Embraer ERJ170

Full Narrative

HISTORY OF FLIGHTOn November 6, 2019, about 2115 eastern standard time, Republic Airways flight 4439, an Embraer EMB-175LR, N117HQ, experienced a pitch trim anomaly shortly after takeoff from Hartsfield-Jackson Atlanta International Airport (ATL), Atlanta, Georgia. The flight crew declared an emergency and returned to ATL. The nine passengers and crewmembers aboard the airplane were not injured, and the airplane was not damaged. The airplane was operating under the provisions of Title 14 Code of Federal Regulations Part 121 as regularly scheduled passenger flight destined for LaGuardia Airport (LGA), New York, New York.

The flight crew reported for duty on the day of the incident about 1400 at Detroit Metropolitan Wayne County Airport (DTW), Detroit, Michigan. The incident occurred during the third flight leg of the day. The captain flew the first leg, from DTW to LGA. According to the captain, while en route, the engine indicating and crew alerting system (EICAS) annunciated the “PITCH TRIM SW 1 [switch 1] FAIL” message. The captain stated that he and the first officer referred to the company’s quick reference handbook and saw that the EICAS message was advisory. As a result, they noted the message in the airplane’s logbook and planned to have the discrepancy addressed after the airplane landed at LGA.

According to the flight crewmembers, maintenance personnel at LGA initially advised that they would change the pitch trim switch on the captain’s yoke to resolve the EICAS message and that it would take about 20 minutes to obtain the part. The maintenance personnel reported that they partially removed the switch before deciding to defer the maintenance per the minimum equipment list. The maintenance personnel then reinstalled the partially removed switch but did not perform a functional test because the switch was a deferred maintenance item. The maintenance personnel placarded the switch inoperative and advised the captain to use the backup trim switch instead of the faulty trim switch on his yoke.

The first officer flew the second leg of the day, from LGA to ATL, which he described as “just a normal leg.” The first officer stated that no further maintenance was performed after arriving at ATL.

The captain was the pilot flying for the third (incident) leg of the day, from ATL to LGA. Air traffic control (ATC) communications showed that the airplane was cleared for takeoff at 2105:05. The flight crew stated the taxi and takeoff were normal. The first officer stated that, during takeoff, the airplane’s climb rate was “moving pretty rapidly” and reached about 4,000 ft per minute, which he described as normal given that the airplane was “very light” with only six passengers aboard.

The captain reported that he was unable to engage the autopilot when the airplane reached an altitude of about 2,200 ft mean sea level. The captain stated that he “knew that something was wrong,” so the captain instructed the first officer to declare an emergency. ATC communications showed that, at 2106:53, the emergency was declared to the controller. The controller confirmed that the airplane needed to return to the airport and provided instructions to the flight crew to enter the downwind leg for runway 10.

The captain thought that a pitch trim runaway was occurring, so he conducted the single memory item on Republic Airways’ runaway trim emergency checklist, which was to push and hold the autopilot/trim disconnect button on his yoke. The captain also stated that he kept pushing the button and that he was unable to pick up the quick reference card from his lap to continue to troubleshoot the issue because he had to keep both of his hands on the yoke to control the airplane.

The first officer stated that the captain was struggling to control the airplane. The captain asked the first officer to push and hold the autopilot/trim disconnect button located on the first officer’s yoke. The flight crewmembers reported that they did not notice any changes in the airplane’s pitch condition and were having difficulty holding the airplane’s nose down. According to the captain, both he and the first officer had to push forward on their control columns to keep the airplane from pitching up.

According to the flight data recorder (FDR), the horizontal stabilizer was initially positioned about 4° nose up. The stabilizer began moving about 2105:50 and reached a maximum noseup position of 13° at 2107:45. Between 2105:50 and 2107:50, the FDR recorded multiple trim-up commands from the captain’s switch (and only one trim-down command from the first officer switch). The airplane experienced several pitch oscillations, reaching a maximum pitch-up attitude of about 27° at 2108:08. About 7 second later, the flight crew told the controller that the airplane was “in a stalling situation.” About 1 minute later, the flight crew reported that “we can’t pitch down,” and FDR data showed that the flight crew banked the airplane to maintain control.

