[Federal Register Volume 72, Number 180 (Tuesday, September 18, 2007)]
[Proposed Rules]
[Pages 53196-53201]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E7-18342]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. CE273; Notice No. 23-07-03-SC]


Special Conditions: Adam Aircraft Industries Model A700; External 
Fuel Tank Protection During Gear-Up or Emergency Landing

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

-----------------------------------------------------------------------

SUMMARY: This notice proposes special conditions for the Adam Aircraft 
Industries Model A700 airplane. This airplane will have a novel or 
unusual design feature(s) associated with an External Centerline Fuel 
Tank (ECFT) that increases the total capacity of fuel by 184 gallons. 
The tank is located below the fuselage pressure shell immediately below 
the wing. The Adam A700 ECFT is a novel, unusual and a potentially 
unsafe design feature that may pose a hazard to the occupants during a 
gear-up or emergency landing due to fuel leakage and subsequent fire. 
Traditional aircraft construction places the fuel tanks in a protected 
area within the wings and/or fuselage. Fuel tanks located in these 
areas are well above the fuselage skin and are inherently protected by 
the wing and fuselage structure. The applicable airworthiness 
regulations do not contain adequate or appropriate safety standards for 
this design feature. These proposed special conditions contain the 
additional safety standards that the Administrator considers necessary 
to establish a level of safety equivalent to that established by the 
existing airworthiness standards.

DATES: Comments must be received on or before November 19, 2007.

ADDRESSES: Comments on this proposal may be mailed in duplicate to: 
Federal Aviation Administration (FAA), Regional Counsel, ACE-7, 
Attention: Rules Docket, Docket No. CE273, 901 Locust, Room 506, Kansas 
City, Missouri 64106, or delivered in duplicate to the Regional Counsel 
at the above address. Comments must be marked: CE273. Comments may be 
inspected in the Rules Docket weekdays, except Federal holidays, 
between 7:30 a.m. and 4 p.m.

FOR FURTHER INFORMATION CONTACT: Mr. Peter L. Rouse, Federal Aviation 
Administration, Aircraft Certification Service, Small Airplane 
Directorate, ACE-111, 901 Locust, Kansas City, Missouri, 816-329-4135, 
fax 816-329-4090.

SUPPLEMENTARY INFORMATION: 

Comments Invited

    Interested persons are invited to participate in the making of 
these proposed special conditions by submitting such written data, 
views, or arguments, as they may desire. Communications should identify 
the

[[Page 53197]]

regulatory docket or notice number and be submitted in duplicate to the 
address specified above. All communications received on or before the 
closing date for comments will be considered by the Administrator. The 
proposals described in this notice may be changed in light of the 
comments received. All comments received will be available in the Rules 
Docket for examination by interested persons, both before and after the 
closing date for comments. A report summarizing each substantive public 
contact with FAA personnel concerning this rulemaking will be filed in 
the docket. Persons wishing the FAA to acknowledge receipt of their 
comments submitted in response to this notice must include with those 
comments a self-addressed, stamped postcard on which the following 
statement is made: ``Comments to CE273.'' The postcard will be date 
stamped and returned to the commenter.

Background

    On April 12, 2004, Adam Aircraft Industries applied for a type 
certificate for their new model A700. The model A700 aircraft is a 6-8 
seat pressurized, retractable-gear, carbon composite structure, 
airplane with two turbofan engines mounted on the aft fuselage. The 
A700 aircraft is a design evolution of the previously certificated Adam 
A500, with the aft fuselage mounted turbofan engines replacing the two 
centerline thrust, turbocharged, reciprocating engines. To maintain a 
max cruise range similar to the A500 and consistent with other aircraft 
in the same class as the A700, an external fuel tank located below the 
fuselage pressure shell and immediately below the wing, has been 
incorporated in to the A700 design. The A700 and its external fuel tank 
location are shown in Figure 1:
[GRAPHIC] [TIFF OMITTED] TP18SE07.034

