Ground Operations and Servicing

Chapter: Ground Operations and Servicing

Overview

This chapter covers the fundamental knowledge and procedures required for safe and compliant aircraft ground operations and servicing. It encompasses the regulatory framework governing maintenance documentation, inspection requirements, ground handling procedures, fueling operations, and the servicing of aircraft systems. Mastery of these topics is essential for aircraft maintenance engineers (AMEs) to ensure airworthiness, safety, and regulatory compliance in all ground-based activities.

Regulatory Framework for Maintenance and Inspections

Return to Service Requirements (14 CFR 43.9)

When an aircraft is returned to service after maintenance, the mechanic must make a complete logbook entry that includes:

The entry must be specific and clear. Vague descriptions or entries lacking necessary details are not legally acceptable. For example, a minor repair on a flap actuator requires a logbook entry describing the work, the method of compliance, the date, and the mechanic's certification information.

Inspection Requirements (14 CFR 91.409)

The 100-hour inspection is a mandatory requirement for aircraft operated under Part 91 when carrying passengers for hire or providing flight instruction. Key points include:

Annual Inspection Requirements (14 CFR 43.15)

The annual inspection follows similar principles to the 100-hour inspection but is required on an annual basis regardless of flight hours. The inspection scope includes all items listed in 14 CFR Part 43 Appendix D, which covers airframe, powerplant, and systems checks.

Major Repairs and Alterations (FAA Form 337)

Major repairs and alterations require special documentation and approval processes:

Airworthiness Directives (ADs)

An aircraft with an uncomplied Airworthiness Directive is not airworthy under 14 CFR 91.403. When an AD is discovered during an inspection:

Mechanic Responsibilities and Certification

Mechanics must only certify work that has been completed and found satisfactory. Signing a logbook entry for an inspection that was not performed is a violation of 14 CFR 43.9 and 14 CFR 65.83. This is a federal offense that can lead to certificate action and safety risks. The correct action is to refuse to sign and complete the inspection before signing.

Weight and Balance Procedures

Leveling Requirements

Accurate weight and balance calculations require the aircraft to be in a level attitude to ensure the scales measure the true vertical load at each weighing point. If the aircraft is not level (e.g., tail 2 inches low):

The correct procedure is to level the aircraft with shims and re-weigh to ensure accuracy.

Documentation of Weight and Balance Data

Any major alteration that affects weight and balance requires:

The Pilot's Operating Handbook (POH) is updated, but the legal record is the Form 337 and logbook. This ensures traceability and airworthiness documentation.

Ground Handling and Towing Operations

Towing Preparation

Before beginning any towing operation, the technician must:

The steering bypass pin disconnects the steering actuator from the nose gear, allowing free castering during the tow. Failure to install this pin can damage the steering system. The shear pin is a secondary safety device designed to fail under excessive load.

Towing Procedures

During towing operations:

Tow Bar Failure

If the tow bar shear pin fails during towing:

A failed shear pin indicates excessive tow load or an obstruction. Continuing could damage the nose gear or aircraft structure. A broken tow bar means loss of control; the aircraft must be secured immediately to prevent movement.

Marshaling Signals

The wing walker's primary responsibility is to ensure wingtip and obstacle clearance during ground movement. A stop signal from a wing walker is a critical safety command indicating an imminent collision hazard. The pilot must comply immediately. Clear ground communication and adherence to standard marshaling signals are essential for ramp safety.

Fueling Operations

Fuel Spill Response

Any fuel spill presents a fire hazard and must be addressed immediately. The correct sequence of actions is:

Continuing fueling or using a dry rag is unsafe and violates standard fueling procedures. Wiping with a dry rag can spread the fuel and create a fire hazard. Solvent dilution is not appropriate, and leaving fuel to evaporate is unsafe.

Fuel Truck Positioning

When positioning a fuel truck near an aircraft:

Fuel Contamination

Water and debris in fuel samples are a safety hazard and a common cause of engine failure. The correct procedure is:

Engine Ground Operations

Reciprocating Engine Oil Pressure Fluctuations

Fluctuating oil pressure, even within manufacturer's limits, can indicate serious problems such as:

Immediate shutdown prevents potential engine damage. Continuing the run-up risks catastrophic failure. Reducing RPM may not resolve the issue, and returning to service ignores a potential safety hazard.

Turbine Engine EGT Limits

Exceeding Exhaust Gas Temperature (EGT) limits can cause severe thermal damage to turbine blades and other hot-section components. The immediate action when EGT exceeds limits is:

Turbine Engine EGT Troubleshooting

If EGT is high but N1, N2, and fuel flow are normal, the most likely cause is an instrumentation error, such as:

Actual engine problems like FOD, blocked nozzles, or compressor issues would typically affect other parameters (e.g., fuel flow, RPM, or vibrations). Troubleshooting should start with verifying the EGT system.

