Table of Contents
The importance of the Cockpit Task Management (CTM)
The increased level of aircraft’s automation makes the Cockpit Task Management (CTM) to be a crucial part of completing a successful flight mission. In consideration of flight safety and economic issues, the new generation aircrafts have been equipped with highly advanced automation, in which the fly-by–wire and glass cockpit concepts are widely applied. Due to the improvement of airplane’s automation, today’s pilot is no longer need to do a moment to moment operation instead of more tasks with a system monitor and supervisor. However, the increased level of automation also reduces the number of crew members needed in cockpit, this means that each crew member not only need monitor more subsystems, but also need do airplane control occasionally at least. Today, with the fast growth of air traffic and more regulations, the flight crew has to fulfil even more tasks with different situation than before, which hence request that pilots not only need acquire the skills of task performance, but also need have the skills of task management. Proper task management has become a critical part of completing a successful flight mission. For example, unexpected events occurred in cockpit may lead to excessive demands of concurrent tasks on a limited flight crew resources, if flight crew is not able to effectively manage these tasks, e.g. improperly allocation of available flight crew resources to concurrent tasks, which may negatively affect flight safety, or may result in incident or accident (Chou &Funk, 1990).
The seven functions performed in CTM
The concept of Cockpit Task Management (CTM) was proposed by Funk, the aim of the concept is to facilitate flight crew to better manage multiple tasks and concurrent tasks in flight mission so as to improve flight crew’s performance. “CTM is defined as the management of limited human and cockpit resources so as to allow effective task initiation, task monitoring, task prioritization, resource allocation, task interruption, task resumption, and task termination” (Chou et al, 1990, p.471).
- Task initiation: is to activate tasks when appropriate conditions have occurred.
- Task monitoring: is assessment of progress and status of active tasks.
- Task prioritization: is to assess the priorities of active tasks based on their level of importance and urgency for safely completing flight mission.
- Resource allocation: is to assess the both human and machine resources to tasks so that those tasks can be completed.
- Task interruption: the relatively lower priority of tasks can be interrupted temporarily in order to allocate available resources to higher priority tasks.
- Task resumption: is to resume the interrupted tasks when resources become available or the priority of tasks change.
- Task termination may result in three possible situations, in where one situation is that the tasks have been successfully accomplished; another is tthe tasks cannot be completed; or lastly, the tasks are no longer relevant.
(Chou et al, 1990)
CTM Error Classification
Corresponding to the context of seven functions of CTM, a preliminary CTM error taxonomy with seven general CTM error categories was exploited by Chou and Funk, and in which the specific error classification associating with each of seven categories was further described (is shown in Table 1.). The utilization of this CTM error taxonomy would make a redundant and taxonomic error classes in the introductory analysis of accident and incident reports(Chou, Madhavan & Funk, 1996).
|General Level||Special Level|
Table 1: A Preliminary CTM Error Taxonomy (Chou et al, 1990, p.473)
CTM Errors in Aircraft Accidents
Chou and Funk’s study (1990) which conducted a broad analysis of aircraft accident reports provided by NTSB (Natioanl Transportation Safety Board), of the ASRS (Aviation Safety Reporting System) database, and of data from simulation experiments, identified a number of aircraft accident or incidents relating to CTM errors. However, “they cannot conclude the CTM errors were the only reasons for accidents” (Chou et al, 1990, p.472), because the aviation accidents or incidents could be caused by a number of contributing factors.
The example of aircraft accidents involved in CTM error
- Eastern Flight 401, a Lockheed L1011 aircraft crashed into Florida Everglades while on approach to Miami international Airport on December 29, 1972. In this accident, the flightcrew put all of its resources to preoccupy with a possible faulty of landing gear indicator, and failed to monitor the aircraft’s gradual descent, which eventually caused the crash. This air crash killed 101. Investigators determined that the autopilot was inadvertently switched from altitude hold to a slow descend mode. However, before the accidents, flight crew all focus on the landing gear indicator fault to the exclusion of flight control task. This case shows that flighttcrew did not manage their tasks performance effectively, and fail to allocate adequate resources to the higher priority task (controlling the aircraft) (Chou et al, 1996).
Video embedded from YouTube on 02Oct2011
- Another example of aircraft accident involved in a CTM error occurred in 1984, when a China Airlines B-747SP lost thrust on its No.4 engine 300 nautical miles northwest of San Francisco, the captain begin an inflight engine restart task at an altitude of 40,000 feet which is well above the maximum inflight engine restart envelope, and meanwhile fail to switch the autopilot mode to manually control mode. Fortunately, the captain eventually recovered the aircraft while the aircraft fell over 30,000 feet. However, the incorrect decision of too early restarting the engine was an error in task initiation, because before inflight engine restart task, flightcrew should first descend the aircraft to a certain altitude for adequate air density, which was taught by the engine operation manual and his training. An error in task initiation could adversely affect the task initiation, human and machine resources allocation and termination on other concurrent tasks (Chou et al, 1990).
