Special Conditions: Adam Aircraft Industries Model A700; External Fuel Tank Protection During Gear-Up or Emergency Landing, 53196-53201 [E7-18342]
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Federal Register / Vol. 72, No. 180 / Tuesday, September 18, 2007 / Proposed Rules
where DSi,T is institution i’s current dividend
share, T is the end of the most recent quarter
for which assessment base data is available,
wT is the weight assigned to the 1996 ratio
for period T, ab96,i is the 1996 assessment
base for institution i, T-k is the earliest
period to be covered, which could be all
periods after 2006 or some recent period,
such as the most recent 3, 5, 10 or 15 years,
pi,t is eligible premiums paid by institution
i at time t for the quarter ending at time t1, and mT is total institutions as of time
T.23, 24
Appendix B—Model Assumptions
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Among other things, the model assumes
the following:
1. Investment income in 2007 equals 4.7
percent of the start-of-year fund balance. For
each year thereafter, it equals 4.57 percent of
that year’s starting fund balance. These
estimates are based on projections from an
investment model that relies on Blue Chip
forecasts of the yield curve through 3rd
quarter 2008.
2. The initial assessment rate schedule is
3 basis points above the base rate schedule;
thus, the initial minimum rate is 5 basis
points. Rates fall to base rates the year after
the fund reserve ratio reaches or exceeds 1.25
percent. Risk Category I institutions that pay
rates between the minimum and maximum
rate for the category are assumed to pay 0.6
basis points above the minimum rate, which
reflects the current weighted average rate for
the group.
3. Any restoration plan is assumed to be a
5 year plan. Surcharges in a restoration plan
are estimated using an iterative procedure to
account for the effect of credit use. During a
restoration plan, an institution may use no
more than 3 basis points in credit use.
4. Operating expenses for 2007 are $988
million and grow at an annual rate of 5
percent thereafter.
5. Insured and domestic deposits are
assumed to grow at 5 percent per year.
6. The beginning fund balance at 2007
equals $50,165 million.
7. Credit use is limited by the 90 percent
rule during 2008, 2009, and 2010. (No
institution may apply credits to offset more
23 Under Variation 2 described in the text, T-k
would not include any year before 2007. When a
dividend share in any year depended upon
premiums paid before 1997, the premiums would
be factored into wT rather than being included in
pi,t.
24 If an institution failed after the end of the
quarter on which dividend shares were calculated
(which will always be the fourth quarter), but before
distribution of a dividend, a final adjustment of
dividend shares may be necessary. This share
would be calculated simply by deleting the failed
institution’s payments and 1996 ratio from the
preceding formulas.
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than 90 percent of an assessment for these
years.)
8. Institutions are assigned to 1 of 10 credit
groups and 1 of 6 assessment rate groups
based on December 31, 2006 Call Report and
TFR data, CAMELS information, and onetime credits. An institution’s credits are
determined by its share of the December 31,
1996 assessment base. An institution’s credit
group is determined by the ratio of its credits
to its December 31, 2006 deposits. Because
an institution’s initial relative dividend share
is determined analogously, based upon the
ratio of its share of the December 31, 1996
assessment base to its share of the December
31, 2006 deposits, institutions in the same
credit group will have similar relative
dividend shares. In the tables and charts in
the text comparing the relative dividend
shares under alternative allocation methods,
the ‘‘oldest’’ group refers to the credit group
with the most credits relative to their
December 31, 2006 deposits, those whose
credits are more than 12 basis points of their
December 31, 2006 deposits. The initial
weighted average of credits-to-deposits for
the credit group is 15.6 basis points.
9. High fund losses correspond to the
losses incurred by the Bank Insurance Fund
from 1987 to 1994, with losses measured
relative to total domestic deposits. Low fund
losses assume losses are equal to 0.1 basis
points of domestic deposits each year.
Dated at Washington, DC, this 11th day of
September, 2007.
By order of the Board of Directors.
Federal Deposit Insurance Corporation.
Robert E. Feldman,
Executive Secretary.
[FR Doc. 07–4596 Filed 9–17–07; 8:45 am]
BILLING CODE 6714–01–P
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
Federal Aviation
Administration (FAA), DOT.
ACTION: Notice of proposed special
conditions.
AGENCY:
SUMMARY: This notice proposes special
conditions for the Adam Aircraft
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Sfmt 4702
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
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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.
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 gearup 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.
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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
Regulatory Review and Discussion
14 CFR part 11, 21, 23 and 25
regulations that pertain to the location
of the ECFT location are §§ 11.19, 21.16,
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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:
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, § 11.19:
§ 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,
§ 21.16:
§ 21.16
[If the Administrator finds that the
airworthiness regulations of this subchapter
do not contain adequate or appropriate safety
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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
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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, § 21.21(b)(2):
§ 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.
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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.
§ 23.303
Unless otherwise provided, a factor of
safety of 1.5 must be used.
§ 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.
§ 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
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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,
§ 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:
§ 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.
§ 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.
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§ 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.
§ 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 § 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.
§ 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
§ 23.967(e)(1) refer to § 23.561(b)(2),
which is an occupant protection rule.
The requirements of § 23.561(b)(2) do
not have a downward component for
non commuter category airplanes. To
comply with the requirements of
§ 23.967(e)(2), the moderate descent
velocity identified in § 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, § 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
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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 § 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
§ 21.16.
b. Other Design Changes. Not applicable
for new TCs.
c. Unsafe Features or Characteristics.
