
[Federal Register Volume 78, Number 33 (Tuesday, February 19, 2013)]
[Rules and Regulations]
[Pages 11556-11560]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2013-03678]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2012-1246; Special Conditions No. 25-481-SC]


Special Conditions: Embraer S.A., Model EMB-550 Airplane; 
Interaction of Systems and Structures

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 the interaction of systems and structures. 
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: Todd Martin, FAA, Airframe and Cabin 
Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone 425-227-1178; facsimile 425-227-1232.

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 Model Embraer EMB-550 airplane is equipped with systems that, 
directly or as a result of failure or malfunction, affect its 
structural performance. Current regulations do not take into account 
loads for the airplane due to the effects of systems on structural 
performance including normal operation and failure conditions with 
strength levels related to probability of occurrence. Special 
conditions are needed to account for these features.

Type Certification Basis

    Under the provisions of Title 14, Code of Federal Regulations (14 
CFR) 21.17,

[[Page 11557]]

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 Embraer S.A. 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 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 Embraer S.A. Model EMB-550 airplane is equipped with systems 
that, directly or as a result of failure or malfunction, affect its 
structural performance. Current regulations do not take into account 
loads for the airplane due to the effects of systems on structural 
performance including normal operation and failure conditions with 
strength levels related to probability of occurrence. Special 
conditions are needed to account for these features.
    These special conditions define criteria to be used in the 
assessment of the effects of these systems on structures. The general 
approach of accounting for the effect of system failures on structural 
performance would be extended to include any system in which partial or 
complete failure, alone or in combination with other system partial or 
complete failures, would affect structural performance.

Discussion

    These airplanes are equipped with systems that, directly or as a 
result of failure or malfunction, affect its structural performance. 
Current regulations do not take into account loads for the aircraft due 
to the effects of systems on structural performance including normal 
operation and failure conditions with strength levels related to 
probability of occurrence. These special conditions define criteria to 
be used in the assessment of the effects of these systems on 
structures.
    Special conditions have been applied on past airplane programs to 
require consideration of the effects of systems on structures. The 
regulatory authorities and industry developed standardized criteria in 
the Aviation Rulemaking Advisory Committee (ARAC) forum based on the 
criteria defined in Advisory Circular 25.672, Active Flight Controls, 
dated November 11, 1983. The ARAC recommendations have been 
incorporated in European Aviation Safety Agency (EASA) Certification 
Specifications (CS) 25.302 and CS 25 Appendix K. FAA rulemaking on this 
subject is not complete, thus the need for the special conditions.
    The proposed special conditions are similar to those previously 
applied to other airplane models and to CS 25.302. The major 
differences between these proposed special conditions and the current 
CS 25.302 are as follows:
    1. Both these special conditions and CS 25.302 specify the design 
load conditions to be considered. In paragraphs 2(a)(1) and 2(b)(2)(i) 
of these special conditions, the special conditions clarify that, in 
some cases, different load conditions are to be considered due to other 
special conditions or equivalent level of safety findings.
    2. Paragraph 2(b)(2)(i) of these special conditions include the 
additional ground-handling conditions of Sec. Sec.  25.493(d) and 
25.503. These conditions are added in case the Embraer S.A. Model EMB-
550 airplane has systems that affect braking and pivoting.
    3. Both CS 25.302 and paragraph (2)(d) of these special conditions 
allow consideration of the probability of being in a dispatched 
configuration when assessing subsequent failures and potential 
``continuation of flight'' loads. However, these special conditions 
also allow using probability when assessing failures that induce loads 
at the ``time of occurrence,'' whereas CS 25.302 does not.

Discussion of Comments

    Notice of proposed special conditions No. 25-12-16-SC for the 
Embraer S.A. Model EMB-550 airplanes was published in the Federal 
Register on November 28, 2012, (77 FR 70941). No comments were 
received, and the special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
Embraer S.A. 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 Embraer S.A. Model EMB-550 airplanes 
to address the effects of systems on structures.
    1. General interaction of systems and structures.
    For airplanes equipped with systems that affect structural 
performance, either directly or as a result of a failure or 
malfunction, the influence of these systems and their failure 
conditions must be taken into account when showing compliance with the 
requirements of Title 14, Code of Federal Regulations (14 CFR) part 25 
subparts C and D.
    The following criteria must be used for showing compliance with 
these special conditions for airplanes equipped with flight control 
systems, autopilots, stability augmentation systems, load alleviation 
systems, fuel management systems, and other systems that either 
directly or as a result of failure or malfunction affect structural 
performance. If these special conditions are used for other systems, it 
may be necessary to adapt the criteria to the specific system.