Results of a preliminary CTM error analysis
The revised CTM Error Taxonomy
In 1996,Chou, Madhavan and Funk published their research results of CTM error analysis. In the research, they revised the taxonomy to include the CTM error categories shown in Table 2. This revised taxonomy served as the basis for their aviation accident and incident studies (Chou et al, 1996).
|Error Categories||Possible Classification|
Table 2: CTM Error Taxonomy (Chou et al, 1996, p.310)
CTM errors identified and classified in NTSB accident reports
In their study, they examined the abstracts of 324 National Transportation Safety Board (NTSB) aircraft accident reports relating to accidents occurring between 1960 and 1989, and found that CTM errors occurred in 76 of 324 accident reports, which is about 23% of the accident reviewed (is shown in table 3) (Chou et al, 1996).
|CTM Error||Number of Accidents||Percentage of CTM Accidents||Number of CTM Errors||Percentage of All CTM Errors|
Table 3: CTM Errors Identified and Classified in 76 (23%) of 324 NTSB Accident Reports. (Note: total number of CTM errors = 80) (Chou et al, 1996, p.312).
According to the analytical result shown in table2, task initiation seems to be the most remarkable CTM error category, accounting for 44% of the CTM errors involved; beside, 30% of CTM errors is concerned to task prioritization; the task termination error accounted for remaining 26% of the CTM errors.
CTM errors identified and classified in ASRS incident reports
Furthermore, they also examined 540 ASRS (Aviation Safety Reporting System) incident reports. Except the duplicated cases, there were 470 ASRS incident reports left for further analysis, and then they found that CTM errors occurred in 231 of the 470 ASRS incident reports, accounting about 49% of 470 incidents (is shown in table 4) (Chou et al, 1996).
|CTM Error||Number of Incidents||Percentage of CTM Incidents||Number of CTM Errors||Percentage of All CTM Errors|
Table 4: CTM Errors Identified and Classified in 231 (49%) of 470 ASRS Incident Reports. (Note: total number of CTM errors = 349) (Chou et al, 1996, p.312).
Compare with the analysis of CTM errors in aircraft accidents, inferences made from analysis of CTM errors in aviation incidents may have more relevance to reduce the likelihood of future accident happened, because the problems existing in incidents used to be the foreshadow of future accident.
The data from table 4 shows that task initiation seems to be the most remarkable CTM error category, accounting for 42% of CTM errors identified. Task initiation errors contain prematurely descents, configurations too late, and failures to tune navigation and communication radios. Secondly, 35% of CTM errors is relating in task prioritization, including control distraction influenced by weather and traffic watches. Lastly, the task termination error accounted for remaining 23% of the CTM errors, which errors include autopilot inadvertently disengagements, altitude overshoots, and forced landing under unsafe conditions.
Although task priority error is just the second large CTM error category, it may adversely effect on task initiation, which may lead to not timely activate a task, or to begin a task too early. Many errors occurred in task initiation may be originally caused by misprioritization. Likewise, the similar argument can be applied between task prioritization and task termination. Excessive priority given one task may influence to active the following tasks. Although the task initiation and task termination categories give more sense for understanding the causes and consequences of errors, Chou (1996) points out that “task prioritization should perhaps draw our greatest attention for the development of countermeasures” (et al, p.314).
Four recommendations from the study of CTM errors
First, pilot need learn from the instruction of Cockpit Task Management in order to know how to eliminate the possibility of CTM errors. More importantly, pilot should be aware the situation of excessive demands of concurrent tasks, which may distract their attention, it is danger that they will not start the highest priority tasks on time (or at all). Therefore, CTM instruction might be most recommended to fit into existing crew resource management training programs so that it can facilitate the pilots to realize the precursor conditions and develop personal strategies to cope with CTM errors while these conditions are occurred.
Second, in order to better understand the CTM performance, such as other factors influencing CTM performance, and the relationship between CTM errors and human cognitive characteristics, e.g. the memory limitation in short working term, further studies of CTM should be conducted by high-fidelity training simulators under full-mission scenarios, the participants should be selected from line pilots.
Third, the research which develops and improves formal cockpit procedures should be conducted so as to facilitate the CTM performance, such as the procedure of memory aid, etc.
Fourth, in addition to increasing the pilot’s skills to avoid CTM errors, the research involved with a computational aid to support CTM performance should be conducted as well. For instance, a cockpit task management that is auto-manipulated by airplane’s computer system should be developed so that it can facilitate flightcrew with assessment of priority of tasks, and to remind pilots all of task should be in progress.
(Chou, et al, 1996)
- Chou, C.D., & Funk, K. (1990). Management of multiple tasks: Cockpit task management Errors. Industrial and Manufacturing Engineering. 470-471. Retrieved from the Google Scholar: http://scholar.google.co.nz/scholar
- Chou, C. D., Madhavan, D., & Funk, K. (1996). Studies of cockpit task management errors. International Journal of Aviation Psychology, 6(4). 307-320. Retrieved from the Google Scholar: http://scholar.google.co.nz/scholar
- Airboyd. (14Aug2009). Eastern Air Lines Flight 401 FAA Recreation Safety Film. Retrieved from YouTube on 02Oct 2011
Want to know more?
More introduction about the air crash of Eastern Flight 401 : http://aviationknowledge.wikidot.com/asi:eastern-air-lines-flight-401:the-ghosts-of-flight-401
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