GRASSHOPPER 721D Service Manual
The GRASSHOPPER 721D service manual provides a comprehensive overview of the machine's intended use, major components, and the general maintenance philosophy required to keep the mower operating safely and reliably. This section outlines the purpose and scope of the machine’s service guidelines, including typical operating environments, expected service intervals, and the standard tools and diagnostics used during routine maintenance. Understanding the intended application helps technicians diagnose issues accurately and perform preventive maintenance before problems escalate. The material covered here serves as a foundation for more detailed repair procedures and component-specific guidance that follow in later sections of the manual.
Safety precautions and personal protective equipment (PPE) are emphasized to protect technicians during maintenance and repair tasks. Proper PPE includes eye protection, cut-resistant gloves, hearing protection, and steel-toed footwear as standard, with additional gear such as respiratory protection when working in dusty or fuel-tume environments. The manual stresses the importance of securing the machine on a flat, stable surface, engaging the parking brake, and disconnecting the battery or power source before any service work begins. Lockout/tagout procedures should be observed to prevent accidental start-up, and fire prevention measures must be in place when handling fuels and lubricants. Adherence to these safety guidelines minimizes the risk of injury and equipment damage during routine maintenance or complex repairs.
Equipment identifiers and model coverage are detailed to ensure the correct parts and procedures are used for the GRASSHOPPER 721D. The section clarifies model-specific nomenclature, serial number ranges, and compatibility notes for common replacement components such as blades, belts, filters, and hydraulic parts. It also outlines how to locate critical identifiers on the machine, including decals and sticker codes that indicate production year, OEM specifications, and recommended service intervals. This information is essential when ordering parts or cross-referencing service manuals, helping to avoid substitutions that could compromise performance or safety. Technicians should verify the exact model and variant before performing any repairs or part replacements.
Hazard analysis and risk factors are identified to support proactive risk mitigation during service tasks. Potential hazards include stored energy from springs or hydraulic systems, fuel and oil exposure, moving parts during blade or drivetrain maintenance, and hot surfaces after operation. The manual provides a framework for assessing risk in each service scenario, documenting control measures, and implementing safe work practices such as relieving pressure, draining fluids when appropriate, and using stand-by equipment for support. By understanding the specific hazards associated with the GRASSHOPPER 721D, technicians can develop a site-specific safety plan, select appropriate tools, and follow step-by-step procedures that reduce the likelihood of injury and equipment damage during maintenance and repair work.
Specifications and tools required
The GRASSHOPPER 721D is designed for reliable performance in a variety of turf management tasks. A clear understanding of its technical specifications helps technicians diagnose issues accurately and perform maintenance safely. Key parameters include engine type, displacement, horsepower, and cooling method, as well as fuel requirements and electrical system details. Ensuring compatibility with replacement parts and fluids is essential to preserve OEM performance and warranty coverage. This section provides a concise overview to guide preventive maintenance and fault diagnosis without delving into disassembly procedures.
Technical specifications overview: The mower operates with a robust powerplant tuned for steady torque delivery across varying load conditions. It uses a liquid-cooled, air-cooled hybrid cooling approach in some configurations to maintain optimal operating temperatures during extended use. The cutting system is designed for uniform grass dispersion and consistent blade engagement, with blade tip speeds calibrated to balance cut quality and safety. Electrical systems include a standard 12-volt battery setup, charging circuit, and safety interlocks that must be verified functional during service checks. Overall dimensions, weight, and center-of-gravity considerations affect transport, storage, and maneuverability during field servicing. Technicians should confirm these specs against the service data plate prior to any repair work to ensure correct part compatibility and torque recommendations.
Recommended tools and torque settings: Assemble a service toolkit that includes a metric and imperial combination wrench set, a torque wrench with a range suitable for small fasteners, a set of Allen keys, and a magnetized screwdriver for secure fastener handling. A digital multimeter is essential for diagnosing electrical issues, while a fuel pressure gauge and compression tester may be required for engine-related faults. Specific torque values for critical fasteners should be referenced from the OEM torque chart, but general practice emphasizes clean mating surfaces, proper thread engagement, and the use of appropriate thread lock compounds where recommended. When assembling or reassembling components, always torque to specification in a star or crisscross pattern to promote even seating and prevent distortions. Keeping a calibrated torque wrench and clean, organized fasteners improves service quality and reduces rework risk.
