Which statement is incorrect regarding 'components depreciation'?

a) 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.

b) An entity allocates the amount of initially recognized in respect of an item of property, plant and equipment to its significant part and depreciates separately such part.

c) It may appropriate to depreciate separately the airframe and engines of an aircraft, whether owned or subject to a finance lease.

d) An entity may not depreciate separately the parts of an item that do not have a cost that is significant in relation to the total cost of the item.