
[Federal Register Volume 88, Number 233 (Wednesday, December 6, 2023)]
[Rules and Regulations]
[Pages 84690-84693]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-26636]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2023-1050; Project Identifier AD-2022-00602-E; 
Amendment 39-22620; AD 2023-24-04]
RIN 2120-AA64


Airworthiness Directives; Honeywell International Inc. Engines

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

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SUMMARY: The FAA is adopting a new airworthiness directive (AD) for all 
Honeywell International Inc. (Honeywell) Model AS907-1-1A and AS907-2-
1G engines. This AD was prompted by reports of compressor surge, 
including a dual engine compressor surge, during takeoff climb out 
through a steep temperature inversion, causing a loss of engine thrust 
control. This AD requires either the replacement of a certain 
electronic control unit (ECU) software version installed on AS907-1-1A 
engines with updated software or the replacement of certain ECUs 
installed on AS907-1-1A engines with ECUs eligible for installation. 
This AD also requires the replacement of certain ECUs installed on 
AS907-2-1G engines. The FAA is issuing this AD to address the unsafe 
condition on these products.

DATES: This AD is effective January 10, 2024.

ADDRESSES: 
    AD Docket: You may examine the AD docket at regulations.gov under 
Docket No. FAA-2023-1050; 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 final rule, any comments received, and other 
information. The address for Docket Operations is U.S. Department of 
Transportation, Docket Operations, M-30, West Building Ground Floor, 
Room W12-140, 1200 New Jersey Avenue SE, Washington, DC 20590.

FOR FURTHER INFORMATION CONTACT: Joseph Costa, Aviation Safety 
Engineer, FAA, 3960 Paramount Boulevard, Lakewood, CA 90712; phone: 
(562) 627-5246; email: [email protected].

SUPPLEMENTARY INFORMATION:

Background

    The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 
CFR part 39 by adding an AD that would apply to all Honeywell Model 
AS907-1-1A and AS907-2-1G engines. The NPRM published in the Federal 
Register on May 23, 2023 (88 FR 32980). The NPRM was prompted by 
several reports that Honeywell Model AS907-1-1A and AS907-2-1G engines 
experienced compressor surge, including an AS907-1-1A dual engine 
compressor surge, during takeoff climb out through a steep temperature 
inversion, which resulted in loss of engine thrust control. The FAA 
determined that the installed ECU software version logic locked the 
engine inlet total temperature (Tt2) at 60 knots on a takeoff roll and 
that reference Tt2 remained locked until the aircraft reached 400 feet 
above ground level (AGL) or the pilot moved the throttle before 
reaching 400 AGL. The locked Tt2 is mathematically adjusted by the ECU 
software for altitude and Mach number changes as the takeoff 
progresses. During a climb to 400 feet AGL with a thermal inversion, 
the actual engine Tt2 can increase above the Tt2 that is being 
calculated by the ECU, which causes the compressor guide vanes' (CGVs) 
and surge bleed valves' (SBVs) positions to be off-schedule for the 
actual ambient conditions. Significant off-scheduling of the CGVs and 
the SBVs can lead to a compressor surge event. The compressor surge 
margin is decreased when scheduling is based on a colder Tt2 
temperature than what the engine is actually running. Engine 
deterioration impacts compressor surge margin and can increase the 
likelihood of a dual engine compressor surge as the AS907-1-1A and 
AS907-2-1G engine fleets age. Dual engine power loss due to a 
temperature inversion may result in significant loss of airplane 
thrust, which could reduce the climb gradient and result in the 
airplane's inability to clear obstacles. As a result, the manufacturer 
updated the software.
    In the NPRM, the FAA proposed to require either the replacement of 
a certain ECU software version installed on AS907-1-1A engines with an 
updated software version eligible for installation or the replacement 
of certain ECUs installed on AS907-1-1A engines with ECUs eligible for 
installation. The NPRM also proposed to require the replacement of 
certain ECUs installed on AS907-2-1G engines with ECUs eligible for 
installation. The FAA is issuing this AD to address the unsafe 
condition on these products.

[[Page 84691]]

Discussion of Final Airworthiness Directive

Comments

    The FAA received comments from three commenters. The commenters 
were Bombardier Inc. (Bombardier), Duncan Aviation, and Honeywell. All 
three commenters requested changes to the proposed AD. The following 
presents the comments received on the NPRM and the FAA's response to 
each comment.

