Report: ATR-72 control difficulties following rudder maintenance

April 18, 2011

The U.K. AAIB published a Special Bulletin including three safety recommendations regarding control difficulties that were encountered by the crew of an ATR-72 during a post-maintance flight.

The aircraft had undergone routine maintenance at an engineering facility at Edinburgh Airport immediately prior to the incident flight.
Everything appeared normal during the crew’s pre-flight checks, which included a full-and-free check of the flying controls.
The aircraft took off at 21:22 from runway 24 at Edinburgh, with the co-pilot acting as the handling pilot.
After carrying out a standard instrument departure the crew climbed the aircraft to FL 230 at a speed of 170 kt with the autopilot engaged. As the aircraft levelled and accelerated through about 185 kt, the crew felt the aircraft roll to the left by about 5 to 10° and they noticed that the slip ball and rudder trim were both indicating fully right. The co-pilot disengaged the autopilot and applied right rudder in an attempt to correct the sideslip and applied aileron to correct the roll. He reported that the rudder felt unusually “spongy” and that the aircraft did not respond to his rudder inputs. Approximately 15° to 20° of right bank was required to hold a constant heading with the speed stabilised above 185 kt and a limited amount of aileron trim was applied to assist. Shortly after regaining directional control a FTL CTL caption appeared on the Crew Alert Panel (CAP) and the FLT CTL fault light illuminated on the overhead panel, indicating a fault with the rudder Travel Limitation Unit (TLU). The commander requested radar vectors from ATC for a return to Edinburgh, later declaring a PAN.

The crew carried out the required procedure from the Quick Reference Handbook (QRH). As part of the procedure they established that both Air Data Computers (ADC) were operating, before manually selecting the TLU switch to the LO SPD position. The aircraft had at this point temporarily slowed to below 180 kt. The co-pilot reported that on selection of LO SPD more roll control input was required to maintain heading and that roll authority to the right was further reduced. The commander therefore decided to return the TLU switch to AUTO and the required roll control input reduced. The green LO SPD indicator light did not illuminate.

An approach was made to runway 24, the aircraft was established on the ILS and was normally configured for a full flap landing. The crew added 10 kt to their approach speed, in accordance with the QRH. The co-pilot had to operate the control wheel with both hands in order to maintain directional control; the commander operated the power levers in the latter stages of the final approach. The co-pilot reported that the aircraft became slightly more difficult to control as the speed reduced, but remained controllable.

The aircraft landed just to the left of the runway centreline, whereupon the commander assumed control of the aircraft and applied reverse thrust. Despite the application of full right rudder pedal during the rollout, the aircraft diverged towards the left side of the runway. The commander re-established directional control using the steering wheel tiller. The aircraft was taxied clear of the runway and back to the engineering facility for inspection.

Th subsequent investigation and testing demonstrated that it is possible to incorrectly install the cams on the rear rudder quadrant shaft during maintenance. In this incident, the right hand cam was installed in the incorrect orientation and neither an independent inspection nor an operational test of the TLU system was performed. The incorrectly installed right hand cam was not detected prior to releasing the aircraft to service. When the TLU system automatically activated as the aircraft accelerated through 185 kt, the right hand roller encountered resistance as it came into contact with the upper lobe of the incorrectly installed cam, rather than slotting into the vee groove. This caused an uncommanded rudder input and associated control difficulties.

Three safety recommendations were made to the manufacturer, ATR.

The investigation is ongoing.

More information:


FAA proposes $2.5 Million in civil penalties against Trans States, GoJet

July 1, 2010

FAA logoThe U.S. Federal Aviation Administration (FAA) is proposing $2,476,075 in civil penalties against Trans States Airlines and GoJet Airlines of Bridgeton, Mo., for violation of various maintenance procedures and operating nine jets on 320 revenue passenger flights when the aircraft were not in compliance with Federal Aviation Regulations.

Trans States Airlines and GoJet Airlines are both owned and operated by Trans States Holdings. Trans States Airlines performs maintenance and training on GoJet aircraft.

The proposed civil penalties involve seven GoJet+ Canadair Regional Jets and two Trans States Embraer 145 regional jets. The FAA alleges Trans States and GoJet operated aircraft when maintenance had been carried out incorrectly, and that the company failed to complete required maintenance record-keeping.

The FAA alleges Trans States and GoJet violated a number of maintenance regulations and procedures, including use of outdated manufacturers’ maintenance instructions to perform repairs; failure to connect a wing flap actuator to its torque tube, rendering the flaps inoperative; failure to document an inspection after an aircraft was damaged by severe turbulence; failure to document and carry out proper repairs after aircraft warning systems identified problems; improper repair of an engine oil leak and failure to comply with minimum equipment list regulations.

Trans States and GoJet have 30 days from receipt of the civil penalty letters to respond to the agency.

FAA proposes $700,000 civil penalty against Executive Airlines

June 28, 2010

The U.S. Federal Aviation Administration (FAA) is proposing a civil penalty of $700,000 against Executive Airlines.  The San Juan, Puerto Rico airline, which does business as American Eagle Airlines, allegedly operated eight of its ATR-42 twin-turboprop airliners when they were not in compliance with Federal Aviation Regulations.

The FAA alleges that when Executive Airlines did heavy maintenance checks on its aircraft in 2007 and 2008, mechanics did not perform and document required, detailed visual inspections to detect possible cracks on the aileron center hinge bearing fittings.  Executive Airlines operated the eight aircraft on 6,479 flights between the incomplete earlier inspections and September 26-27, 2008, when the company completed the proper inspections and procedures.

Executive Airlines has 30 days from the date of receipt of the FAA’s letter to respond to the agency.

