Boeing has started telling its customers to expect serious delivery delays for the Boeing 787 as far out as this summer.

Norwegian confirmed on Friday that it has been alerted by Boeing and that delivery of its first two aircraft, previously scheduled for April and June, could be affected. The company stated that Boeing has not announced a new delivery date or given written confirmation of a potential delay.

The customer warning is only the latest sign that Boeing itself now recognizes what others have been predicting for some time: that the 787 grounding is likely going to be a matter of several, if not many months, rather than a short-term issue that can be resolved quickly. The National Transportation Safety Board (NTSB) had indicated that it will take weeks until the root causes of thermal runaway in a lithium-ion battery on board a Japan Airlines aircraft in January have been identified. The 50-strong 787-fleet has since been grounded.

Several carriers in addition to Norwegian are due to receive their first 787s over the next few months, including British Airways, TUIfly, China Southern Airlines and Aeromexico. These come on top of existing operators that have been looking at growing their fleet, the list includes United, Qatar Airways, All Nippon Airways, Japan Airlines, Air India, LOT Polish Airlines and LAN. Boeing planned to deliver 70 aircraft this year and was about to raise the rate of production for the aircraft from 5 per month to ten per month by the end of 2013. So far, a single aircraft has been delivered this year to Air India on January 3. Unlike Norwegian, the other affected carriers are so far refusing to make public comments about the impact on their operations, even though massive disruptions are already occurring. Carriers like Qatar Airways have based the launch of new routes on 787 arrivals and are now forced to revise their plans because they are lacking aircraft.

Norwegian says it still plans to go ahead with its plans to launch long-haul services to New York and Bangkok. The airline is looking at leasing in another aircraft type for a period of three months in order not to have to cancel the launch of the new operation, which is crucial to its strategy. “As one of Boeing’s biggest customers in Europe, we expect that the aircraft manufacturer does everything in its power to get the aircraft ready for delivery as soon as possible,” Norwegian CEO Bjorn Kjos said.