    The Adam A700 ECFT is a novel, unusual and a potentially unsafe 
design feature that may pose a hazard to the occupants during a gear-up 
or emergency landing due to fuel leakage and subsequent fire. 
Conventional aircraft construction places the fuel tanks in a protected 
area within the wings and/or fuselage. Fuel tanks located in these 
areas are well above the fuselage skin and are inherently protected by 
the wing and fuselage structure.
    The A700 ECFT must meet the inherent qualities associated with the 
protection of the fuel system as provided by 14 CFR part 23. The FAA 
requires Adam Aircraft to address the following areas with their ECFT 
design:
    1. Load Path: Conventional design approaches establish independent 
load paths from the keel/skid plate to the airframe major structure 
where the fuel tanks are isolated from reacting the gear-up or 
emergency landing loads. The A700 ECFT design must react to the gear-up 
or emergency landing loads in a similar manner.
    2. Fuel Management: Conventional design approaches use fuel tanks 
located outside of the wings, or wing centerbox, as auxiliary fuel 
tanks, and not primary fuel tanks. The fuel in the auxiliary fuel tanks 
is depleted before the primary fuel tanks, thus the auxiliary tanks are 
usually empty upon landing. In a similar manner, the A700 ECFT must be 
an auxiliary fuel tank, and not primary fuel tank. The A700 must 
deplete the fuel in the ECFT before depleting the fuel in the primary 
fuel tanks.
    3. Location/Geometry: A700 must preclude the scenario where the 
fuel tank is the first point of contact with the ground in a gear-up or 
emergency landing.

Regulatory Review and Discussion

    14 CFR part 11, 21, 23 and 25 regulations that pertain to the 
location of the ECFT location are Sec. Sec.  11.19, 21.16, 21.21(b)(2), 
23.303, 23.473(d), 23.561, 23.721, 23.967, 23.994 and 25.963.
    The following rules provide a regulatory framework in which to 
apply additional requirements, beyond the existing requirements, in 
order to address novel, unusual and potentially unsafe design features.
    A special condition is defined in 14 CFR part 11, Sec.  11.19:

Sec.  11.19

    A special condition is a regulation that applies to a particular 
aircraft design. The FAA issues special conditions when we find that 
the airworthiness regulations for an aircraft, aircraft engine, or 
propeller design do not contain adequate or appropriate safety 
standards, because of a novel or unusual design feature.

    A special condition is applied via the criteria defined in 14 CFR 
part 21, Sec.  21.16:

Sec.  21.16

    [If the Administrator finds that the airworthiness regulations 
of this subchapter do not contain adequate or appropriate safety

[[Page 53198]]

standards for an aircraft, aircraft engine, or propeller because of 
a novel or unusual design feature of the aircraft, aircraft engine 
or propeller, he prescribes special conditions and amendments 
thereto for the product. The special conditions are issued in 
accordance with Part 11 of this chapter and contain such safety 
standards for the aircraft, aircraft engine or propeller as the 
Administrator finds necessary to establish a level of safety 
equivalent to that established in the regulations.]

    An unsafe condition is spoken to in 14 CFR part 21, Sec.  
21.21(b)(2):

Sec.  21.21

    An applicant is entitled to a type certificate for an aircraft 
in the normal, utility, acrobatic, commuter, or transport category, 
or for a manned free balloon, special class of aircraft, or an 
aircraft engine or propeller, if--
    (b) The applicant submits the type design, test reports, and 
computations necessary to show that the product to be certificated 
meets the applicable airworthiness, aircraft noise, fuel venting, 
and exhaust emission requirements of the Federal Aviation 
Regulations and any special conditions prescribed by the 
Administrator, and the Administrator finds--
    (2) For an aircraft, that no feature or characteristic makes it 
unsafe for the category in which certification is requested.

    External fuel tank installations below the wing or fuselage were 
not envisioned in the development of 14 CFR part 23 fuel tank (and fuel 
system) regulations. As such, regulations that are not directly 
applicable to conventional fuel tank installations, but related to the 
novel, unusual and potentially unsafe design features, were reviewed. 
The following 14 CFR part 23 certification requirements do contain 
regulatory language that can be used to determine the adequate or 
appropriate safety standards for novel, unusual and potentially unsafe 
design features of the Adam A700 ECFT.

Sec.  23.303

    Unless otherwise provided, a factor of safety of 1.5 must be 
used.

Sec.  23.473(d)

    The selected limit vertical inertia load factor at the center of 
gravity of the airplane for the ground load conditions prescribed in 
this subpart may not be less than that which would be obtained when 
landing with a descent velocity (V), in feet per second, equal to 
4.4 (W/S) \1/4\ except that this velocity need not be more than 10 
feet per second and may not be less than seven feet per second.

