Citing its preliminary investigation of a Nov. 6, 2019, incident involving an Embraer 175, the U.S. National Transportation Safety Board (NTSB) has issued safety recommendations to address problems associated with wire chafing, the pitch trim switch and memory items in the checklist used by the pilots in dealing with the incident.
In the incident, the crew of Republic Airways Flight 4439 reported a flight control issue related to the airplane’s pitch trim and declared an emergency after takeoff from Hartsfield-Jackson Atlanta (Georgia, U.S.) International Airport. They returned to the airport and landed safely.
The NTSB’s preliminary investigation found chafing on the wires that connect the horizontal stabilizer actuator control electronics and the captain’s pitch trim switch and autopilot/trim disconnect button. The NTSB said in a statement issued Wednesday that the chafing resulted from “contact with the incorrectly untucked pigtail of the mechanical stop bolt safety wire.”
“When the captain’s pitch trim switch was removed from the yoke, marks were observed that indicated at some point before the incident flight, the pitch trim switch had been installed in an inverted position,” the NTSB said, noting that Embraer had issued three service bulletins regarding errors in the installation of pitch trim switches in EMB-175 airplanes after receiving reports from flight crews in 2015. At the time, neither the U.S. Federal Aviation Administration (FAA) nor the National Civil Aviation Agency of Brazil (ANAC) moved to require the actions detailed in the service bulletins.
“While it is not yet known if inverted switch installation was a factor in the incident, the NTSB is concerned the condition could lead to flight crew confusion, delaying appropriate recognition of and response to increased control forces,” the NTSB said.
The preliminary investigation also determined that unintended pitch trim operation “may be masked and go undetected” during takeoff and some other phases of flight and that “limitations in the checklist memory items may delay pilots in properly responding to and regaining control of the Embraer EMB-170/175/190/195 and Lineage 1000 series airplanes.”
The recommendations to the FAA and ANAC called for, among other things, inspections of control column wiring and replacement of the wiring, if necessary; and the mandatory incorporation of Embraer Service Bulletins 170-27-0051, 190-27-0039, and 190LIN-27-0019 on the affected airplanes.” In addition, the NTSB called on the FAA, ANAC, Embraer and airplane operators to work together to determine whether changes are needed in the Pitch Trim Runaway checklists for EMB-170/175/190/195/Lineage 100.
