has accelerated their depreciation taking advantage of a lucrative company tax regime in Ireland.
Companies get Capital Allowances from Govts to offset investing in new equipment / buildings all allowed against tax. Every EU country gives capital allowances.
Its why Tesco in UK is continually investing in new stores as means they pay little tax.
Depreciation has no impact on tax so writing aircraft down in 5 years or 10 years matters little as this is ignored for tax purposes.