Special Conditions: Gulfstream Aerospace Corporation Model GVII-G500 Series Airplanes; Flight Envelope Protection-High Incidence Protection System., 22214-22219 [2018-10168]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 83, Number 93 (Monday, May 14, 2018)]
[Proposed Rules]
[Pages 22214-22219]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2018-10168]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

Docket No. FAA-2015-0310; Notice No. 25-18-02-SC]


Special Conditions: Gulfstream Aerospace Corporation Model GVII-
G500 Series Airplanes; Flight Envelope Protection--High Incidence 
Protection System.

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

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SUMMARY: This action proposes special conditions for the Gulfstream 
Aerospace Corporation (Gulfstream) Model GVII-G500 series airplanes. 
These airplanes will have a novel or unusual design feature when 
compared to the state of technology and design envisioned in the 
airworthiness standards for transport category airplanes. This design 
feature is a high incidence protection system that limits the angle of 
attack at which the airplane can be flown during normal low speed 
operation. 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: Send your comments on or before June 4, 2018.

ADDRESSES: Send comments identified by docket number FAA-2015-0310 
using any of the following methods:
     Federal eRegulations Portal: Go to https://www.regulations.gov/ and follow the online instructions for sending 
your comments electronically.
     Mail: Send comments to Docket Operations, M-30, U.S. 
Department of Transportation (DOT), 1200 New Jersey Avenue SE, Room 
W12-140, West Building Ground Floor, Washington, DC 20590-0001.
     Hand Delivery or Courier: Take comments to Docket 
Operations in Room W12-140 of the West Building Ground Floor at 1200 
New Jersey Avenue SE, Washington, DC, between 9 a.m. and 5 p.m., Monday 
through Friday, except Federal holidays.
     Fax: Fax comments to Docket Operations at 202-493-2251.
    Privacy: The FAA will post all comments it receives, without 
change, to https://www.regulations.gov/, including any personal 
information the commenter provides. Using the search function of the 
docket website, anyone can find and read the electronic form of all 
comments received into any FAA docket, including the name of the 
individual sending the comment (or signing the comment for an 
association, business, labor union, etc.). DOT's complete Privacy Act 
Statement can be found in the Federal Register published on April 11, 
2000 (65 FR 19477-19478).
    Docket: Background documents or comments received may be read at 
https://www.regulations.gov/ at any time. Follow the online instructions 
for accessing the docket or go to Docket Operations in Room W12-140 of 
the West Building Ground Floor at 1200 New Jersey Avenue SE, 
Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Joe Jacobsen, Airframe & Flight Crew 
Interface Section, AIR-671, Transport Standards Branch, Policy and 
Innovation Division, Aircraft Certification Service, Federal Aviation 
Administration, 2200 SE 216th Street, Des Moines, Washington 98098; 
telephone and facsimile 206-231-3158; email [email protected].

SUPPLEMENTARY INFORMATION: Certification of the Gulfstream Model GVII-
G500 series airplanes is currently scheduled for July 2018. Because a 
delay in design approval would significantly affect the certification 
of the airplane and thus delivery of the airplane, we are shortening 
the public-comment period to 20 days.

Comments Invited

    We invite interested people to take part in this rulemaking by 
sending 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 will consider all comments we receive by the closing date for 
comments. We may change these special conditions based on the comments 
we receive.

