Mar 31

Aircraft Parking and Storage: Airworthiness Guidelines for Inactive Aircraft

David Lapesa Barrera

Essential aircraft parking, preservation, and return-to-service strategies to maintain airworthiness.

Geopolitical disruptions are keeping more aircraft grounded than usual.

Aircraft parking and storage present operational, safety, and regulatory challenges. Proper management is essential to ensure compliance with aviation regulations, maintain airworthiness, minimize unnecessary maintenance costs, and enable an efficient return to service. Whether an aircraft is briefly between flights or grounded for an extended period, understanding the types of parking and required preservation measures is key for operators.

Types of Aircraft Parking and Storage

Normal Parking – Aircraft in normal parking remain on the ground between flights or maintenance events, typically for a few hours to overnight. These aircraft are immediately ready to fly. Basic servicing tasks, such as verifying tire pressure, refueling, and removing safety pins or protective covers, are generally sufficient. No extensive preservation measures are required.
Active (Short-Term) Parking – Active parking applies to aircraft out of operation for several days to a few weeks. At the start of parking, safety pins, protective covers, and plugs are installed, and initial preservation actions are applied. Periodic maintenance ensures operational readiness, including engine and APU operation, hydraulic and electrical system checks, and operation of environmental control systems (ECS). While not continuously ready for flight, aircraft in active parking can return to service on short notice.
Prolonged (Long-Term) Parking – Aircraft inactive for weeks to months require more comprehensive preservation. This includes lubrication of landing gear, protection of engine and APU fuel circuits, corrosion prevention on exposed metal surfaces, and inspection of seals and gaskets. Only essential periodic maintenance is conducted, and some components, such as engines or APUs, may be temporarily removed. Aircraft in prolonged parking are not immediately flight-ready and require careful preparation before returning to service.
Storage – Long-term storage refers to aircraft grounded for medium to extended durations, often exceeding three to six months. These aircraft are often located in areas with limited technical support. Major systems may be preserved or partially removed, including batteries, engines, APUs, oxygen bottles, or fire suppression equipment. Ballast may be installed to maintain balance, and a structured maintenance plan is necessary to prepare the aircraft for safe return to service.
Permanently Withdrawn from Service – The term ‘permanently withdrawn from service’ refers to moving the aircraft to a location that is not intended for storage or future return to service. Unlike storage or prolonged parking, no preservation or maintenance efforts are applied, and the aircraft is effectively retired from operational use.

Maintenance Clock Considerations

It is important to note that the aircraft maintenance clock does not stop during parking or storage. Calendar-based maintenance tasks defined in the Aircraft Maintenance Program (AMP) continue to accrue time even when the aircraft is inactive. Operators cannot unilaterally stop or skip these tasks; however, temporary adjustments or extensions may be authorized in consultation with the aircraft manufacturer and applicable regulatory authorities.

These adjustments are typically case-specific and require formal approval. The purpose is to ensure that safety and airworthiness are not compromised while allowing flexibility in scheduling maintenance during extended parking or storage periods. Operators must carefully track any changes to calendar-based tasks to ensure compliance and readiness for return-to-service operations.

Key Considerations for Aircraft Preservation

Exterior Protection and Corrosion Control

Exposed metal surfaces are vulnerable to corrosion during inactivity. Standard Corrosion Prevention and Control Programs (CPCP), including the application of corrosion preventive compounds and regular cleaning, reduce risk. Certain critical areas prone to corrosion may require additional inspections beyond the routine CPCP. Protective covers for engines, sensors, and landing gear further reduce environmental exposure, and periodic inspections help detect early corrosion to prevent costly repairs.

Interior Care

Aircraft interiors can be affected by moisture, contamination, or pest activity. Thorough cleaning before parking or storage removes debris, food, and waste. Cabin humidity should be maintained below 70% to prevent mold and material degradation. Periodic checks ensure seats, carpets, and other components remain in good condition.

