requirements of §91.313(e)
and §137.51(b)(4).) Useful information concerning the need for slow
speed and low altitude for both these special purpose operations would
confirm our assumptions about these two special purpose operations.
Also, useful information would address the kinds of airfields from which
these airplanes will operate. This information will help us gauge the
potential risks and benefits to the public and the operators if we
accept this aircraft design proposal. We are particularly looking for
information to confirm or increase our knowledge of these operations, so
we can address the hazard potential for agricultural airplane with
multiple engines. We will ask for a submittal from the agricultural
aviation industry to help on this decision.

#### [(3) Certification Criteria for a Large Multi-Engine Firefighting Airplane]{.underline}

A manufacturer of restricted category airplanes (used for agricultural
and firefighting special purpose operations) is proposing a new 36,000
pound twin engine airplane design. The manufacturer wants to build upon
the experience of its current aircraft that are designed for
agricultural and firefighting special purpose operations. We have
developed, with the manufacturer, a certification basis for the 36,000
pound airplane that is a combination of small and large aircraft
airworthiness standards. This combined certification basis is a
significant departure from current practice. We believe that it is an
appropriate certification basis for an aircraft intended solely for
restricted category operations.

We developed this combined certification basis to permit the
certification of agricultural airplanes weighing significantly more than
the 12,500 pound limit for small aircraft. We did this because we agreed
with the manufacturer's opinion that turboprop engine technology permits
the consideration of large airplanes that need not be certificated to
solely transport category airplane airworthiness standards. We believe
this combined certification basis will permit development of airplanes
with characteristics similar to those of existing agricultural
airplanes. We believe this will result in greater safety for
agricultural aircraft operators than if the part 25 airworthiness
standards only are used for the 36,000 pound airplane design.

# 

# *Why Is This Certification Basis Proposal Needed?* 

We believe this combined certification basis proposal is in the public
interest, because we believe that a large restricted category airplane
for agricultural or firefighting operations serves a public need. The
only categories for aircraft certification that address large aircraft
airworthiness standards are transport category (14 C.F.R. part 25) and
commuter category (contained in 14 C.F.R. part 23). For both of these
airplane categories, they are design criteria appropriate for aircraft
engaged in transportation of passengers or cargo. As stated above in
***Restricted Category Background***, this level of safety and certitude
is greater than that intended for restricted category aircraft.

The FAA notes that currently most large airplane restricted category
type certificates are issued to military surplus aircraft. This is done
in accordance with §21.25(a)(2). If a military surplus airplane is
modified to obtain a restricted category type certificate, the FAA's
certification is only to the civil airworthiness standards that pertain
to the modification for the special purpose. Most of the design criteria
for the military surplus restricted category airplane type certificate
are accepted on the basis of the original military evaluation of the
airplane and its subsequent service experience. We think that the level
of confidence resulting from this proposed combined certification basis
for this large agricultural airplane restricted category type
certificate is equivalent to the level of certitude for a modified
military surplus large airplane intended for a restricted category type
certificate approval. For these reasons, and because representatives of
the agricultural aviation community asked us to do so, we agreed to work
with an agricultural airplane manufacturer to develop appropriate type
certificate requirements for a large agricultural airplane design.

## 

## **Limitations on the Intended Applicability of the Certification Basis Proposal**

This certification basis proposal is for a particular airplane design
proposal. For administrative purposes, it is a rule of particular
applicability. However, the FAA and the manufacturer expended
significant effort in developing this proposal. Therefore, if a similar
project to this airplane design proposal occurs in the near future, we
will use this proposal as its starting point to establish a
certification basis. We intend for this proposal to be appropriate for
what we consider to be medium sized aerial firefighting airplanes, no
larger than what would correspond to Lockheed P2V Neptune aircraft
replacements.

Airplane features key to the applicability of this proposal are:

-   Weight less than 60,000 pounds;

-   Wing span less than 90 feet; aspect ratio less than 9.5; fuselage
    length less than 65 feet (each dimension is the approximate size of
    a DC-3 airplane);

-   Maximum operating altitude is 15,000 feet or less;

-   Design dive speed (V~D~) less than 260 knots; unpowered flight
    controls; "conventional" empennage; irreversible control surface
    tabs.

-   Metal construction; unpressurized cabin; fixed landing gear.

-   Propeller powered; twin engine.

-   Visual Flight Rules (VFR) operations only.

