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 PW Model PW4052, PW4056, PW4060, PW4060A, PW4060C, PW4062, PW4062A, PW4152, PW4156, PW4156A, PW4158, PW4460, and PW4462 engines. The NPRM was published in the Federal Register on May 26, 2026 (91 FR 30514). The NPRM was prompted by multiple events involving PW PW4000-94 engines in which tailpipe fire, loss of thrust control, and engine in-flight shutdown occurred. A manufacturer investigation revealed that these events were caused by undetected deterioration of Pb sensors due to epoxy deterioration, which can lead to erroneous Pb sensor measurements and incorrect fuel commands. In the NPRM, the FAA proposed to require replacing Pb sensors within certain compliance times. The FAA is issuing this AD to address the unsafe condition on these products.

Discussion of Final Airworthiness Directive

Comments

The FAA received comments from 10 commenters. Commenters included Air Line Pilots Association, International (ALPA), Atlas Air, Boeing Commercial Airplanes (Boeing), Delta Air Lines, Inc (DAL), European Air Transport Leipzig GmbH, FedEx, the Foundation for Aviation Safety, PW, United Airlines (United), and United Parcel Service (UPS). ALPA and Boeing supported the NPRM without change. The following presents the comments received on the NPRM and the FAA's response to each comment.

Request To Include Service Material as an Approved Method of Compliance

Atlas Air and UPS requested that the FAA revise the NPRM to include the use of certain service material as acceptable forms of compliance with the NPRM. Specifically, Atlas Air requested that the FAA include Collins Aerospace Service Bulletin (SB) EEC1-73-62 or PW SB PW4ENG 73-221 as approved methods of compliance. UPS requested that the FAA include replacement of Pb sensors with new Pb sensors (in accordance with the component maintenance manual or other approved procedures) and accomplishment of Collins Aerospace SB EEC1-73-62 as approved methods of compliance. Atlas Air noted that all required actions in the NPRM were derived from the accomplishment instructions in Collins Aerospace SB EEC1-73-62.

The FAA disagrees with the request. The FAA acknowledges that Collins Aerospace SB EEC1-73-62 and PW SB PW4ENG 73-221, Revision No. 3, dated July 1, 2024 (PW SB PW4ENG 73-221, Revision No. 3) are acceptable methods for compliance with this AD, but notes that incorporating these materials by reference is unnecessary because this AD already includes all relevant information for compliance. The FAA did not change this AD as a result of this comment.

Request To Include Additional Engine Models

DAL and PW requested that the FAA revise paragraph (c) of the proposed AD to include engine models with a dash number suffix identified in PW SB PW4ENG 73-221, Revision No. 3. Specifically, DAL requested all dash number suffix variants, while PW requested only -3 (Phase III) models be included. PW noted that all -3 (Phase III) engine model configurations are included in both the FAA type certificate data sheet (TCDS) and PW SB PW4ENG 73-221, Revision No. 3. PW also stated that this revision would improve alignment between the NPRM and PW maintenance instructions and would eliminate ambiguity for operators during compliance planning.

The FAA disagrees with the request because dash number suffixes and other configuration designations are not separate engine models recognized by the TCDS and therefore, are not listed in the applicability of this AD. The FAA notes that engines identified by dash number suffixes that correspond to listed TCDS engine models are already included within the applicability of this AD. The FAA did not change this AD as a result of this comment.

Request To Limit Applicability to Engines With Certain Pb Sensors

DAL requested that the FAA revise paragraph (c) of the proposed AD to only include engines with electronic engine controls (EEC) that have Pb sensor part number (P/N) 800833-1 or P/N 796163-1 installed. DAL stated that if Collins Aerospace certifies a new Pb sensor P/N, the certification process would ensure that the same deterioration, as addressed by the NPRM, would not exist.

The FAA disagrees with the request. If a new configuration Pb sensor is released and proven not susceptible to the unsafe condition, then the FAA would consider adjusting the required actions for that Pb sensor at that time, including alternative methods of compliance (AMOC) requested under the provisions of paragraph (i) of this AD. The FAA did not change this AD as a result of this comment.

Request To Clarify Tracking Method for Flight Hours (FH)

DAL and United requested that the FAA revise paragraph (h) of the proposed AD to clarify that if the FH cannot be determined for the Pb sensor, guidance for determining the age of the Pb sensors may be found in PW SB PW4ENG 73-221, Revision No. 3. Specifically, United requested that guidance stating that the EEC operational hours can also be established by multiplying years in service by 3,048 hours or average utilization per year be included in the NPRM. United stated that industry experience indicates that while the EEC timer tracks sensor replacement intervals based on operational hours, a significant number of units arrive at shop visits with unreliable EEC times that cannot be used to determine operating hours. DAL noted that most operators track operating times (including time since new) and operating cycles (including cycles since new) of the EEC, similar to how operators track life limits on life limited parts, making EEC flight hour tracking a sufficient method for monitoring the 30,000 FH limit on the Pb sensor.

