For long-term aerospace contracts, we generally recognize sales and income based on the percentage-of-completion method of accounting, which allows for recognition of revenue as work on a contract progresses. We recognize sales and profit based upon either (1) the cost-to-cost method, in which sales and profit are recorded based upon the ratio of costs incurred to estimated total costs to complete the contract, or (2) the units-of-delivery method, in which sales are recognized as deliveries are made and cost of sales is computed on the basis of the estimated ratio of total cost to total sales.

Management performs detailed quarterly reviews of all of our significant long-term contracts. Based upon these reviews, we record the effects of adjustments in profit estimates each period. If at any time management determines that in the case of a particular contract total costs will exceed total contract revenue, we record a provision for the entire anticipated contract loss at that time.

The percentage-of-completion method requires that we estimate future revenues and costs over the life of a contract. Revenues are estimated based upon the original contract price, with consideration being given to exercised contract options, change orders and in some cases projected customer requirements. Contract costs may be incurred over a period of several years, and the estimation of these costs requires significant judgment based upon the acquired knowledge and experience of program managers, engineers, and financial professionals. Estimated costs are based primarily on anticipated purchase contract terms, historical performance trends, business base and other economic projections. The complexity of certain programs as well as technical risks and uncertainty as to the future availability of materials and labor resources could affect the company's ability to accurately estimate future contract costs.

While we do not believe there is a reasonable likelihood there will be a material change in estimates or assumptions used to calculate our long-term revenues and costs, estimating the percentage of work complete on certain programs is a complex task. As a result, changes to these estimates could have a significant impact on our results of operations. These programs include the Sikorsky Canadian MH-92 program, the Sikorsky BLACK HAWK program, the JPF program, the Boeing A-10 program, our Bell Helicopter programs and several other programs. Estimating the ultimate total cost of these programs is challenging due to the complexity of the programs, the increase in production of new programs, the nature of the materials needed to complete these programs, change orders related to the programs and the need to manage our customers' expectations. These programs are an important element in our continuing strategy to increase operating efficiencies and profitability as well as broaden our business base. Management continues to monitor and update program cost estimates quarterly for these contracts. A significant change in an estimate on one or more of these programs could have a material effect on our financial position and results of operations.

The allowance for doubtful accounts represents management's best estimate of probable losses inherent in the receivable balance. These estimates are based on known past due amounts and historical write-off experience, as well as trends and factors impacting the credit risk associated with specific customers. In an effort to identify adverse trends for trade receivables, we perform ongoing reviews of account balances and the aging of receivables. Amounts are considered past due when payment has not been received within a pre-determined time frame based upon the credit terms extended. For our government and commercial contracts, we evaluate, on an ongoing basis, the amount of recoverable costs. The recoverability of costs is evaluated on a contract-by-contract basis based upon historical trends of payments, program viability and the customer's credit-worthiness.

Write-offs are charged against the allowance for doubtful accounts only after we have exhausted all collection efforts. Actual write-offs and adjustments could differ from the allowance estimates due to unanticipated changes in the business environment as well as factors and risks associated with specific customers.

As of December 31, 2011 and 2010, our allowance for doubtful accounts was $3.3 million and $3.8 million, respectively. Receivables written off, net of recoveries, in 2011 and 2010 were $1.9 million and $1.2 million, respectively.

Currently we do not believe that we have a significant amount of risk relative to the allowance for doubtful accounts. A 10% change in the allowance would have a $0.3 million effect on pre-tax earnings.

We have four types of inventory (a) merchandise for resale, (b) contracts in process, (c) other work in process, and (d) finished goods. Merchandise for resale is stated at the lower of the cost of the inventory or its fair market value. Contracts in process, other work in process and finished goods are valued at production cost comprised of material, labor and overhead, including general and administrative expenses on certain government contracts. Contracts in process, other work in process, and finished goods are reported at the lower of cost or net realizable value. We include raw material amounts in the contracts in process and other work in process balances. Raw material includes certain general stock materials but primarily relates to purchases that were made in anticipation of specific programs that have not been started as of the balance sheet date. The total amount of raw material included in these in process amounts was less than 5% of the total inventory balance as of both December 31, 2011 and 2010.

The process for evaluating inventory obsolescence or market value often requires the company to make subjective judgments and estimates concerning future sales levels, quantities and prices at which such inventory will be sold in the normal course of business. We adjust our inventory by the difference between the estimated market value and the actual cost of our inventory to arrive at net realizable value. Changes in estimates of future sales volume may necessitate future write-downs of inventory value. The K-MAX® inventory balance, consisting of work in process and finished goods, was $20.3 million as of December 31, 2011. We believe that it is stated at net realizable value, although lack of demand for spare parts in the future could result in additional write-downs of the inventory value. Overall, management believes that our inventory is appropriately valued and not subject to further obsolescence in the near term.

On February 12, 2009, we completed the transfer of title to the 11 Australian SH-2G(A) Super Seasprite helicopters, including related inventory and equipment. At December 31, 2011, $52.7 million of SH-2G(I), formerly SH-2G(A), inventory was included in contracts and other work in process inventory. We believe there is market potential for these aircraft and we are actively marketing them to interested potential customers; however a significant portion of this inventory will be sold after December 31, 2012, based upon the time needed to market the aircraft and prepare them for sale.

Inventory valuation at our Industrial Distribution segment generally requires less subjective management judgment than the valuation of certain inventory in the Aerospace segment.

Management reviews the K-MAX® inventory balance on an annual basis to determine whether any additional write-downs are necessary. If such a write down were to occur, this could have a significant impact on our operating results. A 10% write down of the December 31, 2011 inventory balance would have affected pre-tax earnings by approximately $2.0 million in 2011.

Management reviewed the SH-2G(I) inventory balance at December 31, 2011 to determine that no write-down was necessary. If such a write down were to occur, this could have a significant impact on our operating results. A 10% write down of the December 31, 2011 inventory balance would have affected pre-tax earnings by approximately $5.3 million in 2011.