U.S. ARMY LEAD THE FLEET USAGE ANALYSIS David White Westar Corporation Michael McFalls U.S. Army Aviation & Missile Command David Largess COBRO (a Westar Company) ABSTRACT The purpose of the U.S. Army Lead the Fleet (LTF) program is to rapidly accumulate flight hours on selected U.S. Army helicopters to identify safety, Reliability, Availability, and Maintainability (RAM) issues before they occur during fleet operational usage. The assets of the LTF Program currently include one helicopter of each of the following model mission design series: UH-60A and UH-60L Black Hawk, CH-47D Chinook, AH-64A Apache, and AH-64D Longbow Apache. The LTF Program was originally conducted from 1986 to 1995 and re-instituted in April 2002. This paper will report the approach, status, and early results of the LTF usage analysis. The U.S. Army Aviation Technical Test Center (ATTC) pilots fly aggressive mission profiles and rapidly accumulate flight hours to stimulate usage-related discrepancies prior to operational occurrences. Structural and system deficiencies are to be identified, addressed, and corrected prior to the need for costly fleet-wide groundings, restorations, modifications, or retrofits. LTF provides aircraft usage information to correlate with discrepancies and establish meaningful usagerelated safety and RAM trends. The amount of time each airframe and each dynamic component is exposed to damaging flight regimes is monitored and recorded. The basic parameters used to identify the flight regimes include gross weight, stores configuration, airspeed, altitude, roll angle, vertical acceleration, and ground-air-ground cycles. This paper discusses in detail the approach used to identify the helicopter flight regimes and usage intensity from data provided by the LTF instrumentation. ATTC, with support from COBRO (a Westar Company), collects, verifies, processes, and archives LTF operational and maintenance data using the Unified RAM (UniRAM) Data Management System. The UniRAM database is transmitted to the LTF Data Analysis Team to process, evaluate, and analyze trends. The Westar Corporation LTF Data Analysis Team is under the direction of the U.S. Army Aviation and Missile Command (AMCOM) Test and Evaluation Management Office (TEMO). The team structured the data analysis effort to evaluate LTF aircraft discrepancies and analyze the UniRAM database to establish safety and RAM trends that result from the rate and intensity of LTF usage. HUMS 2003 Conference 125
A review of the previous FY86-95 LTF Program shows that LTF is able to identify problems that include:! Airframe and dynamic component degradation.! Engine, drive train, fuel systems, and hydraulics failures.! Vibration and torsional stability related problems.! Weapons effectiveness and avionics / electronics malfunctions. This paper concentrates on the current LTF Program mechanical system and dynamic component structural issues. BACKGROUND The LTF Program Manager is Mr. Mike McFalls, who heads TEMO within the Aviation and Missile Research, Development, and Engineering Center (AMRDEC) of AMCOM at Redstone Arsenal, AL. ATTC at Ft. Rucker, AL, with the support of Westar and COBRO, is responsible for all aspects of the LTF Program execution including aircraft operation; usage and maintenance data collection; and data verification, archival, and transmission. Westar analyzes data for the AMCOM TEMO in Huntsville, AL. Each Program Management Office (PMO) with responsibility for the oversight of the following systems participates in the LTF Program:! AH-64A/D Apache! UH-60A/L/M Black Hawk! CH-47D/F Chinook! Aircraft Survivability Equipment (ASE) The PMO is responsible for defining solutions and implementing fleet-wide fixes for adverse trends identified in the LTF Program. The LTF Program findings are coordinated and shared with the following organizations:! Aircraft System PMOs! Aviation Engineering Directorate (AED)! Integrated Materiel Management Center (IMMC)! U.S. Army Safety Center (USASC)! Army Materiel Systems Analysis Activity (AMSAA) LTF APPROACH AND OBJECTIVE The LTF Program approach is to fly controlled conditions and scenarios and accelerate up the reliability curve ahead of the fielded aircraft in order to:! Identify helicopter system and component deficiencies and failure modes.! Provide information to resolve safety, RAM, and logistics issues.! Optimize