# NTSB DCA99IA058: Airbus Industrie 300-600, N7082A, Miami, FL, May 11, 1999 - Type: NTSB incident investigation - Classification: Incident · No injuries · Incident investigation · Final report - Date: May 11, 1999, 14:45 local (18:45 UTC) - Place: Miami, FL - Location: 25.7743° N, 80.1937° W: Placed by OpenAirDocs: center of Miami, FL, within about 6 miles (OpenAirDocs) - Nearby events: https://openairdocs.org/map.md?lat=25.7743&lon=-80.1937&mi=10 - Phase of flight: [Other](https://openairdocs.org/ntsb-phases/800) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 129 uninjured - Status: Completed, report November 14, 2002 - Report: Approved by Office Director - NTSB office: Major Investigations Division - NTSB case key (mKey): 46296 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DCA99IA058 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/46296/pdf - Page: https://openairdocs.org/ntsb/DCA99IA058 ## Probable cause Uncommanded rudder movement caused by a contaminant in the engagement valve solenoid that prevented disengagement of the autopilot yaw actuator and cross-connected wiring of the autopilot yaw actuator's main valve solenoids by the operator. Factors contributing to the incident were the lack of proper controls in the solenoid assembly process and the lack of procedures to detect miswired solenoids. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Miscellaneous/other, other - misc eqpt/furnishings - assembly (contributing factor) - procedures/directives - inadequate, manufacturer - procedure inadequate, manufacturer - Miscellaneous/other, other - misc eqpt/furnishings - contamination (cause) - Miscellaneous/other, other - misc eqpt/furnishings - misrouted (cause) - maintenance,installation - improper, other maintenance personnel - Airframe/component/system failure/malfunction, approach - flt control syst,rudder control - oscillation (cause) ## Analysis During final approach to the airport and after the crew turned the autopilot off, American Airlines flight 916 began experiencing uncommanded rudder motion and high rudder pedal forces. The flight crew executed a go-around about 360 feet above ground level. Despite continued difficulties with the rudder, the flight crew was able to land the airplane successfully. Examination of the autopilot yaw actuator revealed two main findings: (1) the wiring to the two main valve solenoids had been cross connected, and (2) a foreign-particle contaminant in the green system engagement valve solenoid had prevented disengagement of the yaw actuator. Investigators found that when these two conditions exist, turn coordination system inputs can cause uncommanded rudder movements. Inspections of A300 and A310 airplanes after the incident resulted in the discovery of another American A300 with cross-connected solenoid wiring. American indicated that it had installed new autopilot actuator solenoids on this airplane and the rest of its A300 fleet. At the time the solenoids were installed, American's procedures did not include a check for proper installation of the solenoid wiring. The manufacturers of the airplane and the actuator have since incorporated new procedures to ensure that the solenoids are wired properly. As part of the investigation, numerous additional solenoids were examined for the presence of contaminants. Although contaminants were discovered on several other solenoids, they were smaller than that found on the incident airplane's engagement solenoid and did not affect solenoid functionality. Audits of the solenoid assembly process revealed the need to update production and inspection documentation and the need to include measures to prevent foreign particles from contaminating adjacent workstations. The manufacturer of the solenoids took corrective actions that included improving production facilities, implementing more stringent sampling and inspection procedures, and clarifying assembly instructions. ## Factual narrative HISTORY OF FLIGHT At approximately 1450 eastern daylight time on May 11, 1999, American Airlines (American) flight 916, an Airbus A300-605R (N7082A), experienced high rudder pedal forces and uncommanded rudder motion during final approach to runway 9R at Miami International Airport, Miami, Florida. The motion started soon after the autopilot was turned off in preparation for landing. (The autopilot remained off throughout the remainder of the flight.) Flight data recorder (FDR) data show small rudder oscillations within the range of about 1.0 degree left to about 4.0 degrees right when the airplane was at an altitude of approximately 1,450 feet and an airspeed of 152 knots. The flight crew switched off the yaw dampers, but the uncommanded rudder motion worsened, and the crew switched the yaw dampers back on. During the airplane's descent and approach (at an airspeed of 137 knots), the amplitude of the rudder oscillations reached as high as 5 degrees left and 12 degrees right. The FDR data indicate that the airplane descended to about 360 feet before a go-around was initiated and the airplane began to climb. Large rudder oscillations continued during the climb, and maximum lateral accelerations of +0.342 to -0.240 g were recorded. Although the uncommanded rudder motion continued during the go-around, the crew was able to land on runway 27L successfully. No passengers or crewmembers were injured, and the airplane was not damaged. The flight was a regularly scheduled flight from Bogota, Colombia, to Miami being conducted under 14 Code of Federal Regulations Part 121. During postincident tests conducted at the American maintenance hangar in Miami, investigators reproduced rudder behavior similar to that experienced on flight 916 by pressurizing the green hydraulic servo control system and energizing at least one of the flight control computers (FCC). (The airplane has three independent hydraulic systems, designated as green, yellow, and blue.) The autopilot remained off. Rudder operation returned to normal when either testing condition was not satisfied. After the rudder anomaly had been reproduced several times, the FCC fault data for the incident flight were reviewed by American technical specialists, who reported that the data indicated faults with the autopilot yaw actuator and the No. 1 FCC. (FCC fault data are recorded when an uncommanded autopilot disengagement occurs.) After the rudder testing was complete, the autopilot yaw actuator was removed from the airplane at Safety Board request and replaced with a new yaw actuator