SOW Aircraft Engine Vibration Alerting for Failure Mitigation_Draft.pdf

DRAFT

FEDERAL AVIATION ADMINISTRATION

STATEMENT OF WORK

AIRCRAFT ENGINE VIBRATION ALERTING FOR FAILURE MITIGATION

1.0 OBJECTIVES

Evaluate normal and abnormal vibration levels and broadband signatures on aircraft engines during engine development, certification testing, and in airline service.

Demonstrate strategy to generate alerts or advisories for abnormal vibration and inform maintenance inspections to avoid progression to a more severe engine or aircraft damage condition or potential aircraft safety hazard. The contractor must validate the proposed strategy with data from the field or from in-house testing.

Document the process (excluding company proprietary data) for sharing with industry standard groups, such as Society of Automotive Engineers (SAE), etc, to advance their guidance documents (References 1, 2).

2.0 BACKGROUND

Multiple engine models from different engine OEMs have experienced engine and sometimes aircraft damage events due to engine internal failures (e.g. partial blade loss, seal cracks or breaks) or anomalies (e.g. excessive wear due to undetected manufacturing assembly errors) that have led to airline fleet disruptions, Airworthiness Directives, and NTSB investigations.

These events have been associated with abnormal vibration levels or non-synchronous vibration (NSV) signatures in High Pressure or Low Pressure rotor systems (or sometimes Accessory drives) that were identified during the subsequent event investigations - leading to corrective actions after the fact.

The Congressional Recommendation in Section 309 of 2018 FAA Re-Authorization Bill calls to promote Engine Health Monitoring and Artificial Intelligence to improve Engine Safety.

3.0 GENERAL REQUIREMENTS

The contractor must perform a study to evaluate engine vibration levels and broadband signatures obtained during development and certification testing and in-service operations in order to develop detection thresholds and alerting strategies. The contractor must develop a methodology to proactively provide alerts or advisories of abnormal vibration levels and signatures and to prompt maintenance decisions (such as inspections) to avoid progression of the condition to a more severe damage level. This will entail participation by engine OEMs with large number of engines in the fleet (on aircraft such as the B737, B787, B777, A320, A330, A350), with on-board broadband vibration measurement and analysis capability; and having some history of events involving engine damage or unscheduled engine removal, inflight shutdowns (IFSDs) or air-turnback/diversion events to support the evaluation. The events would include uncontained failures or risks; liberation of turbomachinery hardware, inflight shutdowns, or dual power loss risks.

The concept of using vibration signatures to detect incipient failures in machinery has been studied and tested in academia and research institutions (References 3-8) at the turbomachinery component or module level. The contractor must demonstrate these concepts for application to complex gas turbine engines on transport aircraft in order to mitigate high severity field events.

The contractor must have the technical expertise to develop project plans, obtain necessary data, and the ability to analyze the data so as to demonstrate that a proposed methodology could be used to mitigate field failures.

4.0 SPECIFIC REQUIREMENTS

Task Task Outline Task Output

4.1 Develop plan for data gathering, analysis and program schedule. Identify engine model(s), data sources and program schedule.

4.2 Quantify the synchronous and nonsynchronous vibration levels and signatures for engine rotors (high pressure, low pressure sections and gearbox drives) in different flight phases (e.g. Takeoff, Climb, Cruise), ambient conditions, engine to engine variation, and normal aging (within the same model). Target a sample population of recent model engines which have broadband vibration monitoring capability. Sample set should include approximately 30 engines (combination of development, cert compliance or in-service engines) or a comparable sample size with statistical corrections for variance.

The normal operational scenarios should include normal rotor imbalances and environmental factors such as icing, rain, or hail ingestion. The contractor must quantify the normal variation in vibration levels in at least one area of the engine (e.g. HP rotor, LP rotor or gearbox); for comparison to the levels seen in malfunction events in Task 4.3

4.2.1 Mid-task progress report

on data gathering and analysis activities.

4.2.2 Report establishing

normal statistical variation in engine vibration levels in engine fan, core rotors; include gearbox parameters if available.

4.3 Evaluate the synchronous and non-synchronous vibration signatures associated with actual field events from FMD (Failures, Malfunction & Defects) reports or events during development or certification testing.