The captain pressed the button to cut out pitch trim system 1 because that was the system associated with the EICAS message. FDR data showed that all recorded pitch trim commands from both the captain’s and the first officer’s pitch trim control switches corresponded to the stabilizer movement until 2110:36, at which time the stabilizer parameter suddenly went to 0°, which was consistent with trim cutout switch actuation. According to Embraer, if only one cutout switch is pressed, the system is still capable of moving the horizontal stabilizer, but if both cutout switches are pressed, the system stops moving the horizontal stabilizer. The first officer stated that the airspeed dropped to 138 knots before they regained control of the airplane.

Between 2110:40 and 2113:30, the FDR recorded multiple trim-down commands from only the first officer’s switch (except for one instance of backup switch usage at 2111:00). Between 2114:30 and 2116:40, the FDR recorded multiple trim-up commands from only the captain’s switch. Afterward, the captain transferred control of the airplane to the first officer. (The captain wanted to talk with ATC and continue to troubleshoot.) The first officer stated that, with pitch trim system 1 cut out, he was able to trim the airplane nose down and regain airspeed. Between 2116:40 and the 2118:10, the FDR recorded multiple trim-down commands from only the first officer’s switch; between 2118:10 and the end of the flight, the FDR recorded multiple trim-up and -down commands from only the first officer’s switch.
At 2119:58, the controller instructed the flight crew to join the localizer for runway 10. At 2121:16, the controller cleared the airplane to land on runway 10. The crew acknowledged those instructions. The airplane landed uneventfully about 2125. A cockpit voice recorder summery transcript was prepared to document the communications between maintenance personnel after the incident airplane arrived at the gate. The incident flight had been recorded over. AIRCRAFT INFORMATIONPitch Trim System

The horizontal stabilizer control surface provides the airplane with stability and control during pitch trim adjustments. The control surface is moved by the horizontal stabilizer trim actuator, which is driven by two electric motors.

A manual pitch trim control switch is located on each control yoke, and a backup manual pitch trim control switch is located on the center pedestal. All three switches are dual-split switches that are spring loaded to neutral. Two stabilizer cutout switches are located on the center pedestal. If both cutout switches are pressed, the stabilizer actuator would be locked in place. If one cutout switch is pressed, the pitch trim system, including all three manual pitch trim switches, would continue to work normally.

An autopilot/trim quick disconnect switch button is located on each control yoke. Pressing and holding either quick disconnect switch, while both cutout switches are in the normal (not pressed) position, prevents any active manual or autotrim command. Pressing either switch also disengages the autopilot. Releasing the pressed quick disconnect button allows trim commands. If only one cutout switch is pressed, the associated quick disconnect switch would not function.

Pitch Trim Runaway Procedures

Republic Airways’ quick reference handbook had one memory item for a pitch trim runaway: the autopilot/trim disconnect button was required to be pressed in and held. The Embraer 170/175 Airplane Operations Manual required two memory items; the autopilot/trim disconnect button had to be pressed in and held, and both cutout buttons had to be pushed in. Figure 1 compares the two documents and shows other steps to address a pitch trim runaway.



Figure 1. Company and manufacturer pitch trim runaway procedures (Source: Republic Airways and Embraer).

Maintenance Records

The airplane’s flight logs from August 7 to November 5, 2019, were reviewed for items related to the pitch trim system. The table below shows the items that were noted.

Table. Pitch trim system discrepancies before the incident.