Required fluids and lubrication: Use only specified fluids and lubricants to maintain cooling efficiency, fuel system integrity, and drive train reliability. The engine requires a high-quality gasoline or diesel fuel per OEM guidelines, with consideration for seasonal and regional octane or cetane requirements. Lubricants for the engine, transmission, and lubrication points should align with the manufacturer’s viscosity ratings and service intervals. Regular oil changes, auxiliary lubrication, and proper greasing of pivot points and bearings extend component life and reduce risk of seizing or uneven wear. Always verify fluid compatibility, color, and odor when inspecting during routine maintenance, and replace filters in accordance with the maintenance schedule to sustain peak performance and prevent contamination from degrading performance. Proper drainage and containment procedures are essential when servicing, to prevent environmental exposure and ensure safe operation upon startup.
Initial inspection and preparing for service begins with a systematic approach to verify overall condition before disassembly. Begin by reviewing the operator’s manual for any model-specific cautions and ensuring the machine is on a flat, stable surface with the parking brake engaged. Visually inspect the exterior for signs of fluid leakage, damaged panels, loose fasteners, or unusual wear on tires, belts, and blades. Record any abnormal conditions and prepare a concise checklist to compare against the service findings as you progress. This preparation helps prevent accidental damage during service and ensures you address the most critical maintenance tasks first.
Pre service inspection steps involve gathering essential tools, identification of model and serial numbers, and confirming battery status if applicable. Remove the key and disconnect power sources as required by the manufacturer to minimize the risk of accidental engine start or electrical shock. Check fluid levels including fuel, oil, coolant, and hydraulic circuits, noting any low readings or signs of contamination. Use a calibrated dipstick or sight glass where provided and verify that level indicators fall within the recommended ranges. Documenting these readings provides a baseline for future maintenance and helps identify leaks or consumption issues early.
Removing the cover panels and access points requires careful attention to retaining fasteners and electrical connectors. Start with the primary access panels that give you visibility to the engine compartment and drive components, using the correct screwdriver or socket to avoid rounding the fasteners. As panels are removed, label or photograph connections to simplify reassembly, and check for heat damage, corrosion, or frayed wiring behind the covers. Exercise caution around moving parts and hot surfaces, allowing the engine and components to cool before handling. A methodical approach to panel removal prevents damage to clips, gaskets, and plastic housings while exposing critical serviceable areas.
Safety checks and battery handling are essential to protect personnel and ensure reliable operation after service. Inspect the battery condition, terminals, and mounting to confirm there are no cracks, swelling, or loose connections. Clean terminals if corrosion is present and apply a suitable anti-corrosion treatment as recommended by the manufacturer. When handling the battery, use insulated tools and wear appropriate PPE, including eye protection and gloves, particularly if there is a risk of electrolyte exposure. Finally, ensure all safety interlocks, guards, and shields are reinstalled correctly after service to maintain the integrity of the machine’s protective systems and reduce the likelihood of injury during subsequent operation.
Engine and fuel system maintenance
The Grasshopper 721D is designed with a compact, integrated engine and fuel system that emphasizes reliability and ease of service. A clear understanding of the fuel system overview helps technicians identify potential failure points and plan preventive maintenance. Regular inspection of fuel lines, tanks, and connections reduces the risk of leaks, air ingress, and fuel contamination, which can compromise performance and engine longevity. Visual checks should be complemented by listening for abnormal engine sounds, investigating popping or misfiring, and noting changes in throttle response or idle stability. Keeping a clean environment around the fuel system also guards against dirt and debris entering critical components during service procedures.
Engine and fuel system maintenance starts with confirming fuel type, proper specifications, and ensuring the fuel is clean and free of water. The system relies on precise fuel delivery for optimal combustion and performance, so using fresh fuel and approved additives when recommended by the manufacturer is crucial. Periodic testing of fuel quality, including appearance, odor, and phase separation, helps detect issues before they affect operation. It is important to follow correct procedures when depressurizing lines or removing components to prevent fuel spills and ensure personal safety. Additionally, maintaining proper ventilation around the engine compartment reduces the risk of vapors accumulating in enclosed spaces during service.
