Shaken and Stirred: the influence of bunk orientation on the effectiveness of inflight crew rest : a pilot study
Pre existing information and evidence regarding the influence of vibration on sleep quality was sought during a literature review process. Sixty four papers and sources were screened to determine those that addressed or related to the issue to the greatest extent. Although many papers were associated with peripheral matters, none were identified that specifically addressed the influence of bunk orientation on the effectiveness of inflight crew rest.
Key words: Crew rest, vibration, fatigue, z-axis
As described in the seminal work ‘A Survey of Sleep Quantity and Quality in On-Board Crew Rest Facilities’ (Rosekind et al. 2000), long haul flight operations result in “fatigue, cumulative sleep loss, decreased alertness, and degraded performance”, and that as a result “operational effectiveness and the safety margin may be reduced by pilot fatigue” such that “crewmember fatigue in commercial long-haul operations presents a substantial safety concern”. Caldwell (Caldwell 2004)indicated fatigue was involved in more than 4 to 8 percent of aviation mishaps (from official statistics), and surveys reveal that fatigue is an important concern amongst crew members, and that much remains to be done to mitigate “this insidious threat to air safety”.
There have been many accidents that validate this concern (Caldwell 2004). Additionally, future aviation traffic increases are expected to place greater demands on equipment and airspace usage, magnifying the need for alert, high performing flight crews despite the detrimental and deleterious nature of their duties.
The only method to counter sleepiness is sleep (Rosekind et al. 2000). However, sleep is a complex process influenced by many factors, and the effectiveness of an individuals sleep may be dependent on time of day, prior sleep and wakefulness, age, and the local environment. Local environmental characteristics confound zeitgeber by presenting contradictory information, particularly from the variance of normal or expected light/dark ambient lighting cues or other variances from the ’sleepers’ normal, habitual sleeping environment.. These aspects all interact to affect sleep quantity and quality. Therefore, control of the ‘sleeping environment’ is required to minimize interfering effects, and to enhance sleep promotion.
There have been many studies conducted on sleep quality and quantity in on-board crew rest facilities, for example; Rosekind (Rosekind et al. 2000), Roach (Roach et al. 2010), and Signal (Signal et al. 2012). As will be discussed later in detail, these studies consider many aspects of the ‘sleepers’ interaction with the environment. However, there is paucity of information on the impact of the orientation of prone sleeping bunks on the effectiveness of sleep or rest in vehicles that are in motion. Specifically,
Does the orientation of the bunk in aircraft crew rest facilities influence sleep latency and sleep quality, and subsequently result in higher residual levels of fatigue and reduced alertness post inflight rest periods; particularly in turbulent inflight conditions?
From the investigation of academic literature to date (June 2016) (including that conducted by a professional research librarian), there appears to be a scarcity of information on the influence of bunk orientation on the effectiveness of crew rest inflight; but also more generally for all vehicle types.
The literature review process included analysis of the papers cited by Rosekind (Rosekind et al. 2000), and also examination of the papers which had cited that paper. The review also sought documents on the issue of motion and sleeping position. Neurophysiological resources were also examined. Documents to support the current aircraft seating/sleeping facility design for crew and passengers were also sought.
The search was conducted extensively on EMBASE, SCIENCEDIRECT and Web of Science; including using the Web of Science Citation index to check whether any of the NASA (Rosekind et al. 2000)authors had written other papers.
A plethora of literature identifies and addresses conditions which are conducive to sleep. This range narrows as the locus changes to inflight crew rest facilities. Rosekind (Rosekind et al. 2000) identified, and in some cases addressed, factors influencing sleep effectiveness in on board crew rest facilities. These included:
- Thoughts persisting, negating restfulness
- Random noises
- Requirement to use the toilet
- Background lighting
- Background noise
- The presence of a sleeping partner
- Comfortable clothes
- Readiness for sleep
- The sleeping surface
- Availability of pillows
- Facility size
- Bed size
- Storage space
The majority of these are pertinent to sleep quality irrespective of the fact that they are in relation to on board crew rest facilities; and would equally apply at ‘home’ and ‘away’. The only one that has implications due to vehicle motion is turbulence, and although turbulence appeared on the list it was assessed in a generalized nature, and consideration of the direction, frequency, and amplitude of any movement of the bunk relative to the ‘sleepers’ orientation was not appraised.