Background

    On June 30, 2013, Gulfstream Aerospace Corporation applied for a 
type certificate for its new Model GVII-G500 series airplane. The 
Gulfstream Model GVII-G500 series airplane will be a business jet with 
seating for up to 19 passengers. It will incorporate a low, swept-wing 
design with a T-tail. The powerplant will consist of two aft-fuselage-
mounted turbofan engines. The Gulfstream Model GVII-G500 series 
airplane's maximum takeoff weight will be approximately 79,600 lbs.
    The high incidence protection system prevents the airplane from 
stalling at low speeds and, therefore, a stall warning system is not 
needed during normal flight conditions.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.17, Gulfstream Aerospace Corporation must show that the Model 
GVII-G500 series airplane meets the applicable provisions of 14 CFR 
part 25, as amended by amendments 25-1 through 25-137.
    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 Gulfstream Model GVII-G500 series 
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 novel or 
unusual design feature, these special conditions would also apply to 
the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the Gulfstream Model GVII-

[[Page 22215]]

G500 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.
    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 Gulfstream Model GVII-G500 series airplane will incorporate the 
following novel or unusual design feature: A high incidence protection 
system, which limits the angle of attack at which the airplane can be 
flown during normal low speed operation, prohibits the airplane from 
stalling, and cannot be overridden by the flightcrew. The application 
of this angle of attack limit influences the stall speed determination, 
stall characteristics, stall warning demonstration, and longitudinal 
handling characteristics of the airplane. Existing airworthiness 
regulations do not contain adequate standards to address this feature.

Discussion

    The high incidence protection system prevents the airplane from 
stalling at low speeds and, therefore, a stall warning system is not 
needed during normal flight conditions. However, during failures, which 
are not shown to be extremely improbable, the requirements of 
Sec. Sec.  25.203 and 25.207 apply, although slightly modified by these 
conditions. If there are failures of the high incidence protection 
system that are not shown to be extremely improbable, the flight 
characteristics at the angle of attack for CLMAX must be 
suitable in the traditional sense, and stall warning must be provided 
in a conventional manner.
    Part I of the following special conditions is in lieu of Sec. Sec.  
25.21(b), 25.103, 25.145(a), 25.145(b)(6), 25.175(c) and (d), 25.201, 
25.203, 25.207, and 25.1323(d). Part II is in lieu of Sec. Sec.  
25.21(g)(1), 25.105(a)(2)(i), 25.107(c) and (g), 25.121(b)(2)(ii)(A), 
25.121(c)(2)(ii)(A), 25.121(d)(2)(ii), 25.123(b)(2)(i), 
25.125(b)(2)(ii)(B), and 25.143(j).
    These proposed special conditions address this novel or unusual 
design feature on the Gulfstream Model GVII-G500 airplane, and 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.
    These proposed special conditions are different from special 
conditions previously issued on this topic. In Part 1, sections 
3.b.iv., 3.b.vi., 3.e.vi., 5.a.i.1., 5.a.i.4., 5.a.i.6., 5.a.i.7., 
5.c.i.4., 5.c.i.5., 5.c.i.6, 5.c.ii.4., and 5.cii.5., previously used 
verbiage was updated to reflect language recommended in the ARAC Flight 
Test Harmonization Working Group (FTHWG) Phase 2 report. This language 
more accurately describes the actions required and formulas to be used 
to obtain the required result. In Part 1, sections 3.b.ii and 
5.a.ii.4., the ARAC FTHWG language was adapted to reflect specific 
Gulfstream design features.
    In several previous special conditions on this subject, we used the 
nomenclature VCLMAX. To avoid confusion with previous 
Gulfstream special conditions, we have changed the nomenclature to 
VCLMAX Demo to highlight a difference. The difference is not 
significant, but the change in nomenclature was considered clarifying 
and therefore was adopted in this instance.

Applicability

    As discussed above, these special conditions are applicable to the 
Gulfstream Model GVII-G500 series airplanes. Should Gulfstream 
Aerospace Corporation apply at a later date for a change to the type 
certificate to include another model incorporating the same novel or 
unusual design feature, these special conditions would apply to that 
model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on Gulfstream Model GVII-G500 series 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.

    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(f), 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 Gulfstream Model GVII-G500 series airplanes.

