Document ID: FAA-2020-0686-0001
Agency: faa
Document Type: Proposed Rule
Title: Airworthiness Directives: The Boeing Company Airplanes
Posted Date: 2020-08-06T04:00Z

[Federal Register Volume 85, Number 152 (Thursday, August 6, 2020)]
[Proposed Rules]
[Pages 47698-47712]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2020-17221]

 ========================================================================
 Proposed Rules
                                                 Federal Register
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 This section of the FEDERAL REGISTER contains notices to the public of 
 the proposed issuance of rules and regulations. The purpose of these 
 notices is to give interested persons an opportunity to participate in 
 the rule making prior to the adoption of the final rules.
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  Federal Register / Vol. 85, No. 152 / Thursday, August 6, 2020 / 
Proposed Rules  

[[Page 47698]]

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2020-0686; Product Identifier 2019-NM-035-AD]
RIN 2120-AA64

Airworthiness Directives; The Boeing Company Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: The FAA proposes to supersede Airworthiness Directive (AD) 
2018-23-51, which applies to all The Boeing Company Model 737-8 and 
737-9 (737 MAX) airplanes. Since AD 2018-23-51 was issued, the agency 
has determined that final corrective action is necessary to address the 
unsafe condition. This proposed AD would require installing new flight 
control computer (FCC) software, revising the existing Airplane Flight 
Manual (AFM) to incorporate new and revised flightcrew procedures, 
installing new MAX display system (MDS) software, changing the 
horizontal stabilizer trim wire routing installations, completing an 
angle of attack sensor system test, and performing an operational 
readiness flight. This proposed AD would also apply to a narrower set 
of airplanes than the superseded AD, and allow operation (dispatch) of 
an airplane with certain inoperative systems only if certain provisions 
are incorporated in the operator's existing FAA-approved minimum 
equipment list (MEL). The FAA is proposing this AD to address the 
unsafe condition on these products.

DATES: The FAA must receive comments on this proposed AD by September 
21, 2020.

ADDRESSES: You may send comments, using the procedures found in 14 CFR 
11.43 and 11.45, by any of the following methods:
     Federal eRulemaking Portal: Go to https://www.regulations.gov. Follow the instructions for submitting comments.
     Fax: 202-493-2251.
     Mail: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue SE, Washington, DC 20590.
     Hand Delivery: Deliver to Mail address above between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    For Boeing service information identified in this NPRM, contact 
Boeing Commercial Airplanes, Attention: Contractual & Data Services 
(C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-5600; 
telephone 562-797-1717; internet https://www.myboeingfleet.com. You may 
view this referenced service information at the FAA, Airworthiness 
Products Section, Operational Safety Branch, 2200 South 216th St., Des 
Moines, WA. For information on the availability of this material at the 
FAA, call 206-231-3195. It is also available in the Docket for this 
rulemaking, which may be found on the internet at https://www.regulations.gov by searching for and locating Docket No. FAA-2020-
0686.

Examining the AD Docket

    You may examine the AD docket on the internet at https://www.regulations.gov by searching for and locating Docket No. FAA-2020-
0686; or in person at Docket Operations between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays. The AD docket contains 
this NPRM, any comments received, and other information. The street 
address for Docket Operations is listed above. Comments will be 
available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT: Ian Won, Manager, Seattle ACO Branch, 
FAA, 2200 South 216th St., Des Moines, WA 98198; phone and fax: 206-
231-3500; email: 9-FAA-SACO-AD-Inquiry@faa.gov.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites you to participate in this rulemaking by submitting 
written comments, data, or views about this proposal. The most helpful 
comments reference a specific portion of the proposal, explain the 
reason for any recommended change, and include supporting data. To 
ensure the docket does not contain duplicate comments, commenters 
should submit only one copy of the comments. Send your comments to an 
address listed under the ADDRESSES section. Include ``Docket No. FAA-
2020-0686; Product Identifier 2019-NM-035-AD'' at the beginning of your 
comments.
    Except for Confidential Business Information (CBI) as described in 
the following paragraph, and other information as described in 14 CFR 
11.35, the FAA will post all comments received, without change, as well 
as a report summarizing each substantive public contact with FAA 
personnel concerning this proposed rulemaking. Before acting on this 
proposal, the FAA will consider all comments received by the closing 
date for comments. The FAA will consider comments filed after the 
comment period has closed if it is possible to do so without incurring 
expense or delay. The FAA may change this NPRM because of those 
comments.

Confidential Business Information (CBI)

    CBI is commercial or financial information that is both customarily 
and actually treated as private by its owner. Under the Freedom of 
Information Act (FOIA) (5 U.S.C. 552), CBI is exempt from public 
disclosure. If comments responsive to this NPRM contain commercial or 
financial information that is customarily treated as private, that you 
actually treat as private, and that is relevant or responsive to this 
NPRM, it is important that you clearly designate the submitted comments 
as CBI. Please mark each page of your submission containing CBI as 
``PROPIN.'' The FAA will treat such marked submissions as confidential 
under the FOIA, and they will not be placed in the public docket of 
this NPRM. Submissions containing CBI should be sent to the person 
identified in the FOR FURTHER INFORMATION CONTACT section. Any 
commentary that the FAA receives which is not specifically designated 
as CBI will be placed in the public docket for this rulemaking.