The air filter service and intake maintenance play a pivotal role in protecting the engine from particulates that can cause wear and reduced efficiency. Inspect the air filter housing for cracks or damage and replace the filter according to the maintenance schedule or after a high-humidity, dusty, or wet environment. When removing and reinstalling the filter, ensure the sealing surfaces are clean and free of debris to prevent unmetered air entering the intake. A clean, properly seated air filter delivers consistent airflow, improves fuel economy, and minimizes engine strain during load changes. For hard-to-reach air intakes, consider using a soft-bristle brush and compressed air in short bursts to preserve filter integrity while removing embedded dust.
Fuel filter replacement and fuel lines inspection are critical for ensuring the engine receives clean, unobstructed fuel flow. Replace the fuel filter at intervals specified by the manufacturer or whenever it appears dirty, saturated, or damaged. When replacing, pre-fill with clean fuel if recommended to minimize air in the line and to facilitate easier priming. Inspect all fuel lines for signs of cracking, swelling, or hardening, and replace any suspect sections promptly. Secure all clamps and fittings to prevent leaks and ensure that routing avoids hot surfaces or moving parts that could cause abrasion. After service, perform a thorough check for leaks around the filter housing, connections, and any injector lines to confirm system integrity before returning the machine to service.
The engine cooling system inspection is essential to prevent overheating, which can lead to reduced performance and accelerated wear. Check coolant levels and verify that the mixture complies with the specification for the operating environment. Inspect the radiator or cooling fins for debris, damage, and proper airflow; clean or repair as necessary to maintain efficient heat exchange. Examine hoses, clamps, and the thermostat for signs of wear or failure, replacing any components with visible cracks, bulges, or leaks. For liquid-cooled engines, ensure the overflow reservoir is functioning correctly and that cap seals are intact. Regularly verify that the cooling system operates within the recommended temperature range during idle and under load to avoid stressing the engine and to sustain longevity of both fuel and cooling components.
Electrical system and controls
The electrical system of the Grasshopper 721D is designed to provide reliable operation across all essential functions, including starting, charging, lighting if equipped, and safety interlocks. Begin by visually inspecting the battery terminals for corrosion, looseness, or bent posts before performing any electrical tests. Use a digital multimeter to confirm battery voltage is within the recommended range, typically around 12 to 12.6 volts for a fully charged lead-acid battery. If voltage is low, perform a careful charge following the manufacturer’s specifications and avoid overcharging, which can damage both the battery and electrical components. Always disconnect the negative terminal first when performing any service to minimize the risk of short circuits. Throughout inspection, look for signs of heat damage, melted insulation, or frayed wires that could indicate excessive resistance or impending failure.
Wiring harness and connector checks are critical for reliable operation, as a compromised harness can cause intermittent starting problems or sensor failures. Inspect the entire harness for cracked insulation, loose or corroded connectors, and pin retention. Disconnect plugs one at a time using the appropriate sequence to avoid mislabeling, and perform a gentle tug test to ensure pins remain seated. Apply dielectric grease to weather-sealed connections to improve resistance to moisture ingress, but avoid excessive lubrication that could attract dirt. When tracing wires, follow the harness routing to ensure it remains protected from moving parts and hot surfaces, securing with appropriate fasteners or zip ties where necessary. Any damaged sections should be replaced with OEM-spec harnesses to maintain electrical integrity and safety compliance.
The ignition system inspection and troubleshooting should focus on the key and switch assemblies, spark paths (where applicable), and related sensors. Check the ignition switch for smooth operation without sticking or excessive play, and verify that it returns to the “off” position reliably. For engines with electronic ignition, verify that the ecu or ignition module receives proper signals by testing the relevant sensor outputs with a multimeter or oscilloscope if available. Inspect ignition coils or spark plugs for signs of fouling, wear, or cracks, and replace as recommended by service data. Ensure that ground connections are solid and free of corrosion, as poor grounding can cause erratic starting behavior or misfires. When diagnosing no-start conditions, confirm battery voltage during crank and inspect related fuses and relays in the circuit path to isolate the fault efficiently.
Safety interlock and switch verification is essential to ensuring the machine operates only when all safety conditions are met. Begin by testing each interlock according to the service data, ensuring that the mower will not start if the operator is not seated or if the safety bar is disengaged. Check the wiring to interlocks for continuity and correct orientation, ensuring that any pins or harness connectors are properly seated. If a switch shows intermittent operation, replace it rather than attempting to bypass for safety reasons. Validate that all protective covers and guards are in place and that their associated switches are depressed during normal operation. Finally, test the full sequence of starting, engaging systems, and cutting operations to confirm that safety interlocks prevent operation in unsafe conditions and function correctly under typical use scenarios.