to determine whether the rudder anomaly remained and to preserve any failures within the original actuator. The incident actuator, including the hydraulic lines, torque limiter, connector, and wiring, was inspected before and after it was removed. No anomalies were noted. No shorts were found during continuity checks between the FCC connectors and the autopilot yaw actuator (pin-to-pin and pin-to-ground). With the new yaw actuator installed in the airplane, investigators repeated the test series. No rudder stiffness or uncommanded movements were noted during any testing. A300 AUTOPILOT ACTUATOR DESCRIPTION The A300-600 contains three autopilot actuators: one each for the pitch, roll, and yaw axes. The actuators are identical although the output lever is unique to each position. When the autopilot is active, the actuators transform signals from the FCC into commands for movement of the respective flight controls. Each actuator consists of two independent, redundant control channels-the green and yellow systems-each with its own electric and hydraulic operation. Operation of each actuator is controlled by two pairs of solenoids (one pair for each channel). Each solenoid pair consists of a main valve solenoid that controls hydraulic pressure to the actuator and an engagement valve solenoid that controls engagement of the autopilot clutch for autopilot commands. Except for tags on the wiring to the end caps that distinguish the two main valves (both marked "P") from the two engagement valves (both marked "E"), the four solenoids (part number 38215-262) are identical in appearance. The main valve solenoid is always energized in the ON position when the respective FCC is powered, and the FCCs are continuously powered in flight. Once the appropriate autopilot mode is engaged, the engagement valve solenoids for the roll and pitch autopilot actuators are energized and actuator movement is controlled by FCC commands. For the autopilot yaw actuator, the leading edge slats must also be extended to at least 15 degrees before the engagement valve solenoid is energized. For each autopilot actuator channel, the FCC monitors the position of the autopilot clutch to ensure that it agrees with the autopilot selection made by the crew. If the FCC detects a disagreement between the autopilot clutch and the autopilot selection, the FCC will command the respective main valve solenoid to close, thus depressurizing that channel of the autopilot actuator. AUTOPILOT YAW ACTUATOR EXAMINATION The autopilot yaw actuator was produced by Lucas Aerospace, which is now known as TRW Aeronautical Systems. Although the actuator was the original unit installed in the airplane at delivery, American had replaced all four solenoids with upgraded units during a C check on January 19, 1998. Safety Board investigators transported the incident airplane's autopilot yaw actuator, serial number (S/N) 2011, to the Lucas facility in St. Ouen, France, for examination. The examinations revealed two main findings: (1) the wiring to the two main valve solenoids had been cross-connected, and (2) a foreign-particle contaminant was found in the green system engagement valve solenoid. Cross-connected Wiring of the Two Main Valve Solenoids Examination of the actuator at the Lucas facility revealed that its two main valve solenoids were cross-connected so that the electrical connection for the yellow system was connected to the green system solenoid, and vice versa. In this configuration, the FCC for the green system would actually control the main valve for the yellow system, and the FCC for the yellow system would control the main valve for the green system. After the cross-connected wiring on N7082A was discovered, Airbus issued an All Operators Telex (AOT) on May 27, 1999, to all operators of Airbus A300, A310, and A300-600 airplanes. The AOT specified that a one-time inspection be conducted within 10 days to confirm proper connection of the main valve solenoids. Both the French Directeur General de L'Aviation Civile and the Federal Aviation Administration subsequently issued airworthiness directives on June 30 and August 24, 1999, respectively, to require the AOT actions. As a result of the AOT checks, another American A300-600 (N3075A) autopilot yaw actuator (S/N 1630) was discovered with cross-connected autopilot solenoid wiring. American indicated that it had installed new solenoids on the three actuators (pitch, roll, and yaw) on this airplane and the rest of its A300 fleet between July 1997 and July 1999. At the time the new solenoids were installed, procedures did not specifically include a check to ensure that the solenoid wiring was installed properly. Both Airbus and Lucas have since developed new procedures to ensure that the autopilot actuator solenoids are properly wired. Solenoid Contamination Investigators found that a cylindrical particle in the green autopilot engagement valve solenoid, S/N 4287, on the incident airplane's yaw actuator had prevented the solenoid from disengaging. The particle was analyzed at the Lucas facilities under supervision by the French Bureau Enquêtes-Accidents. Analysis revealed that the particle was composed of a copper-zinc alloy covered by a layer of gold and nickel. Spectroscopic examination and analysis of the solenoid componen ## Aircraft - Registration: [N7082A](https://openairdocs.org/deregistered/N7082A-2011-11-30), registration cancelled 2011-11-30, S/N 643, built 1992 (OpenAirDocs) - Reported make and model: Airbus Industrie 300-600 - Registry model: [Airbus Industrie A300 B4-605R](https://openairdocs.org/model/airbus-industrie-a300-b4-605r) (registry code 3930308) (OpenAirDocs) - Registry engine: [GE CF6-80 series](https://openairdocs.org/engine/ge-cf6-80-series) (registry code 30025, turbo-fan) (OpenAirDocs) - Category: Airplane - Engines: unknown - Damage: No damage - Flight: Part 121 - Operator: American Airlines - Departed: BOGOTA - Destination: MIA, MIAMI, FL - Flight plan: IFR ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; medical: unknown, unknown ## Weather - Conditions: Visual (VMC), Not reported - Wind: 200° at 8 knots ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Incident 19990511016029I](https://openairdocs.org/incident/19990511016029I), May 11, 1999: Airbus A300B4605R, Miami, FL. Operators A300-600 reported erratic rudder movements during manual approach, caused by a double fault with the autopilot yaw actuator. After replacement of the… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.