Rule2025-09414
Special Conditions: The Boeing Company Model 777-9 Airplane; Operation Without Normal Electrical Power
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Published
May 23, 2025
Effective
June 23, 2025
Issuing agencies
Transportation DepartmentFederal Aviation Administration
Abstract
These special conditions are issued for the Boeing Company (Boeing) Model 777-9 series airplane. This airplane will have a novel or unusual design feature when compared to the state of technology envisioned in the airworthiness standards for transport category airplanes. This design feature is electrical and electronic systems that perform critical functions, the loss of which could be catastrophic to the airplane. 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.
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<title>Federal Register, Volume 90 Issue 99 (Friday, May 23, 2025)</title>
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[Federal Register Volume 90, Number 99 (Friday, May 23, 2025)]
[Rules and Regulations]
[Pages 22005-22007]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2025-09414]
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Rules and Regulations
Federal Register
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Federal Register / Vol. 90, No. 99 / Friday, May 23, 2025 / Rules and
Regulations
[[Page 22005]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. FAA-2021-0894; Special Conditions No. 25-791A-SC]
Special Conditions: The Boeing Company Model 777-9 Airplane;
Operation Without Normal Electrical Power
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Final special conditions; amendment.
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SUMMARY: These special conditions are issued for the Boeing Company
(Boeing) Model 777-9 series airplane. This airplane will have a novel
or unusual design feature when compared to the state of technology
envisioned in the airworthiness standards for transport category
airplanes. This design feature is electrical and electronic systems
that perform critical functions, the loss of which could be
catastrophic to the airplane. 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 June 23, 2025.
FOR FURTHER INFORMATION CONTACT: Nazih Khaouly, Electrical Systems,
AIR-626A, Technical Policy Branch, Policy and Standards Division,
Aircraft Certification Service, Federal Aviation Administration, 2200
South 216th Street, Des Moines, Washington 98198; telephone 206-231-
3160; email; <a href="/cdn-cgi/l/email-protection#82ece3f8ebeaace9eae3edf7eefbc2e4e3e3ace5edf4"><span class="__cf_email__" data-cfemail="711f100b18195f1a19101e041d08311710105f161e07">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION:
Background
On September 30, 2018, Boeing applied for an amendment to Type
Certificate No. T00001SE to include the new Model 777-9 series
airplane. The Boeing Model 777-9 airplane, which is a derivative of the
Boeing Model 777 airplane currently approved under Type Certificate No.
T00001SE, is a twin-engine, transport category airplane with seating
for 495 passengers, and a maximum takeoff weight of 775,000 lbs.
On September 29, 2021, special conditions (No. 25-791-SC) were
issued for this design feature and became effective on October 4, 2021
(86 FR 54588, Oct. 4, 2021).
Type Certification Basis
Under the provisions of title 14, Code of Federal Regulations (14
CFR) 21.101, Boeing must show that the Model 777-9 series airplane
meets the applicable provisions of the regulations listed in Type
Certificate No. T00001SE, or the applicable regulations in effect on
the date of application for the change, except for earlier amendments
as agreed upon by the FAA.
If the Administrator finds that the applicable airworthiness
regulations (e.g., 14 CFR part 25) do not contain adequate or
appropriate safety standards for the Boeing Model 777-9 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, or should any other model already included on
the same type certificate be modified to incorporate 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 Boeing Model 777-9 series 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.
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. 21.101.
Novel or Unusual Design Features
The Boeing Model 777-9 series airplane will incorporate the
following novel or unusual design feature:
Electrical and electronic systems that perform critical functions,
the loss of which may result in loss of flight controls and other
critical systems and may be catastrophic to the airplane.
Discussion
The Boeing Model 777-9 series airplane has a fly-by-wire flight
control system that requires a continuous source of electrical power in
order to maintain an operable flight control system. Section
25.1351(d), ``Operation without normal electrical power,'' requires
safe operation in visual flight rule (VFR) conditions for at least 5
minutes after the loss of normal electrical power excluding the
battery. This rule is structured around a traditional design using
mechanical control cables and linkages for flight control. These manual
controls allow the crew to maintain aerodynamic control of the airplane
for an indefinite period of time after loss of all electrical power.
Under these conditions, a mechanical flight control system provides the
crew with the ability to fly the airplane while attempting to identify
the cause of the electrical failure, restart engine(s) if necessary,
and attempt to re-establish some of the electrical power generation
capability.
A critical assumption in Sec. 25.1351(d) is that the airplane is
in VFR conditions at the time of the failure. This is not a valid
assumption in today's airline operating environment where airplanes fly
much of the time in instrument meteorological conditions (IMC) on air
traffic control defined flight paths. Another assumption in the
existing rule is that the loss of all normal electrical power is the
result of the loss of all engines. The 5-minute period in the rule is
to allow at least one engine to be restarted following an all-engine
power loss in order to continue the flight to a safe landing. However,
service experience on airplane models with similar electrical power
system architecture as the Boeing Model 777-9 airplane has shown that
at least the temporary loss of all electrical power for causes other
than all-engine failure is not extremely improbable.