## **The Proposal**

The detailed proposal is documented in a report titled "Large
Agricultural Restricted Category Airplane Certification Basis Proposal
-- Twin Engine AT-2002 Project", dated August, 2003. This report is
based on a paragraph-by-paragraph comparison of part 23 and part 25
airworthiness standards, and identifies the requirement selected for
certification basis. The report explains why the part 25 requirement is
needed for this project, and states the reason why our policy permits
using the Part 23 requirement for this large agricultural airplane
project. The report also refers to any published guidance material, such
as advisory circulars or FAA Directorate correspondence, for acceptable
methods of compliance for the airworthiness standard in the
certification basis. You may obtain a copy of this report by calling the
individual identified in the section above titled "For Further
Information". The report is also available for review or copy on the
Internet at this website.

***Summary of the Report***

We considered many part 23 requirements acceptable for this project.
Typically, our justification for accepting part 23 requirements instead
of part 25 for this large agricultural restricted category airplane is
that the operating environment for an agricultural airplane permits less
stringent requirements (a different level of certitude) than that which
is the basis for the transport category airworthiness standards. Because
this is a large airplane, typically we have identified requirements that
are waived as Part 25 rather than Part 23 requirements. In a few cases,
we have identified a waived requirement as Part 25 and also listed a
Part 23 requirement. This indicates a waived Part 25 requirement that
corresponds to a waived Part 23 requirement listed in existing small
agricultural airplane policy (either AC 21.25-1 or the corresponding
Small Airplane Directorate policy memorandum dated December 1, 1997.)
For the most part, the cited guidance material describing an acceptable
method of compliance is an advisory circular that generally addresses
all of the requirements in a subpart in either part 23 or part 25.

For *Subpart A* - General, neither part 23 nor part 25 is used in the
certification basis proposal. Instead, a restricted category type
certificate will be issued to show that compliance has been found to the
stated certification basis.

For *Subpart B* -- Flight, part 23 requirements are proposed with the
exception of requiring §25.143 qualitative controllability and
maneuverability evaluations. The following requirements are waived:
§25.21©, (d), (e); §25.27; §25.109-115; §25.125(a)(2) \[§23.75(a)\];
§25.125(f) \[23.75(g)\]; §25.237; §25.253-255.

For *Subpart C* -- Structure, part 23 requirements are proposed with the
exception of the following part 25 requirements: §25.305; §25.337(a),
(b); §25.349-351; §25.371; §25.397; §25.415; §25.485-491; §25.495;
§25.503. The following requirements are waived: §25.341(b); §25.487;
§25.507. Alternative requirements are proposed for §25.337, §25.562 and
§25.571.

For *Subpart D* -- Design and Construction, part 23 requirements are
proposed with the exception of the following part 25 requirements:
§25.651(b); §25.657; §25.689. The following requirements are waived:
§25.631; §25.703; §25.721; §25.809; §25.810; §25.857-858; §25.867;
§25.869; §25.875.

For *Subpart E* -- Powerplant, part 23 requirements are proposed with
the exception of the following part 25 requirement: §25.963(d). The
following requirements are waived: §25.941; §25.945; §25.981; §25.1107;
§25.1167; §25.1197-1201; §25.1207. Alternative requirements are proposed
for §25.954 and §25.1093.

For *Subpart F* -- Equipment, part 23 requirements are proposed in place
of all the part 25 requirements. The following requirements are waived:
§23.1305(e); §25.1316; §23.1321(d), (e); §23.1325(b)(2)(ii) and (b)(3);
§25.1433. Alternative requirements are proposed for §25.1419.

For *Subpart G* -- Operating Limitations and Information, part 23
requirements are proposed with the exception of the following part 25
requirements: §25.1503; §25.1521. The following requirements are waived:
§23.1305(cc); §25.1531-1533; §23.1581(e); §23.1583(g), (j).

## **Request for Comments on the Certification Basis Proposal**

This notice advises the public and the agricultural aircraft industry of
a proposal that establishes certification requirements for a large
restricted category airplane. We solicit public comments concerning the
possible consequences of relaxing certification requirements because we
believe that there is potential public benefit for larger and more
efficient agricultural airplanes. We believe that the public's risk (of
consequences) from this approach is minor compared to the potential
benefits. We also believe that the operating limitations of restricted
category and certificated agricultural aircraft operations will further
limit public risk.