Hydraulic system maintenance
The hydraulic system in the GRASSHOPPER 721D requires careful inspection and routine service to ensure optimal performance and long component life. Begin with a thorough visual check of all hydraulic lines, hoses, fittings, and the reservoir area for signs of wear, cracking, or leaks. Note any discoloration, oil sheen, or signs of seepage around seals and connections, and address these issues before operating the machine further. Maintain a clean work environment during service to prevent dirt ingress, which can compromise seals and valves. Always follow the manufacturer’s specified service intervals and use only approved hydraulic fluids and filters to avoid compatibility problems that could degrade system performance. Regular filter service and line checks are essential for maintaining clean, contaminant-free hydraulic fluid and preventing premature wear. Start by removing and inspecting the hydraulic reservoir cap and breather to ensure it is clean and free of debris. Replace the primary and secondary filters at the recommended intervals using filters that meet the OEM specifications. When inspecting hydraulic lines, look for soft spots, bulging, or corrosion on metal sections, and replace any damaged portions promptly. During line checks, ensure all clamps and brackets are secure to prevent movement that could cause abrasion or leaks during operation. After completing maintenance, perform a visual proof test with the hydraulic system at low pressure to verify that there are no active leaks. Detecting leaks and troubleshooting requires a systematic approach to isolate the source and determine the appropriate corrective action. Start by cleaning the suspected area to ensure any new leaks are easy to identify. Check inlet and outlet ports on pumps, valves, and actuators for tightness; re-torque if specified, and replace any worn seals or gaskets as needed. Monitor hydraulic fluid level and quality; dark or milky fluid can indicate contamination or moisture ingress and should be tested and treated accordingly. If a leak is found at a connection, reseal with the correct sealant or replace the fitting, ensuring threads and surfaces are clean before reassembly. In persistent cases, consult the service manual for torque settings and component-specific leak troubleshooting steps to avoid over-tightening that could damage parts. Pressure testing procedures are performed to confirm system integrity and verify proper valve operation under operating conditions. With the engine off, gradually pressurize the system and observe all gauges for stable readings within the manufacturer’s specified range. Conduct a functional test of each hydraulic circuit, including lift, tilt, and drive functions, to ensure smooth and predictable responses. If pressure fluctuations or drops occur, identify potential restrictions, air entrainment, or internal component wear that could be causing the issue. Use antimicrobial-grade transmission fluid or hydraulic oil as recommended by the OEM to prevent microbial growth and maintain fluid properties. Record all test results, including any adjustments made, and verify that pressure readings return to normal after the test cycle is complete. By following these procedures, you can sustain reliable hydraulic performance and extend the service life of the GRASSHOPPER 721D.Mower deck and cutting system
The mower deck on the GRASSHOPPER 721D is a precision component designed to deliver consistent cutting height and even discharge. Regular inspection of the deck structure, spindles, and belt drive is essential to maintain peak performance and extend service life. Begin by visually inspecting the deck for any signs of distortion, cracks, or corrosion, paying particular attention to welded joints and bracket mounts. When a deformation is detected, remove the deck from the machine and perform a thorough check for straightness using a flat reference surface or a dial indicator setup if available. Any misalignment can lead to uneven cutting height, increased belt wear, and accelerated bearing failure. Deck alignment is critical for uniform blade height across the cutting path. Measure from a common reference point on the deck plate to each blade spindle, ensuring that the height across all four quadrants matches the target setting specified in the operator’s manual. If misalignment is found, adjust deck lift arms and mounting points in small increments, rechecking dimensions after each adjustment. After completing alignment, run the mower on a level surface with the blades disengaged to verify that the cutting edges sit parallel to the ground. Use a calibrated blade gauge to confirm consistent clearance between the blade tips and the ground, and document the results in the maintenance log for future reference. Blades inspection and sharpening is a routine task that directly affects cut quality and safety. Remove the blades one at a time using proper PPE and a blade removal tool to prevent injuries. Inspect for cracks, nicks, and excessive wear, especially at the blade root and edge. If damage is found, replace the blade with an OEM part and balance the replacement