Date
Discrepancy
Corrective action
8/7/2019
Pitch trim switch 1 fail
Performed related Fault Isolation Manual (FIM) task. Message cleared; operational check good.
8/19/2019
Pitch trim switch 1 fail EICAS message with aural trim
Performed related FIM task. Removed and replaced captain’s side pitch trim switch.
8/24/2019
Pitch trim switch 1 fail
Performed related FIM task and aircraft maintenance manual (AMM) procedure. Operational checks okay.
9/3/2019
EICAS message en route while on autopilot pitch trim switch-1 fail. Captain trim switch verified inoperative.
Performed related FIM task. Message cleared; operational checks good.
9/8/2019
Pitch trim switch 1 fail
Deferred captain’s pitch trim switch in accordance with the minimum equipment list. Removed and replaced captain’s pitch trim switch; operational checks good.
9/8/2019
Backup pitch trim switch has no “TRIM” aural callout at the 3second cutout
Reset trim system cutouts. Trim aural warning operational checks okay.
9/25/2019
Pitch trim switch 1 fail EICAS message
Performed related AMM procedure and operational check of pitch trim controls. Operational check good; no defects noted.
9/27/2019
Aileron cable fairlead broken off at frame 22
Replaced fairlead.
10/12/2019
Pitch trim switch 1 fail
Deferred per MEL 27-43-02-01.
10/13/2019
When rolling right to full deflection, ailerons felt like they were binding
Performed aileron operational check; no defects noted. Found aileron autopilot servo cable frayed. Replaced autopilot servo bracket and frayed cable. Operational checks good.
10/15/2019
Pitch trim switch 1 fail
Removed and replaced pilot pitch control yoke switch. No fix. Removed and replaced horizontal stabilizer actuator control electronics. Operational checks good.
10/23/2019
Pitch trim 1 switch fail message
Deferred pitch trim 1 switch. 10/25/2019: Removed and replaced yoke trim switch. Operational checks good.
11/2/2019
Pitch trim switch 1 fail; captain’s switch on yoke inoperative
Replaced captain’s yoke trim switch Operational checks good.
11/3/2019
Pitch trim switch 1 fail EICAS message
Replaced horizontal stabilizer actuator control electronics. Operational checks good.

From May 1 to November 5, 2019, Republic Airways provided 15 mechanical interruption summary reports to the Federal Aviation Administration (FAA) for the incident airplane, which included several of the trim switch items.


Pitch Trim Anomaly During Incident Flight

As previously stated, maintenance personnel at LGA deferred changing the pitch trim switch on the captain’s yoke, per the minimum equipment list, and placarded the faulty switch as inoperative. Note: There was no requirement to disconnect or disarm a faulty pitch trim switch.

Maintenance records showed that, after the incident, the maintainer found fault code 27430200HS2. The definition for this fault code is "HSACE2 (X CHANNEL PWR)/WRG FAULT” and means there is a loss of power to channel 1 of the HS-ACE. It will be logged when channel 2 detects that channel 1 has been cut out, which is consistent with the activation of the channel 1 pitch trim cutout switch during the event flight as reported by the flight crew.

A senior maintenance manager from Republic arrived on 11/7/2019 to secure the airplane and remove the FDR/CVR. Republic reported that no additional work was done to the aircraft until two additional Republic Airways mechanics arrived from their Headquarters on November 8.

The maintenance crew stated that they confirmed the correct operation of all three switches per the AMM Part II 1963, Rev 80, Task 27-40-00-710-801-A (Horizontal Stabilizer System – Operational Check). They stated that the technician performing the procedure was very familiar with the horizontal stabilizer trim system, indication, and associated direction of movement. In addition, a technician was placed near the horizontal stabilizer, one at the pitch trim controls, and one in between, and verbal communication was used to verify that the stabilizer moved in the correct direction when operated. The maintenance crew stated that they did not observe any anomalies with the operation of the pitch trim system.

The captains yoke pitch trim control inputs to horizontal stabilizer actuator control electronics (HS-ACE) were removed and an operational check of horizontal stabilizer system to confirm that the captain’s yoke pitch trim was deactivated and the first officer’s and backup switch was still active was accomplished. The switch was not disturbed at the control column during this procedure. The aircraft was ferried to Indianapolis for further maintenance.
 
The ferry flight occurred on 11/9/2021 with no anomalies noted. Once in Indianapolis, the Republic Airways maintenance crew performed wire inspections and identified damaged wiring at the base of the captain’s control column.
In response to this incident, on April 13, 2020, Embraer and the FAA revised their master minimum equipment lists to remove the yoke pitch trim switches from the list of deferrable items. AIRPORT INFORMATIONPitch Trim System

The horizontal stabilizer control surface provides the airplane with stability and control during pitch trim adjustments. The control surface is moved by the horizontal stabilizer trim actuator, which is driven by two electric motors.

