How component depreciation works under IAS 16 and ASC 360

Component depreciation is the practice of splitting the cost of a single item of property, plant and equipment into its significant parts and depreciating each part over its own useful life. Under IFRS it is not a choice: IAS 16 Property, Plant and Equipment requires each part of an item with a cost that is significant in relation to the total cost of the item to be depreciated separately. Under US GAAP, ASC 360 Property, Plant, and Equipment contains no equivalent requirement, and many US entities depreciate assets as a single unit or through group and composite methods.

The difference looks technical, but it changes the depreciation charge, the carrying amount of the asset, the gain or loss when parts are replaced and the treatment of major inspections and overhauls. It matters most for long-lived assets built from parts that wear out at very different speeds: aircraft, ships, rolling stock, power plants, furnaces, data centres, hotels and large buildings. A group that reports under IFRS but has US subsidiaries, or a US company converting to IFRS, usually discovers that its fixed asset register has to be rebuilt at a more detailed level.

This article explains what IAS 16 requires, how US GAAP approaches the same question, how replacements and major inspections are treated under each framework, and works through a numeric example with journal entries for an aircraft, which is the example IAS 16 itself uses.

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WHEN THE QUESTION ARISES.

The question arises at three points in the life of an asset. The first is initial recognition, when the entity decides the unit of account and allocates the purchase or construction cost across parts. The second is each reporting period, when depreciation is calculated and useful lives, residual values and methods are reviewed. The third is replacement, when a part is renewed, a major inspection is performed or a component fails early and has to be scrapped.

IAS 16 does not prescribe the unit of measure for recognition. The standard states that judgement is needed in applying the recognition criteria to an entity's specific circumstances, and that individually insignificant items such as moulds, tools and dies may be aggregated. Component depreciation sits on top of that judgement: once an item has been identified, the entity must look inside it and ask whether any part has a cost that is significant relative to the whole and a useful life or consumption pattern that differs from the rest.

In practice, the decision is driven by three facts that engineering and operations teams usually know better than accountants: which parts are replaced on a cycle shorter than the life of the main asset, how much those parts cost relative to the whole, and how their consumption is measured (time, hours, cycles or output). Gathering that information at acquisition is far easier than reconstructing it years later.

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THE IFRS TREATMENT UNDER IAS 16.

IAS 16 paragraph 43 sets the core rule: each part of an item of property, plant and equipment with a cost that is significant in relation to the total cost of the item shall be depreciated separately. Paragraph 44 explains the mechanics. The entity allocates the amount initially recognised for the item to its significant parts and depreciates each part separately, and the standard gives the example of depreciating the airframe and the engines of an aircraft separately.

The standard then adds three refinements. Paragraph 45 allows significant parts that have the same useful life and depreciation method to be grouped in determining the depreciation charge, so an entity does not need a separate calculation for every significant part if several of them behave identically. Paragraph 46 deals with the remainder: if an entity depreciates some parts separately, it also depreciates the rest of the item, which consists of the parts that are individually not significant, and approximation techniques may be needed if those parts have varied lives or patterns of consumption. Paragraph 47 permits an entity to depreciate separately parts that are not significant, which is a choice rather than a requirement.

Each component is then depreciated under the general IAS 16 rules. The depreciable amount is allocated on a systematic basis over the component's useful life, depreciation begins when the asset is available for use, and the method must reflect the pattern in which the component's future economic benefits are expected to be consumed. Paragraph 51 requires the residual value and useful life to be reviewed at least at each financial year-end, and changes are accounted for as changes in accounting estimates under IAS 8. In a componentised register, that review is performed part by part, which often reveals that one component's life has shortened while the main structure is unaffected.

IAS 16 does not define "significant" with a numeric threshold. Entities set their own policy, typically combining a relative cost threshold with a qualitative test on whether the part has a materially different useful life. The policy should be documented and applied consistently, because the same item can produce noticeably different depreciation charges depending on how finely it is split.

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REPLACEMENTS AND MAJOR INSPECTIONS UNDER IFRS.

Component accounting under IAS 16 is closely linked to the treatment of subsequent costs. Paragraph 12 states that the costs of day-to-day servicing, which are primarily labour, consumables and sometimes small parts, are not added to the carrying amount and are recognised in profit or loss as incurred. Paragraph 13 deals with parts that require replacement at regular intervals, giving the examples of a furnace that needs relining after a specified number of hours and aircraft interiors such as seats and galleys that are replaced several times during the life of the airframe. The cost of such a replacement is recognised in the carrying amount of the item when the recognition criteria are met, and the carrying amount of the replaced part is derecognised.