system and component replacements and improvements in the ongoing U.S. Army Aviation recapitalization efforts. The objectives of the LTF Program are to reduce operational and sustainment costs, improve system reliability, and increase safety across Army Aviation. LTF FLIGHT OPERATIONS LTF Flight Profiles: LTF pilots fly profiles that replicate the operational missions and exercises flown in the field. The LTF flight profiles include the following:! Combat missions! Maintenance test flights! Internal / external loads! Training flights! Range operations! Live fire operations LTF pilots exercise all the aircraft systems:! ASE! Weapons! Navigation equipment! Night vision systems! Communication equipment! Auxiliary equipment (hoists, etc.) LTF pilots operate the aircraft in representative field environments:! High altitude! Desert conditions! Cold weather! Aircraft are not hangared LTF pilots fly engineering regimes to stress the aircraft and systems to detect problems before they occur in the field. LTF Aircraft Plan: The aircraft planned for participation in the LTF Program are shown in Fig. 1. The aircraft currently in the LTF Program include the following:! A/C with data bus:! AH-64A Apache! AH-64D Longbow Apache! A/C without data bus:! UH-60A Black Hawk! UH-60L Black Hawk! CH-47D Chinook Aircraft that will be added to the LTF as they become available include:! A/C with data bus:! CH-47F (FY03)! UH-60M (FY04)! OH-58D (FY05) 126 HUMS 2003 Conference
Fig. 3 LTF Data and Action Flow Fig. 1 LTF Aircraft Plan The remainder of this paper will concentrate on the LTF data collection and analysis for the AH-64A aircraft. AH-64A LTF OPERATIONS TEMPO (OPTEMPO): The AH-64A planned LTF usage is 60 hours per month as shown in Fig. 2. This planned OPTEMPO is approximately 3.6 times the flight hour rate of the average U.S. Army AH-64A. The LTF execution plan is not linear because it includes scheduled phased maintenance at 250 flight hour intervals. Fig. 2 AH-64A LTF OPTEMPO LTF DATA ACQUISITION, ANALYSIS, AND DISTRIBUTION LTF Data and Action Flow: Fig. 3 shows the LTF usage and maintenance data and action flow. The AMCOM AMRDEC TEMO, who is responsible to a General Officer Steering Group for the overall success of the LTF Program, provides LTF Program Management. ATTC pilots fly the aggressive flight plan that includes the accelerated OPTEMPO, operational missions and flight profiles, and engineering regimes. ATTC, with support of COBRO, collects all LTF aircraft usage and maintenance data in the UniRAM database. COBRO acquires the data; checks the data quality; archives the database at ATTC, Ft. Rucker, AL; and replicates a copy to Westar in Huntsville, AL, daily. Unscheduled maintenance write-ups are scored as the events occur. A failure review board meets quarterly, validates the faults, and determines the final scoring of each event. Westar evaluates the usage information to identify adverse maintenance and fault occurrence trends, and analyzes aircraft incidents. The resulting information is coordinated with the aircraft and aircraft equipment PMOs. LTF aircraft usage analysis information is reported to the PMOs quarterly. The PMOs are ultimately responsible for resolution of adverse trends identified by the LTF data analysis. The PMOs coordinate with IMMC, USASC, and Quality on an on-condition basis to resolve LTF-identified issues. The PMOs also coordinate with the Systems Engineering Division of AED to resolve fault, failure, and adverse usage trends. If required, the PMO will work with the Original Equipment Manufacturer (OEM) to resolve aircraft problems and implement fleet-wide fixes. AED Structures and Materials, Propulsion, Aeromechanics, and Mission Equipment Divisions participate in fault, failure, and adverse trend solutions as required to resolve aircraft problems. UniRAM Data: UniRAM Data consists of aircraft operational usage and maintenance data, including:! Pilot profile card! Aircraft configuration fuel weight, stores, etc.! Profile flown external fuel, external loads, etc.! Qualitative comments! Enhanced Logbook Automation System (ELAS)! Operational information! Scheduled maintenance! Unscheduled maintenance! Aircraft state and motion from AMPOL HUMS 2003 Conference 127