Part I: Stall Protection and Scheduled Operating Speeds

    In the following sections, ``in icing conditions,'' means with ice 
accretions (relative to the relevant flight phase) as defined in 
appendix C to part 25, at amendment 25-121.
1. Definitions
    These special conditions use terminology that does not appear in 14 
CFR part 25. For the purpose of these special conditions, the following 
terms describe certain aspects of this novel or unusual design feature:
High-Incidence Protection System
    A system that operates directly and automatically on the airplane's 
flight controls to limit the maximum angle of attack that can be 
attained to a value below that at which an aerodynamic stall would 
occur.
Alpha-Limit
    The maximum angle of attack at which an airplane stabilizes with 
the high incidence protection system operating and the longitudinal 
control held on its aft stop.
VMIN
    The minimum steady flight speed in the airplane's configuration 
under consideration with the high incidence protection system 
operating. See Part I, Section 3, ``Minimum Steady Flight Speed and 
Reference Stall Speed,'' of these special conditions.
VMIN1g
    VMIN corrected to 1g acceleration of gravity conditions. 
See Part I, Section 3, ``Minimum Steady Flight Speed and Reference 
Stall Speed,'' of these special conditions. This is the minimum 
calibrated airspeed at which the airplane can develop a lift force 
normal to the flight path and equal to its weight when at an angle of 
attack not greater than that determined for VMIN.
2. Capability and Reliability of the High Incidence Protection System
    The applicant must establish the capability and reliability of the 
high incidence protection system. The applicant may establish this 
capability and reliability by flight testing, simulation, or analysis 
as appropriate. The capability and reliability required are:
    a. It must not be possible to encounter a stall during the pilot-
induced maneuvers required by Part I, section 5(a), ``High Incidence 
Handling Demonstrations,'' and the handling characteristics must be 
acceptable as required by Part I, section 5(b), ``Characteristics in 
High Incidence Maneuvers'' of these special conditions;
    b. The airplane must be protected against stalling due to the 
effects of wind shears and gusts at low speeds as required by Section 
6, ``Atmospheric Disturbances'' of these special conditions;

[[Page 22216]]

    c. The ability of the high incidence protection system to 
accommodate any reduction in stalling incidence must be verified in 
icing conditions;
    d. The high incidence protection system must be provided in each 
abnormal configuration of the high lift devices that is likely to be 
used in flight following system failures; and
    e. The reliability of the system and the effects of failures must 
be acceptable in accordance with Sec.  25.1309.
3. Minimum Steady Flight Speed and Reference Stall Speed
    In lieu of Sec.  25.103, ``Stall speed,'' the following applies:
    a. The minimum steady flight speed, VMIN, is the final, 
stabilized, calibrated airspeed obtained when an airplane is 
decelerated until the longitudinal control is on its stop in such a way 
that the entry rate does not exceed 1 knot per second.
    b. The minimum steady flight speed, VMIN, must be 
determined in icing and non-icing conditions with:
    i. The high incidence protection system operating normally;
    ii. Idle thrust;
    iii. All combinations of flap settings and landing gear positions 
for which VMIN is required to be determined;
    iv. The weight used when the reference stall speed, VSR, 
is used as a factor to determine compliance with a required performance 
standard;
    v. The most unfavorable center of gravity (CG) allowable; and
    vi. The airplane trimmed for straight flight at a speed selected by 
the applicant, but not less than 1.13 VSR and not greater 
than 1.3 VSR.
    c. The 1g minimum steady flight speed, VMIN1g, is the 
minimum calibrated airspeed at which an airplane can develop a lift 
force (normal to the flight path) equal to its weight, while at an 
angle of attack not greater than that at which the minimum steady 
flight speed referenced in section 3(a) of this special condition is 
determined. These minimum calibrated airspeeds must be determined for 
both icing and non-icing conditions.
    d. The reference stall speed, VSR, is a calibrated 
airspeed defined by the applicant. VSR may not be less than 
a 1g stall speed. VSR must be determined in non-icing 
conditions and expressed as:
[GRAPHIC] [TIFF OMITTED] TP14MY18.000

