CRJ-200 Landing Incident Highlighted US Maintenance Competency Inadequacies (Air Wisconsin N707AW)
On 14 December 2008, Air Wisconsin Bombardier CRJ-200 (CL-600-2B19) N407AW, made an emergency landing at Philadelphia International (PHL), Pennsylvania, with the left Main Landing Gear (MLG) retracted position. The long delayed US National Transportation Safety Board (NTSB) final report points to a series of maintenance standards and competency issues in this incident. Planned rulemaking to solve these was abandoned by FAA after 5 years however.
The Incident Flight
The NTSB explain in their safety investigation report (only issued 6 April 2020 after 11.25 years!) that the aircraft on a flight from Norfolk International (ORF), Virginia to operate for US Airways after scheduled maintenance, namely…
…both the right and left main landing gear uplock assemblies were replaced as required by the air carrier’s airplane component time limitation (20,000 cycles).
The flight crew had indications of a landing gear problem during approach. After unsuccessfully attempting to lower the gear, the flight crew elected to make an emergency landing with only the nose gear and right main landing gear “down and locked”. After touch down, the airplane came to rest on its right main landing gear, nose gear and the left wingtip and flaps, resulting in minor damage.
The Safety Investigation
The left and right MLG uplock assemblies had been replaced during the maintenance.
No anomalies were found with the installation of the right MLG uplock assembly; however, the upper attachment bolt in the left MLG uplock assembly was improperly installed and had not properly been inspected.
The left uplock assembly’s upper attachment bolt, nut, and cotter pin assembly were installed but the NTSB say “these did not engage the uplock assembly”. This allowed the uplock assembly to pivot about the lower bolt. As the upper attachment bolt did not engage the uplock assembly, the left MLG remained in the up-and-locked position and could not be released by the flight crew.
The investigative team reviewed the Air Wisconsin, Inc. removal and installation maintenance manual for the MLG Uplock Assembly (MM 32-32-05 page 401-407, dated April 20, 2004). The contents of the maintenance manual were the same as the Bombardier CRJ MLG Uplock Assembly manual. Both manuals outline instructions to install both bolts through the uplock assembly and to the aircraft structure. It was noted that the instructions did not mention of the spacer located between the uplock assembly attachment lugs and that the orientation of Figure 401 was confusing when referenced to install the left uplock assembly. The instructions also failed to reference a nearby hydraulic line cover that had to be removed in order to remove the uplock assembly attachment bolts.
NTSB explain that:
The investigation revealed that at the maintenance facility two separate mechanics had been assigned to replace each of the uplock assemblies on the airplane.
The installation of both assemblies could not be completed during the midnight shift (2130 to 0730), and the mechanic who replaced the left uplock departed when the shift was over.
Removal and installation of the uplock assemblies is a required inspection item (RII) and must be inspected by an RII inspector. The inspection noted [three] discrepancies in the installation of the left gear assembly installation, which were corrected by the mechanic (at the request of the inspector) who stayed past his shift and installed the right uplock assembly; however the discrepancies were not properly documented.
It is not clear how long the second mechanic extended his 10 hour shift by.
Both mechanics signed off the work package as being complete having made a verbal turnover to the day shift supervisor…and departed prior to completing the functional check and manual gear swing on the airplane… inconsistent with Air Wisconsin, Inc., policies and procedures (Air Wisconsin GMM Chapter 21, Section 9 – Work Interruption Procedures).
The investigation revealed that the RII inspector performed a functional check and manually extended the landing gear, however the RII inspector stated that he could not actually see the gear being extended from his position during the test as he was only watching the flight instrument panel for the indication of a full extension.
Further discussions with the RII inspector revealed that he did not follow the manual extend procedures outlined in the manuals, but instead followed an abbreviated procedure. In addition, the RII inspector did not use a flash light or inspection mirror as part of the inspection to see in the darkened MLG wheel-well.
Training and task experience were examined:
The mechanic that had installed the left gear uplock assembly had never before done such installation, nor had he received pertinent training. The mechanic who replaced the right uplock assembly stated that he had replaced uplocks on other airplanes but not the accident type airplane.
The inspector stated that he had no experience inspecting uplock assemblies, nor did he recall ever having removed or replaced a gear uplock assembly as a mechanic.
Air Wisconsin’s Maintenance Training Program Manual was described as comprehensive by the NTSB. It contained a requirement for 32 On the Job (OJT) tasks however there was no deadline to complete the tasks and if they were not complete:
…the mechanic may still perform maintenance tasks without limitations or restrictions. No formal supervision process exists, but mechanics are encouraged to request guidance from a more experienced mechanic if performing a task for the first time.
