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[Federal Register Volume 78, Number 33 (Tuesday, February 19, 2013)]
[Rules and Regulations]
[Pages 11560-11562]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2013-03677]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2012-1218; Special Conditions No. 25-483-SC]

Special Conditions: Embraer S.A., Model EMB-550 Airplane; 
Electronic Flight Control System: Lateral-Directional and Longitudinal 
Stability and Low Energy Awareness

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Embraer S.A. Model 
EMB-550 airplane. This airplane will have a novel or unusual design 
feature(s) associated with an electronic flight control system with 
respect to lateral-directional and longitudinal stability and low 
energy awareness. The applicable airworthiness regulations do not 
contain adequate or appropriate safety standards for this design 
feature. 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.

DATES: Effective date: March 21, 2013.

FOR FURTHER INFORMATION CONTACT: Joe Jacobsen, FAA, Airplane and Flight 
Crew Interface Branch, ANM-111 Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone 425-227-2011; facsimile 425-227-1149.

SUPPLEMENTARY INFORMATION: 

Background

    On May 14, 2009, Embraer S.A. applied for a type certificate for 
their new Model EMB-550 airplane. The Model EMB-550 airplane is the 
first of a new family of jet airplanes designed for corporate flight, 
fractional, charter, and private owner operations. The aircraft has a 
conventional configuration with low wing and T-tail empennage. The 
primary structure is metal with composite empennage and control 
surfaces. The Model EMB-550 airplane is designed for 8 passengers, with 
a maximum of 12 passengers. It is equipped with two Honeywell HTF7500-E 
medium bypass ratio turbofan engines mounted on aft fuselage pylons. 
Each engine produces approximately 6,540 pounds of thrust for normal 
takeoff. The primary flight controls consist of hydraulically powered 
fly-by-wire elevators, aileron and rudder, controlled by the pilot or 
copilot sidestick.
    The Embraer S.A. Model EMB-550 airplane has a flight control design 
feature within the normal operational envelope in which sidestick 
deflection in the roll axis commands roll rate. As a result, the stick 
force in the roll axis will be zero (neutral stability) during the 
straight, steady sideslip flight maneuver required by Title 14, Code of 
Federal Regulations (14 CFR) 25.177(c) and will not be ``substantially 
proportional to the angle of sideslip'' as required by the rule.
    The longitudinal flight control laws for the Model EMB-550 airplane 
provide neutral static stability within the normal operational 
envelope; therefore, the airplane design does not comply with the 
static longitudinal stability requirements of Sec. Sec.  25.171, 
25.173, and 25.175.
    Static longitudinal stability provides awareness to the flightcrew 
of a low energy state (i.e., low speed and thrust at low altitude). 
Recovery from a low energy state may become hazardous when associated 
with a low altitude and performance-limiting conditions. These low 
energy situations must therefore be avoided, and pilots must be given 
adequate cues when approaching such situations.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, Embraer S.A. must show that 
the Model EMB-550 airplane meets the applicable provisions of part 25, 
as amended by Amendments 25-1 through 25-127 thereto.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for the Model EMB-550 airplane because of 
a novel or unusual design feature, special conditions are prescribed 
under the provisions of Sec.  21.16.
    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 or similar 
novel or unusual design feature, the special conditions would also 
apply to the other model under Sec.  21.101.

[[Page 11561]]

    In addition to the applicable airworthiness regulations and special 
conditions, the Model EMB-550 airplane 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 under section 611 of Public Law 92-574, 
the ``Noise Control Act of 1972.''
    The FAA issues special conditions, as defined in 14 CFR part 11.19, 
in accordance with Sec.  11.38, and they become part of the type-
certification basis under Sec.  21.17(a)(2).