Where:

VCLMAX Demo = Demonstrated calibrated airspeed obtained 
when the corrected lift coefficient of the load factor
[GRAPHIC] [TIFF OMITTED] TP14MY18.001

 is first a maximum during the
 maneuver prescribed in
 section 3(e)(viii)
 of this
 special condition.
nZW = Load factor normal to the flight path at 
VCLMAX Demo
W = Airplane gross weight;
S = Aerodynamic reference wing area; and
q = Dynamic pressure.

    e. VCLMAX Demo is determined in non-icing conditions 
with:
    i. Engines idling, or, if that resultant thrust causes an 
appreciable decrease in stall speed, not more than zero thrust at the 
stall speed;
    ii. The airplane in other respects (such as flaps and landing gear) 
in the condition existing in the test or performance standard in which 
VSR is being used;
    iii. The weight used when VSR is being used as a factor 
to determine compliance with a required performance standard;
    iv. The CG position that results in the highest value of the 
reference stall speed;
    v. The airplane trimmed for straight flight at a speed selected by 
the applicant, but not less than 1.13 VSR and not greater 
than 1.3 VSR;
    vi. At the option of the applicant, the high incidence protection 
system can be disabled or adjusted to allow full development of the 
maneuver to the angle of attack corresponding to VSR; and
    vii. Starting from the stabilized trim condition, with an 
application of the longitudinal control to decelerate the airplane so 
that the speed reduction does not exceed 1 knot per second.
4. Stall Warning
    In lieu of Sec.  25.207, the following apply:
a. Normal Operation
    If the design meets all conditions of Part I, section 2 of these 
special conditions, then the airplane need not provide stall warning 
during normal operation. The conditions of Part I, section 2 provide a 
level of safety equal to the intent of Sec.  25.207, ``Stall warning,'' 
so the provision of an additional, unique warning device for normal 
operations is not required.
b. High Incidence Protection System Failure
    For any failures of the high incidence protection system that the 
applicant cannot show to be extremely improbable, and that result in 
the capability of the system no longer satisfying any part of sections 
2(a), (b), and (c) of Part I of these special conditions: The design 
must provide stall warning that protects against encountering 
unacceptable characteristics and against encountering stall.
    i. This stall warning, with the flaps and landing gear in any 
normal position, must be clear and distinctive to the pilot, and must 
meet the requirements specified in sections 4(b)(iv) and 4(b)(v) of 
Part I of these special conditions.
    ii. The design must also provide this stall warning in each 
abnormal configuration of the high lift devices that is likely to be 
used in flight following system failures.
    iii. The design may furnish this stall warning either through the 
inherent aerodynamic qualities of the airplane or by a device that will 
provide clearly distinguishable indications to the flightcrew under all 
expected conditions of flight. However, a visual stall warning device 
that requires the attention of the flightcrew within the flight deck is 
not acceptable by itself. If a warning device is used, it must provide 
a warning in each of the airplane configurations prescribed in section 
4(b)(i), above, and for the conditions prescribed in sections 4(b)(iv) 
and 4(b)(v) of Part I of these special conditions.
    iv. In non-icing conditions, the stall warning must provide 
sufficient margin to prevent encountering unacceptable characteristics 
and encountering stall in the following conditions:
    1. In power-off straight deceleration not exceeding 1 knot per 
second to a speed of 5 knots or 5 percent calibrated airspeed (CAS), 
whichever is greater, below the warning onset; and
    2. In turning flight, stall deceleration at entry rates up to 3 
knots per second when recovery is initiated not less than 1 second 
after the warning onset.
    v. In icing conditions, the stall warning must provide sufficient 
margin to prevent encountering unacceptable characteristics and 
encountering stall in power-off straight and turning flight 
decelerations not exceeding 1 knot per second, when the pilot starts a 
recovery maneuver not less than three seconds after the onset of stall 
warning.
    vi. An airplane is considered stalled when the behavior of the 
airplane gives the pilot a clear, distinctive, and acceptable 
indication that the airplane is stalled. Acceptable indications of a 
stall, occurring either individually or in combination, are:
    1. A nose-down pitch that cannot be readily arrested;
    2. Buffeting of a magnitude and severity that is strong and thereby 
an