Request To Update Software Update Language

    Bombardier requested that the FAA update the NPRM so that 
references to software are consistent. Bombardier noted that in the 
NPRM SUMMARY section, the phrase ``updated software'' was used, while 
other portions of the AD refer to the ``software version eligible for 
installation.''
    The FAA acknowledges the inconsistency and has provided detail 
about the updated software in the Background of this final rule.

Request To Clarify Background

    Bombardier requested that the FAA include language in the 
Background paragraph of this AD to explain the effect of Tt2 locking on 
the SBVs.
    The FAA agrees. As a result, the FAA has added language to the 
Background paragraph of this AD to explain the effect of Tt2 locking 
and clarify the surge bleed valves that affect surge margin.

Request To Update Unsafe Condition Description

    Bombardier requested that the FAA update the language in the unsafe 
condition of the NPRM Background and paragraph (e) of the proposed AD 
to the following: ``may result in significant loss of overall airplane 
thrust which can lead to inability of the airplane to clear the AFM OEI 
net flight path (risk of obstacle collision).''
    The FAA partially agrees. The unsafe condition description in 
Background of this final rule was clarified to include ``which could 
reduce the climb gradient and result in the airplane's inability to 
clear obstacles.'' However, paragraph (e) of this AD was not changed as 
a result of this comment because the consequence remains consistent 
with the end-level effect if the unsafe condition is not addressed.

Request To Correct the Costs of Compliance

    Honeywell suggested a change to the second sentence of the Cost of 
Compliance to remove an erratum.
    The FAA agrees and has changed the second sentence of the Costs of 
Compliance of this final rule to refer to AS907-2-1G engines installed 
on airplanes of U.S. registry.

Request To Update Labor Cost

    Bombardier questioned why the work-hours for removing the ECU for 
the AS907-1-1A engine are less than the work-hours for removing the ECU 
for the AS907-2-1G engine.
    The FAA acknowledges that the estimated work-hours should be the 
same for removing an ECU from both engine models. However, the FAA 
estimated one ECU will need to be replaced in the AS907-1-1A fleet. 
Therefore, the FAA estimated 1 work-hour to replace the ECU and 1 work-
hour to complete the power assurance run for one engine. The FAA did 
not change this AD as a result of this comment.

Request To Clarify Estimated Costs Table

    Honeywell noted that the structure of the Estimated Costs table is 
such that the total or individual engine model fleet cost to the U.S. 
registered operators is not clearly presented.
    The FAA agrees and has clarified the Costs of Compliance of this 
final rule. The cost per product columns reflect the estimated costs 
per engine. The AS907-1-1A cost to replace ECU software was moved to 
the Estimated Costs table to show a total fleet cost assuming all ECUs 
receive the software upgrade. The cost to replace the AS907-1-1A ECU 
remains unchanged. The FAA has no way of knowing how many AS907-1-1A 
engine operators will replace the ECU instead of the software.

Request To Change the Expression of Compliance Times

    Duncan Aviation and Honeywell requested that the FAA change the 
expression of compliance times throughout Tables 1 and 2 of the NPRM to 
be more concise. Each of the two commenters suggested slightly 
different phrasing of compliance times. Each suggested removal of the 
terms ``before exceeding'' and ``hours time-in-service (TIS).'' Duncan 
Aviation and Honeywell requested the order of ``whichever occurs 
first'' and ``after the effective date of this AD'' be reversed. Duncan 
Aviation stated that ``hours TIS'' could be misinterpreted as time 
since new.
    The FAA agrees that the expression of compliance times should be 
clear. The FAA clarifies that ``hours TIS'' is equivalent to flight 
hours. The FAA changed the compliance times in Table 1 to paragraph 
(g)(1) and Table 2 to paragraph (g)(2) of this AD to read as follows: 
Within X months/years or Y flight hours after the effective date of 
this AD, whichever occurs first.

Request To Correct ECU Software Version Number

    Honeywell requested that the FAA change the ECU software version 
number in paragraph (g)(1) of the proposed AD from ``AS907_1011'' to 
``AS907_1001.'' Bombardier requested that the FAA change the ECU 
software part version number in paragraph (g)(1) of the proposed AD 
from ``AS907_1011'' to ``AS907-1001.''
    The FAA agrees with changing the ECU software version number in 
paragraph (g)(1) to ``AS907_1001'' because ``AS907_1001'' is the 
correct nomenclature.