Caldwell (Caldwell 2004) stated that inflight sleep rest opportunities are less restful than sleep at home, largely due to noise, turbulence, temperature, lighting, and other comfort factors. Again there was acknowledgement of the influence of turbulence but the paper was mute as to its manifestations and implications.
Dhahran (Dharani 2005), although focusing on low or zero gravity environments, addressed how the brain uses a gravitoinertial-centered reference frame and an internal self-object model to evaluate and integrate inputs from several sensory systems. This is dependent on “ancient brain areas using ‘primal’ gravity dependent coordinates” including vestibular sensation, and that REM sleep is dependent on the correct functioning of this system. Obviously this ‘reference system can be disrupted if the ‘apparent gravity’ direction is altered, such as in turbulence encountered by a vehicle in motion, thus requiring constant brain ‘workload’ and hence the lost opportunity for REM sleep. Further, intermittent hypoxia (as encountered at typical cabin altitudes) evokes other adaptations.
Riccio (Riccio & Stoffregen 1999) discussed dynamic orientation, and that the vestibular system has significantly different inputs for upright, terrestrial situations versus dynamic gravitoinertial forces. As will be demonstrated in the Research Proposal, these dynamic gravitointernatial forces manifest themselves in different anatomical planes during turbulence or vehicle motion, dependent on bunk orientation
Jay (Jay et al. 2015) discussed mobile workplaces, and that occupations such as aviation, rail and maritime necessitate sleeping in a moving vehicle, yet principally address timeframes and structures of rest periods yet remain silent the aspect of vehicle motion.
Roach (Roach et al. 2010) discussed the relative effectiveness of onboard sleep by flight crew members compared to ‘at home’ sleep, but minimally address environmental factors, with reference to the NASA publication(Rosekind et al. 2000)
A number of patents for sleeping facility design were also reviewed for pertinent data. Airbus Groups Patent Application US20140298582 A1 discussed longitudinal bunk arrangement, but does not discuss the impacts of this arrangement of crew rest effectiveness. The Boeing Company’s Patent Grant US6848654 B1 also identified a longitudinal bunk arrangement. The bunk orientation in both these patents seems to be driven by physical location specifications rather than an assessment of orientation effectiveness on crew rest.
From the proceedings of the Ocean 75 Conference (Martin n.d.), conducted in San Diego 22-25 September 1975, there is mention in an abstract that longitudinal berthing has been used traditionally aboard most Navy ships. As a mixture of athwartship and longitudinal berthing could result in improved habitability and space utilization, information was needed to indicate whether there were any deleterious effects of athwartship (lateral) berthing which would prohibit its use. It was recognized that athwartship (lateral) berthing was extensively used aboard passenger, cargo, and fishing vessels. In every category examined, from large to small, both stabilized and unstabilised, there were ships possessing significant percentages of athwartship (lateral) berthing orientations. Interviews with knowledgeable personnel resulted in a wide variety of strongly felt opinions about personal preferences for berth orientation, but no respondent was able to cite deleterious effects of this orientation.
Whole-body vibration exerts a substantive influence in many work environments (Conway et al. 2007) . However, the basis for this meta analysis research was the implications of vibration in completing various tasks. The results indicated that vibration acts to degrade the majority of goal-related activities, especially those with high demands on visual perception and fine motor control. This research was silent on the aspect of vibration intrusiveness on sleep quality.
Only a limited number of studies methodically examine the influence of vibration on sleep. A study by Arnberg (Arnberg et al. 1990) , although having a small number of participants, revealed that sleep is more disturbed from a combination of road traffic noise and vibration than from noise alone. It was also shown that sleep quality (both subjectively rated and measured as amount of REM-sleep) decreased, as did performance in the morning. Swedish research (Ögren et al. 2009) found that self-reported sleep disturbance was greater for high vibration amplitude, irrespective of noise level. However, due to study limitations vibrations were created only in the vertical direction. This equates to x-axis or y-axis movement in regards to human reference, and does not address the z-axis motion that will be the basis for the Research Proposal. Further research by Öhrström(Öhrström et al. 2009) within the coincident research project confirmed the strong effect of railway vibrations on sleep. An interaction effect exists between noise and vibration and general annoyance to railway noise increases when combined with railway vibration.