to prevent vibration that can stress spindles. When sharpening, use the correct angle and technique recommended by the manufacturer, and preserve a consistent bevel to maintain efficient airflow and balanced cutting. After reinstalling, torque all blade retainers to the specified specification and recheck blade runout with a dial indicator to ensure there is no runout that could cause vibration or uneven cut. Spindle and bearing service is essential for smooth operation and long spindle life. Before service, disconnect power and lock out any electrical sources as required by your safety protocol. Inspect spindle housings for signs of leakage, scoring, or unusual heat symptoms after recent operation. If bearings feel gritty or exhibit play, replace them and check the spindle seals for integrity. When performing bearing service, remove the spindle, clean all oil passages, and repack or replace bearings with manufacturer-approved lubricants. Reassemble with proper torque on all mounting bolts and verify that the spindle rotates freely with minimal radial play. Run the deck at low speed to listen for any abnormal noise that could indicate a failing bearing or misalignment, and address issues promptly. Deck belt and pulley inspection is necessary to ensure efficient power transfer and consistent cutting performance. Visually inspect belts for wear, cracks, fraying, glazing, or missing teeth, and replace any damaged belts immediately. Check belt tension according to the specified range, and adjust the belt idlers and pulleys to achieve even tension across all drive belts. Inspect the pulleys for groove wear and ensure alignment with the belt path to prevent rapid belt wear and heat buildup. After servicing belts, run the mower briefly with the blades disengaged to listen for unusual noises and verify that the belt tracks evenly within the belt guides. Maintain a clean belt path, removing grass clippings and debris after each use to minimize heat buildup and prolong belt life.Maintaining the tires, wheels, and chassis of a Grasshopper 721D is essential for reliable operation and safe handling. Regular inspection helps identify wear patterns, mounting issues, and corrosion before they lead to performance problems or safety hazards. Begin with a thorough visual examination of all tires for cracks, bulges, uneven tread wear, and embedded objects. Check the sidewalls for cuts or gouges that could compromise pneumatic integrity, and verify that the tread depth remains within the manufacturer’s specified limits. Tire pressure should be measured when cold and adjusted to the recommended PSI specified in the operator’s manual, paying close attention to any differential pressures between the front and rear tires that could affect steering and traction. If tire wear indicators are present, assess whether the wear is uniform across the tread or concentrated in specific areas, which may indicate misalignment or overloading. Any tire showing excessive wear or damage should be replaced promptly to maintain traction and load-bearing capacity.
Wheel mounting and balancing play a critical role in vibration control and steering precision. Before operation, loosen and inspect lug nuts for tightness and signs of loosening, corrosion, or elongation of the wheel studs. When removing and reinstalling wheels, clean mounting surfaces thoroughly to remove rust, dirt, and old lubricant residues that can compromise the seating of the wheel. After mounting, use a torque wrench to tighten studs to the manufacturer’s specified torque in a star or crisscross pattern to ensure even clamping force. If vibration is detected during operation, recheck wheel balance with appropriate equipment and consider adding or relocating wheel weights to restore smooth operation. Regularly inspect wheels for cracks, corrosion, or bent rims, and replace any wheel that shows structural damage or out-of-roundness. Maintain proper hub cleanliness and ensure that any wheel adapters or spacers are installed only if specified by Grasshopper’s service guidelines.
Chassis frame checks and rust prevention are vital for longevity and stability of the machine during heavy use. Inspect the frame rails and cross members for signs of cracks, weld failure, or deformation that could affect alignment or load distribution. Look for rust at welds, joints, and underbody surfaces where moisture collects, and address any corrosion with appropriate rust inhibitors and coatings recommended by Grasshopper. Treat exposed metal surfaces with a rust-preventive primer and paint system designed for outdoor equipment, ensuring complete coverage of seams and hidden areas where moisture tends to accumulate. Regular cleaning to remove soil, sap, and salt exposure, followed by drying, helps slow corrosion; consider applying a protective wax or sealant on exposed metal after cleaning. Keep drainage paths clear around the chassis to prevent water pooling, which accelerates rust formation. Finally, establish a maintenance schedule that documents inspection intervals, findings, and corrective actions to support traceability and long-term reliability of the Grasshopper 721D chassis.