Sec.  23.721

    [For commuter category airplanes that have a passenger seating 
configuration, excluding pilot seats, of 10 or more, the following 
general requirements for the landing gear apply:
    (a) The main landing-gear system must be designed so that if it 
fails due to overloads during takeoff and landing (assuming the 
overloads to act in the upward and aft directions), the failure mode 
is not likely to cause the spillage of enough fuel from any part of 
the fuel system to constitute a fire hazard.
    (b) Each airplane must be designed so that, with the airplane 
under control, it can be landed on a paved runway with any one or 
more landing-gear legs not extended without sustaining a structural 
component failure that is likely to cause the spillage of enough 
fuel to constitute a fire hazard.
    (c) Compliance with the provisions of this section may be shown 
by analysis or tests, or both.]

    14 CFR part 23, 23.303 and 23.473(d) relate to the associated 
margin of safety required above the limit loading condition and the 
required limit ground loading conditions. 14 CFR part 23, Sec.  23.721 
is applicable to commuter category airplanes; however, the intent is to 
ensure that the failure of the landing gear does not cause the spillage 
of enough fuel from any part of the fuel system to constitute a fire 
hazard. The location of the ECFT, in direct line behind the nose 
landing gear, makes it particularly vulnerable to failures of the nose 
landing gear.
    14 CFR part 23 contains a limited scope of regulatory requirements 
pertaining to fuel tank (and fuel system) protection during a gear-up 
or emergency landing. These current regulations pertaining to the fuel 
tank (and fuel system) state:

Sec.  23.561(b)

    The structure must be designed to [give each occupant every 
reasonable chance of escaping serious injury when--]
    (1) Proper use is made of seats, safety belts, and shoulder 
harnesses provided for in the design;
    (2) The occupant experiences the static inertia loads 
corresponding to the following ultimate load factors--
    (i) Upward, 3.0g for normal, utility, and commuter category 
airplanes, or 4.5g for acrobatic category airplanes;
    (ii) Forward, 9.0g;
    (iii) Sideward, 1.5g; and
    (iv) Downward, 6.0g when certification to the emergency exit 
provisions of Sec. 23.807(d)(4) is requested; and
    (3) The items of mass within the cabin, that could injure an 
occupant, experience the static inertia loads corresponding to the 
following ultimate load factors--
    (i) Upward, 3.0g;
    (ii) Forward, 18.0g; and
    (iii) Sideward, 4.5g.

Sec.  23.561(c)

    Each airplane with retractable landing gear must be designed to 
protect each occupant in a landing--
    (1) With the wheels retracted;
    (2) With moderate descent velocity; and
    (3) Assuming, in the absence of a more rational analysis--
    (i) A downward ultimate inertia force of 3g; and
    (ii) A coefficient of friction of 0.5 at the ground.

Sec.  23.967(a):

    Each fuel tank must be able to withstand, without failure, the 
vibration, inertia, fluid, and structural loads that it may be 
subjected to in operation.

Sec.  23.967(e):

    Fuel tanks must be designed, located, and installed so as to 
retain fuel:
    (1) When subjected to the inertia loads resulting from the 
ultimate static load factors prescribed in Sec.  23.561(b)(2) of 
this part; and
    (2) Under conditions likely to occur when the airplane lands on 
a paved runway at a normal landing speed under each of the following 
conditions:
    (i) The airplane in a normal attitude and its landing gear 
retracted.
    (ii) The most critical landing gear leg collapsed and the other 
landing gear legs extended.

Sec.  23.994

    Fuel system components in an engine nacelle or in the fuselage 
must be protected from damage which could result in spillage of 
enough fuel to constitute a fire hazard as a result of a wheels-up 
landing on a paved runway.