The closest identifiable adaption of information relating to vibration and sleep quality is derived from literature pertaining to the influence of freight trains on humans; in particular the impact of nocturnal low frequency vibration and noise on sleep and heart rate (Smith et al. 2013). This study acknowledged there is a lack of research and understanding of how vibration influences sleep. The impacts of various amplitudes of horizontal vibrations on sleep disturbance and heart rate were investigated in a laboratory study. This study concluded that nocturnal vibration has a negative impact on sleep and that the impact increases with greater vibration amplitude. Of note, the World Health Organization recommends a nocturnal bedroom noise level upper limit of L Aeq,8h = 30dB and L AF,max = 45dB . However, no such recommendation exists for vibration. Smith et al consolidated the earlier work (Smith et al. 2016) and confirmed the lack of research:
“To our knowledge, only three studies have previously investigated the physiological effects of vibration on sleep.” : (Öhrström et al. 2009; Ögren et al. 2009; Arnberg et al. 1990), as discussed previously.
Their further research confirmed that vibration and noise from railway freight traffic was found to impact on sleep. The amplitude of vibration contribruted towards arousal, awakening and sleep stage change probabilities. Vibration amplitude contributed towards effects on sleep macrostructure, whereby the number of sleep depth changes, slow wave sleep continuity and nocturnal wakefulness were negatively affected during the high vibration conditions.
Explanatory material regarding the correlation between the motion of an aircraft about its various axes, bunk orientation, and anatomical planes of motion are included in the Research Proposal. However, manifest in the outcome of the Literature Review is an absence of scientifically validated information pertaining to the implications and effects of these associations. The existing reviews of the suitability of inflight crew rest facilities, and in particular bunks, hones in on pertinent aspects that would be applicable irrespective of the vehicle being in motion. They fail to address the inevitable interface of the bunk being within a moving platform, and the variations this creates. The impact of this motion within the varying anatomical planes will be the basis for the research, which will be evolved in the subsequent Research Proposal, which aims to address:
Does the orientation of the bunk in aircraft crew rest facilities influence sleep latency and sleep quality, and subsequently result in higher residual levels of fatigue and reduced alertness post inflight rest periods; particularly in turbulent inflight conditions?
Arnberg, P.W., Bennerhult, O. & Eberhardt, J.L., 1990. Sleep disturbances caused by vibrations from heavy road traffic. The Journal of the Acoustical Society of America, 88(3), pp.1486–1493. Available at: http://scitation.aip.org/content/asa/journal/jasa/88/3/10.1121/1.400305.
Caldwell, J.A., 2004. Fatigue in Aviation. Travel Medicine and Infectious Disease, 2005(3), pp.85–96. Available at: message:%3C2935600.3684.1432030411823.JavaMail.prodapps@nschwweba03-app%3E.
Conway, G.E., Szalma, J.L. & Hancock, P.A., 2007. A quantitative meta-analytic examination of whole-body vibration effects on human performance. Ergonomics, 50(2), pp.228–245. Available at: http://www.tandfonline.com/doi/abs/10.1080/00140130600980888.
Dharani, N.E., 2005. The role of vestibular system and the cerebellum in adapting to gravitoinertial, spatial orientation and postural challenges of REM sleep. Medical Hypotheses, 65(1), pp.83–89. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0306987705000794.
Jay, S.M. et al., 2015. Sleeping at work: not all about location, location, location. Sleep Medicine Reviews, 19, pp.59–66. Available at: http://dx.doi.org/10.1016/j.smrv.2014.04.003.
Martin, J.I., Ocean 75. Ocean 75, pp.668–671. Available at: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1154034.
Ögren, M., Öhrström, E. & Gidlöf-Gunnarsson, A., 2009. Effects of railway noise and vibrations on sleep : experimental studies within the Swedish research program TVANE. , pp.1214–1221. Available at: http://www.diva-portal.org/smash/record.jsf?pid=diva2:674178.