Fire Protection Systems

Ground operations involving engine runs require that all fire protection systems are fully serviceable. A missing discharge indicator or broken detection loop constitutes a fire protection system malfunction, making the aircraft unairworthy for engine operation. Deferring the test and performing necessary repairs complies with 14 CFR 91.7 and manufacturer's maintenance requirements.

Aircraft Servicing Procedures

Oil Servicing

When adding oil to an engine:

Oil Level Checks on Warm Engines

Oil expands when warm. A warm engine reading at minimum may actually be at the correct cold level. Adding oil while warm could overfill the system, causing foaming and potential engine damage. Always check fluid levels under specified temperature conditions per the engine manufacturer's manuals.

Landing Gear Strut Servicing

A low strut with correct tire pressure and weight indicates a loss of both nitrogen and hydraulic fluid. The correct procedure is:

Simply adding fluid or nitrogen without deflating can trap air and create an unsafe condition.

Tire Pressure and Condition

Brake Components

Brake discs worn beyond the manufacturer's service limit are unairworthy and must be replaced. Replacement of a brake disc is typically considered a minor repair or preventive maintenance but must be documented in the aircraft maintenance records per 14 CFR 43.9. Sanding or lubricating a brake disc is not acceptable practice and could compromise braking performance.

Oxygen Systems

The green discharge disc on an oxygen cylinder is a safety device that ruptures to relieve pressure in case of overheat or fire. A missing disc compromises system safety. The aircraft is not airworthy until the correct disc is installed.

Deicing Procedures

Deicing fluids can be corrosive to acrylic windshields and may cause crazing or cracking. Standard deicing procedures require:

Continuing application is unsafe; using higher concentration or wiping can worsen damage.

Inspection Findings and Corrective Actions

Metallic Particles in Oil Filters

Metallic particles in the oil filter are a serious indicator of internal engine wear or damage, such as bearing or gear wear. Even if engine operation appears normal, continued operation could lead to catastrophic failure. The correct action is to ground the aircraft and perform a thorough inspection.

Control Cables

Control cables with broken wires, even if the diameter is still within limits, must be replaced. Broken wires indicate fatigue and potential failure under load, compromising flight control integrity. This complies with 14 CFR 43.13(a) and manufacturer's maintenance instructions.

Fluid Lines

Fluid lines with damage exceeding allowable limits (chafing, nicks, or corrosion) must be replaced. A 10% wall thickness loss in a fuel line compromises pressure integrity and could lead to a fuel leak and fire hazard. Replace the line and address the chafing cause with a cushioned clamp.

Fasteners

Any fastener showing corrosion, stretched threads, or other damage must be replaced. Reusing corroded fasteners can lead to failure under load, and a stretched bolt indicates over-torque or fatigue. Install new fasteners and torque per the applicable manual.

Pitot-Static Systems

A blocked static port affects pitot-static instruments critical for IFR flight, including altimeter, airspeed, and vertical speed indicators. Operating under IFR with a blocked static port is unsafe and violates 14 CFR 91.7. Clear the port and test the system to ensure accurate instrument indications.

Landing Light Lenses

A cracked landing light lens is a defect that must be corrected to return the aircraft to service after a 100-hour inspection. The lens is part of the airframe, and its failure could lead to bulb damage or foreign object debris. Placarding the landing light inoperative is not allowed because it is required for night flight under 14 CFR 91.205.

Structural Damage

Without approved data or a repair method, the effect of structural damage on integrity is unknown. The mechanic must ensure the aircraft is airworthy before returning it to service. AC 43.13-1B is not a blanket approval without assessing the specific damage per its guidelines. A ferry permit is not appropriate for a known unairworthy condition.

Key Principles and Relationships

Safety Priority

Safety is paramount in all ground operations. When any anomaly is detected:

Documentation Integrity

Accurate documentation is a legal requirement, not just a procedural formality. Every maintenance action must be properly recorded with:

Manufacturer's Data vs. General Practices

While AC 43.13-1B provides acceptable methods, techniques, and practices, the manufacturer's maintenance manual takes precedence. Always consult the AMM for specific procedures, fluid types, pressures, and limits.

Airworthiness Determination

The determination of airworthiness is based on:

An aircraft with any known unairworthy condition must not be returned to service until the condition is corrected.

Summary

Ground operations and servicing require a comprehensive understanding of regulatory requirements, safety procedures, and technical practices. The AME must balance operational demands with strict adherence to airworthiness standards. Key takeaways include:

Mastery of these principles ensures safe ground operations and compliant maintenance practices.