Hazard identification process in the selected analysis domain of the F 100 turbofan engines maintenance system

The multirole F-16 is the most advanced aircraft in the Polish Air Forces. It has been equipped with the very modern, sophisticated and advanced turbofan engine F100-PW-229. Due to the fact, that there is only one engine, its reliability, durability efficiency and performance are the crucial factors for the safety reasons. In the article authors researched maintenance system of the F100 turbofan engines, which are built on the multirole F-16 aircraft. For the study purposes F100 maintenance system model has been created. From this model, the main analysis domain was derived, comprising “Major engine objects discrepancies removal” process. Considering such an analysis domain, on the basis of the schematic diagram of the hazard identification process, authors presented the following procedures: tools preparation for the hazard sources identification, hazard sources identification, hazard sources grouping and hazards formulation. The main goal of this article was to provide hazard identification process results as hazard specifications, which include: a group of hazard sources, hazards formulation and the most probable/predictable consequences, severities and losses/harms of the hazard activation.


Introduction
The F-16C/D Block 52 is powered by the Pratt & Whitney F100-PW-229 low-bypass, high compression ratio, fully ducted, twin-spool turbofan engine with an annular combustor and a mixed flow augmentor.The engine is also equipped with a full length annular duct and a variable convergent/divergent exhaust nozzle.It also incorporates variable vanes at the inlet of both compressors and a variable exhaust nozzle.The major rotating sections are supported by five main bearings.
The F100-PW-229 engine is designed to maximize its performance.Some features are: -High thrust to weight ratio • 29,100 lbs./3,800 lbs.= 7.7:1 -Variable vanes • Compressor inlet variable vanes (CIVV) • Rear compressor variable vanes (RCVV) -Fully ducted engine -Mixed flow augmentor • Mixes core air flow with bypass air flow -Variable exhaust nozzle The engine is constructed using the modular concept, allowing the removal of functionally and physically associated parts as units, called modules.
The modular concept helps increase maintainability by: -Allows removal of parts as units (modules).
-Allows replacement of unserviceable modules with serviceable modules.-Allows rapid return of the engine and modules to service.
The modular concept does not prevent replacement of subassemblies or parts when replacement is the most effective repair method.Designed with the modular concept, the engine consists of the five modules (Fig. 1): 1. Inlet fan module 2. Core engine module 3. Fan drive turbine module 4. Augmentor duct and nozzle module 5. Gearbox module.

Engine maintenance system model as an aggregated analysis domain
The purpose of the engine maintenance system is to assess the F100-PW-229 engines powering the PLAF F-16 aircraft for serviceability and safety of flight.
The F100 family of engines has been designed to be maintained using three levels of maintenance explained in this section.Engine maintenance system is based on Modular Maintenance Concept.F100 engine comprises of five major modules: Fig. 1.F100 engine design structure [1] The whole maintenance concept is organized in the way, which is based on the main idea that 97% of nonoverhaul maintenance should be completed at the base -Fig.2. The main reason for such an arrangement is to keep as many engines and engine modules, as well as engine LRUs (Line replaceable units) on base, available for the fast discrepancy removal.Immediate removal and replacement of the engine broken object is the key element for the engine operational readiness and aircraft mission capability rate.To summarize, we are able to distinguish three different engine maintenance levels (Fig. 3

3.Hazard identification
In order to identify hazards, hazard sources we should try to recognize what are the most common undesired events as far as the engine maintenance is concerned.The main events being tracked by all the international safety management personnel and engine manufacturers are: Authors of this article researched F100-PW-229 engine maintenance system and analyzed this area of interest as a combination of three elements: human-hardwareenvironment. Considering all the relations between these elements we could identify single or multiple hazard sources.In this case the F100 engine maintenance system has been presented as an aggregated analysis domain model in order to implement procedures into the hazard identification process.This aggregated analysis domain is a combination of the three domains (Fig. 3), where hazards could be generated as a result of the maintenance processed performed at different levels of the F100 engine maintenance system.
For the study purposes, analysis domain 2 has been selected, representing second level of the engine maintenance system (engine intermediate level maintenance).One of the main maintenance processes performed at this level is major engine objects discrepancies removal.In this article this process is an area of the hazard identification.The selected process consists of the eleven following steps: 1. Engine receiving inspection 2. Pre-test cell engine mount 3. Engine/LRU preservation (engine run on TC) 4. Broken module removal (Gearbox, Augmentor, Fan, Core, LPT) 5. Modules/LRU inspections 6. Spare module installation 7. Engine Final assembly 8. Pre-test cell inspections 9. Pre-test cell engine mount 10.Test cell run 11.Engine Final Inspection In this article, due to complexity of the F100 turbofan engine, authors considered only one process of the major engine object discrepancy removal.The main reason for the following research was that aircraft crew chief reported engine oil leakage during postflight inspection.After borescope inspection it was determined that this leakage is beyond acceptable limits.

Hazard sources identification
Hazard sources identification in the selected analysis domain is being conducted in accordance with the procedures of the forward hazard identification process.The list of the selected identified hazard sources within process 1.3 (major engine object discrepancies removal) is presented in Table 1.
Table 1.List of the selected identified hazard sources in the analysis domain (Engine Intermediate level maintenance) within process 1.3 (major engine objects discrepancies removal) -Fig.3 and 6 No.

Hazards specification
Hazards specification process is conducted in accordance with the following procedures: hazards sources grouping and hazards formulation.

Fig. 2 .
Fig. 2. Engine maintenance concept model ). I. Organizational (O) -Level, Flightline Maintenance Maintenance repairs and inspections with engine installed in aircraft: -Engine servicing -Replacement of line replaceable units (LRU) Main aspects of this level are: -significant on-wing maintenance and troubleshooting -easy access for routine maintenance -Engine Maintenance & Monitoring System (EMMS) or Engine Maintenance & Tracking Systems (EMATS) -fast line replaceable unit (LRU) replacement -state of the art engine fault system identifies problems quickly to ensure operational safety II.Intermediate (I) -Level, Base Engine Shop Maintenance repair of engines and modules that cannot be repaired with engine installed in aircraft.Main aspects of this level are: -return to service by module replacement reduces engine down time -simple and quick engine testing -avionics shop and jet engine intermediate maintenance (JEIM) shop can maintain controls -engine design maximizes base-level repair ability -I-level maintenance arranged around horizontal repair and vertical (modular) maintenance.

Fig. 6 .
Fig. 6.Detailed schematic diagram of the aggregated analysis domain structure (detailed: Analysis domain 2. -Engine Intermediate level maintenance) being the model of the F100 engine maintenance system