The delivery of Boeing 787 Dreamliners may be further delayed with the company deciding to inspect the entire fleet after finding assembly problems in the tail area on some of the 23 completed planes.

Air India and Jet Airways have ordered 27 and 10 of the planes, already more than two and a half years late to market. In all 866 Dreamliners have been ordered by 57 customers worldwide.

For Boeing, the latest issue with the new plane puts additional pressure on the company’s ambitious flight-test schedule, the Wall Street Journal reported Saturday.

Boeing last December gave itself roughly a year to complete thousands of hours of flight tests to receive government certification before delivering the first plane to All Nippon Airways Co. sometime before the end of the year.

Last week, Chicago-based Boeing said the five planes currently being used in the test programme had already flown a combined 1,000 hours, or about 40 percent of the planned hours.

But in the past few months, senior executives have acknowledged the programme is behind schedule and that routine delays have consumed much of the test program’s extra padding, the Journal said.

The company said Friday that even with the latest hiccup, it’s still on track to complete the test programme this year.

In a conference call with reporters, Scott Fancher, head of the 787 Dreamliner programme, said Boeing was first aware of the horizontal stabilizer issue last week, but it didn’t escalate into an issue affecting flight tests until Thursday morning.

Mr. Fancher declined to specify whether the issue was found on any of the five Dreamliners that are currently being used in the test—flight programme.

“Obviously, we’re very disappointed about this issue,” the Journal quoted him as saying. “But it’s a fact of life with start-up programme issues and one we have to deal with.”

On Thursday, the company said that the problem involves improper installation of small, composite pieces called “shims” where the horizontal stabilizers, small wing-like structures that extend outward and help control the up-and-down pitch of the aircraft, meet the fuselage.

Separately, the company said it would likely again pause shipment of Dreamliner components to its final assembly plant in Everett, Washington, in September as it incorporates changes to its global supply chain.

The move is similar to a recent five-week delay in shipments as Boeing sought to allow the supply chain to catch up and address another issue Boeing found in the tail area of the jets, the Journal said.

However, Mr. Fancher was quoted as saying the number of Dreamliners expected to be delivered to customers this year and in 2011 would not be affected.