A manual pitch trim control switch is located on each control yoke, and a backup manual pitch trim control switch is located on the center pedestal. All three switches are dual-split switches that are spring loaded to neutral. Two stabilizer cutout switches are located on the center pedestal. If both cutout switches are pressed, the stabilizer actuator would be locked in place. If one cutout switch is pressed, the pitch trim system, including all three manual pitch trim switches, would continue to work normally.

An autopilot/trim quick disconnect switch button is located on each control yoke. Pressing and holding either quick disconnect switch, while both cutout switches are in the normal (not pressed) position, prevents any active manual or autotrim command. Pressing either switch also disengages the autopilot. Releasing the pressed quick disconnect button allows trim commands. If only one cutout switch is pressed, the associated quick disconnect switch would not function.

Pitch Trim Runaway Procedures

Republic Airways’ quick reference handbook had one memory item for a pitch trim runaway: the autopilot/trim disconnect button was required to be pressed in and held. The Embraer 170/175 Airplane Operations Manual required two memory items; the autopilot/trim disconnect button had to be pressed in and held, and both cutout buttons had to be pushed in. Figure 1 compares the two documents and shows other steps to address a pitch trim runaway.



Figure 1. Company and manufacturer pitch trim runaway procedures (Source: Republic Airways and Embraer).

Maintenance Records

The airplane’s flight logs from August 7 to November 5, 2019, were reviewed for items related to the pitch trim system. The table below shows the items that were noted.

Table. Pitch trim system discrepancies before the incident.

Date
Discrepancy
Corrective action
8/7/2019
Pitch trim switch 1 fail
Performed related Fault Isolation Manual (FIM) task. Message cleared; operational check good.
8/19/2019
Pitch trim switch 1 fail EICAS message with aural trim
Performed related FIM task. Removed and replaced captain’s side pitch trim switch.
8/24/2019
Pitch trim switch 1 fail
Performed related FIM task and aircraft maintenance manual (AMM) procedure. Operational checks okay.
9/3/2019
EICAS message en route while on autopilot pitch trim switch-1 fail. Captain trim switch verified inoperative.
Performed related FIM task. Message cleared; operational checks good.
9/8/2019
Pitch trim switch 1 fail
Deferred captain’s pitch trim switch in accordance with the minimum equipment list. Removed and replaced captain’s pitch trim switch; operational checks good.
9/8/2019
Backup pitch trim switch has no “TRIM” aural callout at the 3second cutout
Reset trim system cutouts. Trim aural warning operational checks okay.
9/25/2019
Pitch trim switch 1 fail EICAS message
Performed related AMM procedure and operational check of pitch trim controls. Operational check good; no defects noted.
9/27/2019
Aileron cable fairlead broken off at frame 22
Replaced fairlead.
10/12/2019
Pitch trim switch 1 fail
Deferred per MEL 27-43-02-01.
10/13/2019
When rolling right to full deflection, ailerons felt like they were binding
Performed aileron operational check; no defects noted. Found aileron autopilot servo cable frayed. Replaced autopilot servo bracket and frayed cable. Operational checks good.
10/15/2019
Pitch trim switch 1 fail
Removed and replaced pilot pitch control yoke switch. No fix. Removed and replaced horizontal stabilizer actuator control electronics. Operational checks good.
10/23/2019
Pitch trim 1 switch fail message
Deferred pitch trim 1 switch. 10/25/2019: Removed and replaced yoke trim switch. Operational checks good.
11/2/2019
Pitch trim switch 1 fail; captain’s switch on yoke inoperative
Replaced captain’s yoke trim switch Operational checks good.
11/3/2019
Pitch trim switch 1 fail EICAS message
Replaced horizontal stabilizer actuator control electronics. Operational checks good.

From May 1 to November 5, 2019, Republic Airways provided 15 mechanical interruption summary reports to the Federal Aviation Administration (FAA) for the incident airplane, which included several of the trim switch items.


Pitch Trim Anomaly During Incident Flight

As previously stated, maintenance personnel at LGA deferred changing the pitch trim switch on the captain’s yoke, per the minimum equipment list, and placarded the faulty switch as inoperative. Note: There was no requirement to disconnect or disarm a faulty pitch trim switch.

