PPE + impairment

I posted this question before,but I still got some questions.

Cost Model

On 1 Jan 2011, the information of an equipment is given as below:
Equipment cost: $400,000
Estimated useful life: 10 years
Residual value: $40,000

On 1 Jan 2015, the information of the equipment is revised as below:
Remaining useful life: 5 years from 1 January 2015 Residual value: $46,000

31 Dec 2011,2012,2013,2014
Dr. Depreciation ($400,000 – $40,000) ÷ 10 $36,000
Cr. Accumulated depreciation $36,000
On 1 Jan 2015
– Carrying amount = $400,000 – ($36,000 × 4) = $256,000

Revised annual depreciation
= ($256,000 – $46,000) ÷ 5 = $42,000

31 Dec 2015
Dr. Depreciation $42,000
Cr. Accumulated depreciation $42,000

If I add an impairment loss, says the recoverable amount on 31 Dec 2015 is $114,000

Carrying amount on 31 Dec 2015
($256,000-42,000)=$214,000

31 Dec 2015
Dr. Accumulated depreciation $42,000
Cr. PPE $42,000
Dr. Impairment Loss (214-114) $100,000
Cr. PPE $100,000

If in the next 2 years continue recoverable amount on 31 Dec 2017 becomes $280,000

The carrying amount on 31 Dec 2017 is it ($256,000-(42,000×2)-100,000(since the impairment loss becomes accumulated impairment loss?)= $72,000

Then RA>CA

31 Dec 2017
Dr. Depreciation $42,000
Cr. Accumulated dep $42,000
Dr. Accumulated depreciation $84,000
Dr. PPE $124,000
Cr. reversal of impairment loss $208,000

Is it like this?
Besides, I would like to know why need to dr. acc. Dep when impairment loss occurred?

If this change to Revaluation Model

On 1 Jan 2011, the information of an equipment is given as below:
Equipment cost: $400,000
Estimated useful life: 10 years
Residual value: $40,000

31 Dec 2013 revalued to $312,000

31 Dec 2011,2012,2013
Dr. Depreciation ($400,000 – $40,000) / 10 $36,000
Cr. Accumulated depreciation $36,000

31 Dec 2013 carrying amount= $400,000 – ($36,000 x 3) = $292,000
Dr. Accumulated depreciation ($36,000 x 3) $108,000
Cr. PPE $108,000
Dr PPE ( $312,000- $292,000) $20,000
Cr Revaluation Surplus $20,000

If the equipment is also revised as below:
Remaining useful life: 5 years from 1 January 2014 Residual value: $46,000

is it use the fair value as a new cost?
Annual depreciation = ($312,000- $46,000)/5 =$53,200

31 Dec 2014, 2015, 2016
Dr. Depreciation $53,200
Cr. Accumulated Depreciation $53,200

31 Dec 2016 carrying amount=($312,000-($53,200×3))=$152,400

31 Dec 2016 revalued to $52,400

31 Dec 2016
Dr. Accumulated depreciation ($53,200×3) $159,600
Cr. PPE $159,600
Dr. Reversal of revaluation surplus $20,000
Dr Revaluation Deficit ( $152,400- $52,400-$20,000) $80,000
Cr PPE $80,000

I have correct entry on 31 Dec 2016. Is this what you mean?

Also, I got a question on which situations we need to make the entry about revaluation surplus realised?

Do we need to do this when residual value of lifetime changed?