[[Page 22217]]

effective deterrent to further speed reduction; or
    3. The pitch control reaches the aft stop, and no further increase 
in pitch attitude occurs when the control is held full aft for a short 
time before recovery is initiated.
    vii. An airplane exhibits unacceptable characteristics during 
straight or turning flight decelerations if it is not always possible 
to produce and to correct roll and yaw by unreversed use of aileron and 
rudder controls, or abnormal nose-up pitching occurs.
5. Handling Characteristics at High Incidence
a. High Incidence Handling Demonstrations
    In lieu of Sec.  25.201, ``Stall demonstration,'' the following is 
required:
    i. Maneuvers to the limit of the longitudinal control, in the nose-
up sense, must be demonstrated in straight flight and in 30-degree 
banked turns with:
    1. The high incidence protection system operating normally;
    2. Initial power conditions of:
    a. Power off; and
    b. Power necessary to maintain level flight at 1.5 VSR1, 
where VSR1 is the reference stall speed with flaps in 
approach position, landing gear retracted, and maximum landing weight;
    3. None;
    4. Flaps, landing gear, and deceleration devices in any likely 
combination of positions not prohibited by the airplane flight manual 
(AFM);
    5. Representative weights within the range for which certification 
is requested;
    6. The most adverse CG for recovery; and
    7. The airplane trimmed for straight flight at the speed prescribed 
in section 3(e)(v) of these special conditions.
    ii. The following procedures must be used to show compliance in 
non-icing and icing conditions:
    1. Starting at a speed sufficiently above the minimum steady flight 
speed to ensure that a steady rate of speed reduction can be 
established, apply the longitudinal control so that the speed reduction 
does not exceed 1 knot per second until the control reaches the stop.
    2. The longitudinal control must be maintained at the stop until 
the airplane has reached a stabilized flight condition, and must then 
be recovered by normal recovery techniques.
    3. Maneuvers with increased deceleration rates:
    a. In non-icing conditions, the requirements must also be met with 
increased rates of entry to the incidence limit, up to the maximum rate 
achievable.
    b. In icing conditions, with the anti-ice system working normally, 
the requirements must also be met with increased rates of entry to the 
incidence limit, up to three knots per second.
    4. Maneuvers with ice accretion prior to normal operation of the 
ice protection system:
    For flight in icing conditions before the ice protection system has 
been activated and is performing its intended function, the handling 
demonstration requirements identified in section 5(a)(i) must be 
satisfied using the procedures specified in sections 5(a)(ii)(1) and 
5(a)(ii)(2) of these special conditions. The airplane configurations 
required to be tested must be in accordance with the limitations and 
procedures for operating the ice protection system provided in the AFM, 
per Sec.  25.21(g)(1), as modified by and Part II of these special 
conditions.
b. Characteristics in High Incidence Maneuvers
    In lieu of Sec.  25.203, ``Stall characteristics,'' the following 
apply:
    i. Throughout maneuvers with a rate of deceleration of not more 
than 1 knot per second, both in straight flight and in 30-degree banked 
turns, the airplane's characteristics must be as follows:
    1. There must not be any abnormal nose-up pitching;
    2. There must not be any uncommanded nose-down pitching, which 
would be indicative of stall. However, reasonable attitude changes 
associated with stabilizing the incidence at Alpha limit, as the 
longitudinal control reaches the stop would be acceptable;
    3. There must not be any uncommanded lateral or directional motion, 
and the pilot must retain good lateral and directional control by 
conventional use of the controls throughout the maneuver; and
    4. The airplane must not exhibit buffeting of a magnitude and 
severity that would act as a deterrent from completing the maneuver 
specified in section 5(a)(i) of these special conditions.
    ii. In maneuvers with increased rates of deceleration, some 
degradation of characteristics is acceptable, associated with a 
transient excursion beyond the stabilized Alpha limit. However, the 
airplane must not exhibit dangerous characteristics or characteristics 
that would deter the pilot from holding the longitudinal control on the 
stop for a period of time appropriate to the maneuver.
    iii. It must always be possible for flightcrew to reduce incidence 
by conventional use of the controls.
    iv. The rate at which the airplane can be maneuvered from trim 
speeds, associated with scheduled operating speeds such as 
V2 and VREF up to Alpha limit, must not be unduly 
damped or be significantly slower than can be achieved on 
conventionally controlled transport airplanes.
c. Characteristics Up to the Maximum Lift Angle of Attack
    In addition to the requirements in section 5(b) of this special 
condition, the following requirements apply:
    i. In non-icing conditions, maneuvers with a rate of deceleration 
of not more than 1 knot per second, up to the angle of attack 
corresponding to VSR obtained using sections 3(d) and (e) of 
this special condition, must be demonstrated in straight flight and in 
30-degree banked turns in the following configurations:
    1. The high incidence protection system deactivated or adjusted, at 
the option of the applicant, to allow higher incidence than is possible 
with the normal production system;
    2. Automatic-thrust-increase system inhibited (if applicable);
    3. Engines idling;
    4. Flaps, landing gear, and deceleration devices in any likely 
combination of positions not prohibited by the AFM;
    5. The most adverse CG for recovery; and
    6. The airplane trimmed for straight flight at the speed prescribed 
in section 3(e)(v) of this special condition.
    ii. In icing conditions, maneuvers with a rate of deceleration of 
not more than 1 knot per second up to the maximum angle of attack 
reached during maneuvers from section 5(a)(ii)(3)(b) must be 
demonstrated in straight flight with:
    1. The high incidence protection system deactivated or adjusted, at 
the option of the applicant, to allow higher incidence than is possible 
with the normal production system;
    2. Automatic-thrust-increase system inhibited (if applicable);
    3. Engines idling;
    4. Flaps, landing gear, and deceleration devices in any likely 
combination of positions not prohibited by the AFM;
    5. The most adverse CG for recovery; and
    6. The airplane trimmed for straight flight at the speed prescribed 
in section 3(e)(v) of this special condition.

