- Delta Air Lines MD-88 Flight 1288
- Accident Overview
- Accident Board Findings
- Accident Board Recommendations
- Relevant Regulations / Policy / Background
- Prevailing Cultural / Organizational Factors
- Key Safety Issue(s)
- Safety Assumptions
- Resulting Safety Initiatives
- Airworthiness Directives (ADs) Issued
- Common Themes
- Related Accidents / Incidents
- Lessons Learned
- Delta Air Lines MD-88 Flight 1288
Resulting Safety Initiatives
14 CFR 33.70, Engine life-limited parts.
While the requirement to establish the maximum allowable number of flight cycles for each engine life-limited part previously existed, this new rule also requires the establishment of an engineering plan, a manufacturing plan and a service management plan to help assure the integrity of each engine life-limited part.
14 CFR Part 193, Protection of voluntarily submitted information.
To assure increased FAA/Industry collaboration through the sharing of safety significant data, 14 CFR Part 193 was developed. Under this part, all safety significant data voluntarily submitted by industry is designated as information protected under this part and will not be disclosed by the FAA.
AC 33.4-2, Instructions for Continued Airworthiness: In-Service Inspection of Safety Critical Turbine Engine Parts at Piece-Part Opportunity.
To significantly reduce the occurrence of uncontained engine failures of safety critical parts, this AC requests part features most critical to safety should be subjected to in-service inspections at each piece-part opportunity during their service lives, using methods that detect flaws that could lead to failure.
AC 33.14-1, Damage Tolerance of High Energy Turbine Engine Rotors.
This AC requests the use of an enhanced damage tolerance approach that would address anomalous material or manufacturing conditions such as abusive machining.
AC 33.70-1, Guidance Material for Aircraft Engine Life-Limited Parts Requirements.
This AC provides guidance for development and execution of an engineering plan, a manufacturing plan, and a service management plan for the design and life management of propulsion system life-limited parts including high-energy rotating parts. These three plans form a closed-loop system that links the assumptions made in the engineering plan, to how the part is manufactured, and to how the part is maintained in service.
AC 33.70-2, Damage Tolerance of Hole Features in High-Energy Turbine Engine Rotors.
This AC provides guidance for the introduction of surface damage tolerance assessment methodologies to address manufacturing and operationally-induced anomalies in circular hole features in rotor parts.
Note: The above regulations and ACs were all introduced as a result of manufacturing and in-service shortfalls identified during this accident investigation.
FAA / Industry Teams and Activities:
Rotor Manufacturing (ROMAN) Project
As a result of this accident and a 1997 summary of engine disk fracture root cause from the Aerospace Industries Association (AIA) Rotor Integrity Sub-Committee which revealed that post-forging manufacturing induced anomalies accounted for about 25% of rotor cracks/events, the AIA and FAA formed the ROMAN project. This project includes 11 engine companies and their primary suppliers. The ROMAN goal is to reduce uncontained engine failures due to manufacturing induced defects and to facilitate the implementation of best available technology for manufacturing, inspection and quality control of critical rotating engine parts. A report prepared by the ROMAN project advocated several actions, including: 1) development of an industry consensus standard that documents best practices for substantiation of critical manufacturing processes and procedures and that would ultimately preclude the onset of deleterious manufacturing induced anomalies; 2) characterization of those anomalies; 3) sponsorship of research and development (R&D) programs for enhancing process and inspection methodologies and 4) to encourage the engine industry to improve continuously through the development and implementation of an Industry/FAA Lessons Learned Data Base.
Comprehensive information of the ROMAN Project is provided by the following links:
To date, the ROMAN Project has initiated several safety significant programs:
ROMAN Lessons Learned Database (LLDB)
The eleven ROMAN industry members and the FAA developed, implemented, populated and currently maintains the LLDB. The LLDB is a central location for all engine industry manufacturing induced anomaly data and directly aids in identifying industry trends that could be the precursors to catastrophic failure events. The LLDB has helped to establish "best manufacturing practices" for production of engine rotors as a direct result of lessons learned from the root cause of manufacturing induced anomalies. The ROMAN LLDB has supported the Rotor Integrity Subcommittee's (RISC) development of a Probabilistic Damage Tolerance approach to the design of critical to life engine rotors by enabling a comprehensive statistical understanding of process yield and then inputting this data into this damage tolerance design system for enhanced lifing of engine rotors. The LLDB has also facilitated industry development of process specifications for hole making, broaching, turning, edge treatment, etc.
ROMAN LLDB - First Utilization of 14 CFR part 193 (Protection of Voluntarily Submitted Information)
The ROMAN LLDB was the first utilization of 14 CFR Part 193. Under this part, all data voluntarily submitted by industry for input into the LLDB is designated as information protected under this part and will not be disclosed by the FAA. The FAA designates information as protected under this part when the FAA finds that (1) The information is provided voluntarily; (2) The information is safety or security related; (3) The disclosure of the information would inhibit the voluntary provision of that type of information; (4) The receipt of that type of information aids in fulfilling the FAA's safety and security responsibilities; and (5) Withholding such information from disclosure, under the circumstances provided in this part, will be consistent with the FAA's safety and security responsibilities.
Additional information of 14 CFR Part 193 is provided by the following links:
Protection of Voluntarily Submitted Information; Final Rule (14 CFR Part 193).