Notwithstanding compliance with the
established certification basis, § 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, § 25.963 has
regulatory requirements that ensure that
fuel tanks within the fuselage contour
are in a protected position.
§ 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.
§ 25.963(e)(1):
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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, § 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.
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14 CFR part 25, § 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 § 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 Nregistered 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
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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
§ 23.561(c)(2) as an acceptable means of
compliance to the requirements of
§ 23.967(e)(2). Fuel tank installations are
not bound by regulatory requirements to
use § 23.561(c)(2) as an acceptable
means of compliance to the
requirements of § 23.967(e)(2). The
standards contained in § 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
§ 23.562 as a means of compliance to the
requirements of § 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 § 23.561(c)(2) is the
velocity for a minor crash landing,
where the velocity in § 23.562 is the
upper limit of a survivable crash
landing. The requirements contained in
§ 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 § 23.562 as a means of
compliance to the requirements of
§ 23.967(e)(2) for the initially proposed
ECFT design, was withdrawn by the
FAA due to Adam Aircraft proposing to
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2
VLimit = 2
Thus, the relationship between limit
velocity and ultimate velocity is shown
by the equation:
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VUltimate = VLimit C FactorofSafety
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
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FLimit
d
m
and
2
VUltimate = 2
m
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
Frm 00030
Fmt 4702
Sfmt 4702
F = ma
The relationship between limit force
(load) and ultimate force (load) is shown
by the equation:
FUltimate = FLimit CFactorofSafety
Assuming a constant mass of the object,
an ending velocity of zero and grouping
the terms:
FLimit C FactorofSafety
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.
PO 00000
The relationship between force and
acceleration is shown by the equation:
d
for the model A700 because of a novel
or unusual design feature, special
conditions are prescribed under the
provisions of § 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 § 611 of Public
Law 92–574, the ‘‘Noise Control Act of
1972’’.
Special conditions, as appropriate, as
defined in § 11.19, are issued in
accordance with § 11.38, and become
part of the type certification basis in
accordance with § 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 § 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
E:\FR\FM\18SEP1.SGM
18SEP1
EP18SE07.022</MATH>
The relationship between velocity,
acceleration and distance is shown by
the equation:
2
V 2 = V 1 + 2ad
2
EP18SE07.021</MATH>
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 § 23.473(d) and
a commensurate 1.5 factor of safety, as
required by § 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 § 23.473(d) limit vertical
inertia load and the factor of safety
defined in § 23.303 is shown below:
EP18SE07.020</MATH>
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, § 23.473(d)
EP18SE07.018</MATH> EP18SE07.019</MATH>
53200
Federal Register / Vol. 72, No. 180 / Tuesday, September 18, 2007 / Proposed Rules
conditions would apply to that model as
well under the provisions of
§ 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:
rwilkins on PROD1PC63 with PROPOSALS
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
VerDate Aug<31>2005
18:58 Sep 17, 2007
Jkt 211001
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
PO 00000
Frm 00031
Fmt 4702
Sfmt 4702
53201
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 71
[Docket No. FAA–2007–28649; Airspace
Docket No. 07–ANM–10]
Proposed Establishment of Class E
Airspace; Wheatland, WY
Federal Aviation
Administration (FAA), DOT.
ACTION: Notice of proposed rulemaking
(NPRM).
AGENCY:
SUMMARY: This action proposes to
establish Class E airspace at Wheatland,
WY. Additional controlled airspace is
necessary to accommodate aircraft using
a new Area Navigation (RNAV) Global
Positioning System (GPS) Standard
Instrument Approach Procedure (SIAP)
at Phifer Airfield. The FAA is proposing
this action to enhance the safety and
management of aircraft operations at
Phifer Airfield, Wheatland, WY.
DATES: Comments must be received on
or before November 2, 2007.
ADDRESSES: Send comments on this
proposal to the U.S. Department of
Transportation, Docket Operations, M–
30, West Building Ground Floor, Room
@12–140, 1200 New Jersey Avenue, SE.,
Washington, DC 20590. Telephone (202)
366–9826. You must identify FAA
Docket No. FAA–2007–28649; Airspace
Docket No. 07–ANM–10, at the
beginning of your comments. You may
also submit comments through the
Internet at https://dms.dot.gov.
FOR FURTHER INFORMATION CONTACT:
Eldon Taylor, Federal Aviation
Administration, Western Service Area
Office, System Support Group, 1601
Lind Avenue, SW., Renton, WA 98057;
telephone (425) 917–6726.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested parties are invited to
participate in this proposed rulemaking
by submitting such written data, views,
or arguments, as they may desire.
Comments that provide the factual basis
supporting the views and suggestions
presented are particularly helpful in
developing reasoned regulatory
decisions on the proposal. Comments
are specifically invited on the overall
regulatory, aeronautical, economic,
environmental, and energy-related
aspects of the proposal.
Communications should identify both
docket numbers (FAA Docket No. FAA–
2007–28649 and Airspace Docket No.
07–ANM–10) and be submitted in
triplicate to Docket Operations (see
E:\FR\FM\18SEP1.SGM
18SEP1
]]>Agencies
[Federal Register Volume 72, Number 180 (Tuesday, September 18, 2007)]
[Proposed Rules]
[Pages 53196-53201]
From the Federal Register Online via the Government Printing 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