Comparison of vibration data from malfunction events to the normal variation identified in Task 4.2

4.4 Identify the vibration level thresholds, signature attributes for synchronous and non-synchronous; and relationships to other engine/aircraft parameters (e.g. EGT, N2, oil debris signal) to delineate abnormal conditions from normal (non-failure) conditions.

Account for normal transient vibration in events such as bird strike;

ice slab ingestion in identifying signature of incipient internal failure, damage, stall/surge/IFSD, potential uncontained release of engine hardware.

Methodology for analytical thresholds and mitigations for potential false positives and false negatives.

4.5 Summarize analyses and data supporting the proposed strategy and thresholds for generating alerts or advisories

Report (non-public version) with supporting technical data.

4.6 Document the technical process for generating alerts or advisories based on vibration levels and signatures; for use by industry and by standards developing organizations (SDOs) such as SAE, etc.

(As an example of a technical process document see the 2017 Report

Technical process document for use by industry SDOs.

by the AIA/EIWG Subcommittee on Engine Probe Icing: A Process for Evaluating the Performance of Temperature Probes, Combined Temperature and Pressure Probes, and Static Pressure Probes in Icing Conditions)

5.0 SCHEDULE

TASK NO. SCHEDULE DELIVERABLE

4.1 30 days after date of award Project Plan

4.2.1 90 days after date of award Progress update on data gathering and analysis.

4.2.2 180 days after date of award Summary of Normal Variance data analysis.

4.3 270 days after date of award. Comparison of Vibration data from

Malfunction events and Normal Variation from Task 4.2.2.

4.4.1 12 months after date of award Proposed methodology for analytical thresholds for detection of abnormal synchronous or non-synchronous vibration levels

4.4.2 15 months after date of award Proposed mitigations for potential false positives and false negatives.

4.5.1 18 months after date of award Draft non-public report on methodology with supporting data summary for 30-day FAA review.

4.5.2 20 months after date of award Revised non-public report addressing FAA comments from 4.5.1

4.6.1 22 months after date of award. Draft public version report for 30-day FAA review.

4.6.2 24 months after date of award Final report revised to address FAA comments from 4.6.1

6.0 GENERAL REPORTING REQUIREMENTS

Monthly Coordination: In addition to the deliverables listed in the above schedule, monthly telecoms will be held with the FAA Project Manager and Sponsors to discuss progress and to address questions. These telecoms are to occur within ten (10) business days of the end of each month during the period of performance with the contractor distributing meeting notes to the team within five (5) days of the meeting.

Technical Reports: The FAA will supply the final report template. All deliverables are submitted as draft and upon return of FAA comments, the contractor should provide a preliminary response within ten (10) business days and revise the report(s) per the schedule of deliverables in Section 5.0.

7.0 PERIOD OF PERFORMANCE

The period of performance is 24 months.

8.0 TRAVEL

Majority of the coordination will be with virtual meetings, presentations, and documents.

It is anticipated that the contractor will travel to the FAA’s Burlington, MA office for one in-person meeting per year to review progress.

9.0 REFERENCES

1. SAE AIR4174A – A Guide to Aircraft Powertrain Monitoring (2017)

2. SAE ARP1839 – A Guide to Aircraft Turbine Engine Vibration Monitoring Systems (2015)

3. Hall, K.C. et al, Non-synchronous Vibration in Turbo-machinery Airfoils, Hall, Duke U.

(2004)

4. Staplefeldt, S. and Brandstetter, C., Non-synchronous Vibration in Axial Compressors, Imperial College, J. of Sound & Vibration (2020)

5. Willams, E. & Badini, J., Causes of Sub-synchronous Vibration in Integrally Geared Compressors (Elliott), Turbomachinery & Pump Symposium, 2015

6. Rajgopalan, V. & Vance, J., Diagnosing Sub-synchronous Vibration, Texas A&M, ASME International Design Engineering Technical Conference, (2007)

7. Qu, L. et al, Investigation of Sub-synchronous Vibration in Rotating Machinery, J. of Sound & Vibration (2018)

8. Allaire, P. et al, Subsynchronous Vibration in Multistage Centrifugal Compressors, Univ. of Virginia, Turbomachinery Symposium, 1987