The FAA disagrees with the request because operators are responsible for tracking and determining the FH and years since new or since repair for Pb sensors, and the methodology for this practice is not specifically required in this AD. Note 1 to paragraph (h) of this ( printed page 65946) AD identifies that guidance for determining the age of Pb sensors may be found in PW Service Bulletin PW4ENG 73-221, Revision No. 3. The FAA did not change this AD as a result of this comment.

Request To Clarify Use of “Years in Service”

European Air Transport Leipzig GmbH requested that the FAA explain the use of the term “years in service” in the NPRM, and DAL requested that the FAA change the term “10 years in service” to “10 calendar years since the EEC was made serviceable with a new or repaired Pb sensor installed.” European Air Transport Leipzig GmbH stated that EECs stored in a controlled environment (individually or on preserved spare engines) do not experience epoxy deterioration in the same manner as EECs actively operated on aircraft, so the “years in service” counter should be applied differently for stored/preserved EECs versus those in active operation. DAL noted that the accomplishment instructions in PW SB PW4ENG 73-221, Revision No. 3 and Hamilton Sundstrand SB EEC131-73-62, Revision 1, dated January 20, 2023, determine Pb sensor operational hours and years of service based on EEC operating hours. DAL added that if the Pb sensor is not installed in an operating EEC, hours and years would not accrue, and time outside of an EEC would not count toward years of service.

The FAA partially agrees with the request. The FAA agrees that the term “years in service” should be revised to provide clarity as to the intent of the compliance time, but the FAA disagrees with the proposed language. The FAA has revised the language in paragraphs (g) and (h) of this AD to “years since new or since last repair.” The FAA disagrees with commenter's position regarding epoxy deterioration on stored EECs because the FAA has no data demonstrating that EECs stored separately or installed on preserved spare engines experience a different rate of deterioration than EECs in active operation. However, the FAA notes that once this AD is published, any person may request approval of an AMOC under the provisions of paragraph (i) of this AD.

Request To Remove Extra Asterisk in Table 1 to Paragraph (h)

DAL and FedEx requested that the FAA remove the second asterisk from the heading in the fourth column of table 1 to paragraph (h) in the proposed AD. DAL noted that they believe the second asterisk was inadvertently added.

The FAA agrees with the request and has removed the second asterisk from the heading in the fourth column of table 1 to paragraph (h) of this AD.

Request To Clarify Definition of “Part Eligible for Installation”

FedEx requested that the FAA clarify the definition of a “part eligible for installation” in paragraph (g) of the proposed AD. Specifically, FedEx noted that the current definition permits installation of a used Pb sensor that is near its service limits ( e.g., 29,999 FH and 9 years 11 months) and asked how operators should handle such a sensor once it exceeds the AD limits shortly after return to service. Additionally, FedEx requested clarification on whether a repair resets both the flight-hour and calendar-service times to zero, and if so, whether a new calendar date label must be applied to the sensor to reflect the updated service times.

The FAA agrees to clarify. The FAA has revised the language in paragraphs (g) and (h) of this AD from “years in service” to “years since new or since last repair.” For the scenario provided, a Pb sensor with 29,999 FH and 9 years 11 months since new or since last repair require replacement in accordance with paragraph (h)(2) of this AD. The FAA notes that operators are responsible for tracking and determining the FH and years since new or since repair for Pb sensors, and the methodology for this practice is not specifically required in this AD. The FAA did not change this AD as a result of this comment.

Request To Refer to Service Material

FedEx requested that the FAA revise paragraph (h)(1) of the proposed AD to require the step to be performed in accordance with PW SB PW4ENG 73-221, Revision No. 3. FedEx noted that currently, the instructions for continued airworthiness are not directly cited and the NPRM only includes PW SB PW4ENG 73-221, Revision No. 3, as a reference for determining utilization.

The FAA disagrees with the request to incorporate PW SB PW4ENG 73-221, Revision No. 3, by reference. Paragraph (h)(1) of this AD identifies the part that needs to be replaced, the part eligible for installation, and the compliance times for replacement. The FAA did not incorporate PW SB PW4ENG 73-221, Revision No. 3, by reference because the AD allows any FAA-approved method for replacing the Pb sensor and incorporating this service bulletin by reference would unnecessarily restrict operators. The FAA did not change this AD as a result of this comment.

