[Federal Register Volume 68, Number 198 (Tuesday, October 14, 2003)]
[Rules and Regulations]
[Pages 59099-59101]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-25949]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM249; Special Conditions No. 25-250-SC]


Special Conditions: Embraer Model ERJ-170 Series Airplanes; 
Electronic Flight Controls (Command Signal Integrity)

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Embraer Model ERJ-
170 series airplanes. These airplanes will have novel or unusual design 
features when compared to the state of technology envisioned in the 
airworthiness standards for transport category airplanes. These design 
features are associated with electronic flight control systems. 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. 
Additional special conditions will be issued for this and other novel 
or unusual design features of Embraer Model 170 series airplanes.

EFFECTIVE DATES: October 6, 2003.

FOR FURTHER INFORMATION CONTACT: Tom Groves, FAA, International Branch, 
ANM-116, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; 
telephone (425) 227-1503; facsimile (425) 227-1149; e-mail 
[email protected].

SUPPLEMENTARY INFORMATION:

Background

    On May 20, 1999, Embraer applied for a type certificate for its new 
Model ERJ-170 airplane. Two basic versions of the Model ERJ-170 are 
included in the application. The ERJ-170-100 airplane is a 69-78 
passenger, twin-engine regional jet with a maximum takeoff weight of 
81,240 pounds. The ERJ-170-200 is a derivative with a lengthened 
fuselage. Passenger capacity for the ERJ-170-200 is increased to 86, 
and maximum takeoff weight is increased to 85,960 pounds.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, Embraer must show that the 
Model ERJ-

[[Page 59100]]

170 series airplanes meet the applicable provisions of 14 CFR part 25, 
as amended by Amendments 25-1 through 25-98.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended) do not contain adequate or 
appropriate safety standards for Embraer Model ERJ-170 series airplanes 
because of novel or unusual design features, special conditions are 
prescribed under the provisions of Sec.  21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, Embraer Model ERJ-170 series airplanes 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 93-574, the ``Noise Control Act of 1972.''
    Special conditions, as defined in 14 CFR 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), Amendment 21-69, effective 
September 16, 1991.
    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 or should any other model already included on 
the same type certificate be modified to incorporate the same novel or 
unusual design features, the special conditions would also apply to the 
other model under the provisions of Sec.  21.101.

Novel or Unusual Design Features

    The ERJ-170 airplane will use fly-by-wire (FBW) technology as a 
means of sending command and control signals to the control surface 
actuators of the rudder, rudder trim, elevator, spoilers, horizontal 
stabilizer, and auto speedbrake. The ailerons will be controlled by a 
traditional cable linkage to the hydraulic actuators.
    The ERJ-170 FBW flight control systems provide two modes of 
operation, direct and normal. Direct mode provides an analog link 
between pilot commands and control surfaces. In direct mode, flight 
control transducers send signals to Actuator Control Electronics units 
(ACE). The ACE sends analog command and control signals to the Power 
Control Units (PCU), which move the control surface actuators of the 
rudder, rudder trim, elevator, spoilers, horizontal stabilizer, and 
auto speedbrake.
    In normal mode, the rudder, elevator and spoiler command-to-surface 
gain schedules are tailored to particular flight conditions to provide 
improved control characteristics. These gains are calculated digitally 
in the Flight Control Module (FCM) and supplement the direct mode 
commands provided by the ACEs.
    In the ERJ-170 FBW design being presented, command and control of 
the airplane's aerodynamic control surfaces will be achieved by 
electronic interfaces. These interfaces involve not only direct 
commands to the PCU but all the necessary feedback sensor signals. A 
successful demonstration of signal integrity must include all the 
elements which contribute to the command and control signals to the 
control surface closed loop system (CSCL). The CSCL may include the 
following:
    (1) The computing components and wiring;
    (2) The input components, such as column position sensors;
    (3) Feedback components, such as control surface position, inertial 
reference, and air data sensors; and
    (4) Actuation components and their structural mounting components.
    A system evaluation that includes all the inputs to and elements of 
the CSCL in an integrated environment (including signals that could 
disturb the system) is necessary to ensure appropriate system 
robustness throughout the flight envelope.
    For the purpose of this proposed special condition, the control 
surface closed loop system does not include pilot input to the flight 
control system. Pilot in the loop control inputs and the associated 
handling requirements are adequately covered by existing regulations, 
including regulations in subpart B as well as Sec. Sec.  25.671 and 
25.672.
    The signal paths within the control surface closed loop system can 
be susceptible to interference from electromagnetic and electrostatic 
sources within the integrated systems environment of the aircraft as 
well as external causes, such as HIRF and lightning (not considered in 
this special condition), which could modify the command and control 
signals.
    The effects of interference sources within the system may include, 
but are not restricted to, the following:
    [sbull] Loss of data bits,
    [sbull] Unwanted transients in the power supply source,
    [sbull] Disruption of normal computer operations,
    [sbull] Misbehavior of signals by parallel computers (e.g., 
redundancy management),
    [sbull] Adverse effects caused by transport lag, and
    [sbull] Any other cause that may alter the command and control 
signals.
    For those reasons, special design measures and laboratory tests 
intended to validate these designs will be required to demonstrate the 
integrity of the FBW Flight Controls System to a level of safety 
equivalent to that which is achieved with traditional hydromechanical 
designs.
    The regulations which primarily address hydromechanical flight 
control systems, (i.e., 14 CFR 25.671 and 25.672) do not specifically 
require that command and control signals remain unaltered from internal 
or external interference. Traditional designs feature steel cables and 
pushrods as means to move surface actuators which are hydraulically 
powered. These designs are not likely to be affected by spurious 
electromagnetic and computer induced signals, as are the FBW designs.
    Similar special conditions have been issued previously for other 
airplanes that utilize FBW flight control systems, such as the Airbus 
A320 series, Airbus A330/340 series, and most recently, the Boeing 777 
series.
    The special conditions applied to the Boeing 777 series include a 
requirement for changes in mode of flight critical control systems. 
This requirement was intended to ensure a minimum level of availability 
for normal mode flight control. For the Boeing 777 series, the FAA did 
not consider Sec.  25.1309(b) adequate for that purpose.
    In the ERJ-170 FBW flight control system, normal mode consists of a 
simple analog control signal augmented by limited authority digitally 
computed signals. Direct mode consists of only the analog signal. The 
FAA believes that the existing 14 CFR 25.1309(b) provides a suitable 
requirement for assessing the effect and frequency of FBW flight 
control system mode changes or lost functionality for the ERJ-170 
series, and thus the specific requirement included with the Boeing 777 
series special conditions was not included in these proposed special 
conditions.
    In addition to the specific difference noted above, a number of 
smaller changes were made to the Boeing 777 series special condition to 
create these proposed special conditions. These additional changes were 
made to improve readability and to define with greater precision the 
intended scope of some of the paragraphs through use of consistent and 
defined terminology.