Fuel System Management

Moisture in fuel tanks can promote microbiological growth and corrosion. Preventive measures include fuel sumping, biocidal treatment where permitted, and maintaining adequate fuel levels. Monitoring fuel quality during storage helps minimize maintenance and operational disruptions when returning to service.

Engines and APU

Engine and APU preservation depends on the parking duration. Short-term parking may require periodic operation, lubrication, and fuel circuit protection. Longer-term storage may involve engine removal or partial deactivation. Tracking these preservation tasks ensures operational readiness and reduces risk of damage.

Landing Gear, Wheels, and Tires

Landing gear systems should be cleaned and lubricated, with tires protected from UV exposure and flat spots. Safety pins and wheel chocks should be in place, and tires rotated periodically. Hydraulic systems, shock absorbers, and steering mechanisms require regular inspection to prevent operational issues upon return to service.

Flight Controls and Sensors

Flight control surfaces, cables, and linkages require maintenance to prevent corrosion, wear, or environmental damage. Lubrication and protective coatings may be applied, and periodic operation ensures functionality. External sensors, including pitot tubes and static ports, should be covered to prevent debris or animal intrusion, with inspection and cleaning before flight.

Electrical and Avionics Systems

During extended parking, electrical components may be partially or fully de-energized. Batteries can be removed and stored in controlled environments, with connectors capped to prevent contamination. For short-term parking, periodic power cycles help maintain readiness. Temperature and humidity management protects sensitive avionics and electronic equipment.

Environmental Control Systems (ECS)

Proper cabin ventilation and humidity control protect interior materials, avionics, and other systems. Air conditioning packs may be operated periodically, and independent dehumidifiers can be used to maintain optimal conditions. External air inlets and exhausts should be protected to prevent debris intrusion.

Return-to-Service Preparation

Each aircraft manufacturer provides tailored procedures for returning aircraft to service after periods of inactivity. These procedures are essential to complement AMP requirements and ensure airworthiness. Operators should follow manufacturer instructions carefully, including any exceptional checks or operational limitations, as part of the return-to-service process. Key steps typically include:

Inspecting all aircraft systems, including engines, APUs, hydraulics, flight controls, landing gear, and electrical systems.
Removing protective covers and plugs, cleaning sensors, and testing system operation.
Performing fuel system checks, including sumping, sampling, and treatment for microbial contamination if needed.
Inspecting the cabin for moisture, cleanliness, and interior integrity.
Ensuring compliance with regulatory requirements, ADs, and AMP.

Following a structured return-to-service plan ensures aircraft resume operations safely and efficiently while minimizing unexpected maintenance or delays.

Aircraft Configuration Verification

During parking or storage, aircraft may have components temporarily removed or transferred to other aircraft as part of operational or maintenance needs. These changes, along with preservation procedures or system deactivations, can result in differences between the aircraft’s actual configuration and the approved operational configuration.

A key part of returning an aircraft to service is confirming its actual configuration against the approved configuration. This includes both hardware and software components. Any deviations must be identified, documented, and corrected to ensure the aircraft meets certified operational standards. Actions may include reinstalling removed components, updating software, or performing additional inspections to restore compliance. Proper configuration verification is essential to ensure airworthiness and operational readiness.

Stay tuned for our upcoming article on safeguarding aircraft systems from cybersecurity risks during parking and storage.

Conclusion

Effective aircraft parking and storage require planning, preventive maintenance, and ongoing monitoring to protect safety and asset value. Understanding the requirements for each type of parking and implementing preservation measures for critical systems—engines, APUs, flight controls, landing gear, electrical systems, and fuel—ensures aircraft return to service reliably. Proper aircraft storage is not merely temporary; it is a strategic approach to safeguarding fleet performance, optimizing maintenance costs, and maintaining airworthiness.

Learn more about the maintenance strategies behind effective aircraft preservation and return-to-service →