[[Page 22218]]

    iii. During the maneuvers used to show compliance with sections 
5(c)(i) and 5(c)(ii) of Part I of these special conditions, the 
airplane must not exhibit dangerous characteristics and it must always 
be possible for flightcrew to reduce angle of attack by conventional 
use of the controls. The pilot must retain good lateral and directional 
control, by conventional use of the controls, throughout the maneuver.
6. Atmospheric Disturbances
    Operation of the high incidence protection system must not 
adversely affect airplane control during expected levels of atmospheric 
disturbances, nor impede the application of recovery procedures in case 
of wind shear. This must be demonstrated in non-icing and icing 
conditions.
7. None
8. Proof of Compliance
    Add the following requirement to that of Sec.  25.21:
    (b) The flying qualities will be evaluated at the most unfavorable 
CG position.
9. The Design Must Meet the Following Modified Requirements

------------------------------------------------------------------------
              14 CFR  section                          Change
------------------------------------------------------------------------
25.145(a).................................  ``VMIN'' in lieu of ``stall
                                             identification''.
25.145(b)(6)..............................  ``VMIN'' in lieu of ``VSW''.
25.175(c) and (d).........................  ``VMIN'' in lieu of ``VSW''.
25.1323(d)................................  ``From 1.23 VSR to VMIN'' in
                                             lieu of ``From 1.23 VSR to
                                             the speed at which stall
                                             warning begins;'' and
                                             ``speeds below VMIN'' in
                                             lieu of ``speeds below
                                             stall warning speed.''
------------------------------------------------------------------------