Paragraph 70 makes the derecognition requirement explicit: the carrying amount of the replaced part is derecognised regardless of whether that part had been depreciated separately. If it is not practicable to determine the carrying amount of the replaced part, the entity may use the cost of the replacement as an indication of what the replaced part cost when it was acquired or constructed. This is why entities that did not componentise at acquisition can still end up with large derecognition losses later: the replaced part's original cost and accumulated depreciation must be estimated and removed.

Paragraph 14 applies the same logic to major inspections. When an item such as an aircraft requires regular major inspections for faults, regardless of whether parts are replaced, the cost of each major inspection is recognised in the carrying amount of the item as a replacement if the recognition criteria are met. Any remaining carrying amount of the previous inspection, as distinct from physical parts, is derecognised. This happens even if the cost of the previous inspection was not separately identified when the item was acquired, and the estimated cost of a future similar inspection may be used to indicate what the existing inspection component cost.

The consequence is that, under IFRS, the cost of the first major inspection is effectively embedded in the purchase price of a new asset and depreciated over the period to the first inspection. The entity does not recognise a provision for future maintenance, because a planned overhaul is not a present obligation: the entity could sell the asset or change its operations and avoid the expenditure.

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THE US GAAP TREATMENT UNDER ASC 360.

US GAAP requires the cost of property, plant and equipment, less salvage value, to be allocated over the asset's estimated useful life in a systematic and rational manner. ASC 360 does not contain a requirement equivalent to IAS 16 paragraph 43 to identify significant parts and depreciate each one separately. Component depreciation is permitted, and some industries use it, but an entity may depreciate an asset as a single unit, or apply group or composite depreciation across a pool of similar assets, as long as the result is systematic and rational. The mechanics of those pooled methods are explained in our article on group depreciation and composite depreciation.

Because the unit of account is often larger under US GAAP, the treatment of replacements also differs in practice. Where an entity does not track a part separately, the cost of replacing it is assessed against the entity's capitalisation policy, typically asking whether the expenditure extends the asset's useful life, increases its capacity or improves its efficiency; costs that only restore the asset to its previous condition are expensed as repairs and maintenance. When a replaced part was tracked as a separate unit, its remaining carrying amount is removed and any loss recognised, which is the same result IAS 16 reaches by requirement.

Planned major maintenance is where the frameworks diverge most visibly. FASB material on the subject describes the AICPA airline industry guidance as permitting three alternative methods for planned major maintenance activities, and notes that these methods are also used outside the airline industry. Under the direct expensing method, the cost of each overhaul is recognised in profit or loss when incurred. Under the built-in overhaul method, part of the acquisition cost is allocated to the first planned maintenance and depreciated to the date of the overhaul, with later overhauls capitalised and depreciated to the next one; the same FASB material states that this method can only be applied when the related assets are accounted for on a component basis. Under the deferral method, the actual cost of each overhaul is capitalised and amortised to the next overhaul. The FASB staff position on planned major maintenance activities, FSP AUG AIR-1, precluded the accrue-in-advance method, so US GAAP, like IFRS, does not allow a liability to be built up for maintenance that has not yet been performed.

US GAAP does not permit the revaluation model, so the componentised revalued assets that can arise under IAS 16 have no US GAAP counterpart. Changes in useful lives and salvage values are changes in accounting estimates under ASC 250, and a change in depreciation method is treated as a change in estimate effected by a change in accounting principle.

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IFRS VS US GAAP COMPARISON.

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Issue	IFRS (IAS 16)	US GAAP (ASC 360)
Component depreciation	Required for significant parts	Permitted, not required
Unit of account	Judgement; parts split when significant	Judgement; single unit, group or composite common
Grouping of parts	Allowed if same life and method	Group and composite methods allowed
Replaced part	Carrying amount derecognised	Removed if tracked separately
Major inspection	Capitalised as a component	Direct expense, built-in overhaul or deferral
Accrual for future overhaul	Not permitted	Not permitted (accrue-in-advance precluded)
Useful life review	At least each year-end	When events indicate a change
Revaluation model	Permitted	Not permitted

........

The useful life row reflects the explicit annual review in IAS 16 paragraph 51; US GAAP has no equivalent annual review requirement, although estimates must be revised when facts change. In practice, the combination of mandatory componentisation and annual review means that IFRS registers tend to be more granular and are revised more often.

For a broader view of how the two frameworks measure and present these assets, see our article on how to measure and present property, plant and equipment under IFRS and US GAAP.

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WORKED EXAMPLE: AN AIRCRAFT SPLIT INTO COMPONENTS.