Background

    On October 29, 2018, a Boeing Model 737-8 airplane operated by Lion 
Air (Lion Air Flight 610) was involved in an accident after takeoff 
from Soekarno-

[[Page 47699]]

Hatta International Airport in Jakarta, Indonesia, resulting in 189 
fatalities. Investigation of the accident has been completed by the 
Indonesian authorities (Komite Nasional Keselamatan Transportasi 
(KNKT)) with assistance from the National Transportation Safety Board 
(NTSB) and the FAA of the United States, the manufacturer, and the 
operator. Reports \1\ from the accident investigation indicate that the 
airplane's flight control system \2\ generated repeated airplane nose-
down horizontal stabilizer trim \3\ commands contributing to the 
accident.
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    \1\ Preliminary KNKT.18.10.35.04 Aircraft Accident Investigation 
Report, dated November 2018, and Final KNKT.18.10.35.04 Aircraft 
Accident Investigation Report, dated October 2019, can be found in 
the AD docket.
    \2\ The flight control system for 737 MAX airplanes includes two 
flight control computers, FCC A and FCC B, which process inputs from 
the pilots and aircraft sensors to move the airplane's control 
surfaces.
    \3\ An airplane's nose-up or nose-down attitude is known as its 
``pitch attitude.'' On the 737 MAX, the airplane's pitch attitude is 
primarily controlled by a combination of two movable surfaces on the 
tail of the airplane: The horizontal stabilizer, which is controlled 
by electric and manual (pilot) trim inputs, and the elevator, which 
is controlled by moving the control columns. ``Pitch trim'' commands 
move the horizontal stabilizer. Pilots use pitch trim to adjust the 
position of the horizontal stabilizer to achieve the desired flight 
path and to manage the forces necessary to keep the airplane in 
stable flight.
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    Following the Lion Air Flight 610 accident on October 29, 2018, 
data from the flight data recorder, which is contained in the 
Indonesian accident report (http://knkt.dephub.go.id/knkt/ntsc_aviation/baru/2018%20-%20035%20-%20PK-LQP%20Final%20Report.pdf), 
indicated that a single erroneously high angle of attack (AOA) sensor 
\4\ input to the flight control system while the flaps are retracted 
can cause repeated airplane nose-down trim of the horizontal stabilizer 
and multiple flightdeck effects.
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    \4\ The angle of attack (or AOA) is the angle at which the 
airplane wing meets the oncoming air. On the current 737 MAX, AOA is 
measured by two independent AOA sensors, which are small vanes 
mounted on either side of the forward exterior of the fuselage. For 
the purposes of this NPRM, ``high'' AOA is a relatively large angle 
(associated with flight conditions outside of the normal flight 
envelope), and ``low'' AOA is a relatively small angle (associated 
with flight conditions within the normal flight envelope). Although 
wing lift increases with increased AOA, an excessively high airplane 
nose-up AOA can be hazardous, since eventually lift can be lost, 
causing the airplane to stall. A stall occurs when the airflow 
around the wing is sufficiently disrupted to cause the wing to no 
longer generate lift. To warn of an impending stall, the 737 MAX is 
equipped with a ``stick shaker,'' which vibrates the control column, 
providing tactile annunciation to the pilot.
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    These effects include stall warning activation, airspeed disagree 
alert, and altitude disagree alert,\5\ and may affect the flightcrew's 
ability to accomplish continued safe flight and landing.
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    \5\ Stall warning indication is the activation of the stick 
shaker and other warnings. An airspeed disagree alert, or ``IAS 
(indicated airspeed) DISAGREE'' on the 737 MAX, is a visual alert on 
the airplane's primary flight displays (PFDs) that the airspeed 
displayed on the captain's and first officer's PFDs, as sensed by 
the pitot tubes on either side of the airplane, disagree by more 
than 5 knots for more than 5 seconds. An altitude disagree alert, or 
``ALT (altitude) DISAGREE'' on the 737 MAX, is a visual alert on the 
PFDs that the altitude, as sensed by the static ports on either side 
of the airplane, disagree by more than 200 feet for more than 5 
seconds.
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    On November 7, 2018, the FAA issued Emergency AD 2018-23-51 as an 
interim corrective action.\6\ The FAA sent Emergency AD 2018-23-51 to 
all known U.S. owners and operators of Boeing Model 737 MAX airplanes 
to require revising certificate limitations and operating procedures of 
the AFM to provide the flightcrew with runaway horizontal stabilizer 
trim procedures to follow under certain conditions. The FAA sent 
Emergency AD 2018-23-51 to all affected civil aviation authorities 
(CAAs) at the same time. AD 2018-23-51, Amendment 39-19512 (83 FR 
62697, December 6, 2018; corrected December 11, 2018 (83 FR 63561)), 
