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| **           |                                                       |
| Memorandum** |                                                       |
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Date: xx/xx/xx

To: SEE DISTRIBUTION

From: Manager, Aircraft Engineering Division, Aircraft Certification
Service

Prepared by: Robert Grant, ANE-110, (781) 238-7757 or
<robert.grant@faa.gov> Timoleon Mouzakis, ANE-111, (781) 238-7114 or
<timoleon.mouzakis@faa.gov>

Subject: **[ACTION:]{.underline}** Policy for Continued Airworthiness
Assessment Methodology for Turbine Engine Rotating Life-Limited Parts
Life Shortfall

**1.** **PURPOSE**.

a\. This policy memorandum provides guidance for corrective action when
turbine engine rotating Life-Limited Parts (LLP) are found cracked due
to Low-Cycle Fatigue (LCF), or a fatigue life analysis reveals a
deficiency, such that the type design LLP is not capable of meeting its
published life limit. This policy does not apply to situations in which
the deficiency is associated with quality escapes, maintenance error,
handling damage, contamination, foreign object damage, etc. that affect
a limited percentage of parts.

b\. This policy memorandum applies to any Aircraft Certification Office
(ACO) when evaluating and mandating corrective actions involving turbine
engine rotating LLP life shortfalls under Title 14 of the Code of
Federal Regulations (14 CFR) part 39.

**2.** **RELATED DOCUMENTS**.

a\. 14 CFR 33.4, Instructions for Continued Airworthiness.

b\. 14 CFR 33.14, Start-stop cyclic stress (low-cycle fatigue).

c\. 14 CFR 33.70, Aircraft Engine Standards for Engine Life Limited
Parts.

d\. Advisory Circular No. 39-8, "Continued Airworthiness Assessments of
Powerplant and Auxiliary Power Unit Installations of Transport Category
Airplanes", dated 9/8/03.

**3. BACKGROUND.**

a\. The Engine and Propeller Directorate (E&PD) has observed
inconsistencies in Airworthiness Directives (ADs) for LLP life
shortfalls, such as:

\(1\) Establishing a new lower life limit, or not.

\(2\) Whether suspect parts are permitted to be re-installed after
inspection, and remain in service until the original life limit is
reached, or not.

Note that for the purposes of this policy, an LLP life shortfall is
defined as the inability of a type design LLP to meet the Federal
Aviation Administration (FAA) approved life limit for that part number.

b\. AC 39-8 provides a means to manage unsafe conditions, such as one
that may be posed by an LLP life shortfall. The AC approach uses risk
analysis to predict the risk associated with the unsafe condition,
including the risk during the control program. This methodology
determines if the proposed control program actions limit the risk of
serious and severe outcomes sufficiently by providing guidance on
control program considerations, including acceptable short-term risk for
level 3 and level 4 events. Overall, a control program involves
activities that limit the risk of failure associated with continued
temporary use of these parts until the product is brought back to the
level of safety intended at certification. In certification, LLP life
limits are established that require removal of LLPs prior to crack
initiation.

c\. Once an unsafe condition is identified, AC 39-8 provides acceptable
level 3 and level 4 short-term guidelines that determine how quickly the
corrective action must be implemented. AC 39-8 includes guidelines for
both the number of future events (risk factor) and the risk per flight.
The control program risk is expected to meet the both the risk factor
and risk per flight short term guidelines. The goal in resolving an LLP
life shortfall is the development and implementation of corrective
actions that, when fully incorporated, meet both the long-term risk
guidelines from AC 39-8 and the rotor integrity standards, such as §§
33.15, 33.27, and 33.14 or 33.70. Even if the control program meets the
AC 39-8 long-term risk guidelines, parts that exceed the reduced life
limit should be removed to bring the product back to the level of safety
intended at certification. The completion of all actions to correct the
unsafe condition should be done as soon as feasible and in accordance
with the risk guidelines and principles.

d\. Section 33.70 states, "By a procedure approved by the FAA, operating
limitations must be established which specify the maximum allowable
number of flight cycles for each engine life-limited part..." Note that
§ 33.70 replaced § 33.14 by refining the requirements of § 33.14, and
adding additional requirements. Lifing procedures approved to satisfy §§
33.14 or 33.70 generally require that an LLP be retired from service
before exceeding the minimum crack initiation life. The minimum crack
initiation life for each affected rotor part is specified within the
engine type design data. Also, Appendix A of Part 33, A33.4
(Airworthiness Limitations Section) requires that all mandatory
replacement times be specified in the airworthiness limitations section
of the engine manual.