Request To Update Definitions

    Bombardier requested that the FAA change the part/version numbers 
defined as eligible for installation. Bombardier requested that the 
definitions change from excluding certain part/version numbers to 
requiring certain part/version numbers because older versions of 
software will not address the unsafe condition.
    The FAA partially agrees. While these items may be the only items 
currently eligible for installation, the definitions also allow future 
approved items. This mitigates the need for an alternative method of 
compliance (AMOC) for future software versions or ECU P/Ns. There is no 
version of software older than AS907_1001 for the AS907-1-1A engine. 
The FAA did not change this AD as a result of this comment.

Conclusion

    The FAA reviewed the relevant data, considered any comments 
received, and determined that air safety requires adopting this AD as 
proposed. Accordingly, the FAA is issuing this AD to address the unsafe 
condition on these products. Except for minor editorial changes, and 
any other changes described previously, this AD is adopted as proposed 
in the NPRM. None of the changes will increase the economic burden on 
any operator.

Costs of Compliance

    The FAA estimates that this AD affects a total of 853 engines 
installed on airplanes of U.S. registry. The FAA estimates that 175 
AS907-2-1G engines installed on airplanes of U.S. registry will require 
replacing two ECUs per engine.
    The FAA estimates the following costs to comply with this AD:

[[Page 84692]]



                                                 Estimated Costs
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                                                                                     Cost per      Cost on U.S.
                Action                         Labor cost           Parts cost        product        operators
----------------------------------------------------------------------------------------------------------------
Replace AS907-2-1G ECUs (2 per engine)  5 work-hours x $85 per          $109,044        $109,469     $19,157,075
                                         hour = $425.
Replace AS907-1-1A ECU software (2 per  5 work-hours x $85 per                 0             425       * 288,150
 engine).                                hour = $425.
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* The FAA assumes that all 678 AS907-1-1A engines installed on airplanes of U.S. registry will replace the
  software in two ECUs per engine. Honeywell Model AS907-1-1A operators may replace the ECU instead of replacing
  the software to comply with this AD. For replacing the ECU, the FAA estimates the following costs:


----------------------------------------------------------------------------------------------------------------
                                                                                                     Cost per
                    Action                                 Labor cost               Parts cost        product
----------------------------------------------------------------------------------------------------------------
Replace AS907-1-1A ECU (per ECU, per engine)..  2 work-hours x $85 per hour =            $61,162         $61,332
                                                 $170.
----------------------------------------------------------------------------------------------------------------

    The FAA has included all known costs in its cost estimate. 
According to the manufacturer, however, some of the costs of this 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

    This AD will not have federalism implications under Executive Order 
13132. This AD will 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 this AD:
    (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 Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA amends 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 adding the following new airworthiness 
directive:

2023-24-04 Honeywell International Inc.: Amendment 39-22620; Docket 
No. FAA-2023-1050; Project Identifier AD-2022-00602-E.

(a) Effective Date

    This airworthiness directive (AD) is effective January 10, 2024.

(b) Affected ADs

    None.

(c) Applicability

    This AD applies to Honeywell International Inc. (Honeywell) 
Model AS907-1-1A and AS907-2-1G engines.

(d) Subject

    Joint Aircraft System Component (JASC) Code 7300, Engine Fuel 
and Control.

(e) Unsafe Condition

    This AD was prompted by reports of compressor surge, including a 
dual engine compressor surge, during takeoff climb out through a 
steep temperature inversion, which caused a loss of engine thrust 
control. The FAA is issuing this AD to prevent loss of engine thrust 
control. The unsafe condition, if not addressed, could result in 
reduced controllability of the airplane, loss of control of the 
airplane, reduced ability of the flight crew to maintain the safe 
flight and landing of the airplane, and loss of the airplane.

(f) Compliance

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

(g) Required Actions

    (1) For AS907-1-1A engines with an electronic control unit (ECU) 
having part number (P/N) 2119576-1011 and software version 
AS907_1001 installed, before exceeding the applicable compliance 
time in Table 1 to paragraph (g)(1) of this AD, either replace 
software version AS907_1001 with a software version eligible for 
installation; or replace the ECU with an ECU eligible for 
installation. Either the software or ECU must be replaced for all 
four ECUs installed in both airplane engines at the same time.
    Note 1 to paragraph (g)(1): Guidance for removing and replacing 
the ECU software or removing and replacing the ECU may be found in 
Honeywell Service Bulletin (SB) AS907-76-9031, Revision 2, dated May 
15, 2022.

