Horizontal stabiliser gaps force 787 inspections and reduced flight envelope

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Boeing has imposed a temporary operating limitation (TOL) on its five flying 787 test aircraft after structural gaps were discovered in the aircraft's horizontal stabiliser.

The horizontal stabilisers, which are built by Alenia Aeronautica in Foggia, Italy, have "issues with improperly installed shims and the torque of associated fasteners", says Boeing.

Programme sources say the gaps, which the shims are intended to fill, range between 0.25 and almost 0.5cm, and were first found near where the rear spar meets the stiffened centre box panel that joins the two rear wings that make up the horizontal stabiliser.

  © Boeing

While Boeing maintains that the fleet has not been "grounded", the company has decided to not fly each aircraft as it undertakes one to two day inspections of each aircraft before returning to flight test operations. If issues are discovered amongst its test fleet, the aircraft can still fly, but with a reduced operating limit that is specified by the airframer and the US Federal Aviation Administration.

"An inspection and rework plan already is implemented for airplanes in production. For those airplanes requiring rework, we expect it will take up to eight days for each airplane," says Boeing.

Shims, or engineered fillers, are traditionally used to fill structural gaps that naturally occur during manufacturing, and the ones used to fill gaps in the horizontal stabiliser became compressed after fasteners were over-torqued as a means of pulling the surfaces together.

Using fasteners to augment structural shims introduces a "pre-load" condition and reduces the long-term fatigue life of the structure if the issue goes unaddressed.

Many of the production 787s in Everett, Washington, where final assembly takes place, have already had their elevators removed for the inspections, say area observers.

The company maintains "it is not unusual for these issues to arise in the course of production programmes - they are identified, dispositioned and dealt with through our normal processes".

However, the setback is another in a series of quality control issues that have arisen from the facilities of its Italian supplier.

On 23 June 2009, Boeing issued a stop work order to Alenia's Grottaglie, Italy operations after wrinkles in the composite skin of the aircraft were found above door frames on fuselage barrels.

The airframer says that this "issue will be addressed within the existing programme schedule" and the first delivery to Japan's All Nippon Airways remains on track for first delivery later this year.