[[Page 11558]]

    (a) The criteria defined herein only address the direct structural 
consequences of the system responses and performances and cannot be 
considered in isolation but should be included in the overall safety 
evaluation of the airplane. These criteria may in some instances 
duplicate standards already established for this evaluation. These 
criteria are only applicable to structure in which failure could 
prevent continued safe flight and landing. Specific criteria that 
define acceptable limits on handling characteristics or stability 
requirements when operating in the system degraded or inoperative mode 
are not provided in these special conditions.
    (b) The following definitions are applicable to these special 
conditions.
    (1) Structural performance: Capability of the airplane to meet the 
structural requirements of 14 CFR part 25.
    (2) Flight limitations: Limitations that can be applied to the 
airplane flight conditions following an in-flight occurrence and that 
are included in the flight manual (e.g., speed limitations and 
avoidance of severe weather conditions).
    (3) Operational limitations: Limitations, including flight 
limitations, that can be applied to the airplane operating conditions 
before dispatch (e.g., fuel, payload, and Master Minimum Equipment List 
limitations).
    (4) Probabilistic terms: The probabilistic terms (i.e., probable, 
improbable, and extremely improbable) used in these special conditions 
are the same as those used in Sec.  25.1309.
    (5) Failure condition: The term ``failure condition'' is the same 
as that used in Sec.  25.1309. However, these special conditions apply 
only to system failure conditions that affect the structural 
performance of the airplane (e.g., system failure conditions that 
induce loads, change the response of the airplane to inputs such as 
gusts or pilot actions, or lower flutter margins).
    2. Effect on Systems and Structures. The following criteria are 
used in determining the influence of a system and its failure 
conditions on the airplane structure.
    (a) System fully operative. With the system fully operative, the 
following apply:
    (1) Limit loads must be derived in all normal operating 
configurations of the system from all the limit conditions specified in 
Subpart C (or defined by special condition or equivalent level of 
safety in lieu of those specified in Subpart C), taking into account 
any special behavior of such a system or associated functions or any 
effect on the structural performance of the airplane that may occur up 
to the limit loads. In particular, any significant nonlinearity (rate 
of displacement of control surface, thresholds or any other system 
nonlinearities) must be accounted for in a realistic or conservative 
way when deriving limit loads from limit conditions.
    (2) The airplane must meet the strength requirements of part 25 
(static strength, residual strength), using the specified factors to 
derive ultimate loads from the limit loads defined above. The effect of 
nonlinearities must be investigated beyond limit conditions to ensure 
the behavior of the system presents no anomaly compared to the behavior 
below limit conditions. However, conditions beyond limit conditions 
need not be considered when it can be shown that the airplane has 
design features that will not allow it to exceed those limit 
conditions.
    (3) The airplane must meet the aeroelastic stability requirements 
of Sec.  25.629.
    (b) System in the failure condition. For any system failure 
condition not shown to be extremely improbable, the following apply:
    (1) At the time of occurrence. Starting from 1-g level flight 
conditions, a realistic scenario, including pilot corrective actions, 
must be established to determine the loads occurring at the time of 
failure and immediately after failure.
    (i) For static strength substantiation, these loads, multiplied by 
an appropriate factor of safety that is related to the probability of 
occurrence of the failure, are ultimate loads to be considered for 
design. The factor of safety (FS) is defined in Figure 1.
[GRAPHIC] [TIFF OMITTED] TR19FE13.001

    (ii) For residual strength substantiation, the airplane must be 
able to withstand two-thirds of the ultimate loads defined in paragraph 
2(b)(1)(i) of these special conditions. For pressurized cabins, these 
loads must be combined with the normal operating differential pressure.
    (iii) Freedom from aeroelastic instability must be shown up to the 
speeds defined in Sec.  25.629(b)(2). For failure conditions that 
result in speeds beyond VC/MC, freedom from 
aeroelastic instability must be shown to increased speeds, so that the 
margins intended by Sec.  25.629(b)(2) are maintained.
    (iv) Failures of the system that result in forced structural 
vibrations (e.g., oscillatory failures) must not produce loads that 
could result in detrimental deformation of primary structure.
    (2) For the continuation of the flight. For the airplane, in the 
system failed state and considering any appropriate reconfiguration and 
flight limitations, the following apply:
    (i) The loads derived from the following conditions (or conditions 
defined by special conditions or equivalent level of safety in lieu of 
the