          Table 1 to Paragraph (g)(1)--Model AS907-1-1A Engines
------------------------------------------------------------------------
      Engine time since new (TSN)                Compliance time
------------------------------------------------------------------------
Greater than 5,000 hours TSN...........  Within 12 months or 400 flight
                                          hours (FH) after the effective
                                          date of this AD, whichever
                                          occurs first.
3,000 to 5,000 hours TSN...............  Within 18 months or 600 FH
                                          after the effective date of
                                          this AD, whichever occurs
                                          first.

[[Page 84693]]

 
Fewer than 3,000 hours TSN.............  Within 24 months or 800 FH
                                          after the effective date of
                                          this AD, whichever occurs
                                          first.
------------------------------------------------------------------------

    (2) For AS907-2-1G engines with serial numbers (S/N) P130101 
through P130240 that have not incorporated Honeywell SB AS907-72-
9063, and for AS907-2-1G engines with S/Ns P130241 through P130336, 
and S/Ns P130101 through P130240 that have incorporated Honeywell SB 
AS907-72-9063, before exceeding the applicable compliance time in 
Table 2 to paragraph (g)(2) of this AD, replace any installed ECU 
having P/N 2119576-3001 or P/N 2119576-3002 with an ECU eligible for 
installation. All four ECUs installed in both airplane engines must 
be replaced at the same time.
    Note 2 to paragraph (g)(2): Guidance for removing and replacing 
the ECU may be found in Honeywell SB AS907-76-9014, Revision 6, 
dated October 10, 2022.
    Note 3 to paragraph (g)(2): Guidance for converting a standard 
flow compressor to a high flow compressor for improving surge margin 
may be found in Honeywell SB AS907-72-9063, Revision 1, dated July 
31, 2019.

          Table 2 to Paragraph (g)(2)--Model AS907-2-1G Engines
------------------------------------------------------------------------
              Engine type                        Compliance time
------------------------------------------------------------------------
Standard Flow Compressor AS907-2-1G      Within 2 years or 800 FH after
 engines (engine S/Ns P130101 through     the effective date of this AD,
 P130240 that have not incorporated       whichever occurs first.
 Honeywell SB AS907-72-9063).
High Flow Compressor AS907-2-1G engines  Within 7 years or 2,800 FH
 (engine S/Ns P130241 through P130336     after the effective date of
 and engines that have incorporated       this AD, whichever occurs
 Honeywell SB AS907-72-9063).             first.
------------------------------------------------------------------------

(h) Installation Prohibition

    (1) After the effective date of this AD, do not install an ECU 
having P/N 2119576-1011 and software version AS907_1001 in any 
AS907-1-1A engine.
    (2) Do not install an ECU having P/N 2119576-3001 or P/N 
2119576-3002 in any AS907-2-1G engine if the ECU has exceeded the 
compliance time specified in Table 2 to paragraph (g)(2) of this AD.

(i) Definitions

    (1) For the purpose of this AD, for the AS907-1-1A engine, a 
``software version eligible for installation'' is a software version 
that is not software version AS907_1001.
    (2) For the purpose of this AD, for the AS907-1-1A engine, an 
``ECU eligible for installation'' is an ECU that does not have P/N 
2119576-1011.
    (3) For the purpose of this AD, for the AS907-2-1G engine, an 
``ECU eligible for installation'' is an ECU that does not have P/N 
2119576-3001 or P/N 2119576-3002.

(j) Alternative Methods of Compliance (AMOCs)

    (1) The Manager, West Certification 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 local Flight 
Standards District Office, as appropriate. If sending information 
directly to the manager of the West Certification Branch, send it to 
the attention of the person identified in paragraph (k) of this AD 
and email to: [email protected].
    (2) Before using any approved AMOC, notify your appropriate 
principal inspector, or lacking a principal inspector, the manager 
of the local flight standards district office/certificate holding 
district office.

(k) Additional Information

    For more information about this AD, contact Joseph Costa, 
Aviation Safety Engineer, FAA, 3960 Paramount Boulevard, Lakewood, 
CA 90712; phone: (562) 627-5246; email: [email protected].

(l) Material Incorporated by Reference

    None.

    Issued on November 29, 2023.
Victor Wicklund,
Deputy Director, Compliance & Airworthiness Division, Aircraft 
Certification Service.
[FR Doc. 2023-26636 Filed 12-5-23; 8:45 am]
BILLING CODE 4910-13-P


