Boeing was due to start flight tests of a revised 737-900 elevator hinge design on 15 January, following an extended lay-up during which the tab was strengthened with a new hinge point and extra layers of material.

The revised design is expected to counter the unexpected 44Hz vibrations which were detected on the first flight of the prototype YD501 last year. The tests will verify the changes already flown on a pre-production version of the revised tab, and will concentrate on elevator tab flight flutter conditions, the effect of the stiffened tab on the elevator's hinge movement, and air data calibration.

The extended lay-up is not expected to delay US Federal Aviation Administration certification, scheduled for mid-March, and deliveries to launch customer Alaska Airlines in April. It has, however, forced the postponement of an evaluation by the European Joint Aviation Authorities (JAA). The knock-on effect, says Boeing, means that JAA certification is now expected at the end of March.

Source: Flight International