Trade-offs among factors shaping operators decision-making: the case of aircraft maintenance technicians

Abstract

The present research deals with aircraft maintenance technicians (AMTs) situated decision-making in a commercial aircraft maintenance department. The aim is twofold: first, to study how AMTs through their situated decisions experience inconsistencies between diverse organizational imperatives and pragmatic constraints and second, to identify persistent factors, dualities and/or trade-offs that affect these decisions. Towards this end, twenty-five cases where AMTs faced ambiguity or dilemmas and took decisions during maintenance work were analysed, after being observed in situ. The analysis followed a bottom-up approach where the decision cases observed were first examined in terms of the contextual factors that influenced their outcome. Such contextual factors did not only include the random events triggering a need for a decision, but also the pragmatic constraints that were taken into account by AMTs after the triggering event in order to choose an action path. An interpretative analysis of the above decision cases towards a more abstract level of description, the study achieved at identifying a set of persistent factors underlying decisions at the sharp edge of a safety critical system. It is argued that such persistent factors and their articulation can be identified in operators’ decision-making in any particular work setting and can form the basis for sound bottom-up metrics for organizational resilience and proactive safety management.

Appendix

Case description	Comments	Decision-Shaping Factors (DSFs)
Decision to keep an already installed off-specs ring on the exhaust pipe of the RH engine despite the fact that the aircraft (a/c) manual calls for the use of a different types of ring	By keeping the off-specs ring, the AMTs save the extra effort to remove the exhaust pipe and reinstall it with the proper ring. This also helps keep the maintenance schedule on time. Nevertheless, the ambient conditions during flight (temperature, pressure, stress) may overtime wear out the ring and affect the a/c’s Airworthiness	Schedule + Airworthiness − Optimize AMT effort +
During service of RH engine exhaust pipe no proper preparation (clearance) of the working area behind the RH engine prior to the task execution	A proper clearance of the working area would affect the daily schedule because the AMTs working on the exhaust pipe had three more tasks to accomplish during their shift. The proper clearance ensures that the surrounding components (cables, electronic devices and sensors) will not be damaged, possibly affecting the Airworthiness. Nevertheless, the team asked for an additional AMT to monitor and safeguard that no surrounding components would be damaged during the process	Schedule + Airworthiness − Optimize AMT effort +
Rivet removal off the a/c’s skin not according to the manufacturer’s instructions. Instead, rivets were removed according to the established practice despite acknowledged risk	Perceived impossibility to follow manufacturer’s instructions in this particular case due to schedule pressure. Eventual delay would result in penalty for the maintenance organization. The removal of the rivets according to the established practice may damage the frame	Schedule + Airworthiness − Optimize AMT effort +
Stress relieving of the a/c prior to the fuel tank panels’ removal located on the top surface of the wings. It is an established practice to stress relief the a/c, unwarily of the manufacturer’s instructions	Stress relieving the aircraft allows more AMTs to work on the removal of the fuel tank’s panels, therefore saving time to accomplish the task (the time needed to stress relief the a/c plus the time to remove the panels is less than the time needed to remove the panels without stress relieving). Nevertheless, stress relieving the a/c does not allow parallel work to be performed inside the cabin	Optimize AMT effort +
Decision for installation of new over temperature bleed-air switches on the a/c without checking the functionality of the ones removed. The used ones were thrown away after their removal. According to the manual, if check result is positive the used components should be reinstalled. Else replacement	Installing new over temperature switches ensures their proper functioning and Airworthiness. In addition, bypassing the check the AMT saves time and effort. Also, shift leader was pressing for task completion. The fact that the switches were thrown away after their removal results in cost increase for the organization	Schedule + Airworthiness + Cost saving − Optimize AMT effort +
Use of an alternative tool (pressing tool) for a modification task, involving the addition of steel bushing at the bell cranks beneath the pilots’ seats. After consultation with an adept AMT. Subsequent judgement over execution quality	Unavailability of liquid nitrogen which is required for the bushing contraction (the prescribed method) means either workaround or jeopardizing maintenance schedule Uncertainty on workaround method leads to seek unofficial advice. Use of pressing tool is tricky and requires more effort compared to the use of liquid nitrogen. Possible dent forming on the surface of the steel bushings (even very small), due to the use of the pressing tool, could overtime cut the cables attached	Schedule pressure + Airworthiness − AMT accountability − Optimize AMT effort −
