Boeing's second flight test 787 is set to make its second flight, a return trip to Everett, for a thorough cleaning of its fuel tank following the discovery of foreign object debris (FOD).
The FOD was found trapped in the fuel filter following the aircraft's 22 December first flight to Boeing Field in Seattle, Washington.
Boeing confirms that "crews discovered very small amounts of debris" inside the aircraft's fuel tank during a planned non-operating period following first flight.
Programme sources say a piece of cheese cloth left in one of the aircraft's fuel tanks is said to be responsible for the return to Everett, where the facilities to accomplish the cleaning are located.
When crews went into the fuel tank to remove the cheese cloth, additional small objects were found in the tank as well, sources add.
Boeing declines to specify what type of FOD was found, saying only that there were "particulates" found in the tank.
While the FOD issue was being addressed at Boeing Field, site of the company's flight test centre, ZA002 remained on test status, concurrently completing ground hours toward the certification campaign.
The company did not specify how long the cleaning process would take, saying only that it "is expected to be completed quickly".
Boeing believes the FOD was left inside the tank during the manufacturing process and the company has already taken steps to refine the process in the factory to avoid future issues.
While several programme sources familiar with the incident call it a "minor setback" and Boeing insists that the cleaning "won't impact the schedule in any significant way", the discovery slows the pace of early accumulation of flight test hours.
ZA001, sistership to ZA002, continues initial airworthiness trials which are said to be going to smoothly.
ZA001 has completed a total of 14 flights to date since its maiden sortie on 15 December, accumulating nearly 60 hours of flight time in the process.
Boeing has provided itself up to a year to conduct certification for its new long-range twin, but aims to deliver the first 787 to Japan's All Nippon Airways in late September. However, Boeing has provided itself additional margin, officially targeting delivery the fourth quarter.