E-Jet Pitch Control Problem Prompts NTSB Recommendations

 - January 29, 2020, 3:06 PM

The National Transportation Safety Board on Wednesday recommended to U.S. and Brazilian aviation authorities that they issue stricter guidelines for inspecting and replacing wiring in the control column of Embraer E-Jets and Lineage 1000 business jets following a November 6 incident in which a Republic Airways E175 experienced pitch-related flight control degradation. The airplane, carrying six passengers, returned safely to Atlanta Hartsfield International Airport 15 minutes after takeoff.

The NTSB issued six safety recommendations to the National Civil Aviation Agency of Brazil (ANAC) and four to the Federal Aviation Administration. They address areas of concern including wire chafing, application of Embraer service bulletins relating to the pitch trim switch, and potential limitations in checklist memory items for pilots to address the unintended operation of the pitch trim system.

The first recommendation to ANAC calls for the Brazilian authority to require Embraer to devise new wiring inspection and replacement instructions and to ensure proper clearance from adjacent components, including the forward mechanical stop bolt and its safety wire. 

The remainder of the recommendations relates to operators’ responsibilities for carrying out the directives.

During the November 6 incident, the flight crew declared an emergency shortly after takeoff from Hartsfield-Jackson Atlanta International Airport, reporting a pitch trim-related flight control problem that caused a nose-up attitude and difficulty controlling the airplane.

Although the cause of the incident remains under investigation, post-incident examination of the airplane revealed chafed insulation around wires connecting the horizontal stabilizer actuator control electronics to the captain’s pitch trim switch and autopilot/trim disconnect button. Contact with the incorrectly untucked pigtail of the forward mechanical stop bolt safety wire caused the chafing, found the NTSB.

When investigators removed the captain’s pitch trim switch from the yoke, they observed marks that indicated at some point before the incident flight, mechanics installed the pitch trim switch in an inverted position. Embraer previously issued three service bulletins related to pitch trim switch installation error following reports from flight crews in 2015 about flight control system difficulties. However, neither the FAA nor the ANAC required incorporation of the service bulletins. While investigators haven’t determined whether the inverted switch installation proved a factor in the incident, the NTSB expressed concern the condition could lead to flight crew confusion, delaying appropriate recognition of and response to increased control forces.

Preliminary information from the NTSB’s investigation also suggests that the condition might mask unintended pitch trim operation during certain phases of flight, such as during takeoff. Further, limitations in the checklist memory items might delay pilots in properly responding to and regaining control of the airplane. The NTSB said the crew’s application of the memory items on the E175 Pitch Trim Runaway checklist might not comprehensively address the circumstances of the trim system operation in a timely manner. 

“Issuing these 10 safety recommendations early in the investigation demonstrates the NTSB’s commitment to take action as soon as we’ve identified and verified a safety issue that needs to be addressed,” said NTSB Chairman Robert Sumwalt. “We don’t need to wait for an investigation to be completed before issuing safety recommendations. We have the responsibility to issue recommendations that when implemented by recipients, can correct safety deficiencies, prevent accidents, and save lives.”