NTSB concerned about training for mechanics and inspectors

May 28, 2010

Based on preliminary findings from the investigation of a partial gear up landing of a CRJ200 in December 2008, as well as prior investigative findings, the U.S. NTSB voiced its concerns about training for mechanics and inspectors. Two safety recommendations were issued and three older recommendations were re-iterated.

On December 14, 2008, about 17:00 local time, Air Wisconsin Airlines flight 3919, a Canadair CL-600-2B19 (CRJ-200), N407AW, landed at Philadelphia International Airport, PA (PHL), with the left main landing gear in the retracted position. The aircraft was being flown as a repositioning flight from Norfolk International Airport, VA (ORF) to PHL. There were no injuries to the two flight crew and one flight attendant on board the aircraft.

The flight crew received indications of a left main landing gear problem prior to landing and stated that they completed the applicable Quick Reference Handbook (QRH) procedures, but were unable to lower the left main landing gear. They elected to land with the nose and right main landing gear in the down and locked position and the left main landing gear up.

Maintenance had been performed on both the left and right main landing gear systems prior to the incident flight. Post-incident inspection of the aircraft revealed that, the upper attachment bolt for the left main landing gear uplock assembly, which is designed to be attached to both the uplock mechanism and the structure, was attached to the airplane structure only.

The NTSB concludes that the incident mechanic was not properly trained or supervised when he replaced the uplock assembly on the incident airplane for the first time, which led to the error in installation. Further, the error was not detected by the inspector. The NTSB is concerned that the Federal Aviation Administration (FAA) does not currently require mechanics to receive on-the-job training (OJT) or be supervised while performing required inspection item (RII) tasks for the first time.

Problems with untrained or unsupervised mechanics performing maintenance tasks for the first time have also been found during the NTSB’s investigation of the January 8, 2003,  fatal accident involving a Beechctaft 1900D  which crashed shortly after takeoff at Charlotte-Douglas International Airport, NC. The accident airplane underwent a detail six maintenance check.  One of the mechanics assigned to check the elevator control cable tension was receiving OJT under the supervision of a quality assurance inspector who failed to adequately supervise and direct the mechanic.

Therefore, the NTSB recommends that the FAA:

Require that mechanics performing required inspection item and other critical tasks receive on-the-job training or supervision when completing the maintenance task until the mechanic demonstrates proficiency in the task. (A-10-96)

Require that required inspection item (RII) inspectors receive supervision or on-the-job training on the proper inspection of RII items until the inspector demonstrates proficiency in inspection. (A-10-97)

Poor maintenance started accident chain that resulted in Learjet high-speed runway excursion

April 7, 2010

Learjet 60 N999LJ came to rest against an embankment (Photo: NTSB)

A chartered business jet crashed at a South Carolina airport 18 months ago because of the operator’s inadequate maintenance of the airplane’s tires and the decision by the captain to attempt a high-speed rejected takeoff, which went against standard operating procedures and training, the NTSB determined.

On September 19, 2008, at 23:53, a Learjet 60 (N999LJ) operated by Global Exec Aviation and destined for Van Nuys, California, overran runway 11 during a rejected takeoff at Columbia Metropolitan Airport. After the airplane left the departure end of runway 11, it struck airport lights, crashed through a perimeter fence, crossed a roadway and came to rest on a berm. The captain, the first officer, and two passengers were killed; two other passengers were seriously injured.

The investigation revealed that prior to the accident the aircraft was operated while the main landing gear tires were severely underinflated because of Global Exec Aviation’s inadequate maintenance. The underinflation compromised the integrity of the tires, which led to the failure of all four of the airplane’s main landing gear tires during the takeoff roll.

Shortly after the first tire failed, which occurred about 1.5 seconds after the airplane passed the maximum speed at which the takeoff attempt could be safely aborted, the first officer indicated that the takeoff should be continued but the captain decided to reject the takeoff and deployed the airplane’s thrust reversers. Pilots are trained to avoid attempting to reject a takeoff at high-speed unless the pilot concludes that the airplane is unable to fly; the investigation found no evidence that the accident airplane was uncontrollable or unable to become airborne.

The tire failure during the takeoff roll damaged a sensor, which caused the airplane’s thrust reversers to return to the stowed position. While the captain was trying to stop the airplane by commanding reverse thrust, forward thrust was being provided at near-takeoff power because the thrust reversers were stowed. The Safety Board determined that the inadvertent forward thrust contributed to the severity of the accident.

The Safety Board also found that neither the Federal Aviation Administration nor Learjet adequately reviewed the Airplane’s design after a similar uncommanded forward thrust accident that occurred during landing in Alabama in 2001. While the modifications put into place after the Alabama accident provided additional protection against uncommanded forward thrust upon landing, no such protection was provided for a rejected takeoff.

The safety recommendations that the NTSB made to the Federal Aviation Administration as a result of this investigation are:

  • provide pilots and maintenance personnel with information on the hazards associated with tire underinflation, including the required intervals for tire pressure checks, and allow pilots to perform pressure checks in air taxi operations to ensure that tires remain safely inflated at all times;
  • require tire pressure monitoring systems for all transport category airplanes;
  • identify and correct deficiencies in both Learjet’s thrust reverser system safety analysis and the FAA’s design certification process to ensure that hazards encountered in all phases of flight are mitigated;
  • require that simulator training for pilots who conduct turbojet operations include opportunities to practice responding to events other than engine failures near takeoff speeds;
  • require that pilots who fly air taxi turbojet operations have a minimum level of pilot operating experience in an airplane type before acting as pilot-in- command in that type; and require that airplane tire testing criteria reflect the loads that may be imposed on tires both during normal operating conditions and after the loss of one tire.

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