Novel or Unusual Design Features

    The Model EMB-550 airplane will incorporate the following novel or 
unusual design features:
    (1) Lateral-Directional Static Stability: The electronic flight 
control system on the Model EMB-550 airplane contains fly-by-wire 
control laws that can result in neutral lateral-directional static 
stability; therefore, the conventional requirements in Sec. Sec.  
25.171, 25.173, 25.175, and 25.177 are not met.
    Positive static directional stability is the tendency to recover 
from a skid with the rudder free. Positive static lateral stability is 
the tendency to raise the low wing in a sideslip with the aileron 
controls free. These control criteria are intended to accomplish all of 
the following:
     Provide additional cues of inadvertent sideslips and skids 
through control force changes,
     Ensure that short periods of unattended operation do not 
result in any significant changes in yaw or bank angle,
     Provide predictable roll and yaw response, and
     Provide an acceptable level of pilot attention and 
workload to attain and maintain a coordinated turn.
    The Flight Test Harmonization Working Group recommended a rule and 
advisory material change for Sec.  25.177, Static lateral-directional 
stability, which was adopted at Amendment 25-135 (76 FR 74654, December 
1, 2011), effective January 30, 2012. (This amendment is not in the 
Model EMB-550 certification basis.) That harmonized text formed the 
basis for these special conditions.
    (2) Longitudinal Static Stability: Static longitudinal stability on 
airplanes with mechanical links to the pitch control surface means that 
a pull force on the controller will result in a reduction in speed 
relative to the trim speed, and a push force will result in higher than 
trim speed. Longitudinal stability is required by the regulations for 
the following reasons:
     Speed change cues are provided to the pilot through 
increased and decreased forces on the controller.
     Short periods of unattended control of the airplane do not 
result in significant changes in attitude, airspeed or load factor.
     A predictable pitch response is provided to the pilot.
     An acceptable level of pilot attention (workload) to 
attain and maintain trim speed and altitude is provided to the pilot.
     Longitudinal stability provides gust stability.
    The pitch control movement of the sidestick on the Model EMB-550 
airplane is designed to be a normal load factor or g command that 
results in an initial movement of the elevator surface to attain the 
commanded load factor that's then followed by integrated movement of 
the stabilizer and elevator to automatically trim the airplane to a 
neutral, 1g, stick-free stability. The flight path commanded by the 
initial sidestick input will remain, stick-free, until the pilot gives 
another command. This control function is applied during ``normal'' 
control law within the speed range from initiation of the angle of 
attack protection limit, to VMO/MMO. Once outside 
this speed range, the control laws introduce the conventional 
longitudinal static stability as described above.
    As a result of neutral static stability, the Model EMB-550 airplane 
does not meet the 14 CFR part 25 requirements for static longitudinal 
stability.
    (3) Low Energy Awareness: Past experience on airplanes fitted with 
a flight control system providing neutral longitudinal stability shows 
there is insufficient feedback cues to the pilot of excursion below 
normal operational speeds. The maximum angle of attack protection 
system limits the airplane angle of attack and prevents stall during 
normal operating speeds, but this system is not sufficient to prevent 
stall at low speed excursions below normal operational speeds. Until 
intervention, there are no stability cues since the airplane remains 
trimmed. Additionally, feedback from the pitching moment due to thrust 
variation is reduced by the flight control laws. Recovery from a low 
speed excursion may become hazardous when the low speed situation is 
associated with a low altitude and with the engines at low thrust or 
with performance-limiting conditions.

Discussion

    In the absence of positive lateral stability, the curve of lateral 
control surface deflections against sideslip angle should be in a 
conventional sense, and reasonably in harmony with rudder deflection 
during steady heading sideslip maneuvers.
    Since conventional relationships between stick forces and control 
surface displacements do not apply to the ``load factor command'' 
flight control system on the Model EMB-550 airplane, longitudinal 
stability characteristics should be evaluated by assessing the airplane 
handling qualities during simulator and flight test maneuvers 
appropriate to operation of the airplane. This may be accomplished by 
using the Handling Qualities Rating Method presented in Appendix 7 of 
Advisory Circular (AC) 25-7B, Flight Test Guide, dated March 29, 2011, 
or an acceptable alternative method proposed by Embraer S.A. Important 
considerations are as follows:
     Adequate speed control without creating excessive pilot 
workload,
     Acceptable high and low speed protection, and
     Providing adequate cues to the pilot of significant speed 
excursions beyond VMO/MMO, and low speed 
awareness flight conditions.
    The airplane should provide adequate awareness cues to the pilot of 
a low energy (i.e., a low speed, low thrust, or low height) state to 
ensure that the airplane retains sufficient energy to recover when 
flight control laws provide neutral longitudinal stability 
significantly below the normal operating speeds. This may be 
accomplished as follows:
     Adequate low speed/low thrust cues at low altitude may be 
provided by a strong positive static stability force gradient (1 pound 
per 6 knots applied through the sidestick), or
     The low energy awareness may be provided by an appropriate 
warning with the following characteristics:
    [cir] It should be unique, unambiguous, and unmistakable.
    [cir] It should be active at appropriate altitudes and in 
appropriate configurations (e.g., at low altitude, in the approach and 
landing configurations).
    [cir] It should be sufficiently timely to allow recovery to a 
stabilized flight condition inside the normal flight envelope while 
maintaining the desired flight path and without entering the flight 
controls angle-of-attack protection mode.
    [cir] It should not be triggered during normal operation, including 
operation in moderate turbulence for recommended maneuvers at 
recommended speeds.

