Based on preliminary findings from its ongoing investigation of an incident involving an Embraer-175 airplane, the National Transportation Safety Board (NTSB) in late January issued 10 safety recommendations to address issues identified in the probe.

One of the issues was that the emergency procedures followed by the pilots didn’t seem to immediately stop the problem. Both pilots needed to push the control column with both hand to maintain control of the plane, preventing them from reaching for their emergency checklists. Eventually, the copilot was able to use a thumb switch to help keep the aircraft's nose level. The aircraft returned to the airport and safely landed about 15 minutes after the crew declared the emergency.

The NTSB issued six recommendations to the National Civil Aviation Agency of Brazil (ANAC) and four to the U.S. Federal Aviation Administration. The recommendations address areas of concern including wire chafing, the incorrect installation of a critical switch and potential limitations in checklist memory items for pilots to address unintended operation of the pitch trim system.

The investigation and recommendations stem from a Nov. 6, 2019, incident involving Republic Airways Flight 4439, an Embraer EMB-175.

The flight crew declared an emergency shortly after takeoff from Hartsfield-Jackson Atlanta International Airport. They reported a pitch trim-related flight control issue and difficulty controlling the airplane. There were six passengers on board the airplane.

Mechanical issues

The NTSB said that a 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. NTSB said the chafing was caused by contact with an incorrectly untucked pigtail of the forward mechanical stop bolt safety wire.

Embraer-175 aircraft, similar to the one involved in the November incident. Source: EmbraerEmbraer-175 aircraft, similar to the one involved in the November incident. Source: EmbraerIn addition, when the captain’s pitch trim switch was removed from the yoke, NTSB said that marks were observed that indicated "at some point before the incident flight, the pitch trim switch had been installed in an inverted position."

Embraer previously issued three service bulletins related to pitch trim switch installation errors, NTSB said. Those bulletins followed reports from flight crews in 2015 about flight control system difficulties. Neither the FAA nor the Brazilian aviation agency required incorporating the service bulletins, leading the NTSB to say it was "concerned the condition could lead to flight crew confusion," delaying crew awareness of, and response to, increased control forces during flight.

Preliminary information from the NTSB’s investigation also suggests that unintended pitch trim operation may be masked and go undetected during certain phases of flight, such as during takeoff. In addition, 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.

Based on its early findings, the NTSB issued the 10 safety recommendations to address the issues.

Incident timeline

On Nov. 6, 2019, the flight crew of Republic Airways Flight 4439, an Embraer EMB-175, declared an emergency shortly after takeoff from ATL with six passengers on board. The crew reported a pitch trim-related flight control issue and difficulty controlling the airplane.

The captain (who was in the left seat and the pilot flying) later reported recognizing the flight control issue after a failed attempt to engage the autopilot about 2,200 ft mean sea level. According to the NTSB, the captain stated that he conducted the single memory item on Republic’s Pitch Trim Runaway checklist to push and hold the autopilot/trim disconnect button on his side.

The captain then asked the first officer to push and hold the right-side autopilot/trim disconnect button. The flight crew members reported that they did not notice any change in the pitch condition and continued to have difficulty holding the nose down.

The captain and first officer later reported that they both needed to use both hands to counter the airplane’s nose-up pitch motion and that doing so involved such effort that neither felt that they could reach for the quick reference handbook to troubleshoot the problem. Ultimately, the flight crew was able to trim the airplane with the first officer’s trim switch, return to Atlanta and land the airplane safely about 15 minutes after declaring the emergency.