Removal of a screw with broken head from the hot section of an engine during the engine’s stripping process in order to send it for service to external entity (authorized engine service workshop)	Leaving the broken screw on would result in financial penalties Asking for instructions would cause delays, and the decision is taken to try to solve the issue immediately using a screw extractor with heads of various diameters to remove the screw according to standard practice. This, however, meant putting extra personal effort	Cost saving + Optimize AMT effort −
Appliance of protective film at the propeller blades. Unavailability of prescribed means/tools leads to judgement over adequacy of alternative tool	Wait for tool would jeopardize schedule. Application by alternative means (combination of hands and scissors) may cause blade wear overtime and need for replacement thus cost. Application by hands and scissors is cumbersome	Schedule pressure + Optimize AMT effort −
The AMTs decided to delay the installation of a cable assembly behind the co-pilot’s seat due to the task’s perceived complexity and erroneous estimation of the time and actions needed to carry it out	Non-previous performance of such task leads to uncertainty over correct performance. Perceived risk of compromising Airworthiness leads to follow official path. As a result the estimated accomplish time was exceeded, but AMTs felt secure over possible liabilities	Schedule pressure − Airworthiness + AMT accountability + Optimize AMT effort −
Instead of performing a general visual inspection (GVI) of the heat transfer system (HTS) on the a/c, the AMT installed a new one. The task demanded the GVI of the old HTS and not its replacement. After consultation of the manual, a GVI of the removed one took place. The AMT decided to leave the new HTS on the a/c and return the old inspected one to the warehouse in place of the new without documenting the change	Due to AMT fatigue, the task was executed before consulting the manual. GVI of HTS is faster than replacement. However, once the error was realized, it would take a lot more time to reinstall the old HTS on the a/c. The proximal Airworthiness of the aircraft is not affected but the recorded lifetime of the HTS is not the correct one (the recorded HTS lifetime was not reset after its installation). This not resetting could probably be traced by quality, although improbable	Schedule pressure + Airworthiness + Cost saving − AMT accountability − Optimize AMT effort +
Removal of the main landing gears to perform maintenance actions at their components, intentionally altering the prescribed procedure	The procedure, if fully followed, is cumbersome, laborious and lengthy. Personal expert judgment resulted in changing procedure to a more comfortable to execute, with minor increase in the possibility of damaging something but not affecting Airworthiness	Optimize AMT effort +
For the replacement of the nose landing gear, the AMT removed the old one with all its components attached, stripped it and built up the new one in parallel and installed the new one on the a/c	The procedure, if fully followed, is cumbersome, laborious and lengthy. Expert judgment resulted in changing procedure to a faster less cognitively demanding to execute. New procedure was judged as not affecting Airworthiness	Schedule pressure + Optimize AMT effort +
The AMTs could not start the auxiliary power unit (APU) of the a/c. After a series of improvised checks and contact with the manufacturer, they decided to replace the APU but with no results. Further investigation revealed that a series of cables were damaged and not the APU	Use of the fault isolation manual is cognitively demanding—only highly experienced AMDS can use it. Checks were based on contextual factors and probably driven by past experience in the pursuit of optimal effort and fatigue. The overall task cost would have been reduced if the prescribed procedures were followed	Cost saving − AMT accountability + Optimize AMT effort +
Removal of the engine pitch control unit from the nose section of the a/c. According to the a/c manual instructions, three adjacent units must first be removed in order to gain access to the pitch unit and remove it. An adept AMT had once removed the unit without first removing three units that blocked its path out	After the adept AMTs proposal for an alternative way of performing the task, some of the AMTs followed his instructions, while some others followed the manual. Following the adept AMTs method resulted in time saving of about 70 % compared to the manual’s instructions. Nevertheless, his method is quite risky, because performing it s/o could cause damage to nearby components	Schedule pressure + Optimize AMT effort + AMT accountability −
For draining and replenishment of hydraulic fluid in the wing flaps’ movement system, two AMTs drained the old fluid and replenished with new. They realized, however, that the quantity of the drained was much less than that of the replenished	Further investigation of the difference in hydraulic fluid quantity could lead to replacements and schedule delays. The AMTs decided not to proceed in further investigation, assuming that any arising defects could be resolved in a future scheduled check	Schedule pressure + Airworthiness − Optimize AMT effort +
Each task that calls for access panel removal–installation seeks for removal prior to the task execution and installation after the task performance. (The maintenance organization later decided to turn into official the access panel removal–installation process that the AMTs unofficially followed by introducing an access panel checklist)	Removing and installing each access panel prior and after the task performance is an overall lengthy and laborious process By letting all access panels open, AMTs gain in time and effort. However, they may be held accountable in case of a quality audit	Schedule pressure + AMT accountability − Optimize AMT effort+