An airline acquires an aircraft on 1 January 2026 for $60,000,000 and places it in service immediately. The figures are illustrative. Engineering data allow the cost to be allocated to four parts: the airframe, the engines, the cabin interior and the heavy maintenance check embedded in the purchase price (the estimated cost of the first heavy check, used as an indication of the inspection component, as IAS 16 paragraph 14 allows). The airline uses the straight-line method for all components.

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Component	Cost ($)	Residual value ($)	Useful life (years)	Annual depreciation ($)
Airframe	38,000,000	3,000,000	25	1,400,000
Engines	14,000,000	0	10	1,400,000
Cabin interior	3,000,000	0	6	500,000
Heavy maintenance check	5,000,000	0	5	1,000,000
Total	60,000,000	3,000,000		4,300,000

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The annual depreciation charge under IAS 16 is $4,300,000. If the same aircraft were depreciated as a single unit over 25 years down to a $3,000,000 residual value, the charge would be ($60,000,000 − $3,000,000) / 25 = $2,280,000. Componentisation therefore increases the charge in the early years by $2,020,000 per year, because the short-lived parts are consumed faster than the airframe.

Entry 1: acquisition on 1 January 2026.

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Account	Debit ($)	Credit ($)
Aircraft: airframe	38,000,000
Aircraft: engines	14,000,000
Aircraft: cabin interior	3,000,000
Aircraft: heavy maintenance check	5,000,000
Cash / payables		60,000,000
Total	60,000,000	60,000,000

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Entry 2: depreciation for each of the years 2026 to 2029.

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Account	Debit ($)	Credit ($)
Depreciation expense	4,300,000
Accumulated depreciation: airframe		1,400,000
Accumulated depreciation: engines		1,400,000
Accumulated depreciation: cabin interior		500,000
Accumulated depreciation: heavy check		1,000,000
Total	4,300,000	4,300,000

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At 31 December 2029, after four years, the carrying amount of the aircraft is $60,000,000 − 4 × $4,300,000 = $42,800,000. Under the single-unit approach it would be $60,000,000 − 4 × $2,280,000 = $50,880,000.

Entry 3: early replacement of the cabin interior on 31 December 2029. The airline refits the cabin after four years instead of six, at a cost of $3,600,000, and the old interior is scrapped with no proceeds. Its accumulated depreciation is 4 × $500,000 = $2,000,000, so its carrying amount of $1,000,000 is derecognised as a loss under IAS 16 paragraphs 13 and 70, and the new interior is capitalised.

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Account	Debit ($)	Credit ($)
Accumulated depreciation: cabin interior	2,000,000
Loss on derecognition of cabin interior	1,000,000
Aircraft: cabin interior (old)		3,000,000
Aircraft: cabin interior (new)	3,600,000
Cash / payables		3,600,000
Total	6,600,000	6,600,000

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The new interior is depreciated over its own six-year life at $3,600,000 / 6 = $600,000 per year, so the total charge for 2030 becomes $1,400,000 + $1,400,000 + $600,000 + $1,000,000 = $4,400,000.

Entry 4: first heavy maintenance check on 1 January 2031. The check costs $5,600,000. The original inspection component of $5,000,000 is fully depreciated after five years, so it is derecognised with no gain or loss, and the new check is capitalised and depreciated over the five years to the next check at $5,600,000 / 5 = $1,120,000 per year.

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Account	Debit ($)	Credit ($)
Accumulated depreciation: heavy check	5,000,000
Aircraft: heavy maintenance check (original)		5,000,000
Aircraft: heavy maintenance check (2031)	5,600,000
Cash / payables		5,600,000
Total	10,600,000	10,600,000

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From 2031 the annual charge is $1,400,000 + $1,400,000 + $600,000 + $1,120,000 = $4,520,000.

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THE SAME HEAVY CHECK UNDER US GAAP METHODS.

Under US GAAP the outcome of the 2031 heavy check depends on the method the airline has chosen as its accounting policy. The table compares the effect on profit or loss in 2031 for the $5,600,000 check.

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Method	Treatment of the $5,600,000 check	Charge in 2031 ($)
IFRS component approach	Capitalised, depreciated over 5 years	1,120,000
US GAAP built-in overhaul	Capitalised, depreciated to next check	1,120,000
US GAAP deferral	Capitalised, amortised to next check	1,120,000
US GAAP direct expensing	Expensed when performed	5,600,000

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The built-in overhaul method produces the same pattern as IAS 16, because it requires the same component split at acquisition. The deferral method gives the same charge for the 2031 check but no separate inspection charge in 2026 to 2030, because no part of the purchase price was allocated to the first check; that $5,000,000 stays inside the cost of the aircraft and is depreciated over the aircraft's life. Direct expensing produces the most volatile profile: a low charge between checks and a $5,600,000 expense in the year the check is performed, on top of the single-unit depreciation of $2,280,000, for a total of $7,880,000 in 2031.

