Document ID: FAA-2011-1387-0003
Agency: faa
Document Type: Notice
Title: Special Conditions: XtremeAir GmbH, XA42; Acrobatic Category Aerodynamic Stability
Posted Date: 2012-03-26T04:00Z

[Federal Register Volume 77, Number 58 (Monday, March 26, 2012)]
[Rules and Regulations]
[Pages 17323-17325]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2012-6837]

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 Rules and Regulations
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  Federal Register / Vol. 77, No. 58 / Monday, March 26, 2012 / Rules 
and Regulations  

[[Page 17323]]

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 23

[Docket No. FAA-2011-1387; Special Conditions No. 23-256-SC]

Special Conditions: XtremeAir GmbH, XA42; Acrobatic Category 
Aerodynamic Stability

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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

SUMMARY: These special conditions are issued for the XtremeAir GmbH 
XA42 airplane. The XA42 airplane has a novel or unusual design feature 
associated with its static stability. This airplane can perform at the 
highest level of aerobatic competition. To be competitive, the aircraft 
was designed with positive and, at some points, neutral stability 
within its flight envelope. Its lateral and directional axes are also 
decoupled from each other providing more precise maneuvering. The 
applicable airworthiness regulations do not contain adequate or 
appropriate safety standards for these design features. These 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. 
These special conditions are only applicable to aircraft certified 
solely in the acrobatic category.

DATES: Effective Date: April 25, 2012.

FOR FURTHER INFORMATION CONTACT: Mr. Ross Schaller, Federal Aviation 
Administration, Small Airplane Directorate, Aircraft Certification 
Service, 901 Locust, Room 301, Kansas City, Missouri 64106; telephone 
(816) 329-4162; facsimile (816) 329-4090.

SUPPLEMENTARY INFORMATION: 

Background

    On May 3, 2011, XtremeAir GmbH applied for a type certificate for 
their new model XA42. The XA42 is certified under EASA authority as a 
dual category (acrobatic/utility) airplane. It has a two-place tandem 
canopy cockpit and a single-engine. It also features a conventional 
landing gear, conventional low-wing planform and is of composite 
construction. The engine is a Lycoming AEIO-580-B1A with a rated power 
of 315 Hp at 2,700 rpm. The airplane is proposed to be approved for 
Day-VFR operations with no icing approval.
    The maximum takeoff weight is 2,200 pounds in utility category, 
1,874 pounds in acrobatic category. VNE is 225 knots, 
VNO is 185 knots and VA is 174 knots, indicated 
airspeed. Maximum altitude is 15,000 feet.
    Acrobatic airplanes previously type certificated by the FAA did 
comply with the stability provisions of Subpart B of 14 CFR part 23. 
However, airplanes like the XA42 are considered as ``unlimited'' 
acrobatic aircraft because they can perform at the highest level of 
aerobatic competition and can perform any of the maneuvers listed in 
the Aresti Catalog. Generally, the evolution of the ``unlimited'' types 
of acrobatic airplanes, with very low mass, exceptional roll rates and 
very high G capabilities, in addition to power to mass ratios that are 
unique to this type of airplane, have led to airplanes that cannot 
comply with the stability provisions of the regulations. These 
airplanes can still be type-certificated, but in the acrobatic category 
only and with an appropriate set of special conditions and associated 
limitations.
    The FAA will only consider certifying the XA42 in the acrobatic 
category. XtremeAir GmbH will not be able to offer a utility category 
operating envelope to accommodate the increased fuel load designed for 
cross-country operations. The FAA does recognize that fuel exhaustion 
is one of the top accident causes associated with this class of 
aircraft. For this reason, the FAA allows XtremeAir to seek 
certification of a limited acrobatic envelope at a higher weight that 
will still meet the minimum load requirements of +6/-3 g associated 
with 14 CFR, part 23, Sec.  23.337. The XA42 airplane would be approved 
for unlimited maneuvers at or below its designed unlimited acrobatic 
weight. The airplane would also be approved at some higher weight (for 
fuel) that would still meet the requirements of Sec.  23.337 for 
acrobatic category and may have restrictions on the maneuvers allowed.

Type Certification Basis

    Under the provisions of 14 CFR, part 21, Sec.  21.17, XtremeAir 
GmbH must show that the XA42 meets the applicable provisions of part 
23, as amended by Amendments 23-1 through 23-59 thereto.
    Part 36 of Title 14 of the Code of Federal Regulations, effective 
December 1, 1969, as amended by Amendments 36-1 through 36-28.
    Not approved for ditching; compliance with provisions for ditching 
equipment in accordance with 14 CFR 23.1415(a)(b) has not been 
demonstrated.
    Approved for VFR-day only. Flight in known icing prohibited.
    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 XA42 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 XA42 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 section 611 of Public Law 92-574, the 
``Noise Control Act of 1972.''
    Special conditions, 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.

Novel or Unusual Design Features

    The XtremeAir GmbH XA42 will incorporate the following novel or 
unusual design features:
    For acrobatic category airplanes with unlimited acrobatic 
capability:

[[Page 17324]]

    Neutral longitudinal and lateral static stability characteristics.

Discussion

    The Code of Federal Regulations states static stability criteria 
for longitudinal, lateral, and directional axes of an airplane. 
However, none of these criteria are adequate to address the specific 
issues raised in the flight characteristics of an unlimited aerobatic 
airplane. Therefore, the FAA has determined after a flight test 
evaluation that, in addition to the requirements of part 21 and part 
23, special conditions are needed to address these static stability 
characteristics.
    Accordingly, these special conditions are for the XtremeAir GmbH 
XA42 static stability characteristics to be certified solely as an 
acrobatic category airplane. Other conditions may be developed, as 
needed, based on further FAA review and discussions with the 
manufacturer and civil aviation authorities.

