Boeing Co  halted test flights of its 787 Dreamliner on Wednesday, a day after an electrical fire aboard one of its test planes forced an emergency landing in Texas.

However, it said it was too early to tell if the incident would push back the plane's delivery schedule.   

Boeing shares fell 3.1 percent to $67.07 on the New York Stock Exchange as investors pondered the likelihood of another setback to the 787 program, already nearly three years behind its original timetable.   

The company, the second-largest commercial plane maker after EADS' Airbus, said it was still investigating the fire. "I would think that now you have to check everything," said Alex Hamilton, managing director at EarlyBird Capital. "You've got to isolate the problem and try to figure out what it was."    

The incident on Tuesday was the first of its kind for the Dreamliner program and raised new questions for the company and for US aviation regulators, who must certify that the aircraft is safe before it can be delivered to customers.   

Boeing said late on Wednesday that the airplane lost primary electrical power because of an onboard electrical fire, which sent smoke into the cabin on the plane's final approach to Laredo, Texas. The pilots never lost control of the aircraft as it landed, Boeing said.   

The company said a power control panel in the electronics bay at the back of the plane will need to be replaced and other repairs may be necessary. The company is now analysing flight data to find the cause of the fire, which it said could take several days.   

Until then, Boeing has postponed flight tests on all six 787s in its airborne testing program but will continue ground tests. "We cannot determine the impact of this event on the overall program schedule until we have worked our way through the data," the company said in a statement.   

Robert Mann, a New York-based consultant and former airline executive, said an electrical problem with test gear could cause a slight delay. But a glitch with the aircraft's embedded electrical system would be another matter.   

"That would seem to be more serious to the program given it is a highly vaunted electric airplane concept they are trying to sell," Mann said.

 The aircraft, carrying 42 crew and test technicians on a test flight from Yuma, Arizona, remained in Laredo on Wednesday while Boeing sent flight data from the aircraft to its facilities in Seattle.
The light-weight, carbon-composite 787 has generated impressive orders but has also been dogged by engineering, labor and supply chain problems.

Boeing is aiming to deliver a Dreamliner to its first customer, Japan's All Nippon Airways, in the first quarter of 2011. The original delivery date was May 2008.  - Reuters