None of the methods allows the airline to accrue a liability for the 2031 check during 2026 to 2030.

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PRESENTATION AND DISCLOSURE.

Component accounting does not usually change the lines presented on the face of the financial statements. Components are aggregated into classes of property, plant and equipment, and the depreciation charge is presented within the relevant expense line, or by function where the entity presents expenses that way. Losses on derecognition of replaced parts are recognised in profit or loss, and IAS 16 paragraph 68 states that gains on derecognition shall not be classified as revenue.

IAS 16 paragraph 73 requires disclosure, for each class of property, plant and equipment, of the measurement bases used, the depreciation methods used, the useful lives or depreciation rates used, the gross carrying amount and accumulated depreciation at the beginning and end of the period, and a reconciliation of the carrying amount showing additions, disposals, depreciation and other movements. Where components within a class have very different lives, entities commonly disclose a range of useful lives and describe the main components in the accounting policy note.

US GAAP requires disclosure of depreciation expense for the period, balances of major classes of depreciable assets, accumulated depreciation, and a general description of the methods used. An entity applying one of the planned major maintenance methods should state which method it uses, since the choice has a direct effect on reported margins.

The depreciation method chosen for each component is itself a policy decision with its own constraints; our article on how revenue-based depreciation methods are evaluated under IFRS and US GAAP covers one method the two frameworks treat differently.

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COMMON ERRORS AND JUDGEMENT AREAS.

The most common error under IFRS is componentising only at the level of the purchase invoice. A single invoice for a building, a production line or an aircraft rarely separates the parts, so the allocation must come from engineering estimates, supplier quotes or replacement cost data. An allocation that is never performed leaves the entity depreciating short-lived parts over the life of the main structure, which understates depreciation for years and then produces a large loss when the part is replaced.

A second error is capitalising the replacement without derecognising the replaced part. IAS 16 paragraph 70 requires derecognition even when the part was not depreciated separately, and allows the cost of the replacement to be used as an indication of the original cost of the replaced part. Without this step, the asset carries two roofs, two engines or two linings at once.

A third area is the treatment of major inspections. Entities sometimes expense the first inspection because no inspection component was identified at acquisition, or recognise a provision for future overhauls. Under IAS 16 the inspection component is identified at acquisition, if necessary by reference to the estimated cost of a future similar inspection, and no provision is recognised.

Judgement is also needed on the significance threshold, on grouping parts with similar lives, on residual values for long-lived structures and on whether usage-based methods (flight hours, cycles, units produced) better reflect consumption than straight-line depreciation. Componentisation also interacts with decommissioning costs, which are added to the cost of the asset and depreciated, as explained in our article on how decommissioning and site restoration costs are recognized under IAS 37, IAS 16 and ASC 410.

For groups that report under both frameworks, the practical risk is maintaining two registers that drift apart. A common solution is to keep the asset register at the component level and derive the US GAAP figures by aggregation, since the reverse, splitting an aggregated register after the fact, requires estimates that are hard to support.

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PRACTICAL CHECKLIST.

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Step	What to check
1	Identify parts with significant cost relative to the whole item
2	Obtain useful lives and consumption patterns for each part
3	Allocate acquisition cost, including any first inspection component
4	Group parts with the same life and method where allowed
5	Depreciate the remainder of the item separately
6	Review lives, residual values and methods at each year-end (IFRS)
7	Derecognise replaced parts and inspection components
8	Document the US GAAP policy for planned major maintenance
9	Disclose methods, useful life ranges and the carrying amount reconciliation

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WHAT IS ESTABLISHED AND WHAT DEPENDS ON JUDGEMENT.

What is established is the structure of the requirements. IAS 16 requires each significant part of an item of property, plant and equipment to be depreciated separately, allows parts with the same life and method to be grouped, requires replaced parts and previous inspection components to be derecognised, and treats major inspections as components rather than as provisions. US GAAP permits but does not require component depreciation, accepts single-unit, group and composite approaches, allows direct expensing, built-in overhaul or deferral for planned major maintenance, and precludes the accrue-in-advance method.

What depends on facts and circumstances is almost everything that drives the numbers: the definition of a significant part, the cost allocation at acquisition, useful lives and residual values, the depreciation method for each component and, under US GAAP, the maintenance method the entity elects. As the worked example shows, the same aircraft can carry an annual depreciation charge of $4,300,000 or $2,280,000 and a 2031 maintenance charge of $1,120,000 or $5,600,000 depending on those choices, which is why the accounting policy note and the asset register deserve the same attention as the calculation itself.

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