was published in the Federal Register as an amendment to 14 CFR 39.13.
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    \6\ Flight data recorder (FDR) data from the Lion Air Flight 610 
accident airplane indicated that on the flight just prior to the 
accident flight (Lion Air Flight 043), the airplane experienced the 
same single erroneously high AOA sensor failure condition upon 
takeoff that the Lion Air Flight 610 crew encountered. The 
flightcrew on Lion Air Flight 043 was able to maintain continued 
safe flight and land at their planned destination airport in 
Jakarta. The flightcrew on Lion Air Flight 043 had no prior 
awareness of this type of failure or how to respond to it. The FAA's 
review of these flights and associated risk assessments provided the 
basis for the revised pilot procedures contained in the interim 
action of the FAA's emergency AD; specifically, the rationale was 
that if pilots were provided awareness of the airplane and 
flightdeck effects of this specific failure scenario and were 
provided appropriate instructions via the emergency AD, this would 
enable appropriate pilot response to the erroneously high AOA 
failure scenario for the period of time needed to fully eliminate 
this unsafe condition with a software revision to the flight control 
computers.
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    On March 10, 2019, a Boeing Model 737-8 airplane operated by 
Ethiopian Airlines (Ethiopian Airlines Flight 302) was involved in an 
accident after takeoff from Addis Ababa Bole International Airport in 
Addis Ababa, Ethiopia, resulting in 157 fatalities. The accident is 
under investigation by the Ethiopian Accident Investigation Bureau 
(EAIB) with assistance from the NTSB and the FAA of the United States, 
the French Bureau of Enquiry and Analysis for Civil Aviation Safety 
(BEA), the European Union Aviation Safety Agency (EASA), the 
manufacturer, the operator, and the Ethiopian Civil Aviation Authority 
(ECAA).
    The data from the flight data recorders, as summarized in reports 
\7\ of the Ethiopian Airlines Flight 302 accident and the Lion Air 
Flight 610 accident, indicated that if a single erroneously high AOA 
sensor input is received by the flight control system, the maneuvering 
characteristics augmentation system (MCAS) \8\ can command repeated 
airplane nose-down trim of the horizontal stabilizer. This unsafe 
condition, if not addressed, could cause the flightcrew to have 
difficulty controlling the airplane, and lead to excessive airplane 
nose-down attitude, significant altitude loss, and impact with terrain.
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    \7\ Ethiopian Aircraft Accident Investigation Preliminary Report 
AI-01/19, dated March 2019, and the Ethiopian Interim Investigation 
Report of accident MAX-8 ET-AVJ, ET-302, dated March 2020, can be 
found in the AD docket.
    \8\ MCAS is a function of the Speed Trim System (STS), which is 
part of the airplane's flight control system. The STS provides 
automatic trim inputs to the horizontal stabilizer during manual 
flight. The STS uses data from a variety of sources, such as pitot 
tubes and the AOA sensors, to calculate when to make commands. MCAS 
is activated only during manual flight, with flaps up, and when the 
AOA sensors detect that the airplane is flying with a high AOA, such 
as when climbing aggressively or performing excessively tight turns 
with high bank angles. MCAS makes pitch trim commands to the 
horizontal stabilizer during a high AOA event so that the 737 MAX 
handling qualities are compliant with FAA regulations (including 14 
CFR 25.173).
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    To address the unsafe condition, the FAA proposes to require four 
design changes: (1) Installing updated flight control software (with 
new control laws) for the FCC operational program software (OPS), (2) 
installing updated MDS display processing computer (DPC) software to 
generate an AOA disagree alert,\9\ (3) revising certain AFM flightcrew 
operating procedures, and (4) changing the routing of horizontal 
stabilizer trim wires. The first design change is intended to prevent 
erroneous MCAS activation. The second design change alerts the pilots 
that the airplane's two AOA sensors are disagreeing by a certain amount 
indicating a potential AOA sensor failure. The third design change is 
intended to ensure that the flightcrew has the means to recognize and 
respond to erroneous stabilizer movement and the effects of a potential 
AOA sensor failure. The fourth design change is intended to restore 
compliance with the FAA's latest wire separation safety standards.
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    \9\ An AOA disagree alert, or ``AOA DISAGREE'' on the 737 MAX, 
is a visual alert on the airplane's PFDs that alerts the flightcrew 
of a disagreement between the angles of attack measured by each of 
the airplane's two AOA sensors.
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    In addition to these four design changes, the FAA also proposes to