DataMARS bus monitor for bus aircraft or C-MIGITS GPS/INS system for non-bus aircraft.! Ground-air-ground cycles! Pitch and bank angle! Airspeed! Load factor! Altitude! Engine torque LTF Bus Aircraft: AMPOL DataMARS: The AH-64A has a limited data bus with limited parameters available for usage analysis as shown in Fig. 4. Aircraft position, attitude, motion, and engine torque are used to identify the AH-64A usage in the engineering flight regimes and evaluate flight incidents. The AMPOL Data Monitoring, Analysis, and Recording System (DataMARS) monitors and records the data available from the AH-64A MIL-STD-1553 Data Bus. Fig. 4 AH-64A/D Data Bus Parameters LTF Data Analysis Process: The LTF data analysis process is shown in Fig. 5. Block 1 of Fig. 5 illustrates the data acquisition, storage, and transmission functions that occur at ATTC. Block 2 summarizes the engineering analysis of aircraft usage performed by Westar to determine the aircraft usage intensity and identify adverse maintenance trends. The results of these usage analyses are saved to the UniRAM database and replicated back to ATTC. The results of the analysis are reported to the PMOs quarterly and are planned to be available on a near real-time basis at a password-protected web portal beginning in January 2003. Blocks 3 and 4 will be discussed later in this paper. AH-64A Percent Time or Number of Events per Hour in Damaging Flight Regimes: A sample analysis of the time and number of events the AH-64A has spent in damaging regimes during LTF usage is shown in Fig. 6. The OEM determined the fatigue lives of AH-64A life-limited, flight-critical components when the aircraft was designed. These component lives were based upon a conservative assumption of the percentage of flight time and number of discrete events that each component could spend in damaging flight regimes. When the AH-64D was designed, the fatigue lives of parts that are common between the AH-64A and AH-64D were re-assessed based upon design assumptions of AH-64D separate fleet and training usage. Since the common parts are not tracked by AH-64A/D mission design series, the Army always assumes that the design fatigue life of a common part is based upon the usage that produces the shortest of the three possible fatigue lives: AH-64A usage, AH-64D fleet usage, or AH-64D training usage. Therefore, flight regime usage for any individual common part may be determined by any of the three usage scenarios. As shown in Fig. 6, the AH-64A and AH-64D have 100 discrete parts in common that may experience damage in any of 1,210 defined combinations of aircraft configurations and flight regimes. For simplicity, Fig. 6 groups the 1,210 flight regimes into 15 types. The sample results shown in Fig. 6 are based upon approximately 53 flight hours of AH-64A LTF usage. Fig. 5 LTF Data Analysis Process Fig. 6 AH-64A Regime Usage 128 HUMS 2003 Conference
The black bars are an aggregate of the percent time or number of events per flight hour in the damaging regimes that the 21 AH-64A component failure modes were designed to experience. The black and gray bars are the aggregate of the AH-64D design training usage. The gray and white bars are the aggregate of the AH-64D design fleet usage, and the red bars are the aggregate of the actual LTF experience. Although a large percentage of LTF time was spent in the most damaging type regimes, such as banked turns, the time was spent in the lower aspects of the regime type. For example, most of the 53-hour sample of damaging LTF banked turns occurred at relatively low angles that produce only mild damage. The actual damage produced by the LTF flight regime experience can be seen in Fig. 7. resulted in loss of aircraft. The second listed QDR resulted from the discovery of excessive play between three PCL rod ends and their bearings. The PCLs are not fatigue life-limited components and are removed and replaced based upon inspection for excessive wear. However, the pitch housing is an adjacent lifelimited component, and the PCLs and pitch housing are subject to similar loads and stresses, and therefore wear and damage, from the same type flight regimes. Fig. 8 AH-64A Damage Rate Accumulation Fig. 7 AH-64A Accumulated Damage AH-64A Accumulated Damage by Damaging Flight Regime: Fig. 7 shows the aggregate of the damage experienced by the 21-component failure modes for each type of flight regime. This chart is a normalized comparison of the aggregate of the 28-component design damage with the actual