AC 33.70-5 H.8 Exceedance Curve.
The distribution of anomaly size and the frequency at which anomalies occur.
H.9 Focused Inspection.
A component inspection in which the inspector has been instructed to pay special attention to specific component feature(s) or location(s) and the necessary specialized processing instructions have been provided.
H.10 Full Field Inspection.
A component inspection without special attention to any specific component feature(s) or location(s).
H.11 Hard Time Inspection Interval.
The number of engine flight cycles since new or since the most recent inspection after which a rotor part must be made available and must receive the inspection specified in the airworthiness limitations section (ALS) of the instructions for continued airworthiness (ICA).
H.12 Hazardous Engine Effects.
Any of the effects listed in § 33.75(g)(2). Failure of rotating parts usually results in the non-containment of high-energy debris, which is the primary hazardous engine effect addressed by this AC. Disks, hubs, impellers, large rotating seals, and other similar large rotating components represent potential sources of high-energy debris.
H.13 Inspection Opportunity.
An occasion when an engine is disassembled to at least the modular level and the hardware in question is accessible for inspection, whether or not the hardware has been reduced to the piece part level.
H.14 Linear Elastic Fracture Mechanics.
For the purposes of this AC, linear elastic fracture mechanics is a method used to predict crack growth rates and component lives using the stress intensity factor (K) to characterize t he stress state near the tip of a crack caused by a remote load or residual stresses.
H.15 Low Cycle Fatigue (LCF).
The process of progressive and permanent local structural deterioration occurring in a material subject to cyclic variations, in stress and strain, of sufficient magnitude and number of repetitions. The process will culminate in detectable crack initiation typically H–2
AC 33.70-5 within 105 cycles. A detectable crack initiation is defined as 0.030 inches in length by
0.015 inches in depth.
H.16 Maintenance Exposure Interval.
A statistical distribution which defines the number of flight cycles between engine shop visits. This interval provides an opportunity to inspect the engine internal parts because the module or parts have been disassembled as a result of normal maintenance activity.
H.17 Manufacturing Anomaly.
A surface-related imperfection introduced during the manufacturing process (subsequent to melting) that is considered potentially detrimental to the structural integrity of a life-limited rotating part during its service life.
H.18 Mean Probability of Detection (POD).
The 50-percent confidence level POD versus anomaly size curve.
H.19 Module.
A combination of assemblies, subassemblies, and parts contained in one package, or arranged to be installed in one maintenance action.
H.20 Operationally-Induced Anomaly.
A surface-related imperfection introduced during service operations (both flight operations and maintenance) that is potentially detrimental to the structural integrity of the life-limited rotating part.
H.21 Part Available.
A part that can be inspected, as required by the ALS of the ICA, without any further disassembly. Depending on the inspection requirements, some parts may require a fully disassembled “piece part” condition, while other parts may be available for inspection while still in the assembled module.
H.22 Probability of Detection.
A quantitative statistical measure for detecting a particular type of anomaly (flaw) over a range of sizes using a specific non-destructive inspection technique under specific conditions. Typically, the mean POD curve is used.
H.23 Probabilistic Risk Assessment.
A fracture-mechanics based simulation procedure that uses statistical techniques to mathematically model and combine the influence of two or more variables to estimate H–3
AC 33.70-5 the likelihood of various outcomes for a product. Since not all variables may be considered or may not be capable of being accurately quantified, the numerical predictions are used on a comparative basis to evaluate various options. Results from these analyses are typically used for design optimization to meet a predefined target or to conduct parametric studies. This type of procedure differs from an absolute risk analysis, which attempts to consider all significant variables and is used to quantify, on an absolute basis, the predicted number of future events with safety and reliability consequences.
H.24 Rotor Life-Limited Parts.
Engine rotor parts whose primary failure is likely to result in a hazardous engine effect, which is any of the conditions listed in § 33.75(g)(2).
H.25 Stage.
The rotor structure that supports and is attached to a single aerodynamic blade row.
H.26 Safe Life.
A low cycle fatigue-based process in which life-limited components are designed, manufactured, and substantiated to have a specified service life or life limit, which is stated in operating flight cycles, operating hours, or both. The “safe life approach” requires that components be removed from service prior to the development of an unsafe condition (i.e., crack initiation). When a component reaches its published life limit, it is retired from service. The safe life approach only applies to components that define crack initiation as the limit of the useful life such as rotating parts.
H.27 Soft Time Inspection Interval.
The number of engine flight cycles since new, or the most recent inspection, after which a rotor part in an available module must receive the inspection specified in the ALS of the ICA.
H–4
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