[[Page 59101]]

Discussion of Comments

    Notice of proposed special conditions No. 25-03-05-SC for the 
Embraer Model ERJ-170 series airplane was published in the Federal 
Register on June 16, 2003 (68 FR 35612). No comments were received, and 
these special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
Embraer Model ERJ-170 series airplanes. Should Embraer apply later for 
a change to the type certificate to include another model incorporating 
the same novel or unusual design features, these special conditions 
would apply to that model as well under the provisions of Sec.  21.101.
    Under standard practice, the effective date of final special 
conditions would be 30 days after the date of publication in the 
Federal Register; however, as the certification date for the Embraer 
Model ERJ-170 series airplane is imminent, the FAA finds that good 
cause exists to make these special conditions effective upon issuance.

Conclusion

    This action affects only certain novel or unusual design features 
on the Embraer Model ERJ-170 series 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 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

0
Accordingly, the Federal Aviation Administration (FAA) issues the 
following special conditions as part of the type certification basis 
for Embraer Model ERJ-170 series airplanes.

Electronic Flight Controls (Command Signal Integrity)

    In addition to compliance with Sec. Sec.  25.671 and 25.672, the 
following requirements must be met:
    (a) It must be shown that either the FBW flight control system 
signals cannot be altered unintentionally or that altered signal 
characteristics would meet the following criteria:
    (1) Stable gain and phase margins are maintained for all control 
surface closed loop systems. Pilot control inputs (pilot in the loop) 
are excluded from this requirement.
    (2) Sufficient pitch, roll, and yaw control power is available to 
provide control for continued safe flight and landing, considering all 
the FBW flight control system signal malfunctions that are not 
extremely improbable.
    (3) The effect of spurious signals on the systems which are 
included in the control surface loop must not result in unacceptable 
transients or degradation of the airplane's performance. Specifically, 
signals that would cause a significant uncommanded motion of a control 
surface actuator must be readily detected and deactivated, or the 
surface motion must be arrested by other means in a satisfactory 
manner. Small amplitude residual system oscillations may be acceptable.
    (b) It must be demonstrated that the output from the control 
surface closed loop system does not result in uncommanded, sustained 
oscillations of flight control surfaces. The effects of minor 
instabilities may be acceptable, provided that they are thoroughly 
investigated, documented, and understood.

    Issued in Renton, Washington, on October 6, 2003.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 03-25949 Filed 10-10-03; 8:45 am]
BILLING CODE 4910-13-P