Part II: Credit for Robust Envelope Protection in Icing Conditions

    1. In lieu of Sec.  25.21(g)(1), the following applies:
    (g) The requirements of this subpart associated with icing 
conditions apply only if certification for flight in icing conditions 
is desired. If certification for flight in icing conditions is desired, 
the following requirements also apply (see AC 25-25):
    (1) Each requirement of this subpart, except Sec. Sec.  25.121(a), 
25.123(c), 25.143(b)(1) and (b)(2), 25.149, 25.201(c)(2), 25.207(c) and 
(d), and 25.251(b) through (e), must be met in icing conditions. 
Compliance must be shown using the ice accretions defined in appendix C 
to part 25, assuming normal operation of the airplane and its ice 
protection system in accordance with the operating limitations and 
operating procedures established by the applicant and provided in the 
Airplane Flight Manual.
    2. In lieu of Sec.  25.103, ``Stall speed,'' define the stall speed 
as provided in Special Conditions Part I, section 3, ``Minimum Steady 
Flight Speed and Reference Stall Speed.''
    3. In lieu of Sec.  25.105(a)(2)(i) to read as follows:
    (2) In icing conditions, if in the configuration of Sec.  25.121(b) 
with the ``Takeoff Ice'' accretion defined in appendix C to part 25:
    (i) the V2 speed scheduled in non-icing conditions does not provide 
the maneuvering capability specified in Sec.  25.143(h) for the takeoff 
configuration, or
    4. In lieu of Sec.  25.107(c) and (g), the following apply, with 
additional sections (c') and (g'):
    (c) In non-icing conditions, V2, in terms of calibrated 
airspeed, must be selected by the applicant to provide at least the 
gradient of climb required by Sec.  25.121(b) but may not be less 
than--
    1. V2MIN;
    2. VR plus the speed increment attained (in accordance 
with Sec.  25.111(c)(2)) before reaching a height of 35 feet above the 
takeoff surface; and
    3. A speed that provides the maneuvering capability specified in 
Sec.  25.143(h).
    (c') In icing conditions with the ``Takeoff Ice'' accretion defined 
in appendix C to part 25, V2 may not be less than--
    1. The V2 speed determined in non-icing conditions.
    2. A speed that provides the maneuvering capability specified in 
Sec.  25.143(h).
    (g) In non-icing conditions, VFTO, in terms of 
calibrated airspeed, must be selected by the applicant to provide at 
least the gradient of climb required by Sec.  25.121(c), but may not be 
less than--
    1. 1.18 VSR; and
    2. A speed that provides the maneuvering capability specified in 
Sec.  25.143(h).
    (g') In icing conditions with the ``Final Takeoff Ice'' accretion 
defined in appendix C to part 25, VFTO may not be less 
than--
    1. The VFTO speed determined in non-icing conditions.
    2. A speed that provides the maneuvering capability specified in 
Sec.  25.143(h).
    5. In lieu of Sec. Sec.  25.121(b)(2)(ii)(A), 25.121(c)(2)(ii)(A), 
and 25.121(d)(2)(ii), the following apply:
    Sec.  25.121 Climb: One-engine inoperative:
    (b) Takeoff; landing gear retracted. In the takeoff configuration 
existing at the point of the flight path at which the landing gear is 
fully retracted, and in the configuration used in Sec.  25.111, but 
without ground effect,
    * * *
    2. The requirements of subparagraph (b)(1) of this section must be 
met:
    * * *
    (ii) In icing conditions with the ``Takeoff Ice'' accretion defined 
in appendix C of part 25, if in the configuration of Sec.  25.121(b) 
with the ``Takeoff Ice'' accretion:
    (A) The V2 speed scheduled in non-icing conditions does 
not provide the maneuvering capability specified in Sec.  25.143(h) for 
the takeoff configuration; or
    (c) Final takeoff. In the en route configuration at the end of the 
takeoff path determined in accordance with Sec.  25.111:
    * * *
    2. The requirements of subparagraph (c)(1) of this section must be 
met:
    * * *
    (ii) In icing conditions with the ``Final Takeoff Ice'' accretion 
defined in appendix C of part 25, if:
    (A) The VFTO speed scheduled in non-icing conditions 
does not provide the maneuvering capability specified in Sec.  
25.143(h) for the en route configuration; or
    (d) Approach. In a configuration corresponding to the normal all-
engines operating procedure in which VSR for this 
configuration does not exceed 110 percent of the VSR for the 
related all-engines-operating landing configuration:
* * * * *
    2. The requirements of sub-paragraph (d)(1) of this section must be 
met:
* * * * *
    (ii) In icing conditions with the ``Approach Ice'' accretion 
defined in appendix C to part 25, in a configuration corresponding to 
the normal all-engines-operating procedure in which VMIN1g 
for this configuration does not exceed 110% of the VMIN1g 
for the related all engines-operating landing configuration in icing, 
with a climb speed established with normal landing procedures, but not 
more than 1.4 VSR (VSR determined in non-icing 
conditions).
    6. In lieu of Sec.  25.123 (b)(2)(i), the following applies:
    Sec.  25.123 En route flight paths:
    (b) The one-engine-inoperative net flight path data must represent 
the actual climb performance diminished by a gradient of climb of 1.1 
percent for two-engine airplanes, 1.4 percent for three-engine 
airplanes, and 1.6 percent for four-engine airplanes.
* * * * *
    2. In icing conditions with the ``En route Ice'' accretion defined 
in appendix C to part 25 if:

