Boeing announced completing a one-week sequence of power-on tests for the first 787 on 20 June.
Completing the much delayed electrical systems testing moves the programme one step closer to first flight scheduled in the fourth quarter this year - more than one year later than originally planned.
"There is plenty of work to be done between now and first flight, but with every step forward we grow more and more confident," says Pat Shanahan, 787 vice-president and general manager.
The 787 programme is working to maintain the current schedule after supply chain breakdowns and a centre wing box redesign prompted a schedule delay of at least 15 months for first delivery. Sections for the fourth flight-test aircraft arrived at the Everett, Washington assembly line in June from Vought Aircraft, Spirit AeroSystems and Global Aeronautica.