[[Page 47700]]

require operators to conduct an AOA sensor system test and perform an 
operational readiness flight prior to returning each airplane to 
service. Finally, operators with an existing FAA-approved MEL would be 
required to incorporate more restrictive provisions to dispatch the 
airplane with certain inoperative equipment. The new master minimum 
equipment list (MMEL), approved by the FAA, was published on April 10, 
2020, after undergoing a public notice and comment process.

Proposed Design Changes

    The FAA proposes mandating the following changes to the 737 MAX 
type design, to address the various aspects of the unsafe condition.
    To ensure that an erroneous signal from a failed single AOA sensor 
does not prevent continued safe flight and landing, and specifically 
that it does not generate erroneous MCAS activation, the FAA proposes 
to require installation of updated FCC software with revised flight 
control laws \10\ associated with MCAS. These revised flight control 
laws would use inputs from both AOA sensors to activate MCAS. This is 
in contrast to the original MCAS design, which relied on data from only 
one sensor at a time, and allowed repeated MCAS activation as a result 
of input from a single AOA sensor.
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    \10\ A flight control law generates commands to move flight 
control surfaces based on inputs from the flightcrew and sensors on 
the airplane. Flight control laws reside in software, and are 
developed to generate commands from the flight control computers 
that will achieve desired airplane performance.
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    The updated FCC software would also compare the inputs from the two 
sensors to detect a failed AOA sensor. If the difference between the 
AOA sensor inputs is above a calculated threshold,\11\ the FCC would 
disable the speed trim system (STS), including its MCAS function, for 
the remainder of that flight, and provide a corresponding indication of 
such deactivation on the flight deck.
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    \11\ The calculated threshold would be a function of the 
magnitude of the disagreement and the rate of change of the AOA 
sensor position values.
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    To ensure that MCAS will not command repeated movements of the 
horizontal stabilizer, the revised flight control laws would permit 
only one activation of MCAS per sensed high AOA event. A subsequent 
activation of MCAS would be possible only after the airplane returns to 
a low AOA state, below the threshold that would cause MCAS activation.
    The updated FCC software would also limit \12\ the magnitude of any 
MCAS command to move the horizontal stabilizer, such that the final 
horizontal stabilizer position (after the MCAS command) would preserve 
the flightcrew's ability to control the airplane pitch by using only 
the control column. The original design allowed MCAS commands to be 
made without consideration of the horizontal stabilizer position--
before or after the MCAS command.
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    \12\ The magnitude of the command varies according to parameters 
such as the airplane's altitude and airspeed, and would be limited 
such that after the command is made, the pilot would be able to 
maintain level flight, climb, and descend, using control column 
inputs only.
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    An undesired MCAS activation could prompt the flightcrew to perform 
a non-normal procedure. To ensure that after any foreseeable failure of 
the stabilizer system, safe flight is not dependent on the timeliness 
of the flightcrew performing a non-normal procedure, the FAA proposes 
multiple changes.
    First, as previously discussed, the flight control laws would be 
changed to instead use inputs from two AOA sensors for MCAS activation, 
so that there would not be an undesired MCAS activation due to a single 
AOA sensor failure that could lead a flightcrew to perform a non-normal 
procedure.
    Second, in the event that MCAS is activated as intended (i.e., 
during a high AOA event), the updated flight control laws software 
would limit the number of MCAS activations to one per high AOA event, 
and limit the magnitude of any single activation so that the flightcrew 
could maintain pitch control without needing to perform a non-normal 
procedure.
    The FAA also proposes requiring an additional software update that 
would alert the flightcrew to a disagreement between the two AOA 
sensors. This disagreement indicates certain AOA sensor failures or a 
significant calibration issue. The updated MDS software would implement 
an AOA DISAGREE alert on all 737 MAX airplanes. Some 737 MAX airplanes 
were delivered without this alert feature, by error. While the lack of 
an AOA DISAGREE alert is not an unsafe condition itself, the FAA is 
proposing to mandate this software update to restore compliance with 14 
CFR 25.1301 and because the flightcrew procedures mandated by this AD 
now rely on this alert to guide flightcrew action. As a result of the 
changes proposed in this AD, differences between the two AOA sensors 
greater than a certain threshold \13\ would cause an AOA DISAGREE alert 
on the primary flight displays (PFDs).
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    \13\ More than 10 degrees difference for more than 10 seconds.
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    Also, as a result of the installation of this revised MDS software, 
operators would be required to remove ``INOP'' markers, if present, 
from the electronic flight instrument system (EFIS) panel of the 
airplane, because the markers would no longer be necessary, due to 
other changes in the updated MDS software that are unrelated to this 
unsafe condition. These markers, labeled ``INOP,'' indicate that one of 
the positions on the dial that selects display settings is inoperative.
    To facilitate the flightcrew's ability to recognize and respond to 
undesired horizontal stabilizer movement and the effects of a potential 
AOA sensor failure, the FAA proposes to mandate revising and adding 
certain operating procedures (checklists) of the AFM \14\ used by the 
flightcrew for the 737 MAX. All transport category airplanes have non-
normal checklists to aid the pilots in responding to airplane failures.
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    \14\ The AFM is an FAA-approved document that manufacturers are 
required to furnish to owners upon delivery of the airplane, and 
that provides necessary safety information. See 14 CFR 25.1581. This 
information includes procedures (emergency and non-normal) for 
foreseeable but unusual situations that necessitate flightcrew 
action. See 14 CFR 25.1585. These procedures provide the flightcrew 
with instructions, including checklists, on how to respond to these 
conditions. Some of these conditions require immediate action by the 
flightcrew, so some checklists identify certain tasks that the 
flightcrew is expected to accomplish from memory; these items are 
commonly known as memory steps or ``recall'' items. Other conditions 
have checklists that do not need to be memorized; these items are 
commonly known as ``reference'' items.
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    The following is a general description of the changes that would be 
made to these checklists,\15\ and the purpose of each change. The FAA 
will conduct an operational evaluation before finalizing these 
checklists. (See Flightcrew Training section in this preamble for 
further information.)
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    \15\ All of the checklists that the FAA proposes to revise or 
add to the AFM are already part of Boeing's Quick Reference 
Handbook, or QRH, for the 737 MAX (except for the IAS Disagree 
checklist, which is new to both the AFM and the QRH). The QRH is a 
nonregulatory tool used by flightcrews that includes information for 
non-normal and emergency conditions, including AFM procedures.
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    To reduce the workload on the flightcrew when they suspect that the 
airspeed indications are unreliable, the FAA proposes to revise the 
Airspeed Unreliable checklist of the AFM. This checklist would be 
revised to (1) add a step to allow the flightcrew to determine a 
reliable airspeed indication without the use of reference tables, (2) 
improve the procedure for go-arounds to allow for increased use of 
automation, (3) add a step to ensure that erroneous altitude 
information is not transmitted via the transponder to air traffic 
control (ATC), and (4) add erroneous AOA as a

[[Page 47701]]

