Brickyard Suffers Trim Runaway | Control Problem at Atlanta [2019]

American Eagle Flight 4439 had only just left Atlanta when the crew encountered a severe controllability problem that made the aircraft difficult to pitch and descend.

A Sudden Control Problem

Flight 4439 departed Runway 09L at 21:05 local time for New York LaGuardia. Shortly after takeoff, the crew declared an emergency and reported that they were in what they described as a stalling situation. They also reported difficulty trying to descend.

The Atlanta tower controller worked with the crew while they dealt with the problem. Once control was regained, the aircraft was vectored back toward Atlanta and landed on Runway 10.

What Maintenance Found

The post-incident examination found chafed insulation around wiring connected to the horizontal-stabilizer actuator control electronics, the captain's pitch-trim switch and the autopilot/trim-disconnect button.

The investigation also found evidence that the captain's pitch-trim switch had previously been installed upside down. The switch was placarded inoperative but had not been deactivated. When the captain used it while trying to trim down, the trim commands were reversed and the aircraft pitched up instead.

The Maintenance Chain

The investigation identified contact between the wiring and an incorrectly untucked pigtail of the forward mechanical stop-bolt safety wire as the source of the chafing.

Investigators identified delayed incorporation of Service Bulletin 170-27-0051 as a contributing factor; the bulletin would have prevented the switch from being installed in the inverted position.

The timing of the control problem made the event particularly serious. The E175 had just departed Runway 09L when the crew began reporting difficulty controlling the aircraft. Their report of a stalling situation was followed by difficulty descending, leaving the crew dependent on the controller while they worked to regain control.

The incident also shows how a maintenance configuration can become an immediate flight-control problem. The aircraft was not simply suffering a random trim malfunction; the investigation connected the abnormal response to the installation and wiring condition of the captain's pitch-trim system.

Once the crew regained control, the aircraft did not continue to LaGuardia. Returning to Atlanta allowed maintenance personnel to examine the aircraft and identify the conditions that had produced the unusual pitch response.

The E175's safe return allowed investigators to examine the aircraft immediately after the event. The findings connected the unusual pitch response to the trim system rather than an unexplained loss of aerodynamic control.

“Date: Wednesday 6 November 2019 Type: Embraer ERJ-175LR (ERJ-170-200 LR) Registration: N117HQ Year of manufacture: 2007 Occupants: 9 Aircraft damage: Unknown Category: Serious incident Departure airport: Atlanta Hartsfield-Jackson International Airport, GA (ATL/KATL) Destination airport: New York-La Guardia Airport, NY (LGA/KLGA) Investigating agency: NTSB Narrative: American Eagle flight AA4439 returned to Atlanta Hartsfield-Jackson International Airport, Georgia, USA, after suffering severe controllability issues after takeoff.”

Accident Facts

Timeline

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