It is widely recognized that the downtime of a single aircraft can reach six-figure costs per day. However, in practice, there are situations where operators intentionally keep an aircraft grounded. Operational constraints, market conditions, or technical considerations can make immediate return to service less sensible, especially when forcing serviceability may create greater cost or risk in the longer term.

Why Operator Chose or Forced to Keep Aircraft Parked

Keeping an aircraft non-operational is rarely ideal and often costly. However, not all grounded aircraft are AOG in the strict technical sense. Various operational, technical, and financial factors can lead to an aircraft being intentionally parked.

• Parts or Tooling Unavailability

Unresolved technical issues that cannot be deferred under the MEL, or that have exceeded allowable deferral cycles, can render an aircraft unserviceable. Current market conditions, including longer lead times for components and engines, as well as higher repair and replacement costs, can make both turnaround time and financial viability limiting factors.

• Outstanding Scheduled Maintenance

Aircraft due for major checks such as C-checks cannot be legally operated once threshold periods are overran. When maintenance slots are limited, costs to do it immidiately are high and less viable for company financials, operators may determine that temporary grounding is the more practical option.

• Demand Reduction

A sudden drop in demand can make operating certain routes or aircraft types financially unfeasible. This was particularly evident during the COVID period but remains relevant in market downturns or seasonal demand shifts.

• Strategic or Financial Considerations

Operators may also park aircraft as part of broader cost-control or asset management strategies. In periods of parts scarcity, some fleets are selectively grounded to support the continued operation of others through parts pooling or cannibalization, especially for engines and other critical components.

What Needs to Be Done: Parking Vs Active Parking vs Storage

When an aircraft is not operating, the required maintenance actions depend largely on expected downtime and OEM guidance.

While terminology may vary slightly between OEMs and operators, the industry generally recognizes three practical states: short-term parking, active storage, and long-term storage.

Example of Difference (Engine & APU)

• Kept for ~2 weeks and must remain flight-ready 

→ Active Storage / Parking

→ Weekly engine ground runs, APU operational checks, and installation of engine inlet and exhaust covers

• Not planned to operate in the near term → Storage / Prolonged Parking

→ Remove engine & APU (as applicable), engine motoring and inhibition, apply corrosion-preventative additives, desiccant bag and humidity control indicator

And other tasks as prescribed by OEM AMM preservation program per OEM AMM

Reference: Categories of parking and storage conditions per ICAO published resource:

Environmental Factors to Consider During Aircraft Parking and Storage

Environmental exposure plays a role in both short- and long-term parking, particularly when aircraft are stored outdoors. The local climate and operating environment can significantly influence preservation needs.

High Winds

Risk

• Cause aircraft movement

• Turn surrounding objects into airborne hazards

• Result in structural damage

Even though larger jets are generally less susceptible, smaller aircraft and turboprops are not immune, such as a documented ATR42 hull loss associated with high-wind parking conditions in Shannon, Ireland in 2014.

Examples of Precautionary Measures

• Parking nose aligned with prevailing wind

• Use of appropriate landing gear chocks

• Mooring/tie-down when required

High Humidity

Risk

• Corrosion can degrade materials and protective layers and contribute to structural deterioration if unmanaged

• Fungal growth in fuel systems can lead to contamination and blockages.

Humidity provides the moisture required for electrochemical reactions and surface condensation and also supports fungal and microbial growth

Examples of Precautionary Measures

• Proper lubrication

• Use of protective covers

• Corrosion protection and inspection

Disclaimer: Always refer to OEM AMM/Storage procedures and operator programs

Southeast Asia Context: High Humidity & Vietnam’s Expanded Regulation on Aircraft Storage

• High Humidity

Southeast Asia has high year-round humidity, commonly above 70% and often exceeding 80%, which increases the risk of corrosion that could weaken aircraft structural integrity.

Corrosion requires constant attention, particularly at frequently affected areas such as flight control mechanisms, aileron tab controls, and overwing panels. Proper preservation must be continuously validated.

• Regulatory News Extra: Vietnam’s Expansion of Aircraft Storage Regulation in 2021

In 2021, Civil Aviation Authority of Vietnam (CAAV) introduced additional regulatory attention related to aircraft storage. This included:

• Requirements for periodic rotation between in-service and stored aircraft to mitigate extended storage risks

• Reporting obligations before returning stored aircraft to operation, with different timelines depending on the downtime duration

Disclaimer: Operators should always refer to the latest CAAV and OEM guidance for current applicability.

Reference: https://www.flightglobal.com/mro/vietnam-further-tightens-rules-on-parked-aircraft/144272.article 

Lessor Perspective: Managing Storage & Reactivation Risk

From a lessor standpoint, prolonged storage is not simply an operational pause. It represents a period where asset condition, environmental exposure, and documentation discipline must be closely monitored. Some of these things need to be continuously monitored to ensure aircraft is properly stored and does not lose its value, in particular during long(er) storage periods.

1. Preservation Completeness

Verify that preservation actions were properly executed and maintained, including for items such as protective covering, lubrication (and replenishment interval), oil additives to prevent fungal growth,  installation of desiccant bags and humidity indicator, etc

2. Environmental Context Review

Need to assess storage exposure and how it would affect preservation tasks => High humidity? High wind? Very low temperature? Coastal?

3. Records & Reactivation Coordination

Ensure early coordination with the operator to confirm: Completeness of operational and storage records and all preservation tasks records, and alignment with OEM-issued SCOB (as applicable)

About TBM Aviation

Aircraft storage and parking represent only one element within the broader lifecycle management of an aircraft asset. Each phase introduces its own technical and documentation considerations, and none should be viewed in isolation.

TBM Aviation combines hands-on expertise with a cost-conscious approach to help lessors, airlines, and asset managers maintain compliance and protect asset value throughout the aircraft lifecycle. Insights from our reports have helped clients identify safety and financial risks. With our experience serving both lessors and lessees, we understand that even the smallest defects can have a significant impact and know how to flag details often overlooked.

If you require support or would like to discuss your specific requirements, please contact info@tbmaviation.com