Boeing has restarted 787 certification flight tests after an almost two-month hiatus following the in-flight electrical fire on the second test aircraft on approach to Laredo, Texas in November.

The resumption of certification flights, confirmed by Boeing on Jan. 17, raises expectations that the long-anticipated announcement on the revised program schedule may be imminent. However, speculation is also growing that analysts’ earlier predictions of an estimated four-month slide from the original target delivery date of mid-February to mid-year may be short of the mark.

Airline fears of more serious delays of six months or worse are growing following comments last week from the European EASA certification agency Executive Director Patrick Goudou. Quoted in a Bloomberg report, Goudou cautions that instead of the June-July certification target expected earlier, the joint FAA and EASA milestone and subsequent first deliveries could come between mid-year and year-end.

Although Boeing is not commenting on the revised program schedule, it has never attempted to minimize the scale of the effort involved in the urgent redesign, development and testing of the updated power distribution system and its control software which followed the Laredo fire. The rush program included laboratory testing of standalone components, integration testing with other systems, flight simulator testing and ground-based testing on the flight test aircraft. The flight simulator, known as ECAB1, has been used extensively for running through numerous scenarios from autoflight failures to control system malfunctions.

The first 787, ZA001, is expected to undertake certification buffet boundary testing on Jan. 18, while ZA002, which returned to flight with a 1.5 hr sortie on Jan. 17, will begin tests of a de-rated thrust setting on the Rolls-Royce Trent 1000 later this week. Boeing says ZA003 is “expected to be flying again within the next week or so,” while ZA004 is undertaking tests of the fuel jettison system. The first General Electric GEnx-1B powered aircraft, ZA005, is conducting long endurance fuel burn measurement flights out of Victorville, Calif. The final 787 test aircraft, GE-powered sistership ZA006, is meanwhile being readied for a return to flight with a functional check mission expected on Jan. 19.