4. Accounts Receivable – Net

Net accounts receivable and billings in excess of costs on uncompleted contracts consisted of the following at September 28, 2014 and September 29, 2013:

	Fiscal Year Ended
	September 28, 2014			September 29, 2013
	(in thousands)
Billed	$	351,693		$	375,149
Unbilled		363,050			306,969
Contract retentions		26,929			23,353

Total accounts receivable – gross		741,672			705,471
Allowance for doubtful accounts		(39,780	)		(44,624	)

Total accounts receivable – net	$	701,892		$	660,847

Billings in excess of costs on uncompleted contracts	$	103,343		$	79,507

Billed accounts receivable represent amounts billed to clients that have not been collected. Unbilled accounts receivable represent revenue recognized but not yet billed pursuant to contract terms or billed after the period end date. Most of our unbilled receivables at September 28, 2014 are expected to be billed and collected within 12 months. Contract retentions represent amounts withheld by clients until certain conditions are met or the project is completed, which may be several months or years. The allowance for doubtful accounts represents amounts that may become uncollectible or unrealizable in the future. We determine an estimated allowance for uncollectible accounts based on management's consideration of trends in the actual and forecasted credit quality of our clients, including delinquency and payment history; type of client, such as a government agency or a commercial sector client; and general economic and particular industry conditions that may affect a client's ability to pay. Billings in excess of costs on uncompleted contracts represent the amount of cash collected from clients and billings to clients on contracts in advance of revenue recognized. The majority of billings in excess of costs on uncompleted contracts, excluding those related to claims, will be earned within 12 months.

Once contract performance is underway, we may experience changes in conditions, client requirements, specifications, designs, materials and expectations regarding the period of performance. Such changes result in "change orders" and may be initiated by us or by our clients. In many cases, agreement with the client as to the terms of change orders is reached prior to work commencing; however, sometimes circumstances require that work progresses without obtaining a definitive client agreement. Unapproved change orders constitute claims in excess of agreed contract prices that we seek to collect from our clients (or other third parties) for delays, errors in specifications and designs, contract terminations, or other causes of unanticipated additional costs. Revenue on claims is recognized when contract costs related to claims have been incurred and when their addition to contract value can be reliably estimated. This can lead to a situation in which costs are recognized in one period and revenue is recognized in a subsequent period such as when client agreement is obtained or a claims resolution occurs.

Total accounts receivable at September 28, 2014 and September 29, 2013 included approximately $79 million and $41 million, respectively, related to claims, including requests for equitable adjustment, on contracts that provide for price redetermination. The increase from the end of fiscal 2013 includes the impact of changes in scope on an oil and gas project in Western Canada in fiscal 2014 that is currently in negotiation with the client. The remainder of the increase in claims primarily related to revenue recognized as progress continued on projects with claims that were in process at the end of fiscal 2013. We regularly evaluate all claim amounts and record appropriate adjustments to operating earnings when it is probable that the claim will result in a different contract value than the amount previously estimated. As a result of this assessment, we recognized revenue and an increase to operating income of $3.4 million in fiscal 2014. We recognized losses of approximately $30.2 million related to the evaluation of the collectability of claims in fiscal 2013, primarily related to contractual disputes with government clients.

Billed accounts receivable related to U.S. federal government contracts were $57.4 million and $50.5 million at September 28, 2014 and September 29, 2013, respectively. U.S. federal government unbilled receivables were $73.2 million and $79.3 million at September 28, 2014 and September 29, 2013, respectively. Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at September 28, 2014 and September 29, 2013.