4. Accounts Receivable – Net

Net accounts receivable and billings in excess of costs on uncompleted contracts consisted of the following at September 29, 2013 and September 30, 2012:

	Fiscal Year Ended

	September 29, 2013			September 30, 2012
	(in thousands)
Billed	$	375,149		$	362,331
Unbilled		306,969			355,793
Contract retentions		23,353			17,908

Total accounts receivable – gross		705,471			736,032
Allowance for doubtful accounts		(44,624	)		(35,552	)

Total accounts receivable – net	$	660,847		$	700,480

Current billings in excess of costs on uncompleted contracts	$	79,507		$	90,909
Non-current billings in excess of costs on uncompleted contracts		–			4,410

Total billings in excess of costs on uncompleted contracts	$	79,507		$	95,319

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 29, 2013 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 is determined based on a review of client-specific accounts, and contract issues resulting from current events and economic circumstances. 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 will be earned within 12 months. Non-current billings in excess of costs on uncompleted contracts are reported as part of our "Other long-term liabilities" on our consolidated balance sheets.

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 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.

Unbilled accounts receivable at September 29, 2013 and September 30, 2012 include approximately $41 million and $21 million, respectively, related to claims, including requests for equitable adjustment, on contracts that provide for price redetermination, primarily with U.S. federal government agencies. We regularly evaluate these 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 reliably estimated. We recognized losses of approximately $30.2 million related to the evaluation of collectability of claims in fiscal 2013 primarily related to contractual disputes with government clients. No losses related to claims were recognized in fiscal 2012.

Billed accounts receivable related to U.S. federal government contracts were $50.5 million and $65.9 million at September 29, 2013 and September 30, 2012, respectively. U.S. federal government unbilled receivables, net of progress payments, were $79.3 million and $100.4 million at September 29, 2013 and September 30, 2012, respectively. Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at September 29, 2013 and September 30, 2012.