To maintain the same level of safety envisioned by the existing
rule with
[[Page 22006]]
traditional mechanical flight controls, the Boeing Model 777-9 series
airplane design must not be time-limited in its operation under all
reasonably foreseeable conditions, including loss of all normal sources
of engine or auxiliary power unit (APU)-generated electrical power.
Unless Boeing can show that the non-restorable loss of the engine and
APU power sources is extremely improbable, Boeing must demonstrate that
the airplanes can maintain safe flight and landing (including steering
and braking on the ground for airplanes using steer/brake-by-wire and/
or fly-by-wire speed brake panels) with the use of its emergency/
alternate electrical power systems. These electrical power systems, or
the minimum restorable electrical power sources, must be able to power
loads that are essential for continued safe flight and landing,
including those required for the maximum length of approved flight
diversion.
The FAA is amending two paragraphs from the original special
conditions. Those paragraphs are (d)(2) and (e)(4). Paragraph (d)(2) of
the original special conditions states that the operating limitations
section of the airplane flight manual (AFM) must incorporate non-normal
procedures that direct the pilot to take appropriate actions to
activate the APU after loss of normal engine-driven generated
electrical power. The FAA is requiring that these non-normal procedures
be incorporated in the AFM instead of requiring them to be in the
operating limitations section of the AFM.
Paragraph (e)(4) of the original special conditions states that the
airplane must provide adequate indication of loss of normal electrical
power to direct the pilot to the non-normal procedures, and the
operating limitations section of the AFM must incorporate non-normal
procedures that will direct the pilot to take appropriate actions. As
in paragraph (d)(2), the FAA is requiring that these non-normal
procedures be incorporated in the AFM instead of specifying the
particular section of the AFM that these procedures need to reside.
These are to remedy an oversight that occurred during the issuance
of the original special conditions where the FAA inadvertently required
the non-normal procedures to be in the limitations section of the AFM.
The FAA found that this requirement is inconsistent with similarly
issued special conditions for other transport category airplanes. The
Boeing 777-9 electrical power system does not require pilot activation
of the APU after loss of normal engine-driven generated electrical
power. Paragraph (d) does not apply to designs that do not rely on the
APU for an alternate source of power. The intent of paragraphs (d)(2)
and (e)(4) is to ensure that non-normal procedures that provide
instructions to the pilot to take appropriate action are incorporated
into the AFM. These procedures are more appropriate for the operating
procedures section of the AFM and were not intended to be an operating
limitation.
The 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
To provide the public with an opportunity to comment on this
amendment, the FAA issued Notice of Proposed Special Conditions No. 25-
791-SC for the Boeing Company Model 777-9 series airplane, which was
published in the Federal Register on August 2, 2024 (89 FR 63111).
The FAA received responses from two commenters.
An individual requested that the FAA not issue this amendment,
stating that the company should not receive special treatment. The
FAA's special conditions process is established by regulation and is
available to all applicants. FAA made no change as a result of this
comment.
The Air Line Pilots Association (ALPA) commented that after
reviewing the FAA's proposal to change two paragraphs of this special
condition, ALPA does not support design features which increase the
psychological and workload burden on flightcrew to recover the supply
of the electrical generation and distribution system to the aircraft
through manual activation of the APU, in addition to the required
multiple start attempt to the engines.
The FAA does not agree that the special conditions, as now amended,
require design features that would increase the psychological and
workload burden on the flightcrew in order to recover the supply
electrical generation and distribution system to the aircraft. Special
conditions are issued by the FAA when a proposed aircraft, aircraft
engine, or propeller incorporates a design feature that is novel or
unusual, i.e., it was not envisaged by the existing design regulations.
Aircraft were originally designed using mechanical cables and linkages
to control flight surfaces. Modern aircraft use fly-by-wire designs to
incorporate enhanced flight envelope protections to increase safety
over the earlier mechanical flight control designs. The FAA's
generally-applicable design standard for operation of transport
airplanes that lack electrical power, 14 CFR 25.1351, envisaged
mechanical flight control systems, therefore the FAA issues special
conditions to address modern fly-by-wire aircraft designs.
Boeing 777-9 Special Conditions No. 25-791-SC, as originally
issued, includes procedures for pilot manual activation of the APU
after loss of normal engine-driven generated electrical power. This
procedure is performed by the pilot, while the flight controls are
operating on battery power to ensure APU electrical power is available
for the flight controls until engine-driven electrical power is
restored. Therefore, these revised special conditions do not change the
flightcrew burden but instead remove the prior requirement that the
procedure be in the Limitations section of the airplane flight manual
(AFM). Activation of the APU after loss of normal engine-driven
generated electrical power is a non-normal pilot procedure, which is
properly in the procedures rather than limitations section. Therefore,
this amendment only changes the location in the AFM for this procedure
from the Limitations section to the Non-Normal section and removes the
requirement for the procedure to be in the Limitation section.