The report highlights the common fallacy that sheep-dipping personnel through human factors training will reduce errors (emphasis added)
[The company] offered a human factors training program for new hires that consisted of an 8-hour PowerPoint presentation covering a wide range of topics, including communication, fatigue, and shift turnovers. The NTSB’s investigation revealed that some of the topics did not relate specifically to maintenance human factors issues, and the exercises did not necessarily correlate to real-world experiences that mechanics might face. The presentation provided knowledge of human factors issues but did not encourage skill development of how to prevent human factors events. For example, the training would have been more useful if it had discussed the challenges faced when working in a confined space with limited lighting and the importance of using a flashlight and mirror to ensure tasks are completed successfully.
The NTSB concludes that the Air Wisconsin 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 concludes that the post-maintenance inspections performed by the incident RII inspector were not adequate to detect the misrigging of the uplock assembly. The incident inspector’s lack of training and experience with the removal and installation procedures of the uplock assemblies may have contributed to his failure to detect installation discrepancies
The NTSB is concerned that the Federal Aviation Administration (FAA) does not currently require mechanics to receive OJT or be supervised while performing RII tasks for the first time.
NTSB Probable Cause
The failure of the maintenance personnel to properly complete the installation, and the inspection personnel to conduct the proper functional test, of the left main landing gear uplock assembly.
NTSB Safety Recommendations and FAA Safety Inaction
NTSB issued Safety Recommendation A-10-96 and A-10-97, dated 28 May 2010. In the recommendation letter they reference this accident: Incorrectly Rigged B1900D Charlotte, NC, 8 January 2003: 21 Fatalities
- 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)
The FAA approved the development Air Carrier Maintenance Training Program rulemaking project promptly in May 2010 to address these. It was cancelled in August 2015 “due to a lack of accident data to support rulemaking activities”. At this point the FAA concluded that “The FAA has determined that the current regulations and guidance are sufficient alternatives to rulemaking and satisfy the intent of these recommendations” and noted OJT was subject of FAA oversight during audits. The NTSB generously classified both as ‘Closed – Acceptable Alternative Action’.
Note: As the accident occurred prior to 1 June 2009 the public docket is not online. Aerossurance requested the key reports from the public docket on 12 April 2020 to help ensure this article was fully comprehensive and capture the learning fully. The NTSB have at time of publication not responded.
We have previously written:
- James Reason’s 12 Principles of Error Management
- Back to the Future: Error Management
- Airworthiness Matters: Next Generation Maintenance Human Factors
- B1900D Emergency Landing: Maintenance Standards & Practices
- B747 Landing Gear Failure Due to Omission of Rig Pin During Maintenance
- When Down Is Up: 747 Actuator Installation Incident
- Lost in Translation: Misrigged Main Landing Gear
- Maintenance Human Factors in Finnish F406 Landing Gear Collapse
- ERJ-190 Flying Control Rigging Error
- NTSB Confirms United Airlines Maintenance Error After 12 Years
- Fire After O-Ring Nipped on Installation
- A Lufthansa MD-11F Nose Wheel Detached after Maintenance Error
- B767 Fire and Uncommanded Evacuation After Lockwire Omitted
- What Leaks in Vegas Stays in Vegas – A320 Hydraulic Failure
- A319 Double Cowling Loss and Fire – AAIB Report
- CFM56-7 HPC Titanium Fire Due to VSV Maintenance Assembly Error (United Boeing 737-924)
- Uncontained CF6-80 Failure: American B767-300 28 Oct 2016
- Inadequate Maintenance, An Engine Failure and Mishandling: Crash of a USAF WC-130H
- Crazy’ KC-10 Boom Loss: Informal Maintenance Shift Handovers and Skipped Tasks
- Hoist Assembly Errors: SAR Personnel Dropped Into Sea
- Contaminated Oxygen on ‘Air Force One’
- Meeting Your Waterloo: Competence Assessment and Remembering the Lessons of Past Accidents
- UPDATE 28 June 2020: Maintenance Issues in Fire-Fighting S-61A Accident
- UPDATE 30 June 2020: 17 Year Old FOD and a TA-4K Ejection
- UPDATE 12 October 2020: Frozen Dash 8-100 Landing Gear After ‘Improper Maintenance Practices’ Say NTSB
Aerossurance worked with the Flight Safety Foundation (FSF) to create a Maintenance Observation Program (MOP) requirement for their contractible BARSOHO offshore helicopter Safety Performance Requirements to help learning about routine maintenance and then to initiate safety improvements:
Aerossurance and its partners can provide proven, practical expertise to successfully implement a MOP, introduce an effective competence assessment process or analyse the hazards of maintenance tasks.
Also see our review of The Field Guide to Understanding Human Error by Sidney Dekker presented to the Royal Aeronautical Society (RAeS): The Field Guide to Understanding Human Error – A Review