Diagnostics and troubleshooting for the GRASSHOPPER 721D begin with a clear understanding of common faults and their typical symptoms. Operators should note patterns such as loss of power, unusual engine noises, misfiring, hard starting, excessive smoke, oil leaks, irregular cutting height, or abnormal vibrations. Documenting exact conditions under which the fault occurs—such as temperature, load, and idle status—helps isolate possible causes. Safety first remains paramount; always disconnect power, follow lockout/tagout procedures, and wear appropriate personal protective equipment when inspecting components. A systematic approach reduces diagnostic time and prevents unnecessary disassembly, preserving warranty coverage and minimizing equipment downtime. Keeping a detailed symptom log supports accurate communication with repair teams and parts departments when escalation is needed.
Diagnostic steps and tools for the GRASSHOPPER 721D are designed to assess both electronic control systems and mechanical subsystems. Begin with a visual inspection for obvious issues such as loose connections, damaged wiring insulation, fuel leaks, or damaged belts. Use a multimeter to verify battery voltage, alternator charging, and sensor signals, ensuring readings are within manufacturer specifications. Functional tests such as a compression check, spark verification, and fuel delivery assessment help pinpoint internal engine faults. For hydraulic-driven components, inspect for fluid contamination, pressure readings, and valve operation. Employ diagnostic software or service tools provided by the manufacturer to read fault codes from the engine control unit and interpret them in the context of observed symptoms. Record all readings methodically to support trend analysis and future troubleshooting efforts.
Repair decision pathways guide the technician from diagnosis to action with efficiency and accuracy. If a fault is isolated to a single subsystem with available serviceable parts, plan a targeted repair or replacement while considering the remaining service life of related components. When fault codes indicate a critical failure or potential safety risk, prioritize immediate repair or component replacement to prevent further damage or hazardous operation. For intermittent faults, consider environmental factors, wiring integrity, and connector corrosion, and reproduce the condition under controlled test runs to confirm the root cause. If multiple issues coexist, assess whether one fault could be causing secondary symptoms and address the primary problem first to simplify the repair and reduce downtime. Always verify the repair by performing a post-repair test run that simulates typical operating conditions, checks for abnormal noises, and confirms proper machine performance across all control modes and safety interlocks.
Maintenance schedules and record keeping
Establishing a structured maintenance routine for the GRASSHOPPER 721D ensures reliable performance, longevity, and safety in operation. Begin with a comprehensive schedule that separates tasks by operating hours, calendar time, and after-event conditions such as unusual vibrations, fuel spills, or impact damage. Document the recommended intervals for critical systems including engine service, lubrication, cooling, belt and pulley inspection, hydraulic components, and electrical connections. Maintain a consistent cadence for both preventive and predictive maintenance to catch wear before it leads to failure. Tailor the schedule to the specific working environment, load, and frequency of use to optimize uptime and minimize unscheduled repairs.
Routine maintenance should be performed by qualified personnel who follow the manufacturer’s specifications and torque recommendations. Use a calibrated timer or hour meter to track running time accurately and align service actions with the recommended intervals. Before performing any service, disconnect power sources and depressurize hydraulic circuits as required to prevent accidental startup or fluid release. Record the date, operating hours, and the technician’s initials for every maintenance action to create a traceable history that can be referenced during future repairs or resale. A well-kept schedule reduces downtime and provides a clear record for warranty validation and fleet management.
Service log templates provide a consistent framework for capturing essential maintenance data. Include fields for date, machine ID, operator, service performed, parts replaced, measurements taken (such as belt tension or fluid levels), tools used, and next due date or hours. Digital logs backed by cloud storage can enhance accessibility across a maintenance team, while printed copies ensure availability in the field. Ensure that log entries are legible, timestamped, and free of ambiguities to support troubleshooting and trend analysis. Regular audits of the log can help identify recurring issues, enabling proactive replacements before a failure occurs.
Parts ordering and inventory management should be integrated into the maintenance workflow to minimize downtime. Maintain a minimum stock level for consumables (oil, filters, belts, seals) and critical replacement items known to have longer lead times. Establish preferred suppliers with clear part numbers, pricing, and lead times to streamline the purchasing process. Create a reorder point system that automatically triggers procurement when stock falls to a specified threshold. Regularly review inventory accuracy, reconcile discrepancies, and rotate stock to prevent deterioration of aging parts. A proactive inventory approach reduces delays, improves service reliability, and supports rapid return-to-service after maintenance tasks.