Request To Revise Unrelated Service Material

FedEx requested that the FAA add a data field to the label field in Figure 2 of Hamilton Sundstrand SB EEC 131-73-64. Fed Ex stated that for cargo and other low-utilization operations, the calendar-date limitation may be more restrictive than the flight-hour limit and making Pb sensor hours and date code readily visible without disassembling the EEC would be helpful for ongoing maintenance and compliance.

The FAA disagrees with the request because the referenced service material is not applicable to this AD. The FAA also notes that the FAA does not control service bulletin content. The FAA did not change this AD as a result of this comment.

Request To Clarify How Average Utilization is Calculated

FedEx requested that the FAA clarify the acceptable method for calculating average utilization. FedEx noted that the NPRM does not define “average utilization” and asked whether this refers to the operator's fleet average, the average for the specific aircraft on which the sensor is installed, or an industry or fleet-wide average. FedEx also stated that the accomplishment instructions of Hamilton Sundstrand SB EEC131-73-62 indicate that operational hours may be determined “by multiplying years in service by 3,048 hours or average utilization per year.”

The FAA disagrees with the request. The FAA notes that operators are responsible for tracking and determining the FH and years since new or since repair for Pb sensors, and the methodology for this practice is not specifically required in this AD. The FAA also notes that the referenced service material is not applicable to this AD, and the FAA does not control service bulletin content. The FAA did not change this AD as a result of this comment.

Request To Clarify Compliance Time

The Foundation for Aviation Safety requested that the FAA clarify why Pb sensor replacement is not an immediate compliance requirement in the NPRM. The Foundation for Aviation Safety stated that Pb sensor replacement is a 2-hour fix to guard against engine fires or other engine catastrophes.

The FAA agrees to clarify. Although Pb sensor replacement is a maintenance task that can be accomplished in a relatively short amount of time, compliance time is not driven by ease of replacement, and the phased replacement approach required by this ( printed page 65947) AD reduces operator burden while still ensuring the overall safety of the fleet. The FAA did not change this AD as a result of this comment.

Request To Update Service Material Revision Number

PW requested that the FAA update the NPRM to reference the appropriate revision number and date for PW SB PW4ENG 73-221, Revision No. 3, if the SB is revised before the FAA final rule is published. PW noted that engine models PW4060A, PW4060C, and PW4156 are included in the NPRM and in the TCDS but do not appear in PW SB PW4ENG 73-221, Revision No. 3. PW stated that since the NPRM proposed actions that are derived from PW SB PW4ENG 73-221, Revision No. 3, PW will review whether a revision to this SB is warranted to ensure that operators of these engine models have the proper guidance necessary to accomplish the AD requirements.

The FAA acknowledges the request but notes that PW SB PW4ENG 73-221, Revision No. 3, is not incorporated by reference in this AD, and the SB was not revised prior to the issuance of this final rule. The FAA did not change this AD as a result of this comment.

Request To Modify Calendar-Time Compliance Option

UPS requested that the FAA modify the calendar-time compliance option for low-utilization operators (less than 1,200 cycles per year). UPS proposed a 15-year compliance interval rather than the 10-year interval specified in paragraph (h)(2) of the proposed AD. UPS noted that they were not requesting a change to the flight-hours requirement for low-utilization operators.

The FAA disagrees with the request. The commenter provided no justification for the request, and the FAA notes that the failure mechanism of the Pb sensor (the epoxy degradation) was analyzed and is driven by both utilization and calendar time, and the compliance times identified in this AD are required to maintain the safe operation of the fleet. The FAA also notes that, in response to a previous comment, the term “years in service” was revised to “years since new or since last repair” in paragraphs (g) and (h) of this AD to provide clarity as to the intent. The FAA did not change this AD as a result of this comment.

Request To Add Methodology for Determining Pb Sensor FH/Calendar Time

UPS requested that the FAA allow for the use of the highest accumulated FH or the oldest repair date of any Pb sensor in the fleet for determining the applicable replacement compliance timeframe for Pb sensors with unknown FH or calendar time since new or since repair.

The FAA disagrees with the request because operators are responsible for tracking and determining the FH and years since new or since repair for Pb sensors, and the methodology for this practice is not specifically required in this AD. 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 210 engines installed on airplanes of U.S. registry.

The FAA estimates the following costs to comply with this AD:

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.

The Amendment

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

91 FR 65944