[Federal Register Volume 68, Number 115 (Monday, June 16, 2003)]
[Proposed Rules]
[Pages 35612-35614]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-15140]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM249; Special Conditions No. 25-03-05-SC]
Special Conditions: Embraer Model ERJ-170 Series Airplanes;
Electronic Flight Controls (Command Signal Integrity)
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Notice of proposed special conditions.
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SUMMARY: This notice proposes special conditions 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 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.
Additional special conditions will be issued for this and other novel
or unusual design features of Embraer Model 170 series airplanes.
DATES: Comments must be received on or before July 16, 2003.
ADDRESSES: Comments on this proposal may be mailed in duplicate to:
Federal Aviation Administration, Transport Airplane Directorate,
Attention: Rules Docket (ANM-113), Docket No. NM249, 1601 Lind Avenue
SW., Renton, Washington 98055-4056; or delivered in duplicate to the
Transport Airplane Directorate at the above address. All comments must
be marked: Docket No. NM249. 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: 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:
Comments Invited
The FAA invites interested persons to participate in this
rulemaking by submitting written comments, data, or views. The most
helpful comments reference a specific portion of the special
conditions, explain the reason for any recommended change, and include
supporting data. We ask that you send us two copies of written
comments.
We will file in the docket all comments we receive, as well as a
report summarizing each substantive public contact with FAA personnel
concerning these proposed special conditions. The docket is available
for public inspection before and after the comment closing date. If you
wish to review the docket in person, go to the address in the ADDRESSES
section of this notice between 7:30 a.m. and 4 p.m., Monday through
Friday, except Federal holidays.
We will consider all comments we receive on or before the closing
date for comments. We will consider comments filed late if it is
possible to do so without incurring expense or delay. We may change the
proposed special conditions in light of the comments we receive.
If you want the FAA to acknowledge receipt of your comments on this
proposal, include with your comments a pre-addressed, stamped postcard
on which the docket number appears. We will stamp the date on the
postcard and mail it back to you.
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-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 Sec. 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(a)(1), Amendment 21-
69, effective September 16, 1991.
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.
[[Page 35613]]
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.
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(a)(1), Amendment 21-69, effective September 16, 1991.
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.
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Proposed Special Conditions
Accordingly, the Federal Aviation Administration (FAA) proposes 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
[[Page 35614]]
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 June 6, 2003.
Ali Bahrami,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 03-15140 Filed 6-13-03; 8:45 am]
BILLING CODE 4910-13-P