    The regulatory requirements of Sec.  23.967(e)(1) refer to Sec.  
23.561(b)(2), which is an occupant protection rule. The requirements of 
Sec.  23.561(b)(2) do not have a downward component for non commuter 
category airplanes. To comply with the requirements of Sec.  
23.967(e)(2), the moderate descent velocity identified in Sec.  
23.561(c)(2), which is also an occupant protection rule, has been used 
as an acceptable means of compliance for traditional fuel tank designs 
that do not have novel, unusual and potentially unsafe design features. 
These regulations have historically demonstrated an acceptable level of 
safety for traditional fuel tank designs that do not have novel, 
unusual and potentially unsafe design features. Existing aircraft 
designs with this satisfactory service history have the fuel tanks 
located well above the fuselage skin and are inherently protected by 
the wing and the fuselage structure, thus providing a ``crush zone.''
    The intent of 14 CFR part 23, Sec.  23.994 is to minimize the 
hazard to the airplane due to fuel system components that are affected 
(those which are traditionally located in the fuselage or engine 
nacelle) when the underside of the airplane contacts the ground in a 
wheels-up landing. The intent is applicable to those components below 
the fuselage.
    14 CFR part 23 guidance materials recognize there may be situations 
when installing auxiliary fuel tanks that require special conditions 
because of a novel, unusual and potentially unsafe design feature. 
Advisory Circular (AC) 23-10, Auxiliary Fuel Systems for

[[Page 53199]]

Reciprocating and Turbine Powered Part 23 Airplanes, states in 
paragraph 5:

5. CERTIFICATION BASIS

    a. New Type Certificates. For the issuance of a new type 
certificate, an airplane must be shown to comply with the 
certification basis established in accordance with Sec.  21.17 of 
the Federal Aviation Regulations (FAR). If the regulations do not 
provide adequate or appropriate standards because of a novel or 
unusual design feature, special conditions will be prescribed in 
accordance with Sec.  21.16.
    b. Other Design Changes. Not applicable for new TCs.
    c. Unsafe Features or Characteristics. Notwithstanding 
compliance with the established certification basis, Sec.  21.21 
precludes approval if there is any feature or characteristic that 
makes the airplane unsafe. The applicant should recognize that it 
may be necessary, because of such a feature or characteristic, to 
impose special requirements which exceed the standards of the 
certification basis, to eliminate the unsafe condition.

    Since 14 CFR part 23 airworthiness regulations do not contain 
adequate or appropriate safety standards for the external fuel tank 
design, a review of the safety standards contained in 14 CFR part 25 
was conducted to evaluate their applicability to the novel, unusual and 
potentially unsafe design feature of the ECFT. 14 CFR part 25, Sec.  
25.963 has regulatory requirements that ensure that fuel tanks within 
the fuselage contour are in a protected position.

Sec.  25.963(d):

    Fuel tanks within the fuselage contour must be able to resist 
rupture, and to retain fuel, under the inertia forces prescribed for 
the emergency landing conditions in Sec. 25.561. In addition, these 
tanks must be in a protected position so that exposure of the tanks 
to scraping action with the ground is unlikely.
Sec.  25.963(e)(1):
    Fuel tank access covers must comply with the following criteria 
in order to avoid loss of hazardous quantities of fuel:
    (1) All covers located in an area where experience or analysis 
indicates a strike is likely must be shown by analysis or tests to 
minimize penetration and deformation by tire fragments, low energy 
engine debris, or other likely debris.

    14 CFR part 25, Sec.  25.963(d) is applicable to transport category 
airplanes; however, the object is to ensure that in the event of an 
emergency landing, the fuel tank is in a protected position so that 
exposure of the tank to scraping action with the ground is unlikely. 
The location of the ECFT, located below the fuselage, makes it 
particularly vulnerable to scraping action with the ground in the event 
of a gear-up landing.
    14 CFR part 25, Sec.  25.963(e) is applicable to transport category 
airplanes, and only applies to the access panels; however, the object 
is to prevent a hazard as a result of the impact by tire fragments or 
debris. This philosophy would be applied to the ECFT (not just access 
panels) to prevent hazardous leakage of fuel in the event of impact 
from tire fragments or other likely debris.
    14 CFR part 25 guidance materials also recognize the need to 
protect the auxiliary fuel tanks beyond the velocities used as an 
acceptable means of compliance. The first chapter of AC 25-8, Auxiliary 
Fuel Systems Installations, is titled ``Fuel System Installation 
Integrity and Crashworthiness'' and the first paragraph states the 
following:

    ``Survivable accidents have occurred at vertical descent 
velocities greater than the 5 feet per second (f.p.s.) referenced in 
Sec.  25.561. The energy from such descents is absorbed by the 
structure along the lower fuselage. As the limits of survivable 
accidents are approached, structure under the main cabin floor is 
crushed and deformed and the volume below the floor, where the 
auxiliary fuel tanks are frequently located, may be reduced and 
reshaped. For this reason the tank material chosen by the applicant 
should provide resilience and flexibility; or, in the absence of 
these characteristics, the tank installation should provide extra 
clearance from structure that can be crushed or be protected by 
primary structure not likely to be crushed.''