The FAA has also restored the statement that these special
conditions are in lieu of 14 CFR 25.1351(d); this statement was
inadvertently left out of the notice but was part of the original
special conditions.
The special conditions are adopted as proposed with the edit as
mentioned above.
Applicability
As discussed above, these special conditions, as amended, are
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 feature, these
special conditions would apply to the other model as well.
Conclusion
This action affects only a certain novel or unusual design feature
on one model series of airplane. It is not a rule of general
applicability.
[[Page 22007]]
List of Subjects in 14 CFR Part 25
Aircraft, Aviation safety, Reporting and recordkeeping
requirements.
Authority Citation
The authority citation for these special conditions is as follows:
Authority: 49 U.S.C. 106(f), 106(g), 40113, 44701, 44702, 44704.
The Special Conditions
Accordingly, the Federal Aviation Administration (FAA) issues the
following special conditions, as amended, as part of the type
certification basis for The Boeing Company Model 777-9 series
airplanes.
In lieu of 14 CFR 25.1351(d), the following special conditions
apply:
(a) The applicant must show by test or a combination of test and
analysis that the airplane is capable of continued safe flight and
landing with all normal electrical power sources inoperative, as
prescribed by paragraphs (a)(1) and (a)(2), below. For purposes of
these special conditions, normal sources of electrical power generation
do not include any alternate power sources such as the battery, ram air
turbine, or independent power systems such as the flight control
permanent magnet generating system. In showing capability for continued
safe flight and landing, the applicant must account for systems
capability, effects on crew workload and operating conditions, and the
physiological needs of the flightcrew and passengers for the longest
diversion time for which the applicant is seeking approval.
(1) In showing compliance with this requirement, the applicant must
account for common-cause failures, cascading failures, and zonal
physical threats.
(2) The applicant may consider the ability to restore operation of
portions of the electrical power generation and distribution system if
it can be shown that unrecoverable loss of those portions of the system
is extremely improbable. The design must provide an alternative source
of electrical power for the time required to restore the minimum
electrical power generation capability required for safe flight and
landing. The applicant may exclude unrecoverable loss of all engines
when showing compliance with this requirement.
(b) Regardless of any electrical generation and distribution system
recovery capability shown under paragraph (a) of these special
conditions, sufficient electrical system capability must be provided
to:
(1) Allow time to descend, with all engines inoperative, at the
speed that provides the best glide distance, from the maximum operating
altitude to the top of the engine restart envelope; and
(2) Subsequently allow multiple start attempts of the engines and
auxiliary power unit (APU). The design must provide this capability in
addition to the electrical capability required by existing part 25
requirements related to operation with all engines inoperative.
(c) The airplane emergency electrical power system must be designed
to supply:
(1) Electrical power required for immediate safety, which must
continue to operate without the need for crew action following the loss
of the normal electrical power, for a duration sufficient to allow
reconfiguration to provide a non-time-limited source of electrical
power.
(2) Electrical power required for continued safe flight and landing
for the maximum diversion time.
(d) If the applicant uses APU-generated electrical power to satisfy
the requirements of these special conditions, and if reaching a
suitable runway for landing is beyond the capacity of the battery
systems, then the APU must be able to be started under any foreseeable
flight condition prior to the depletion of the battery or the
restoration of normal electrical power, whichever occurs first. Flight
test must demonstrate this capability at the most critical condition.
(1) The applicant must show that the APU will provide adequate
electrical power for continued safe flight and landing.
(2) The airplane flight manual (AFM) must incorporate non-normal
procedures that direct the pilot to take appropriate actions to
activate the APU after loss of normal engine-driven generated
electrical power.
(e) As part of showing compliance with these special conditions,
the tests to demonstrate loss of all normal electrical power must also
take into account the following:
(1) The assumption that the failure condition occurs during night
instrument meteorological conditions (IMC) at the most critical phase
of the flight, relative to the worst possible electrical power
distribution and equipment-loads-demand condition.
(2) After the un-restorable loss of normal engine generator power,
the airplane engine restart capability is provided, and operations
continued in IMC.
(3) The airplane is demonstrated to be capable of continued safe
flight and landing. The length of time must be computed based on the
maximum diversion time capability for which the airplane is being
certified. The applicant must account for airspeed reductions resulting
from the associated failure or failures.
(4) The airplane must provide adequate indication of loss of normal
electrical power to direct the pilot to the non-normal procedures, and
the AFM must incorporate non-normal procedures that will direct the
pilot to take appropriate actions.
Issued in in Kansas City, Missouri, on May 20, 2025.
Patrick R. Mullen,
Manager, Technical Policy Branch, Policy and Standards Division,
Aircraft Certification Service.
[FR Doc. 2025-09414 Filed 5-22-25; 8:45 am]
BILLING CODE 4910-13-P
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