Republic E175 at Atlanta on Nov 6th 2019, trim runaway, severe control problems, stalling situation

Last Update: December 2, 2022 / 15:42:47 GMT/Zulu time

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Incident Facts

Date of incident
Nov 6, 2019

Classification
Incident

Aircraft Registration
N117HQ

Aircraft Type
Embraer ERJ-175

ICAO Type Designator
E175

On Nov 18th 2022 the NTSB released their factual report along with the investigation docket.

The NTSB stated that the crew had been flying two sectors prior to the occurrence sector, the first sector was flown by the captain, the second by the first officer. During the first sector the captain received a "PITCH TRIM SW 1 FAIL" message. After landing the captain wrote the message up.

The NTSB wrote: "According to the flight crewmembers, maintenance personnel at LGA initially advised that they would change the pitch trim switch on the captainfs 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 captain was flying the third (occurrence) sector of the day. The NTSB summarized the sequence of events:

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 gknew that something was wrong,h 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 Airwaysf 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 officerfs yoke. The flight crewmembers reported that they did not notice any changes in the airplanefs pitch condition and were having difficulty holding the airplanefs 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 degrees nose up. The stabilizer began moving about 2105:50 and reached a maximum nose-up position of 13 degrees at 2107:45. Between 2105:50 and 2107:50, the FDR recorded multiple trim-up commands from the captainfs switch (and only one trim-down command from the first officer switch). The airplane experienced several pitch oscillations, reaching a maximum pitchup attitude of about 27 degrees at 2108:08. About 7 second later, the flight crew told the controller that the airplane was gin a stalling situation.h About 1 minute later, the flight crew reported that gwe canft pitch down,h 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 captainfs and the first officerfs pitch trim control switches corresponded to the stabilizer movement until 2110:36, at which time the stabilizer parameter suddenly went to 0 degrees, 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 officerfs 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 captainfs 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 officerfs switch; between 2118:10 and the end of the flight, the FDR recorded multiple trim-up and -down commands from only the first officerfs 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.

The NTSB stated: "the Republic Airways maintenance crew performed wire inspections and identified damaged wiring at the base of the captainfs 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."

The NTSB further wrote:

Postincident examination of the area near the captainfs control column revealed wires with chafed insulation. These wires connected the horizontal stabilizer actuator control electronics to the captainfs pitch trim switch and autopilot/trim disconnect button. The wires contacted an incorrectly tucked pigtail on the safety wire retaining the captainfs control column forward mechanical stop bolt, as shown in in figure 2.

Subsequent laboratory testing revealed that the insulation for three wires (the captainfs quick disconnect switch, the captainfs nose-up trim switch A, and the captainfs 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.

On Dec 2nd 2022 the NTSB released their final report concluding the probable causes of the incident were:

The captainfs use of his pitch trim switch, which had been placarded inoperative but not deactivated, resulting in the airplane pitching up when the captain was trying to trim down. The trim commands were reversed due to maintenance personnelfs incorrect installation of the pitch trim switch. Contributing to the incident was the operatorfs delay in incorporating SB 170-27-0051 which would have prevented the switch from being installed inverted.

The NTSB analysed:

The incident flight occurred during the third flight leg of the day. During the first flight leg, the engine indicating and crew alerting system (EICAS) provided the gPITCH TRIM SW 1 [switch 1] FAILh advisory message. After an uneventful landing, maintenance personnel met the airplane to address the issue. 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 switch but did not perform a functional test because the switch was a deferred maintenance item. They also placed a placard to indicate it was inoperative; thus, the captainfs trim switch, although not deactivated, was not supposed to be used during the subsequent flight legs.

After takeoff on the incident flight, the captain instructed the first officer to declare an emergency because of runaway pitch trim. The captain stated that he conducted the single memory item on the pitch trim runaway emergency checklist in Republic Airwaysf quick reference handbook. The memory item required him to push and hold the autopilot/trim disconnect button on his yoke to stop the runaway condition. The captain then instructed the first officer to push and hold the autopilot/trim disconnect button on the first officerfs yoke. The flight crewmembers reported that they did not notice any change in the runaway condition and continued to have difficulty controlling the airplanefs pitch. The captain stated that the flight crew banked the airplane to maintain control.

The captain and the first officer stated that they needed to use both hands at the same time to counter the airplanefs nose-up pitch motion. As a result, neither was able to physically reference the quick reference handbook procedures to troubleshoot the problem.

The captain selected the cutout button for the pitch trim system on his yoke to interrupt the nose-up trim condition and instructed the first officer to use the trim switch on the first officerfs yoke to pitch the airplane down to a normal attitude.

The first officer, now in control of the pitch trim using his pitch trim switch, was able to trim and regain control of the airplane. About three minutes later the captain took back control of the airplane. For about 2.5 minutes afterwards the FDR recorded multiple pitch trim up commands from the captainfs pitch trim switch, and the airplane again went into a mistrimmed condition.

The first officer took back control of the airplane and remained in control until the end of the flight. During this time the FDR showed no pitch trim commands originating from the captainfs trim switch although there were multiple up and down pitch trim commands originating from the first officerfs trim switch. The airplane was controllable and in a trimmed condition and able to return to the departure airport and land uneventfully.

Postincident examination of the captainfs pitch trim control switch identified imprint marks on the back of the switch, indicating that, at some point, the switch was installed in an inverted position. The most likely opportunity for this to occur would have been during maintenance after the first flight leg when the pitch trim switch was partially removed then reinstalled since the decision was made to defer maintenance. Since maintenance was deferred, the switch was not functionally tested.