    Due to the concern of the Adam A700 ECFT to potentially contact the 
ground in a gear-up or emergency landing, we contacted the FAA Office 
of Accident Investigation, Safety Analysis Branch to determine the 
number of incidents/accident where an aircraft landed with the landing 
gear retracted or the landing gear collapsed on the ground. The search 
used was conducted over a 25 year period from January 1982 thru January 
2007, and queried all N-registered aircraft that were not 14 CFR parts 
121, 135, or 129 and that had at least one of the following occurrence 
codes:

Gear Collapsed
Main Gear Collapsed
Nose Gear Collapsed
Tail Gear Collapsed
Complete Gear Collapsed
Other Gear Collapsed
Gear Not Extended
Gear Not Retracted
Gear Retraction On Ground

    During the queried timeframe, there were 740 reported incidents/
accidents, which yields an average of about 30 reported incidents/
accidents per year. There were no injuries or fatalities associated 
with the 740 reported incidents/accidents. All of the reported 
incidents/accidents involved aircraft having fuel in the center section 
of the wing area confined by the front and rear spars and the side of 
body wing ribs. The data shows a high probability for a landing gear 
failure, malfunction or not being extended during landing and that 
there is a good safety record for configurations involved in these 
incidents/accidents. The certification standards for the Adam A700 ECFT 
need to consider the placement of the ECFT outside of the protective 
wing area confined by the front and rear spars and the side of body 
wing ribs configurations, and the high probability of the ECFT 
contacting the ground.
    Because of the Adam A700 ECFT's novel, unusual and potentially 
unsafe design features, it is necessary to impose a specific vertical 
velocity requirement that exceed the 5 feet per second requirement 
normally imposed on conventional airplane fuel tank designs. 
Conventionally installed fuel tanks, located within the fuselage and 
wing primary structure, have used Sec.  23.561(c)(2) as an acceptable 
means of compliance to the requirements of Sec.  23.967(e)(2). Fuel 
tank installations are not bound by regulatory requirements to use 
Sec.  23.561(c)(2) as an acceptable means of compliance to the 
requirements of Sec.  23.967(e)(2). The standards contained in Sec.  
23.561(c)(2), which is an occupant protection rule, provided adequate 
or appropriate standards for conventionally installed fuel tanks. 
Initially, the FAA proposed to use the vertical velocity requirements 
(26.8 feet per second) contained in Sec.  23.562 as a means of 
compliance to the requirements of Sec.  23.967(e)(2), as this rule is 
also an occupant protection rule. The velocities cited in the two 
occupant protection rules range from 5 feet per second to 26.8 feet per 
second. The velocity cited in Sec.  23.561(c)(2) is the velocity for a 
minor crash landing, where the velocity in Sec.  23.562 is the upper 
limit of a survivable crash landing. The requirements contained in 
Sec.  23.967(e)(2) allow for the conditions likely to occur, and the 
range of velocities likely to occur during a survivable crash landing 
is 5 feet per second-26.8 feet per second; therefore, there is ample 
regulatory room in which to determine an acceptable means of 
compliance. The FAA proposal to use the vertical velocity requirements 
contained in Sec.  23.562 as a means of compliance to the requirements 
of Sec.  23.967(e)(2) for the initially proposed ECFT design, was 
withdrawn by the FAA due to Adam Aircraft proposing to

[[Page 53200]]

redesign the ECFT. As such, the FAA researched the standards within 14 
CFR part 23 to determine a vertical velocity within the range of 
velocities likely to occur that provide adequate or appropriate 
standards, mitigate potential unsafe conditions. The normal precision 
approach speed for the Adam A700 will be approximately 120 KIAS. This 
approach speed will result in a normal vertical descent velocity of 
10.6 feet per second. The normal precision approach speed is a speed 
that falls within the speeds that are likely to occur when the airplane 
lands on a paved runway at a normal landing speed. 14 CFR part 23, 
Sec.  23.473(d) requires that the aircraft be able to absorb a limit 
load imposed by a vertical descent velocity of 10 feet per second for 
landing conditions. Combining the velocity requirements of Sec.  
23.473(d) and a commensurate 1.5 factor of safety, as required by Sec.  
23.303, would result in a vertical descent velocity of 12.25 feet per 
second. The derivation used to determine the ultimate velocity based 
upon the Sec.  23.473(d) limit vertical inertia load and the factor of 
safety defined in Sec.  23.303 is shown below:

