Aircraft and Property, Plant and Equipment
 12 Months Ended
Dec. 31, 2014
Property, Plant and Equipment [Abstract]  
Aircraft and Property, Plant and Equipment
Aircraft and Property, Plant and Equipment
Aircraft, net consisted of the following (in thousands):
 
 
December 31, 2014
 
December 31, 2013
Aircraft
$
162,246

 
$
151,044

Less: Accumulated depreciation
(34,025
)
 
(23,865
)

$
128,221

 
$
127,179


The following table represents the changes in aircraft employed in the Company's fleet as of December 31, 2012, 2013, and 2014 respectively.

Aircraft
 
Total Aircraft Employed
Aircraft in our fleet as of December 31, 2012
 
 
21
Aircraft transferred from inventory
2
 
 
Aircraft removed from fleet for maintenance
(1)
 
 
Aircraft purchased as part of the EHI acquisition
28
 
 
Aircraft purchased as part of the Air Amazonia acquisition
6
 
 
Aircraft leased as part of the EHI acquisition
35
 
 
Aircraft leased subsequent to the EHI acquisition
1
 
 
Aircraft returned to the lessor during the period
(2)
 
 
Aircraft in our fleet as December 31, 2013
 
 
90
Aircraft purchased
2
 
 
Aircraft returned to lessor
(2)
 
 
Aircraft sold
(4)
 
 
Aircraft in our fleet at December 31, 2014
 
 
86

Property, plant, and equipment, net consisted of the following (in thousands):
 
 
December 31, 2014
 
December 31, 2013
Land and land improvements
$
308

 
$
308

Buildings
7,926

 
7,597

Vehicles and equipment
29,500

 
29,598

Deferred overhauls, net
86,768

 
68,773

Construction-in-progress
15,926

 
19,923

 
140,428

 
126,199

Less: Accumulated depreciation and amortization
(19,793
)
 
(16,817
)

$
120,635

 
$
109,382


During the years ended December 31, 2014, 2013, and 2012, depreciation expense was $17.8 million, $13.4 million, and $9.0 million, respectively. During the years ended December 31, 2014, 2013, and 2012, amortization expense associated with deferred overhauls was $14.7 million, $18.1 million, and $12.7 million, respectively.

Repairs and maintenance costs were $22.9 million, $20.0 million and $15.9 million for the years ended December 31, 2014, 2013, and 2012, respectively.
During the second quarter of 2014, the Company completed a sale-leaseback transaction pursuant to which the Company sold one S-64 Aircrane for a total purchase price of $24.7 million. The net book value of the Aircrane at the date of the transaction was $12.3 million. The lease has an initial term of seven years commencing on June 30, 2014, and base lease payments of approximately $264 thousand per month. The Company has the right to purchase the aircraft back from the lessor at the end of the fourth year of the lease term at a purchase price based upon the fair market value at that time. At the end of the term of the lease, the lessor has a put right to sell the aircraft back at a purchase price based on the fair market value at that time. The Company has accounted for the transaction as a sale-leaseback under ASC 840-40 “Sale-Leaseback Transactions”. The profit on the sale was deferred and will be recognized ratably over the term of the lease as a reduction to rent expense. The current portion of the deferred gain of $1.8 million is included in other current liabilities, and the non-current portion of deferred gain of $9.7 million is included in other non-current liabilities in the consolidated balance sheet as of December 31, 2014.