Discussion of Comments

    A notice of proposed special conditions No. 23-11-02-SC for the 
XtremeAir GmbH XA42 airplanes was published in the Federal Register on 
December 27, 2011 (76 FR 80829). One comment was received; however, it 
appeared to be made in error. It discussed new hire training through 
approved 142 training centers, which is not relevant to the acrobatic 
category aerodynamic stability special conditions being imposed on 
XtremeAir GmbH's XA42 airplane. For this reason, no further action will 
be taken and the special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
XA42. Should XtremeAir GmbH apply at a later date for a change to the 
type certificate to include another model on the same type certificate 
incorporating the same novel or unusual design feature, the special 
conditions would apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on one model of airplane. 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

0
The authority citation for these 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 Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the type certification basis for XtremeAir GmbH XA42 airplanes.

1. Unlimited Acrobatic-Only Category Static Stability Requirements

    For unlimited, acrobatic-only category aircraft, XtremeAir GmbH 
XA42 will comply with the following stability special conditions in 
lieu of the existing Sec. Sec.  23.171, 23.173, 23.175, and 23.177:
    (A) In place of 14 CFR part 23, Sec.  23.171 Flight--General 
(stability) requirement, comply with the following:
    SC23.171 Flight--General: The airplane must be neutrally or 
positively stable in the longitudinal, directional, and lateral axes 
under sections SC23.173 through SC23.181. In addition, the airplane 
must show suitable stability and control ``feel'' (static stability) in 
any condition normally encountered in service, if flight tests show it 
is necessary for safe operation.
    (B) In place of 14 CFR part 23, Sec.  23.173, Static longitudinal 
stability requirement, comply with the following:
    SC23.173 Static longitudinal stability: Under the conditions 
specified in SC23.175 and with the airplane trimmed as indicated, the 
characteristics of the elevator control forces and the friction within 
the control system must be as follows:
    (a) A pull must be required to obtain and maintain speeds below the 
specified trim speed and a push required to obtain and maintain speeds 
above the specified trim speed. This must be shown at any speed that 
can be obtained, except that speeds requiring a control force in excess 
of 40 pounds or speeds above the maximum allowable speed or below the 
minimum speed for steady unstalled flight need not be considered.
    (b) The stick force or position must vary with speed so that any 
substantial speed change results in a stick force or position clearly 
perceptible to the pilot.
    (C) In place of 14 CFR part 23, Sec.  23.175, Demonstration of 
static longitudinal stability requirement, comply with the following:
    SC23.175 Demonstration of static longitudinal stability:
    (a) Climb. The stick force curve must have, at a minimum, a 
neutrally stable to stable slope at speeds between 85 and 115 percent 
of the trim speed, with--
    (1) Maximum continuous power; and
    (2) The airplane trimmed at the speed used in determining the climb 
performance required by section 23.69(a).
    (b) Cruise. With the airplane in trim with power for level flight 
at representative cruising speeds at high and low altitudes, including 
speeds up to VNO, except that the speed need not exceed 
VH--
    (1) The stick force curve must, at a minimum, have a neutrally 
stable to stable slope at all speeds within a range that is the greater 
of 15 percent of the trim speed plus the resulting free return speed 
range, or 40 knots plus the resulting free return speed range, above 
and below the trim speed, except that the slope need not be stable--
    (i) At speeds less than 1.3 VS1; or
    (ii) For airplanes with VNE established under section 
23.1505(a), at speeds greater than VNE.
    (c) Landing. The stick force curve must, at a minimum, have a 
neutrally stable to stable slope at speeds between 1.1 VS1 
and 1.8 VS1 with--
    (1) Landing gear extended; and
    (2) The airplane trimmed at--
    (i) VREF, or the minimum trim speed if higher, with 
power off; and
    (ii) VREF with enough power to maintain a 3 degree angle 
of descent.
    (D) In place of 14 CFR part 23, Sec.  23.177, Static directional 
and lateral stability requirement, comply with the following:
    SC23.177 Static directional and lateral stability:
    (a) The static directional stability, as shown by the tendency to 
recover from a wings level sideslip with the rudder free, must be 
positive for any landing gear and flap position appropriate to the 
takeoff, climb, cruise, approach, and landing configurations. This must 
be shown with symmetrical power up to maximum continuous power, and at 
speeds from 1.2 VS1 up to the maximum allowable speed for 
the condition being investigated. The angle of sideslip for these tests 
must be appropriate to the type of airplane. At larger angles of 
sideslip, up to that at which full rudder is used or a control force 
limit in section 23.143 is reached, whichever occurs first, and at 
speeds from 1.2 VS1 to VO, the rudder pedal force 
must not reverse.
    (b) In straight, steady slips at 1.2 VS1 for any landing 
gear and flap positions, and for any symmetrical power conditions up to 
50 percent of maximum continuous power, the rudder control movements 
and forces must

[[Page 17325]]

increase steadily, but not necessarily in constant proportion, as the 
angle of sideslip is increased up to the maximum appropriate to the 
type of airplane. The aileron control movements and forces may increase 
steadily, but not necessarily in constant proportion, as the angle of 
sideslip is increased up to the maximum appropriate to the type of 
airplane. At larger slip angles, up to the angle at which the full 
rudder or aileron control is used or a control force limit contained in 
section 23.143 is reached, the aileron and rudder control movements and 
forces must not reverse as the angle of sideslip is increased. Rapid 
entry into, and recovery from, a maximum sideslip considered 
appropriate for the airplane must not result in uncontrollable flight 
characteristics.

    Issued in Kansas City, Missouri, on March 1, 2012.
John R. Colomy,
Acting Manager, Small Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2012-6837 Filed 3-23-12; 8:45 am]
BILLING CODE 4910-13-P