[Federal Register Volume 78, Number 33 (Tuesday, February 19, 2013)]
[Rules and Regulations]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2013-03677]
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.
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
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.
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
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.
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
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
(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.
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
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
[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
[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.
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.
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
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 -
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.
Manager, Transport Airplane Directorate, Aircraft Certification
[FR Doc. 2013-03677 Filed 2-15-13; 8:45 am]
BILLING CODE 4910-13-P