Öhrström, E. et al., 2009. Effects of railway noise and vibration in combination : field and laboratory studies. , pp.1204–1213. Available at: http://www.diva-portal.org/smash/record.jsf?pid=diva2:674179.
Riccio, G.E. & Stoffregen, T.A., 1999. Human orientation and movement control in weightless and artificial gravity environments. Psychological review, 97(1), pp.1–25. Available at: message:%3C21044736.7278.1432010831584.JavaMail.prodapps@nschwweba09-app%3E.
Roach, G.D., Darwent, D. & Dawson, D., 2010. How well do pilots sleep during long-haul flights? Ergonomics, 53(9), pp.1072–1075. Available at: http://www.tandfonline.com/doi/abs/10.1080/00140139.2010.506246.
Rosekind, M.R. et al., 2000. Crew factors in flight operations XII: a survey of sleep quantity and quality in on-board crew rest facilities. Available at: http://ntrs.nasa.gov/search.jsp?R=20010038243.
Signal, T.L. et al., 2012. In-Flight Sleep of Flight Crew During a 7-hour Rest Break: Implications for Research and Flight Safety. SLEEP, pp.1–7. Available at: http://www.journalsleep.org/ViewAbstract.aspx?pid=28739.
Smith, M.G. et al., 2013. On the Influence of Freight Trains on Humans: A Laboratory Investigation of the Impact of Nocturnal Low Frequency Vibration and Noise on Sleep and Heart Rate. PLoS One, 8(2), p.NaN–NaN. Available at: http://dx.plos.org/10.1371/journal.pone.0055829.
Smith, M.G. et al., 2016. Vibration from freight trains fragments sleep: A polysomnographic study. Nature Publishing Group, 6, pp.1–10. Available at: http://dx.doi.org/10.1038/srep24717.
‘Rock a bye baby in the tree top, …’
This nursery rhyme may refer to the way native-American women in the 17th century rocked their babies in birch-bark cradles, which were suspended from the branches of trees, allowing the wind to rock the baby to sleep (Carpenter, 1984); and as per the custom in many societies, the motion was side to side. Why was it side to side, and not up and down, or back and forth?
I am an Airbus A380 pilot by profession, and have been for approximately four years. I have over 32 years of aviation experience, with all but four being involved in extended duration, back of the clock, trans-meridian operations, with variable start and finish times; in both military and commercial operations, in aircraft that contain crew rest facilities.
Through personal experience on the A380, opportunistic surveys of other crew members and anecdotal information, there seems to be a reduction in the quantity and quality of rest obtained on the A380, despite the aircraft having crew rest facilities that seem to have many features identified in academic literature as being conducive for adequate rest and superior to many other aircraft types. Different to previous aircraft types I have operated, the crew rest berth facility in the A380 is orientated laterally (across the aircraft) rather than longitudinally (aligned with the fuselage). This apparent reduction in the quality of rest is often associated with turbulence (as would be reasonably expected), but anecdotally, in such turbulence, it is greater than in aircraft with longitudinally arranged berths (e.g. Boeing 747 or 767)
Does body motion in certain directions impact on the attainment of mental rest, the inducement and quality of sleep and the subsequent effectiveness in reducing fatigue?
Are long standing societal practices more cognisant of the answer to this question than existing academic research and industry practice? In the absence of research and guidance, are environments being created by manufacturers and operators that are not optimum for human performance, particularly for the rest or sleep of the operating crews of vehicles such as aircraft, trains, buses and boats?
The aim of this project is to explore the impact of body z-axis motion, induced by vehicular movement, on the quality of rest and sleep by using experimental research to determine the causal relationships of berth orientation within the vehicle. It will attempt to negate or diminish other environmental aspects that influence rest quality, and obtain data associated with vehicle motion that creates body z-axis motion, and subsequently identify variances in post-rest fatigue levels between people exposed to body z-axis motion and those that were not.
As described in the seminal work ‘A Survey of Sleep Quantity and Quality in On-Board Crew Rest Facilities’ (Rosekind et al. 2000), long haul flight operations result in “fatigue, cumulative sleep loss, decreased alertness, and degraded performance”, and that as a result “operational effectiveness and the safety margin may be reduced by pilot fatigue” such that “crewmember fatigue in commercial long-haul operations presents a substantial safety concern”. Caldwell (Caldwell 2004) indicated fatigue was involved in more than 4 to 8 percent of aviation mishaps (from official statistics), and surveys reveal that fatigue is an important concern amongst crewmembers, and that much remains to be done to mitigate “this insidious threat to air safety”.