Maintenance records showed that, after the incident, the maintainer found fault code 27430200HS2. The definition for this fault code is "HSACE2 (X CHANNEL PWR)/WRG FAULT” and means there is a loss of power to channel 1 of the HS-ACE. It will be logged when channel 2 detects that channel 1 has been cut out, which is consistent with the activation of the channel 1 pitch trim cutout switch during the event flight as reported by the flight crew.

A senior maintenance manager from Republic arrived on 11/7/2019 to secure the airplane and remove the FDR/CVR. Republic reported that no additional work was done to the aircraft until two additional Republic Airways mechanics arrived from their Headquarters on November 8.

The maintenance crew stated that they confirmed the correct operation of all three switches per the AMM Part II 1963, Rev 80, Task 27-40-00-710-801-A (Horizontal Stabilizer System – Operational Check). They stated that the technician performing the procedure was very familiar with the horizontal stabilizer trim system, indication, and associated direction of movement. In addition, a technician was placed near the horizontal stabilizer, one at the pitch trim controls, and one in between, and verbal communication was used to verify that the stabilizer moved in the correct direction when operated. The maintenance crew stated that they did not observe any anomalies with the operation of the pitch trim system.

The captains yoke pitch trim control inputs to horizontal stabilizer actuator control electronics (HS-ACE) were removed and an operational check of horizontal stabilizer system to confirm that the captain’s yoke pitch trim was deactivated and the first officer’s and backup switch was still active was accomplished. The switch was not disturbed at the control column during this procedure. The aircraft was ferried to Indianapolis for further maintenance.
 
The ferry flight occurred on 11/9/2021 with no anomalies noted. Once in Indianapolis, the Republic Airways maintenance crew performed wire inspections and identified damaged wiring at the base of the captain’s control column.
In response to this incident, on April 13, 2020, Embraer and the FAA revised their master minimum equipment lists to remove the yoke pitch trim switches from the list of deferrable items. WRECKAGE AND IMPACT INFORMATIONPostincident examination of the area near the captain’s control column revealed wires with chafed insulation. These wires connected the horizontal stabilizer actuator control electronics to the captain’s pitch trim switch and autopilot/trim disconnect button. The wires contacted an incorrectly tucked pigtail on the safety wire retaining the captain’s control column forward mechanical stop bolt, as shown in in figure 2.



Figure 2. Bolt with pigtail contacting wires (Source: Republic Airways).

Subsequent laboratory testing revealed that the insulation for three wires (the captain’s quick disconnect switch, the captain’s nose-up trim switch A, and the captain’s nose-up trim switch B) was damaged but that continuity to the internal wire strands could be achieved. Specifically, the quick disconnect switch wire insulation was damaged completely around the wire strands, and multiple exposed wire strands were severed. The nose-up trim switch A wire insulation was chafed, and a small section of exposed conducting wire showed signs of mechanical scraping. The nose-up trim switch B wire insulation was chafed and damaged, and the conducting wire strands were not visible. Continuity was achieved by using both a cotton swab soaked in soapy water placed on the damage area as well as a sample piece of cut safety wire pressed lightly on the damaged area. No evidence of arcing was observed.

Examination of the pitch trim control switch revealed an imprint mark in the silicone area on the back of the switch, as shown in figure 3. According to Embraer, this mark was caused by contact against a spring and was consistent with the switch being installed inverted at some point.


Figure 3. Captain-side pitch trim control switch after removal from the incident airplane (Source: Republic Airways).
Note: The red circles show the location of the imprint marks on the back of the control switch. ADDITIONAL INFORMATIONEmbraer released Service Bulletin (SB) 170-27- 0051 on February 27, 2015, to alert operators of the possibility that the pitch trim switch could be installed inverted. The SB recommended the installation of a support in the control yoke to prevent the incorrect installation of the switch. The SB compliance time was 7,500 hours or 36 months, whichever occurred first. This SB had not been performed on the airplane before the incident.