The relationship between velocity, acceleration and distance is shown 
by the equation:
[GRAPHIC] [TIFF OMITTED] TP18SE07.018

The relationship between force and acceleration is shown by the 
equation:
[GRAPHIC] [TIFF OMITTED] TP18SE07.019

The relationship between limit force (load) and ultimate force (load) 
is shown by the equation:
[GRAPHIC] [TIFF OMITTED] TP18SE07.020

Assuming a constant mass of the object, an ending velocity of zero and 
grouping the terms:
[GRAPHIC] [TIFF OMITTED] TP18SE07.021

Thus, the relationship between limit velocity and ultimate velocity is 
shown by the equation:
[GRAPHIC] [TIFF OMITTED] TP18SE07.022

    Conventional airplanes with fuel tanks located below the fuselage 
are designed such that the ground impact loads are not absorbed by the 
tanks. Fuel tanks in these locations are especially vulnerable to these 
ground impact loads if design precautions/mitigations are not taken. If 
the ECFT is designed such that it absorbs gear-up landing loads, a 
gear-up landing could damage the ECFT and result in the spillage of 
enough fuel to constitute a fire hazard. The location of the A700 ECFT 
should be evaluated for ground impact in a gear-up landing, and design 
precautions/mitigations should be taken such that load paths do not go 
through the fuel tanks. The location of the A700 ECFT should be 
evaluated for exposure of the tank to impact from runway debris or from 
fragments emanating from failures of the tires. The location of the 
ECFT, below and in direct line behind the nose landing gear, makes it 
particularly vulnerable to debris from failures of the nose landing 
gear tires.
    The A700 ECFT, compared to other somewhat similar designs, was the 
only design that contained a significant percentage of the total fuel 
quantity of fuel below the fuselage and the wing box. Existing somewhat 
similar designs have their relatively smaller percentage of the total 
fuel quantity in their lower fuselage tanks and it is transferred out 
to the primary fuel tanks, so they are emptied early in the flight. The 
existing somewhat similar designs use the fuel tanks below the fuselage 
as auxiliary fuel tanks, and they do not feed the engines directly, but 
rather are used to replenish the primary fuel tanks. The A700 ECFT 
design indicates the ECFT is an auxiliary fuel tank, does not feed the 
engines directly and is used to replenish the primary fuel tanks.
    Based on our current understanding of the A700 ECTF design, the FAA 
understands that Adam Aircraft may have provided the following 
mitigating design features:
    1. The keel and truss assembly that make up the protective 
structure in current A700 ECFT design configuration affords the 
equivalent level of protection as currently certificated aircraft with 
fuel tanks located in the wings, or wing centerbox.
    2. The ECFT is an auxiliary fuel tank, and it does not feed the 
engines directly and is used to replenish the primary fuel tanks. The 
fuel in the ECFT will be used before the fuel in the wing tanks.
    The mitigating features offered by Adam Aircraft: Independent load 
path, fuel management, and location/geometry, coupled with dynamic drop 
testing and a rational analysis provide the FAA with sufficient 
justification to reduce the descent velocity from 12.25 feet per second 
to no less than 5 feet per second.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, Adam Aircraft Industries must 
show that the model A700 meets the applicable provisions of 14 CFR part 
23, as amended by Amendments 23-1 through 23-55 thereto.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 23) do not contain adequate or 
appropriate safety standards for the model A700 because of a novel or 
unusual design feature, special conditions are prescribed under the 
provisions of Sec.  21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the model A700 must comply with the fuel vent and exhaust 
emission requirements of 14 CFR part 34 and the noise certification 
requirements of 14 CFR part 36, and the FAA must issue a finding of 
regulatory adequacy pursuant to Sec.  611 of Public Law 92-574, the 
``Noise Control Act of 1972''.
    Special conditions, as appropriate, as defined in Sec.  11.19, are 
issued in accordance with Sec.  11.38, and become part of the type 
certification basis in accordance with Sec.  21.17(a)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should the type certificate for that model be amended 
later to include any other model that incorporates the same novel or 
unusual design feature, the special conditions would also apply to the 
other model under the provisions of Sec.  21.101(a)(1).