potential cause for unreliable airspeed conditions.
    The Runaway Stabilizer checklist of the AFM is used when there is 
undesired movement of the airplane's horizontal stabilizer. The FAA 
proposes revisions to the criteria for this checklist's use, to include 
when uncommanded horizontal stabilizer movement occurs continuously or 
in a manner not appropriate for current flight conditions. The revised 
checklist would include an explicit recall item that instructs the 
flightcrew to use their thumb-actuated trim switch to reduce forces on 
the control column. The checklist would also include a recall item to 
use the control column and thrust levers to control the airplane's 
pitch attitude and airspeed. Finally, the checklist would be revised to 
add a reference item to manually trim the horizontal stabilizer for 
pitch control, and note that a two-pilot effort may be used to correct 
an out-of-trim condition.
    The Stabilizer Trim Inoperative checklist of the AFM would be 
revised to better align with the other non-normal checklists, and 
modified to provide guidance for manually trimming the stabilizer for 
pitch control, noting that a two-pilot effort may be used and will not 
cause system damage.
    As previously discussed, one of the design changes proposed by this 
NPRM is a flight control law that would render the STS and MCAS 
functions inoperative if the airplane's AOA sensors disagree. To assist 
the flightcrew in properly responding to such an occurrence, a non-
normal checklist, called the Speed Trim Fail checklist, would be added 
to the AFM. This checklist would be used when the STS and MCAS 
functions are inoperative, and inform the flightcrew to continue normal 
operation. It would also note that the STS will not provide horizontal 
stabilizer trim inputs when the airplane deviates from its trimmed 
airspeed.
    The FAA proposes adding the Stabilizer Out of Trim checklist to the 
AFM. The Stabilizer Out of Trim checklist would be used when the 
autopilot does not set the horizontal stabilizer trim correctly. Under 
the current design, the STAB OUT OF TRIM light illuminates in flight to 
inform the flightcrew that the airplane's autopilot is not setting the 
horizontal stabilizer trim correctly. Under the new design, as part of 
the aforementioned FCC software update, this light will now also 
illuminate on the ground, to inform the flightcrew of a partial failure 
of a flight control computer. If the airplane is on the ground, the 
checklist will instruct the flightcrew to not take off. The checklist 
provides additional information for the flightcrew to use if the 
airplane is in flight.
    The FAA proposes to add an AOA Disagree checklist as a procedure to 
the AFM, because the FAA proposes that the AOA DISAGREE alert be 
available on the PFDs for all 737 MAX airplanes. Therefore, this 
proposed checklist would be used when there is an indication, such as 
an AOA DISAGREE alert, that the airplane's left and right AOA vanes 
disagree. The checklist would inform the flightcrew to accomplish the 
Airspeed Unreliable checklist.
    The FAA proposes to add the ALT Disagree checklist as a procedure 
to the AFM. This checklist is used when the captain's and first 
officer's altitude indicators disagree, generating an ALT DISAGREE 
alert on the airplane's PFDs. This proposed checklist would provide 
procedures to the flightcrew that would initially be driven by whether 
there is also an IAS DISAGREE alert shown on the airplane's PFDs. The 
checklist would also provide additional steps for the flightcrew to 
subsequently complete for the descent, approach, and landing phases of 
flight.
    The final checklist that the FAA proposes to add to the AFM is a 
new IAS Disagree checklist. This checklist is used when captain's and 
first officer's airspeed indicators--their ``indicated airspeed'' or 
``IAS''--disagree. The checklist directs the flightcrew to accomplish 
the Airspeed Unreliable checklist.
    Since this NPRM proposes to supersede AD 2018-23-51, the procedural 
information required by that AD would be outdated when the final rule 
is effective and therefore would be removed.
    As part of the FAA's review of these design changes, the agency 
reviewed the entirety of the 737 MAX horizontal stabilizer control 
system. This review revealed that the physical separation of the 
horizontal stabilizer trim arm wiring and the horizontal stabilizer 
trim control wiring does not meet the criteria specified in 14 CFR 
25.1707. This design standard was promulgated in 2007 and therefore is 
part of the certification basis of the 737 MAX but not of previous 
Boeing Model 737 airplanes. Certain wiring installations must have 
enough physical separation so that a wiring failure cannot create a 
hazard. Since design changes must comply with FAA regulations, the FAA 
proposes to require changes to the wiring installation to meet the 
required physical separation between the horizontal stabilizer trim arm 
wiring and the horizontal stabilizer trim control wiring. The FAA 
proposes this action to bring the airplanes into regulatory compliance.

Proposed Maintenance-Related Actions

    To ensure that each airplane's two AOA sensors are functioning 
properly upon return to service, the FAA proposes to mandate that 
operators perform an AOA sensor system test on each airplane prior to 
its return to service. This test uses a fixture to position the AOA 
vane and verify that the reading provided by each AOA sensor is 
accurate.
    The FAA allows operators to utilize an MEL for time-limited 
operation with certain equipment inoperative, after which the system 
must be fully restored. (See 14 CFR 91.213, 121.628, 125.201, and 
129.14.) This proposed AD would continue to allow use of an existing 
FAA-approved MEL associated with the flight control system modified by 
the actions of this AD, provided that the more restrictive provisions 
of figure 10 to paragraph (i) of this proposed AD are adopted into the 
operator's existing FAA-approved MEL.
    Given the unprecedented length of time that the FAA has limited the 
operation of these airplanes, and the importance of the flight control 
system to safety, the FAA proposes to mandate an operational readiness 
flight after the design changes proposed by this AD have been done, but 
prior to each airplane being introduced into service.

Emergency Order of Prohibition

    On March 13, 2019, the FAA issued an Emergency Order of 
Prohibition, which prohibits the operation of Boeing Model 737-8 and 
737-9 airplanes by U.S.-certificated operators or in U.S. territory.
    The FAA plans to amend the Emergency Order of Prohibition in 
conjunction with adopting the final rule. The amended Emergency Order 
of Prohibition will address the actions that the Administrator deems 
appropriate to return the affected airplanes to service.

Related Service Information Under 1 CFR Part 51

    The FAA reviewed the following service information.
     Boeing Special Attention Service Bulletin 737-31-1860, 
dated June 12, 2020, describes procedures for installation of MDS 
software, a software installation verification and corrective actions, 
and removal of certain INOP markers on the EFIS control panels.
     Boeing Special Attention Service Bulletin 737-27-1318, 
Revision 1, dated June 24, 2020, describes procedures for changing of 
the horizontal stabilizer trim wire routing installations.

[[Page 47702]]

     Boeing Special Attention Service Bulletin 737-00-1028, 
dated July 20, 2020, describes procedures for an AOA sensor system test 
and an operational readiness flight.
    This service information is reasonably available because the 
information is posted in the docket and because the interested parties 
otherwise have access to it through their normal course of business or 
by the means identified in the ADDRESSES section.

FAA's Determination

    The FAA is proposing this AD because the agency evaluated all the 
relevant information and determined the unsafe condition described 
previously is likely to exist or develop in other products of the same 
type design.

Proposed AD Requirements

    This proposed AD would require the following actions:
     Installing new FCC OPS software and doing a software 
installation verification.
     Revising the existing AFM to incorporate new and revised 
information and procedures, and to remove the information from the 
applicable sections that was required by AD 2018-23-51, because that 
information would be no longer applicable based on the design changes 
specified in this proposed AD.
     Requiring, for operators who wish to allow dispatch of an 
airplane with certain inoperative systems, incorporating certain 
provisions into the operator's existing FAA-approved MEL.
    This proposed AD would also require the following actions. For 
information on those procedures, see this service information at 
https://www.regulations.gov by searching for and locating Docket No. 
FAA-2020-0686.
     Changing the horizontal stabilizer trim wire routing 
installation, by accomplishing the actions identified as ``RC'' 
(required for compliance) in the Accomplishment Instructions of Boeing 
Special Attention Service Bulletin 737-27-1318, Revision 1, dated June 
24, 2020.
     Installing revised MDS software, doing a software 
installation verification, and removing INOP markers if applicable, by 
accomplishing the applicable actions identified as ``RC'' in the 
Accomplishment Instructions of Boeing Special Attention Service 
Bulletin 737-31-1860, dated June 12, 2020.
     Performing an AOA sensor system test, by accomplishing the 
applicable actions identified as ``RC'' in the Accomplishment 
Instructions of Boeing Special Attention Service Bulletin 737-00-1028, 
dated July 20, 2020.
     Performing an operational readiness flight, by 
accomplishing the applicable actions identified as ``RC'' in the 
Accomplishment Instructions of Boeing Special Attention Service 
Bulletin 737-00-1028, dated July 20, 2020.