[[Page 11562]]

    [cir] The pilot should only be able to cancel it by achieving a 
higher energy state.
    [cir] An adequate hierarchy should exist among the warnings so that 
the pilot is not confused and led to take inappropriate recovery action 
if multiple warnings occur.
    Simulators and flight test should evaluate global energy awareness 
and ensure that low energy cues are not a nuisance in all take-off and 
landing altitude ranges for which certification is requested. These 
evaluations should include all relevant combinations of weight, center 
of gravity position, configuration, airbrakes position, and available 
thrust, including reduced and derated take-off thrust operations and 
engine failure cases. A sufficient number of tests should be conducted 
to assess the level of energy awareness and the effects of energy 
management errors. 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.

Discussion of Comments

    Notice of proposed special conditions No. 25-12-11-SC for the 
Embraer S.A. Model EMB-550 airplanes was published in the Federal 
Register on November 20, 2012 (77 FR 69573). No comments were received, 
and the special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
Model EMB-550 airplane. Should Embraer S.A. 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 special conditions would 
apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on one model of airplanes. It is not a rule of general applicability.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

0
The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

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 Model EMB-550 airplanes.
    1. Electronic Flight Control System: Lateral-Directional and 
Longitudinal Stability and Low Energy Awareness. In lieu of the 
requirements of Sec. Sec.  25.171, 25.173, 25.175, and 25.177, the 
following special conditions apply:
    a. The airplane must be shown to have suitable static lateral, 
directional, and longitudinal stability in any condition normally 
encountered in service, including the effects of atmospheric 
disturbance. The showing of suitable static lateral, directional, and 
longitudinal stability must be based on the airplane handling 
qualities, including pilot workload and pilot compensation, for 
specific test procedures during the flight test evaluations.
    b. The airplane must provide adequate awareness to the pilot of a 
low energy (e.g., low speed, low thrust, or low height) state when 
fitted with flight control laws presenting neutral longitudinal 
stability significantly below the normal operating speeds. ``Adequate 
awareness'' means warning information must be provided to alert the 
crew of unsafe operating conditions and to enable them to take 
appropriate corrective action.
    c. The static directional stability (as shown by the tendency to 
recover from a skid with the rudder free) must be positive for any 
landing gear and flap position and symmetrical power condition, at 
speeds from 1.13 VSR1, up to VFE, VLE, 
or VFC/MFC (as appropriate).
    d. The static lateral stability (as shown by the tendency to raise 
the low wing in a sideslip with the aileron controls free) for any 
landing gear and wing-flap position and symmetric power condition, may 
not be negative at any airspeed (except that speeds higher than 
VFE need not be considered for wing-flaps extended 
configurations nor speeds higher than VLE for landing gear 
extended configurations) in the following airspeed ranges:
    i. From 1.13 VSR1 to VMO/MMO.
    ii. From VMO/MMO to VFC/
MFC, unless the divergence is -
    1. Gradual;
    2. Easily recognizable by the pilot; and
    3. Easily controllable by the pilot.
    e. In straight, steady sideslips over the range of sideslip angles 
appropriate to the operation of the airplane, but not less than those 
obtained with one-half of the available rudder control movement (but 
not exceeding a rudder control force of 180 pounds), rudder control 
movements and forces must be substantially proportional to the angle of 
sideslip in a stable sense; and the factor of proportionality must lie 
between limits found necessary for safe operation. This requirement 
must be met for the configurations and speeds specified in paragraph 
(c) of this section.
    f. For sideslip angles greater than those prescribed by paragraph 
(e) of this section, up to the angle at which full rudder control is 
used or a rudder control force of 180 pounds is obtained, the rudder 
control forces may not reverse, and increased rudder deflection must be 
needed for increased angles of sideslip. Compliance with this 
requirement must be shown using straight, steady sideslips, unless full 
lateral control input is achieved before reaching either full rudder 
control input or a rudder control force of 180 pounds; a straight, 
steady sideslip need not be maintained after achieving full lateral 
control input. This requirement must be met at all approved landing 
gear and wing-flap positions for the range of operating speeds and 
power conditions appropriate to each landing gear and wing-flap 
position with all engines operating.

    Issued in Renton, Washington, on February 12, 2013.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2013-03677 Filed 2-15-13; 8:45 am]
BILLING CODE 4910-13-P
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