As a result of this incident investigation, the NTSB made the following recommendations to the National Civil Aviation Agency of Brazil and the FAA on January 16, 2020:

To the National Civil Aviation Agency of Brazil:

Require Embraer to develop instructions for operators of Embraer EMB170/175/190/195/Lineage 1000 series airplanes to inspect the wiring in the captain’s and first officer’s control columns for damage, replace where needed, and ensure proper clearance from adjacent components, including the forward mechanical stop bolt and its safety wire. (A-20-1, classified “Closed—Acceptable Action” on September 2, 2020)

Once Embraer develops inspection instructions for the wiring in the captain’s and first officer’s control columns as requested in Safety Recommendation A-20-1, require operators of Embraer EMB170/175/190/195/Lineage 1000 series airplanes to inspect that wiring for damage, in compliance with Embraer’s instructions, replace where needed, and ensure proper clearance from adjacent components, including the forward mechanical stop bolt and its safety wire. (A20-2, classified “Open—Acceptable Response” on September 2, 2020)

Once inspections are completed as outlined in the instructions developed in response to Safety Recommendation A-20-1, require Embraer to review the inspection results and revise design and maintenance documentation for Embraer EMB-170/175/190/195/Lineage 1000 series airplanes as necessary to prevent any hazards identified during the inspections. (A-20-3, classified “Open—Acceptable Response” on September 2, 2020)

Once Embraer revises design and maintenance documentation for Embraer EMB170/175/190/195/Lineage 1000 series airplanes as requested in Safety Recommendation A-20-3, require operators of these airplanes to incorporate these changes. (A-20-4, classified “Open—Acceptable Response” on September 2, 2020)

Mandate the incorporation of Embraer Service Bulletins (SB) 170-27-0051, 19027-0039, and 190LIN-27-0019 on all applicable airplanes, as specified in the SBs. (A-20-5, classified “Closed—Acceptable Action” on September 2, 2020)

In coordination with the Federal Aviation Administration, Embraer, and US operators, determine if changes to the Embraer EMB-170/175/190/195/Lineage 1000 series airplane Pitch Trim Runaway checklists are required to adequately address all potential trim system failures, and make such changes as necessary. (A-20-6, classified “Open—Acceptable Response” on September 2, 2020)

To the FAA:

Once Embraer develops inspection instructions for the wiring on the captain’s and first officer’s control columns as requested in Safety Recommendation A201, require operators of Embraer EMB-170/175/190/195/Lineage 1000 series airplanes to inspect that wiring for damage, in compliance with Embraer’s instructions, replace where needed, and ensure proper clearance from adjacent components, including the forward mechanical stop bolt and its safety wire. (A20-7, classified “Closed—Unacceptable Action” on October 21, 2022)

Once Embraer revises design and maintenance documentation for Embraer EMB-170/175/190/195/Lineage 1000 series airplanes as requested in Safety Recommendation A-20-3, require operators of these airplanes to incorporate these changes. (A-20-8, classified “Closed—Acceptable Alternate Action” on October 21, 2022)

Mandate the incorporation of Embraer Service Bulletins (SB) 170-27-0051, 19027-0039, and 190LIN-27-0019 on all applicable airplanes, as specified in the SBs. (A-20-9, classified “Closed—Acceptable Action” on October 21, 2022)

In coordination with the National Civil Aviation Agency of Brazil, Embraer, and US operators, determine if changes to the Embraer EMB170/175/190/195/ Lineage 1000 series airplane Pitch Trim Runaway checklists are required to adequately address all potential trim system failures, and make such changes as necessary. (A-20-10, classified “Closed—Acceptable Action” on October 21, 2022)
For more information about these recommendations, see Reported Flight Control System Difficulty on Embraer EMB-175 (NTSB/ASR-20-01). FLIGHT RECORDERSDuring the flight from DTW to LGA, the FDR recorded multiple occurrences of the “TRIM FAIL” condition for the captain’s pitch trim control switch. According to Embraer, the FDR records the TRIM FAIL discrete for a disabled pitch trim control switch whenever there is a pitch trim input from any operational source (that is, another pitch trim control switch or autopilot trim input). As a result, the TRIM FAIL discrete indicates that a pitch trim control switch was in a failed state when the horizontal stabilizer actuator control electronics received a pitch trim command from an operational source.