Explanation of Change to the Applicability

    AD 2018-23-51 applies to all 737 MAX airplanes. This proposed AD 
would apply only to the 737 MAX airplanes identified in Boeing Special 
Attention Service Bulletin 737-31-1860, dated June 12, 2020, which 
identifies line numbers for airplanes with an original airworthiness 
certificate or original export certificate of airworthiness issued on 
or before the effective date of the original Emergency Order of 
Prohibition. Airplanes that have not received an original airworthiness 
certificate or original export certificate of airworthiness on or 
before the date of the original Emergency Order of Prohibition will 
have been modified to incorporate the changes required by this AD prior 
to receiving an original, or original export, airworthiness 
certificate.

Flightcrew Training

    The FAA, through an operational evaluation, will assess the impact 
of the proposed aircraft design changes on pilot training. The FAA 
intends to conduct this evaluation jointly with three international 
civil aviation authorities: Ag[ecirc]ncia Nacional de 
Avia[ccedil][atilde]o Civil (ANAC) Brazil, Transport Canada Civil 
Aviation (TCCA), and the EASA. The FAA will issue a draft Boeing 737 
Flight Standardization Board Report documenting the results of the 
operational evaluation on pilot training. The FAA will post the draft 
Boeing 737 Flight Standardization Board Report at https://www.faa.gov/aircraft/draft_docs/fsb/ for public comment. You may subscribe to this 
page to receive notification when the FAA posts the draft report.
    Additionally, during the operational evaluation, the FAA will 
evaluate the operating procedures (checklists) proposed in this AD. If 
the FAA determines that the operational evaluation results necessitate 
additional changes to the checklists proposed in this AD, the FAA will 
post these changes as an addendum to the draft Boeing 737 Flight 
Standardization Board Report for public comment. If an addendum is 
posted, the FAA will announce the availability of it in the Federal 
Register. The FAA will consider the report and the comments submitted 
in finalizing the AD.

Explanation of Certain Provisions for Alternative Methods of Compliance 
(AMOCs)

    Because some operators may use a procedural method for translating 
AFM requirements that is different from that published by Boeing, the 
FAA will consider approving AMOCs, as appropriate, to address those 
differences. For procedural aspects (including how specific AFM wording 
is translated into operationally approved documents such as a Flight 
Crew Operations Manual (FCOM) or related Quick Reference Handbook 
(QRH)), the FAA encourages operators, in coordination with their 
principal inspectors, to contact the appropriate Aircraft Evaluation 
Group (AEG) office for additional guidance.
    In addition, Boeing Special Attention Service Bulletin 737-27-1318, 
Revision 1, dated June 24, 2020, specifies reporting and coordinating 
any deviations from the Accomplishment Instructions with Boeing. Boeing 
will coordinate deviations from ``RC'' actions with the FAA. 
Documenting approval of these deviations will facilitate the approval 
of AMOCs, if needed.

Costs of Compliance

    The FAA estimates that this proposed AD affects 73 airplanes of 
U.S. registry. The agency estimates the following costs to comply with 
this proposed AD:

                                                 Estimated Costs
----------------------------------------------------------------------------------------------------------------
                                                                                                 Cost on U.S.
             Action                   Labor cost          Parts cost       Cost per product        operators
----------------------------------------------------------------------------------------------------------------
FCC OPS installation and          1 work-hour x $85   $0................  $85...............  $6,205.
 verification.                     per hour = $85.
AFM revisions...................  1 work-hour x $85   $0................  $85...............  $6,205.
                                   per hour = $85.
MDS installation and              1 work-hour x $85   $0................  $85...............  $6,205.
 verification, INOP marker         per hour = $85.
 removal.

[[Page 47703]]

 
Stabilizer wiring change........  Up to 79 work-      Up to $3,790......  Up to $10,505.....  Up to $766,865.
                                   hours x $85 per
                                   hour = Up to
                                   $6,715.
AOA sensor system test..........  40 work-hours x     $0................  $3,400............  $248,200.
                                   $85 per hour =
                                   $3,400.
----------------------------------------------------------------------------------------------------------------

    The FAA has received no definitive data that would enable the 
agency to provide cost estimates for the operational readiness flight 
specified in this proposed AD.
    Operators that have a MEL and choose to dispatch an airplane with 
an inoperative flight control system affected by this AD would be 
required to incorporate certain provisions into the operator's existing 
FAA-approved MEL. The FAA has determined that revising the operator's 
existing FAA-approved MEL takes an average of 90 work-hours per 
operator, although the agency recognizes that this number may vary from 
operator to operator. Since operators incorporate MEL changes for their 
affected fleet(s), the FAA has determined that a per-operator estimate 
is more accurate than a per-airplane estimate. Therefore, the FAA 
estimates the average total cost per operator to be $7,650 (90 work-
hours x $85 per work-hour).
    According to the manufacturer, some or all of the costs of this 
proposed AD may be covered under warranty, thereby reducing the cost 
impact on affected operators.

Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to 
issue rules on aviation safety. Subtitle I, Section 106, describes the 
authority of the FAA Administrator. Subtitle VII, Aviation Programs, 
describes in more detail the scope of the Agency's authority.
    The FAA is issuing this rulemaking under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, General requirements. 
Under that section, Congress charges the FAA with promoting safe flight 
of civil aircraft in air commerce by prescribing regulations for 
practices, methods, and procedures the Administrator finds necessary 
for safety in air commerce. This regulation is within the scope of that 
authority because it addresses an unsafe condition that is likely to 
exist or develop on products identified in this rulemaking action.

Regulatory Findings

    The FAA has determined that this proposed AD would not have 
federalism implications under Executive Order 13132. This proposed AD 
would not have a substantial direct effect on the States, on the 
relationship between the national Government and the States, or on the 
distribution of power and responsibilities among the various levels of 
government.
    For the reasons discussed above, I certify that the proposed 
regulation:
    (1) Is not a ``significant regulatory action'' under Executive 
Order 12866,
    (2) Will not affect intrastate aviation in Alaska, and
    (3) Will not have a significant economic impact, positive or 
negative, on a substantial number of small entities under the criteria 
of the Regulatory Flexibility Act.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA proposes to amend 14 CFR part 39 as follows:

PART 39--AIRWORTHINESS DIRECTIVES

0
1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.

Sec.  39.13  [Amended]

0
2. The FAA amends Sec.  39.13 by removing Airworthiness Directive (AD) 
2018-23-51, Amendment 39-19512 (83 FR 62697, December 6, 2018; 
corrected December 11, 2018 (83 FR 63561)), and adding the following 
new AD:

The Boeing Company: Docket No. FAA-2020-0686; Product Identifier 
2019-NM-035-AD.

(a) Comments Due Date

    The FAA must receive comments on this AD action by September 21, 
2020.

(b) Affected ADs

    This AD replaces AD 2018-23-51, Amendment 39-19512 (83 FR 62697, 
December 6, 2018; corrected December 11, 2018 (83 FR 63561)) (``AD 
2018-23-51'').

(c) Applicability

    This AD applies to The Boeing Company Model 737-8 and 737-9 
airplanes, certificated in any category, as identified in Boeing 
Special Attention Service Bulletin 737-31-1860, dated June 12, 2020.

(d) Subject

    Air Transport Association (ATA) of America Code 22, Auto flight; 
27, Flight controls; and 31, Indicating/recording systems.

(e) Unsafe Condition

    This AD was prompted by the potential for a single erroneously 
high angle of attack (AOA) sensor input received by the flight 
control system to result in repeated airplane nose-down trim of the 
horizontal stabilizer, which, in combination with multiple 
flightdeck effects, could affect the flightcrew's ability to 
accomplish continued safe flight and landing.

(f) Compliance

    Comply with this AD within the compliance times specified, 
unless already done.

(g) Installation/Verification of Flight Control Computer (FCC) 
Operational Program Software (OPS)

    Before further flight, install FCC OPS software version P12.1.2, 
part number (P/N) 2274-COL-AC2-26, or later-approved software 
versions, on FCC A and FCC B, and do a software installation 
verification. During the installation verification, if the approved 
software part number is not shown as being installed on FCC A and 
FCC B, before further flight, do corrective actions until the 
approved software part number is installed on FCC A and FCC B. 
Later-approved software versions are only those Boeing software 
versions that are approved as a replacement for the applicable 
software, and are approved as part of the type design by the FAA 
after the effective date of this AD.

    Note 1 to paragraph (g): Guidance for doing the installation and 
installation verification of the FCC OPS software can be found in 
Boeing 737-7/8/8200/9/10 Aircraft Maintenance Manual (AMM), Section 
22-11-33.

(h) Airplane Flight Manual (AFM) Revisions

    Before further flight, revise the existing AFM to include the 
changes specified in paragraphs (h)(1) through (10) of this AD. 
Revising the existing AFM to include the changes specified in 
paragraphs (h)(2) through (10) of this AD may be done by

[[Page 47704]]

inserting a copy of figures 1 through 9 to paragraphs (h)(2) through 
(10) of this AD into the existing AFM.
    (1) In the Certificate Limitations and Operating Procedures 
chapters, remove the information identified as ``Required by AD 
2018-23-51.''
    (2) In the Operating Procedures chapter, revise the General 
paragraph to include the information in figure 1 to paragraph (h)(2) 
of this AD.
[GRAPHIC] [TIFF OMITTED] TP06AU20.010

    (3) In the Operating Procedures chapter, replace the existing 
Airspeed Unreliable paragraph with the information in figure 2 to 
paragraph (h)(3) of this AD.

[[Page 47705]]

[GRAPHIC] [TIFF OMITTED] TP06AU20.011

[[Page 47706]]

[GRAPHIC] [TIFF OMITTED] TP06AU20.012

    (4) In the Operating Procedures chapter, replace the existing 
Runaway Stabilizer paragraph with the information in figure 3 to 
paragraph (h)(4) of this AD.

[[Page 47707]]

[GRAPHIC] [TIFF OMITTED] TP06AU20.013

    (5) In the Operating Procedures chapter, replace the existing 
Stabilizer Trim Inoperative paragraph with the information in figure 
4 to paragraph (h)(5) of this AD.

[[Page 47708]]

[GRAPHIC] [TIFF OMITTED] TP06AU20.014

    (6) In the Operating Procedures chapter, add the information in 
figure 5 to paragraph (h)(6) of this AD.
[GRAPHIC] [TIFF OMITTED] TP06AU20.015

    (7) In the Operating Procedures chapter, add the information in 
figure 6 to paragraph (h)(7) of this AD.

[[Page 47709]]

[GRAPHIC] [TIFF OMITTED] TP06AU20.016

    (8) In the Operating Procedures chapter, add the information in 
figure 7 to paragraph (h)(8) of this AD.
[GRAPHIC] [TIFF OMITTED] TP06AU20.017

    (9) In the Operating Procedures chapter, add the information in 
figure 8 to paragraph (h)(9) of this AD.