Alert and effective operating crewmembers are a significant component in reducing the risks associated with degraded human performance and error in long-haul flight operations. Therefore, it is important to investigate crew rest and berth design issues that may influence the level of alertness. Given that the berth is intrinsic within a moving vehicle, the influences of the motion of the vehicle on body motion, and the subsequent effect of this body motion on crew rest effectiveness needs to be investigated. If there is a correlation between body z-axis motion and degraded crew rest, measures to accommodate or counter this influence may need to be implemented, including retrospective adjustment to existing facilities, modified crew rest practices, or ultimately, changed design principles for future crew rest facilities. These aspects may subsequently or similarly influence arrangements in other transport modes and passenger facilities within vehicles.
Given the limited scope of the research, yet the wide-ranging implications for other transport forms: such as trains, buses and boats: this research may be the pilot study or the basis for further research.
A Literature Review has been submitted as a separate assignment, and it addressed in detail the existing body of knowledge on crew rest facilities and the effects of body motion on alertness and fatigue.
In summary, sixty-four papers and sources were screened to determine those that addressed or related to the Research Question to the greatest extent. There have been many studies conducted on sleep quality and quantity in on-board crew rest facilities; for example, Rosekind (Rosekind et al. 2000), Roach (Roach et al. 2010), and Signal (Signal et al. 2012); and many papers were associated with peripheral matters, however none were identified that specifically addressed the matter of this Research Question. As was discussed in the Literature Review, the ‘crew-rest’ studies considered many aspects of the ‘sleepers’ interaction with the environment and honed in on aspects of the suitability of inflight crew rest facilities, and in particular berths, that would be applicable irrespective of the vehicle being in motion (and therefore just as applicable for a stationary bed). The literature failed to address the inevitable interface of the berth being within a moving platform, and the variations in body motion that this creates and the subsequent impact on the effectiveness of rest or sleep.
Within the academic literature to date (June 2016), there appeared to be a scarcity of information on the influence of body motion or vibration on rest or sleep quality, and in particular the influence of berth orientation and body motion on the effectiveness of crew rest inflight; but also more generally for all vehicle types.
Given that, anecdotally and by individual observation, there appears to be a disparity in the effectiveness of crew rest when body z-axis motion is instigated, be it by turbulence or by aircraft manoeuvre:
Does the orientation of the berth in aircraft crew rest facilities influence rest quality, sleep latency and sleep quality, and subsequently result in differing residual levels of fatigue and alertness post inflight rest periods; particularly due to aircraft manoeuvres or in turbulent inflight conditions?
There are variables that will impact on the ability to accurately answer this question. Many arise from the dynamic nature of the operating environment of a vehicle in motion and the workload of the crewmembers. Items to be considered may include:
- The lack of a longitudinally and laterally arranged prone crew rest facility in one aircraft type, and therefore a requirement to make comparisons with a different aircraft type, with different facilities and operating conditions
- Pre existing propensity for sleep amongst the survey group at the time the rest period commences
- Accuracy and reliability of crewmembers to rate their propensity for sleep, the quality of the sleep and their post rest level of alertness.
- Frequency and amplitude of motion in the vehicle in the axis not related to the intended direction of travel
- Impact of other aspects (such as lighting, temperature, bedding quality, and others) on rest quality, which may mask or enhance the impact of vehicle motion issues.
In appropriately configured long-haul aircraft generally crew rest facilities, including berths, exist for both pilots (Technical crew) and cabin crew. They are usually in separate areas, with pilot crew rest facilities usually being closer to the front of the aircraft (in proximity to the flight deck). Cabin crew rest locations vary widely; for example, being mid aircraft in Qantas A380 aircraft, and near the base of the vertical stabiliser (rear of the aircraft) in Qantas B747 aircraft. Most technical crew pilot berths are orientated longitudinally, the exception being A380 aircraft. Cabin crew berth facilities usually contain a mixture of lateral and longitudinal berths. For example,
Figure 1 Cabin Crew Rest Facility
Pilot crew rest facilities are generally arranged for single occupation, whereas cabin crew rest facilities generally have multiple occupants.
