Boeing says that despite a one month long production freeze starting today at its Everett site, initial deliveries of 747-8 freighter and passenger models remain on track for mid-year and last quarter of 2011 respectively.

The manufacturer is suspending 747-8 production for a month from May 6 to incorporate changes from discoveries made during flight test and to allow workers in Everett to catch up on thousands of unfinished items, or ‘traveled work.’ “We are re-balancing the work on the line to do a bunch of catch up on unfinished work, and perform change incorporation from flight testing as necessary” says a spokesman for Boeing.

The move, which follows similar actions taken three times on the 787 line, is an unwelcome new development to a program desperately trying to catch up on almost two years of program slippage. However, Boeing says it expects to gain some benefit by using the production hold to help prepare for next year’s planned production rate increase to two aircraft per month. While not affecting initial deliveries, Boeing says it is still assessing the overall impact on downstream deliveries next year.

Boeing plans to resume normal production flow in early June, but until then the line will remain static with completion of tasks on aircraft in-situ. Change incorporation, which includes “tweaks” to minor components such as the outboard aileron modal suppression system introduced to counter vibration discovered in flight testing, will also be completed on the 20 aircraft already assembled. Of these, seven have been used for flight testing while 13 are in storage around the Paine Field, Everett delivery ramp alongside a growing number of undelivered, engineless 787s.