damage experienced in the first 53 hours of LTF usage. Fig. 7 shows that most of the first 53 hours of AH-64A LTF damage occurred due to ground-air-ground cycles. AH-64A Damage Rate Accumulation: The normalized cumulative AH-64A LTF damage for the aggregate of the 21 component failure modes is compared to the normalized design values in Fig. 8. The chart is the 53-hour accumulation of 35 flights and shows the overall damage intensity is about 50% of the design value for the aggregate of the 100 life-limited components. AH-64A LTF Quality Deficiency Reports (QDR): The six initial AH-64A LTF QDRs are summarized in Fig. 9. The first two listed QDRs are related to the Pitch Change Link (PCL) assembly. The first was a Category I, or safety of flight, deficiency that involved a worn PCL rod end. The rod was on the verge of separating from the bearing, which could have Fig. 9 AH-64A Initial Quality Deficiency Reports AH-64A Pitch Housing Damage Accumulation: The pitch housing is one of the 21 life-limited component failure modes used in determining the AH-64A damage index. The design and the first 53 flight hours of AH-64A LTF usage are shown in Fig. 10. The pitch housing damage for the flight in which excessive vibrations, due to PCL degradation, were experienced was tacked on to the 53 flight hours of damage as shown in Fig 10. It should be noted that the pitch housing damage rate for that flight exceeded the overall design damage rate by 130%. Although the data are not conclusive, it may be surmised that the intensity of the flight may have exacerbated the PCL wear. HUMS 2003 Conference 129
Fig. 10 AH-64A Pitch Housing Damage Accumulation AH-64A RH NGB Incident: Block 3 of Fig. 5 is a schematic of the LTF flight incident evaluation process. An example of such an incident occurred during an LTF flight at Ft. Rucker, AL, when a chip light indicated a metal chip was detected in the Right Hand (RH) (or No. 1) Nose Gearbox (NGB). The aircrew performed the appropriate corrective action that resulted in the shutdown of the No. 1 engine and landing of the aircraft. The time histories of the pertinent flight parameters for the NGB incident are shown in Fig. 11. Important incident events are noted and chronologically numbered. A post-flight inspection of the RH NGB revealed that there were large metal fragments present in the gearbox. The NGB was held as a QDR exhibit. Teardown at the depot will document the nature of the failure. FLEET USAGE Block 4 of Fig. 5 identifies an essential element in achieving the potential benefits of the LTF Program. Having a better understanding of actual fleet usage can enhance the value of LTF. Downloading and analyzing the AH-64D on-board Maintenance Data Recorder (MDR) data can provide fielded Apache aircraft usage information. These data will be compared to AH-64D LTF usage to ensure achievement of LTF goals. Also, AH-64D usage will be correlated with maintenance actions to determine the impact of usage intensity on maintenance actions. For example, unscheduled gearbox overhauls will be correlated with pertinent usage parameters, such as:! Number of cold starts! Time spent at various engine torque levels! Time spent in stressful aircraft maneuvers AH-64A and AH-64D aircraft have common systems and components; therefore, knowledge obtained on the AH-64D will benefit the AH-64A. SUMMARY The LTF Program is a systems engineering approach to the evaluation and understanding of helicopter usage faults, failures, and trends. This objective is achieved by selectively accelerating U.S. Army helicopter usage to experience usagerelated faults and failures prior to their occurring during fleet usage. The LTF Team accomplishes the data evaluation by collecting, archiving, transmitting, analyzing, and correlating helicopter maintenance, fault, and failure information with helicopter usage information to identify adverse usage trends. The LTF Program is also a systems approach to evaluating inflight faults and failures by analyzing flight recorded parameter time histories to understand the nature and cause of the incident. In some cases, the analysis includes the assessment of the flight s geographic location and environment of the incident. When required, the flight is animated to understand aircraft motion and response at the time of the incident. Fig. 11 AH-64A RH NGB Incident 130 HUMS 2003 Conference