[[Page 11559]]

following special conditions) at speeds up to VC/
MC, or the speed limitation prescribed for the remainder of 
the flight, must be determined:
    (A) The limit symmetrical maneuvering conditions specified in 
Sec. Sec.  25.331 and 25.345.
    (B) The limit gust and turbulence conditions specified in 
Sec. Sec.  25.341 and 25.345.
    (C) The limit rolling conditions specified in Sec.  25.349 and the 
limit unsymmetrical conditions specified in Sec. Sec.  25.367, 
25.427(b), and 25.427(c).
    (D) The limit yaw maneuvering conditions specified in Sec.  25.351.
    (E) The limit ground loading conditions specified in Sec. Sec.  
25.473, 25.491, 25.493(d) and 25.503.
    (ii) For static strength substantiation, each part of the structure 
must be able to withstand the loads in paragraph 2(b)(2)(i) of these 
special conditions multiplied by a factor of safety depending on the 
probability of being in this failure state. The factor of safety (FS) 
is defined in Figure 2.
[GRAPHIC] [TIFF OMITTED] TR19FE13.002

Qj = (Tj)(Pj) where:

Tj = Average time spent in failure condition j (in hours)

Pj = Probability of occurrence of failure mode j (per 
hour)

    Note: If Pj is greater than 10-3 per 
flight hour then a 1.5 factor of safety must be applied to all limit 
load conditions specified in Subpart C.

    (iii) For residual strength substantiation, the airplane must be 
able to withstand two-thirds of the ultimate loads defined in paragraph 
2(b)(2)(ii) of the special conditions. For pressurized cabins, these 
loads must be combined with the normal operating differential pressure.
    (iv) If the loads induced by the failure condition have a 
significant effect on fatigue or damage tolerance then their effects 
must be taken into account.
    (v) Freedom from aeroelastic instability must be shown up to a 
speed determined from Figure 3. Flutter clearance speeds V' and V'' may 
be based on the speed limitation specified for the remainder of the 
flight using the margins defined by Sec.  25.629(b).
[GRAPHIC] [TIFF OMITTED] TR19FE13.003

V' = Clearance speed as defined by Sec.  25.629(b)(2).
V'' = Clearance speed as defined by Sec.  25.629(b)(1).
Qj = (Tj)(Pj) where:
Tj = Average time spent in failure condition j (in hours)
Pj = Probability of occurrence of failure mode j (per 
hour)

    Note: If Pj is greater than 10-3 per 
flight hour, then the flutter clearance speed must not be less than 
V''.

    (vi) Freedom from aeroelastic instability must also be shown up to 
V' in Figure 3 above, for any probable system failure condition 
combined with any damage required or selected for investigation by 
Sec.  25.571(b).
    (3) Consideration of certain failure conditions may be required by 
other sections of 14 CFR part 25 regardless of calculated system 
reliability. Where analysis shows the probability of these failure 
conditions to be less than 10-9, criteria other than those 
specified in this paragraph may be used for structural substantiation 
to show continued safe flight and landing.
    (c) Failure indications. For system failure detection and 
indication, the following apply:
    (1) The system must be checked for failure conditions, not 
extremely improbable, that degrade the structural

[[Page 11560]]

capability below the level required by 14 CFR part 25 or significantly 
reduce the reliability of the remaining system. As far as reasonably 
practicable, the flightcrew must be made aware of these failures before 
flight. Certain elements of the control system, such as mechanical and 
hydraulic components, may use special periodic inspections, and 
electronic components may use daily checks, in lieu of detection and 
indication systems to achieve the objective of this requirement. These 
certification maintenance requirements must be limited to components 
that are not readily detectable by normal detection and indication 
systems and where service history shows that inspections will provide 
an adequate level of safety.
    (2) The existence of any failure condition, not extremely 
improbable, during flight that could significantly affect the 
structural capability of the airplane and for which the associated 
reduction in airworthiness can be minimized by suitable flight 
limitations, must be signaled to the flightcrew. For example, failure 
conditions that result in a factor of safety between the airplane 
strength and the loads of Subpart C below 1.25, or flutter margins 
below V'', must be signaled to the flightcrew during flight.
    (d) Dispatch with known failure conditions. If the airplane is to 
be dispatched in a known system failure condition that affects 
structural performance, or affects the reliability of the remaining 
system to maintain structural performance, then the provisions of these 
special conditions must be met, including the provisions of paragraph 
2(a) for the dispatched condition, and paragraph 2(b) for subsequent 
failures. Expected operational limitations may be taken into account in 
establishing Pj as the probability of failure occurrence for 
determining the safety margin in Figure 1 of these special conditions. 
Flight limitations and expected operational limitations may be taken 
into account in establishing Qj as the combined probability 
of being in the dispatched failure condition and the subsequent failure 
condition for the safety margins in Figures 2 and 3 of these special 
conditions. These limitations must be such that the probability of 
being in this combined failure state and then subsequently encountering 
limit load conditions is extremely improbable. No reduction in these 
safety margins is allowed if the subsequent system failure rate is 
greater than 10-3 per hour.

    Issued in Renton, Washington, on February 12, 2013.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2013-03678 Filed 2-15-13; 8:45 am]
BILLING CODE 4910-13-P