Figure 2 Pilot Crew Rest Facility
The presence of multiple occupants within the rest facility generally introduces extraneous influences on rest quality, such as noise and lighting variability. The magnitude of these influences would be difficult to filter from the results of survey information obtained from shared rest facilities compared to single occupant facilities. Therefore, it is expected that participants will be restricted to the pilot group. Shared crew rest facility users may be surveyed, but with the results assessed being cognisant of the aforementioned aspects.
It will be necessary to obtain surveys from pilots (or cabin crew) that occupy both laterally and longitudinally arranged crew rest facilities. There are no aircraft thus configured for pilots. Therefore surveys of pilots will have to be conducted on various aircraft types, and ideally aircraft that complete operations on similar route structures and having similar flight times. Airbus A380, A330, Boeing B747 and B777 aircraft generally satisfy this requirement. Additionally, it would be beneficial to survey groups, albeit on different aircraft types, that have similar organisational and cultural arrangements regarding crew rest practices with regard to routines and schedules inflight. Therefore, they would ideally be from one airline.
Fundamentally, the problem with regard to obtaining suitable comparative participants is that the pilot group will be from varying aircraft types, whereas the cabin crew will have multiple extraneous influences on their rest by virtue of occupying a shared facility.
Qantas Airlines have both A380 and B747 aircraft, and a relatively homogenous pilot group with respect to crew rest practices. Qantas A330 aircraft generally operate shorter routes and have a lesser crew complement of 3 pilots rather than 4. Other airlines may have similar arrangements, but the difficulty in obtaining access to overseas based crew may be detrimental to the research progress. Additionally, given that there are a limited number of A380 pilots worldwide, and access to the majority of these would be difficult without extensive consultation with various airlines and pilot associations, the focus is to recruit suitable subjects within Australia with the assistance of Qantas Airlines and the Australian and International Pilots Association. It is expected that endorsement for the research will be received from both organisations.
Participants would be recruited from Qantas A380 and B747 pilots, with the possibility to expand this if participant numbers are inadequate; firstly to A330 pilots, and then to A380 and B747 cabin crew. Qantas has 12 A380’s in service and has approximately 360 pilots (of various ranks) crewing these aircraft. The Qantas figure equates to 31 pilots per aircraft, which is above the industry average of 6 to 7 crews (in Qantas’ case, of 4 pilots) per aircraft. Qantas has 11 B747’s in service and approximately 295 pilots crewing these aircraft. A total of approximately 655 pilots are potentially available in the first participant tranche.
For practicality, the sample will be limited to 25 individuals over four to five flights each (usually each flight having two “rest breaks”) should be a sufficient sample. This would represent approximately 30 percent of an individuals flights over an eight week ‘roster period’. Population size, based on worldwide numbers of long-haul pilots and cabin crew, would exceed 100,000 (exact numbers being difficult to calculate).
Participation will be by volunteers. The potential participants within the sample cover a wide range of ages, experience in aviation, and experience in resting in laterally and longitudinally arranged crew rests. Representation of a particular demographic may be skewed by a propensity of a particular group to volunteer.
Advertising will take place using both organisations common communication tools such as emails, news feeds and flyers. Direct recruitment by the researcher may also occur. Participants will not be told pre-research the specific details of the research with regards to berth orientation, but more generally that
“The study looks into the impacts on, and effectiveness of, crew rest in turbulent flight conditions or during aircraft manoeuvres.”
This is to avoid the Hawthorne effect.
Notification will generally consist of one paragraph, directing the potential participants towards a URL, website or download location that will have the Participant Information Sheet.
Materials and Measures
The mechanism used to obtain data within this project is the survey of long-haul flight crew. The survey forms, as at Annex A, may be implemented as paper-based documents, or as offline electronic surveys (using an application such as QuickTapSurvey). The use of offline electronic surveys is preferable as Internet connectivity is not readily available to crewmembers inflight, and information quality may degrade if the crew member waits to enter information online post-flight.