**4. POLICY STATEMENT**.

a\. When LLPs are found cracked, or an analysis reveals a deficiency in
the design such that the type design is not capable of meeting its
published life limit, then the product does not meet the level of safety
intended by §§ 33.14 and 33.70, and corrective action is required. A
corrective action must take the form of an Airworthiness Directive (AD)
to ensure the new life limit is established, and the approved corrective
action is complied with by all operators. When the final corrective
action is implemented, the LLP should once again meet the long-term risk
guidelines and the level of safety intended at certification.

b\. The following control programs are the expected methods for managing
LLPs above their reduced life limits within the short term risk
guidelines.

-   Removal of the LLP at piece part exposure.

-   Removal of the LLP at a scheduled engine shop visit.

-   Removal of the LLP before a scheduled engine shop visit using a
    drawdown schedule.

-   Initial and recurring inspections, in conjunction with implementing
    one of the above three corrective actions.

c\. Inspections should not be used in place of a part replacement when
the type design LLP is not capable of meeting its published life limit.
The AD should require LLPs, whose accumulated cycles in service exceeds
the new reduced life limit on the effective date of the AD, be removed
from service in accordance with one of the control programs noted above.
If the type certificate (TC) holder's plan does not require removal from
service at the first shop visit above the new life limit, the TC holder
must show that it is not practicable to do so. If the FAA certification
office responsible for the TC holder concurs, they must obtain agreement
by the Standards Staff.

d\. If the investigation of a cracked LLP revealed a deficiency in the
LLP design, where the type design is not capable of meeting its
published life, then the FAA must issue an AD to impose a reduced life
limit.

e\. The AD may allow parts in service to remain in service beyond this
new reduced life limit until a final corrective action is implemented by
using the appropriate control program. An AD must mandate the control
program, regardless of the predicted risk level.

f\. Parts installed after the effective date of the AD should be removed
from service before the new reduced life limit is exceeded.

**5. EFFECT OF POLICY.** The general policy stated in this document does
not constitute a new regulation or create a "binding norm." Whenever a
TC holder's proposed method of compliance differs from this policy, the
proposal must be coordinated with the Engine and Propeller Directorate
Standards Staff, ANE-110. In addition, if an office believes that an
applicant's proposal that meets this policy should not be approved, that
office must coordinate its response with the Engine and Propeller
Directorate Standards Staff, ANE-110.

**6. CONCLUSION.**

a\. When LLPs are found cracked, or an analysis reveals a deficiency in
the design, such that the type design is not capable of meeting its
published life limit, then action is necessary to bring the product back
to the level of safety intended at certification.

b\. The Engine and Propeller Directorate has always mandated life limit
reductions through ADs. The use of an AD to accomplish such changes is
consistent with policy and practice, and with the intent of the
regulations to ensure that operators operate safely.

c\. LLPs above the reduced life limit should be removed from service.
The timing and means of accomplishing this action will be based on the
level of risk posed by continued operation.

SIGNATURE BLOCK

DISTRIBUTION:

Manager, Aircraft Manufacturing Division, AIR-200\
Manager, Certification Procedures Branch, AIR-110\
Manager, Brussels Aircraft Certification Staff, AEU-100\
Manager, Engine Certification Office, ANE-140\
Manager, Engine Certification Branch, ANE-141\
Manager, Engine Certification Branch, ANE-142\
Manager, Airframe and Propulsion Branch, ANE-171

Manager, Rotorcraft Directorate, ASW-100\
Manager, Rotorcraft Standards Staff, ASW-110\
Manager, Special Certification Office, ASW-190

Manager, Small Airplane Directorate, ACE-100\
Manager, Small Airplane Standards Office, ACE-110\
Manager, Atlanta Aircraft Certification Office, ACE-115A\
Manager, Airframe and Propulsion Branch, ACE-117A\
Manager, Chicago Aircraft Certification Office, ACE-115C\
Manager, Propulsion Branch, ACE-118C\
Manager, Systems and Propulsion Branch, ACE-116W

Manager, Transport Airplane Directorate, ANM-100\
Manager, Transport Standards Staff, ANM-110\
Manager, Airframe and Propulsion Branch, ANM-112\
Manager, Propulsion Branch, ANM-140S\
Manager, Propulsion Branch, ANM-140L

END