The US Federal Aviation Administration has mandated that operators of certain twinjets in the Embraer ERJ-135 and ERJ-145 families replace mechanical elevator gust lock systems in the aircraft with a more robust electromechanical unit.
The agency is requiring a replacement within 500 flight hours or 90 days after 23 May, the effective date of the rule.
The final airworthiness amendment directive, issued on 8 May, was prompted by "additional reports of in-service failures" of the mechanical gust lock system despite the issuance of two previous ADs.
"Rapid uncommanded movement of the elevator control surface induces inertia loads in the elevator control system, which may result in systematic damage that could ultimately cause failure of the elevator control system and consequent reduced control of the airplane," the FAA says. The protection system is designed to prevent high winds and jet blasts from damaging the elevator.
An AD issued in 2005 gave operators until 2011 (or until reaching an additional 10,000h of flight time) to replace the device, and a follow-on AD in January 2008, required interim inspections to ensure airworthiness until the upgrade could be completed.
The January AD was prompted in part by a report of an ERJ-145 that "did not rotate in response to the command from the yoke during take-off, which resulted in a rejected take-off", the FAA says.
Analysis of the aircraft revealed that both elevator control rods in the ERJ had broken, a problem thought to be linked to the effects of "gale-force winds" when the aircraft was parked.
That aircraft was one of a "small percentage" of ERJs that had not had its mechanical gust lock system replaced with an electromechanical device, says the FAA.
Embraer was not available to advise on how many mechanical gust lock systems remain in the fleet.
Source: Flight International