[[Page 22219]]

    (i) The minimum en route speed scheduled in non-icing conditions 
does not provide the maneuvering capability specified in Sec.  
25.143(h) for the en route configuration, or
    7. In lieu of Sec.  25.125(b)(2)(ii)(B) and Sec.  
25.125(b)(2)(ii)(C), the following applies:
    Sec.  25.125 Landing.
    (b) In determining the distance in (a):
* * * * *
    2. A stabilized approach, with a calibrated airspeed of not less 
than VREF, must be maintained down to the 50-foot height.
* * * * *
    (ii) In icing conditions, VREF may not be less than:
    (A) The speed determined in sub-paragraph (b)(2)(i) of this 
section;
    (B) A speed that provides the maneuvering capability specified in 
Sec.  25.143(h) with the ``Landing Ice'' accretion defined in appendix 
C to part 25.
    8. In lieu of Sec.  25.143(j), the following applies:
    Sec.  25.143 General.
    (j) For flight in icing conditions--before the ice protection 
system has been activated and is performing its intended function--the 
following requirements apply:
    (1) If activating the ice protection system depends on the pilot 
seeing a specified ice accretion on a reference surface (not just the 
first indication of icing), the requirements of Sec.  25.143 apply with 
the ice accretion defined in part II(e) of appendix C to part 25.
    (2) For other means of activating the ice protection system, it 
must be demonstrated in flight with the ice accretion defined in part 
II(e) of appendix C to part 25 that:
    (i) The airplane is controllable in a pull-up maneuver up to 1.5 g 
load factor or lower if limited by AOA protection; and
    (ii) There is no reversal of pitch control force during a pushover 
maneuver down to 0.5 g load factor.
    9. In lieu of Sec.  25.207, ``Stall warning,'' to read as the 
requirements defined in Part I of these special conditions.

    Issued in Renton, Washington, on May 8, 2018.
Victor Wicklund,
Manager, Transport Standards Branch, Policy and Innovation Division, 
Aircraft Certification Service.
[FR Doc. 2018-10168 Filed 5-11-18; 8:45 am]
 BILLING CODE 4910-13-P