The AMTs identified a discrepancy between the a/c structure and the manual illustrations. The illustrations presented a hole not present at the a/c structure and the AMTs decided to open the hole to the dimensions and location illustrated	The AMTs decided to follow the illustration on the manual, thinking that there was an omission in a/c structure and that they should trust the manual. AMTs judged that the hole would not affect the A/Cs Airworthiness, as it was not at a critical zone	AMT accountability +
For the visual inspection of the flap tracks for wear and corrosion, the AMTs must also use hand touch to verify that the flap track surface is smooth and without any dents. In performing this task, two AMT’s discovered one dent on all flap tracks at the same position	The formal procedure, if fully followed, could lead to further investigation and replacement of the flap tracks. This could be lengthy and laborious. The AMTs’ judgment was that the dents position could not affect the proper operation of the flap tracks, so they decided not to investigate more on the issue. ATMs further suspected that the dents were probably structural features due to the fact that they were all of the same size and at the same relative position)	Schedule pressure + Optimize AMT effort + ΑΜΤ Accountability + Airworthiness −
The LH propeller has to be attached to the power plant by tightening a number of fasteners with the use of a torque wrench	The AMTs attached the propeller using a plain wrench and not a torque wrench. His decision was based on his observation that using a torque wrench set on the prescribed torque values resulted in loosened fasteners overtime The AMT claimed that by tightening the fasteners with a plain wrench could be more reliable	Airworthiness + AMT accountability − Optimize AMT effort +
LH engine has to be removed from the aircraft to be replaced by a new one. Removed engine components have to be uninstalled from old engine and installed to the new one	The AMTs decided to start disassembling the engine to be removed without draining first the oil. This resulted to a serious oil leak from the engine during disassembling. The working area was then cleaned, and the AMTs removed the engine from the aircraft to strip it and build up the new one. AMTs’ judgement was that no oil leak would occur during disassembly, as most of the oil is in the engine. They also claimed that this shortcut could save actual work time as they were highly pressured from their daily schedule to finish task ASAP. Oil draining could take place after the task accomplishment while the engine was off the aircraft	Schedule pressure +
An external pipe assembly has to be attached on the aircraft for an air pressure/speed systems check to be performed during scheduled maintenance	AMTs decided to attach the more complicated assembly rather than the prescribed one because (according to an adept AMT) the altimeter system check task card would also need to be performed after the air pressure/speed systems check. Therefore, according to this speculation a more complicated assembly may be attached to the a/c which can assist AMTs to check all systems. Attaching the more complicated assembly is more time and effort consuming than attaching the one prescribed for the present check, but it could save overall effort and time if altimeter system check succeeds the present check	Optimize AMT effort + Schedule pressure +
AMT faced ambiguity after installing a panel on a/c on whether panel is installed properly (screws on position and tightened enough)	AMT decided to resolve ambiguity by checking panel installation. Due to schedule pressure to move on to other tasks, he decided not to remove and reinstall panel. He used a rubber hammer instead in order to save time and not to harm panel surface	Schedule pressure + Optimize AMT effort +
Avionics technician has to perform a panel/instrument check on a/c cockpit. In order to perform the check, the AMT has first to perform various settings	According to the AMT, bypassing the settings step would not affect check results, as settings have never proved to affect the checks. In addition, performing settings is quite a lengthy step. Therefore, the AMT performed checks without performing preceding settings	Schedule pressure + Optimize AMT effort + Airworthiness −
Several GVI tasks have to be performed in cabin underfloor areas. Each task calls for internal visual inspections of a part of the underfloor area for which a certain floor panel has to be removed	The AMT removed all floor panels and performed all GVI tasks at once. According to the AMT, removing all panels at once to perform a general visual inspection of the underfloor area outweighs the sectional underfloor inspections and may save time and give better overview of the underfloor systems condition as each system (electrical, electronic, hydraulic, etc.) lying underfloor is inspected as a whole and not partially	Optimize AMT effort +
LH exhaust pipe cover has to be installed on LH power plant not following prescribed procedure	It has been proved to be a lengthy and laborious task to accomplish if prescribed procedure is followed. AMTs decided to pound the exhaust pipe cover to set in position with risk to damage it and nearby components. Nevertheless, if with pounding exhaust pipe cover comes in position AMTs could save time and effort	Optimize AMT effort + Schedule pressure + Airworthiness −