ROMAN Review of Critical Manufacturing Process Validation (CMPV)
CMPV or Engineering Source Approval as defined by Pratt & Whitney is the manufacturing engineering requirement to verify that a component manufactured to a specific process and drawing requirement meets design intent and ultimately provides assurance that no critical process is detrimental to achieving the design intent. CMPV also assures that parts produced by an alternate source/process are equivalent to the part originally qualified. CMPV requirements may include but are not limited to: part cutups, metallurgical examinations, manufacturing sequence sheets, Critical Process technical plans, first article and selected process validation tests. CMPV is a multi-disciplined function that requires a skill mix that includes Design Engineering, Manufacturing Engineering, Materials Engineering and Quality Assurance. Based on part criticality/failure consequence, material complexity and manufacturing process complexity, critical life-limited rotating part producers determine when CMPV is required for part production.
When a source manufactures a part for the first time, the proposed processes/sequences are reviewed in detail by the CMPV function, critical processes are identified and the requirements for CMPV approval are established. When the source submits objective evidence that these requirements have been satisfied, the CMPV function reviews the data in consultation with the aforementioned skill mix. If the requirements have been met, (i.e., meets design intent, no deleterious affect to materials and establishes a robust process) the CMPV function approves the part/source combination.
Following initial qualification, the source's critical processes may not be changed without a new process review and approval by the CMPV function. The CMPV process change approval, like the initial approval, is not intended to verify the design but rather assures that critical process/sequence changes are not detrimental to design intent.
Parts that are subject to CMPV must fully satisfy all physical, metallurgical and functional engineering requirements as defined by the engineering drawings and applicable process specifications. The CMPV system establishes specific process validation requirements, by process that will be utilized to establish that a given process is not detrimental to the design intent.
The CMPV function is vital for the development of robust manufacturing processes and fabrication techniques. It is this activity that combines manufacturing, quality, materials and engineering towards the disciplined qualification and requalification (as process changes arise) of critical manufacturing processes/fabrication techniques/production source combinations. Ultimately, it is this activity, which assures that critical non-inspectable material characteristics meet the design intent and are not adversely impacted by the manufacturing process utilized.
ROMAN Sponsorship of Research & Development of Advanced Nondestructive Evaluation of Manufacturing Induced Anomalies
The Engine Titanium Consortium (ETC) which comprises of Iowa State University, General Electric Aircraft Engines, Pratt & Whitney and Honeywell was tasked to identify and evaluate advanced nondestructive evaluation (NDE) technologies that maximize the detection of manufacturing induced anomalies. They will also be technologies that do not rely on line of site visual inspections and are capable of detecting rotor surface and surface-connected manufacturing induced material anomalies (i.e., non-geometric) that result from finish and semi-finish manufacturing processes. A four stage program is planned as follows: (Stage 1) fabricate and characterize machining damage specimens, (Stage 2) conduct preliminary evaluation of existing and prototype NDE technologies on a baseline set of specimens, (Stage 3) evaluate a full specimen set with selected optimized NDE technologies to generate data for Probability of Detection analysis and (Stage 4) a final quantitative assessment utilizing a POD subteam.
As a result of this effort, several critical engine part producers are employing advanced NDE technologies. Volvo and MTU are currently utilizing High Speed Rotating Eddy Current Probes and General Electric is using the Meandering Winding Magnetometer method.
Additional information regarding ETC R&D is provided by the following link:
ROMAN Sponsored Research & Development for Characterization of Deleterious Material Anomalies
As part of the ROMAN effort, the European community sponsored R&D under the Manufacturing to Produce High Integrity Rotating Parts (MANHIRP) project. As a parallel effort, MANHIRP was tasked with the need to identify manufacturing induced anomalies associated with material property debits, creation of anomaly specimens, identification of manufacturing process anomaly turn-on's and initial NDE studies for inspections capable of detecting machining induced anomalies. MANHIRP has successfully identified and fabricated eleven defect type specimens for holemaking, turning and broaching in Titanium 6AL-4V and Inconel 718. Note, MANHIRP specimens and technical data were employed by the ETC effort for development and identification of advanced NDT technologies. Machining induced anomalies for both titanium and nickel alloys can result in disturbed microstructure which can have a detrimental effect on local material properties, lead to crack generation, and present a threat to flight safety.
Additional information about the MANHIRP project is provided by the following links:
Research & Development for Advanced Machining Technology
R&D for development of manufacturing process monitoring and adaptive manufacturing is being accomplished at the University of Aachen in Germany. This program is also part of the ROMAN portfolio of opportunities for technology improvements that through research and development. It should also be acknowledged that the University of Aachen founded a new Mechanical Engineering department dedicated to advanced manufacturing technology and they performed initial work under the MANHIRP R&D program.
Additional information of Advanced Machining Technology is provided by the following links:
Enhanced Engine Inspection Initiative
The FAA issued multiple enhanced inspection Airworthiness Directives (ADs) applicable to all gas turbine manufacturers. The ADs were prompted by a FAA study of in-service events involving uncontained failures of critical rotating engine parts that indicated the need for improved inspections. This inspection initiative presumes that not all discs manufactured are defect free and that the current field inspection programs have room for improvement. The improved inspections are needed to identify those critical rotating parts with conditions that if allowed to continue in service, could result in uncontained failures. The actions specified by these ADs are intended to prevent critical life-limited rotating engine part failure, which could result in an uncontained engine failure and damage to the airplane. The ADs require revisions to the engine manufacturer's time limits section of the engine manual to include enhanced inspection of selected critical life-limited parts at each piece-part exposure. These ADs will also require an air carrier's approved continuous airworthiness maintenance program to incorporate these inspection procedures.