If a functional test had been completed, maintenance personnel would likely have identified the reversed switch position. 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, effectively requiring pitch trim switches to be functionally tested and operational before flight.

Embraer issued Service Bulletins (SBs) 170-27-0051, 190-27-0039, and 190LIN-27-0019 in February 2015 after reports about inverted pitch trim switches. The SBs recommended the installation of a support in the control yoke within the next 7,500 flight hours or 36 months after the SBfs issuance (whichever occurred first). However, the SB 170-27-0051 had not been accomplished on the incident airplane. If the SB had been accomplished, the recommended support in the control yoke would have prevented the faulty installation.

In January 2020, the National Transportation Safety Board issued Safety Recommendations A20-5 and -9 to the National Civil Aviation Agency of Brazil (ANAC) and the Federal Aviation Administration (FAA), respectively, to mandate incorporation of the SB. On May 26, 2020, ANAC published Brazilian Airworthiness Directive 2020-05-0051, which mandated compliance with the SB; as a result, Safety Recommendation A-20-5 was classified gClosed—Acceptable Actionh on September 2, 2020. Regarding Safety Recommendation A-20-9 (classified gClosed—Acceptable Actionh on October 21, 2022), the FAA stated that it issued Airworthiness Directive 2020-25-08, which became effective on January 21, 2021, and mandated operator compliance with the ANACfs airworthiness directive requirements.

The installation of the pitch trim switch in reverse and the captainfs use of the deferred trim switch resulted in the pitch excursion; when the captain attempted to trim the airplane nose down, the airplane responded with nose-up inputs. Thus, to effectively control the reversed pitch trim system, the captain would have had to recognize that his trim-down inputs were causing trim-up commands. However, the captain would not have been aware that the switch had been reinstalled incorrectly and was commanding trim opposite of his inputs.

The captain was aware that the pitch trim switch was not to be used because it had been deferred per the minimum equipment list. However, highly practiced behavior, such as making inputs to keep an airplane in trim, can result in typical motor actions being made automatically despite higher-level knowledge indicating that such action might not be appropriate. During the captainfs interview he stated that it was second nature to use the trim switch on the yoke.

Systems with deferred maintenance are typically deactivated to prevent any errant command input from a faulty control. However, there was no requirement, nor was there a published procedure, to disconnect or disarm a faulty pitch trim switch.

Placards for inoperative equipment are typically collocated with the related control to remind pilots that the equipment should not be used. However, the pitch trim switch position on the yoke did not allow space for a placard on or near the switch.

The captainfs use of an inoperative and a placarded flight control was inappropriate and caused the airplane to pitch up when the captain was trying to trim down, resulting in flight crew difficulties in controlling the pitch of the airplane. In addition, the captain thought that the airplane had a runaway trim condition, but, once he transferred control of the airplane to the first officer, the mistrim condition stopped, and the crew was able to regain control of the airplane. Thus, the captainfs trim inputs (and not a runaway trim) caused the pitch trim anomaly. In addition, FDR data show that the captainfs pitch trim only inputted nose up trim and there were no nose down trim commands.

Maintenance records showed a history of gPITCH TRIM SW 1 FAILh EICAS messages on the airplane between August 4, 2019, and the incident date, resulting in five replacements of the captainfs pitch trim control switch and two replacements of the horizontal stabilizer actuator control electronics. Also, during the first flight leg on the day of the incident, the FDR recorded multiple gTRIM FAILh occurrences related to the captainfs pitch trim control switch. The gTRIM FAILh occurrences and the gPITCH TRIM SW 1 FAILh EICAS messages were caused by a short to ground of a single circuit to the captainfs pitch trim switch. The short was created by contact with the incorrectly tucked pigtail from the safety wire retaining the forward mechanical stop bolt for the captainfs control column.

Although both wires enabling the captainfs pitch trim switch trim-up command were damaged and chafed and were capable of allowing continuity to the untucked safety wire pigtail (which would result in a short to ground condition), it is unlikely that the pigtail would have made continuity to both wires at the same time. Both wires would need to short to ground simultaneously to allow the stabilizer trim to activate. If both wires shorted to ground, the horizontal stabilizer control surface movement would automatically stop after three seconds, and if the condition persisted the aural alert gTRIMh would annunciate. This alert was not reported by the crew.

Finally, the maintenance history for the captainfs pitch trim switch had many reports of a gPitch Trim Switch 1 Failh EICAS message, but no reports of a trim runaway. FDR showed that the captain's pitch trim switch only provided trim up commands when there was force being applied to the captain's control column, suggest that the captain was in control of the airplane during those times.
Aircraft Registration Data
Registration mark
N117HQ
Country of Registration
United States
Date of Registration
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Manufacturer
EMBRAER-EMPRESA BRASILEIRA DE
Aircraft Model / Type
ERJ 170-200 LR
Number of Seats
ICAO Aircraft Type
E175
Year of Manufacture
Serial Number
Aircraft Address / Mode S Code (HEX)
Engine Count
Engine Manufacturer
Engine Model
Engine Type
Pounds of Thrust
Main Owner
PgfniAi fchhqkgemie iccmqd nhmjjjqcAgqqAfdkdld gnqhipglkpmdnegdccqbghkpqAgeklkenAlgb Subscribe to unlock
Incident Facts

Date of incident
Nov 6, 2019

Classification
Incident

Aircraft Registration
N117HQ

Aircraft Type
Embraer ERJ-175

ICAO Type Designator
E175

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