Novel or Unusual Design Features

    The model A700 will incorporate the following novel or unusual 
design features: External Centerline Fuel Tank (ECFT).

Applicability

    As discussed above, these proposed special conditions are 
applicable to the Adam Aircraft Industries Model A700. Should Adam 
Aircraft Industries apply at a later date for a change to the type 
certificate to include another model incorporating the same novel or 
unusual design feature, the proposed special

[[Page 53201]]

conditions would apply to that model as well under the provisions of 
Sec.  21.101(a)(1).

Conclusion

    This action affects only certain novel or unusual design features 
on Adam Aircraft Industries Model A700 airplanes. It is not a rule of 
general applicability, and it affects only the applicant who applied to 
the FAA for approval of these features on the airplane.

List of Subjects in 14 CFR Part 23

    Aircraft, Aviation safety, Signs and symbols.

Citation

    The authority citation for these proposed special conditions is as 
follows:

    Authority: 49 U.S.C. 106(g), 40113 and 44701; 14 CFR 21.16 and 
21.17; and 14 CFR 11.38 and 11.19.

The Proposed Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following proposed special conditions are issued as 
part of the type certification basis for the Adam Aircraft Industries 
Model A700.
    1. SC 23.561(c): Each airplane with retractable landing gear and 
external fuel tank system(s) located beneath the fuselage must be 
designed to protect each occupant in a landing--
    1. With the wheels retracted;
    2. With descent velocity of 12.25 feet per second UNLESS mitigating 
design features are incorporated that address:
    i. Independent load path
    ii. Fuel management
    iii. Location/Geometry
    iv. Other safety enhancing design features as proposed by the 
applicant
    If adequate mitigation is demonstrated for all the above design 
features, the FAA will reduce the descent velocity to no less than 5 
feet per second.

and

    3. By defining, based on a rational analysis, supported by tests:
    i. A downward ultimate inertia force; and
    ii. A coefficient of friction of 0.5, or a rational analysis for a 
coefficient of friction, at the ground.
    Compliance with SC 23.561(c)(2) will be demonstrated by dynamic 
drop test.
    2. SC 23.721: The following general requirements for the landing 
gear apply:
    1. The landing-gear system must be designed so that if it fails due 
to overloads during takeoff and landing (assuming the overloads to act 
in the upward and aft directions), the failure mode is not likely to 
cause the spillage of enough fuel from any part of the external fuel 
tank system(s) located beneath the fuselage to constitute a fire 
hazard.
    2. The airplane must be designed so that, with the airplane under 
control, it can be landed on a paved runway with any one or more 
landing-gear legs not extended without sustaining a structural 
component failure that is likely to cause the spillage of enough fuel 
to constitute a fire hazard.
    3. Compliance with the provisions of this section may be shown by 
analysis or tests, or both.
    3. SC 23.994: Fuel system components in external fuel tank 
system(s) located beneath the fuselage must be protected from damage 
which could result in spillage of enough fuel to constitute a fire 
hazard as a result of a wheels-up landing on a paved runway.
    4. SC 23.XXX: Fuel tanks within and below the fuselage contour must 
be installed in accordance with the requirements prescribed in Sec. 
23.967. External fuel tank system(s) located beneath the fuselage must 
have the following design mitigations:
    1. The external fuel tank system(s) must be in a protected position 
so that exposure of the tank to scraping action, or impact, with the 
ground is unlikely during a gear-up landing of the most critical 
landing gear or landing gears, when landing on a paved runway.
    2. The external fuel tank system(s) must be protected by dedicated 
protective structure, and the protective structure load paths must be 
independent of the fuel system during a gear-up landing of the most 
critical landing gear or landing gears, when landing on a paved runway.
    3. The hazard to the external fuel tank system(s) that results from 
impact by landing gear tire fragments or other likely debris must be 
minimized.
    4. The fuel management of the external fuel tank system(s) must be 
such that fuel in the external fuel tank system(s) is to be emptied 
prior to fuel in the main tanks.

    Issued in Kansas City, Missouri on September 11, 2007.
Kim Smith,
Manager, Small Airplane Directorate, Aircraft Certification Service.
 [FR Doc. E7-18342 Filed 9-17-07; 8:45 am]
BILLING CODE 4910-13-P