[[Page 47710]]

[GRAPHIC] [TIFF OMITTED] TP06AU20.018

    (10) In the Operating Procedures chapter, add the information in 
figure 9 to paragraph (h)(10) of this AD.
[GRAPHIC] [TIFF OMITTED] TP06AU20.019

(i) Minimum Equipment List (MEL) Provisions for Inoperative Flight 
Control System Functions

    In the event that the airplane functions associated with the 
flight control system as modified by this AD are inoperative, an 
airplane may be operated (dispatched) only if the provisions 
specified in figure 10 to paragraph (i) of this AD are incorporated 
into the operator's existing FAA-approved MEL.

[[Page 47711]]

[GRAPHIC] [TIFF OMITTED] TP06AU20.020

    Note 2 to paragraph (i): The MEL provisions specified in figure 
10 to paragraph (i) of this AD correspond to Master Minimum 
Equipment List (MMEL) items 22-10-01B, 22-10-02, 22-10-03, 22-11-01, 
22-11-02, 22-11-05-02B, 22-11-06-2B, 22-11-08-01A, 22-11-08-01B, 22-
11-10A, 22-11-10B, and 27-41-01, in the existing FAA-approved Boeing 
737 MAX B-737-8/-9 MMEL, Revision 2, dated April 10, 2020, which can 
be found on the Flight Standards Information Management System 
(FSIMS) website, https://fsims.faa.gov/PICResults.aspx?mode=Publication&doctype=MMELByModel.

(j) Installation/Verification of MAX Display System (MDS) Software, 
Removal of INOP Markers

    Before further flight, do all applicable actions identified as 
``RC'' (required for compliance) in, and in accordance with, the 
Accomplishment Instructions of Boeing Special Attention Service 
Bulletin 737-31-1860, dated June 12, 2020.

(k) Horizontal Stabilizer Trim Wire Bundle Routing Change

    Before further flight, do all applicable actions identified as 
``RC'' in, and in accordance with, the Accomplishment Instructions 
of Boeing Special Attention Service Bulletin 737-27-1318, Revision 
1, dated June 24, 2020.

(l) AOA Sensor System Test

    Before further flight, do all applicable actions identified as 
``RC'' for the ``Angle of Attack (AOA) Sensor System Test'' 
specified in, and in accordance with, the Accomplishment 
Instructions of Boeing Special Attention Service Bulletin 737-00-
1028, dated July 20, 2020.

(m) Operational Readiness Flight

    (1) Before further flight and after accomplishment of all 
applicable required actions in paragraphs (g) through (l) of this 
AD, do all applicable actions identified as ``RC'' for the 
``Operational Readiness Flight'' specified in, and in accordance 
with, the Accomplishment Instructions of Boeing Special Attention 
Service Bulletin 737-00-1028, dated July 20, 2020. A special flight 
permit is not required to accomplish the operational readiness 
flight required by this paragraph.
    (2) After the operational readiness flight and before further 
flight, any mechanical irregularities that occurred during the 
operational readiness flight must be resolved following the 
operator's FAA-approved maintenance or inspection program, as 
applicable.

(n) Special Flight Permits

    Special flight permits may be issued in accordance with 14 CFR 
21.197 and 21.199 to operate the airplane to a location where the 
actions of this AD can be performed.

(o) Credit for Previous Actions

    This paragraph provides credit for the actions specified in 
paragraph (k) of this AD, if those actions were performed before the 
effective date of this AD using Boeing Special Attention Service 
Bulletin 737-27-1318, dated June 10, 2020.

(p) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, Seattle ACO Branch, FAA, has the authority to 
approve AMOCs for this AD, if requested using the procedures found 
in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request 
to your principal inspector or responsible Flight Standards Office, 
as appropriate. If sending information directly to the manager of 
the certification office, send it to the attention of the person 
identified in paragraph (q)(1) of

[[Page 47712]]

this AD. Information may be emailed to: 9-ANM-Seattle-ACO-AMOC-Requests@faa.gov.
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the responsible Flight Standards Office.
    (3) AMOCs approved previously for AD 2018-23-51 are not approved 
as AMOCs for this AD.
    (4) For service information that contains steps that are labeled 
as Required for Compliance (RC), the provisions of paragraphs 
(p)(4)(i) and (ii) of this AD apply.
    (i) The steps labeled as RC, including substeps under an RC step 
and any figures identified in an RC step, must be done to comply 
with the AD. If a step or substep is labeled ``RC Exempt,'' then the 
RC requirement is removed from that step or substep. An AMOC is 
required for any deviations to RC steps, including substeps and 
identified figures.
    (ii) Steps not labeled as RC may be deviated from using accepted 
methods in accordance with the operator's maintenance or inspection 
program without obtaining approval of an AMOC, provided the RC 
steps, including substeps and identified figures, can still be done 
as specified, and the airplane can be put back in an airworthy 
condition.

(q) Related Information

    (1) For more information about this AD, contact Ian Won, 
Manager, Seattle ACO Branch, FAA, 2200 South 216th St., Des Moines, 
WA 98198; phone and fax: 206-231-3500; email: 9-FAA-SACO-AD-Inquiry@faa.gov.
    (2) For service information identified in this AD, contact 
Boeing Commercial Airplanes, Attention: Contractual & Data Services 
(C&DS), 2600 Westminster Blvd., MC 110-SK57, Seal Beach, CA 90740-
5600; telephone 562-797-1717; internet https://www.myboeingfleet.com. You may view this referenced service 
information at the FAA, Airworthiness Products Section, Operational 
Safety Branch, 2200 South 216th St., Des Moines, WA. For information 
on the availability of this material at the FAA, call 206-231-3195.

    Issued on August 3, 2020.
Lance T. Gant,
Director, Compliance & Airworthiness Division, Aircraft Certification 
Service.
[FR Doc. 2020-17221 Filed 8-5-20; 8:45 am]
BILLING CODE 4910-13-P