Extraneous influences on crew rest quality are drawn from the work of Rosekind, and the participant may identify the presence of negative influences of any of these particular influences. (Refer to the associated Literature Review)
To measure subjective fatigue the use of the Samn-Pirelli Crew Status Check is planned, and sleepiness using the Karolinska Sleepiness Scale. These scales are used widely in the aviation industry and are recommended by the International Civil Aviation Organisation as the standard measure for use in Fatigue Risk Management Systems.
Potential objective measures of aircraft motion are still being identified. In particular devices to measure accelerations resulting from aircraft manoeuvres or turbulence are being sought. Various smartphone applications are available that measure these aspects, however because of the required sampling rate and that they would be required to be constantly ‘on’ during the rest period (of possibly more than three hours) the amount of data is excessive and would exceed the capacity of most smartphone memories. Investigations are continuing to identify if it is possible to set a threshold acceleration rate that would initiate recording, then the device acquiesce when acceleration parameters fall below the threshold. Although these recording devices are preferable, they are not critical to the research analysis.
Fundamental to the design of the research is an understanding of berth orientation, aircraft motion, and subsequent body motion.
Firstly, planes of motion for the body are described as per diagram, noting that whilst lying in a berth; irrespective of being prone, supine or on a side; horizontal motion equates to y or z-axis motion, and vertical motion would be x-axis.
Aircraft axes are described as per diagram, with rotation about the centre of gravity (CoG). Note that the greater the distance from the CoG along any axis, the longer the moment arm, and therefore any angular rotation would manifest in a greater distance moved the further from the CoG.
In turbulence, aircraft in ‘cruise’ flight do not significantly accelerate or decelerate in the longitudinal plane, but are in motion within the other axes, thus a longitudinal arranged berth would have insignificant body z-axis motion. However, a laterally arranged berth would manifest body z-axis motion and its amplitude is dependent on the moment arm and frequency on angular rotation rate. That is, a forward or aft crew rest facility will experience greater motion than one in proximity to the centre of gravity.
During aircraft manoeuvring, body axis motion impacts vary with the manoeuvre. During accelerations and decelerations a person in a longitudinally arranged berth will experience body z-axis motion. However, a person in a laterally arranged berth will not; experiencing x or y-axis dependent on body position.
Therefore, in considering the presence of body z-axis motion there needs to be evidence of longitudinal acceleration or deceleration for longitudinally arranged berths, and turbulence creating angular rotation about the aircraft vertical axis for laterally arranged berths.
The fundamental problem is assessing the independent variable, as individuals’ perspective and perception of tiredness and rest effectiveness will inevitably vary. However, they should be consistent for the individual over the four to five flight periods (which is usually one or two rostered sequences of flights over approximately a two week period), hence the desire for the 25 individuals over four to five flights, rather than 100 to 125 individuals. Further, rather than considering absolute values of sleepiness and fatigue based on the planned measures, the expectation is to measure pre and post rest fatigue and sleepiness levels and calculate differentials between occurrences when rest was impinged by body z-axis motion and when not impinged by body z-axis motion, and subsequently identify differences (if any) in the changes between the two sets. In diagrammatic form:
Survey data is collected at the commencement of duty and at the beginning of each crew rest period. Post crew rest period data is collected approximately 20 to 30 minutes after recommencing operating duties to accommodate post sleep cortisol secretion effects (Cortisol awakening response). Immediate post sleep surveys may not accurately reflect alertness levels, and crew rest benefits, as cortisol levels may be relatively low immediately post sleep. If there are concerns regarding the collection of data whilst on duty, the data can be entered in the pertinent forms post flight duties.
Volunteers would indicate their willingness to participate by registration with the researcher via a specific webpage; the URL of which is published in advertising materials. This page would include a ‘Participant Information Guide’.
Participants can subsequently access .pdf files of the survey via a dedicated webpage; the researcher would supply the link from which they can download and print copies of the survey at their own behest. Also available on the webpage will be a link to an offline survey smartphone application, if this aspect can be effectively implemented.
Participants commence the survey at the start of their duty period. The survey has been designed to have minimal impact on their primary duties, and each section should only take a few minutes to complete. Subsequent sections are completed at the beginning and 20 to 30 minutes after the end of each crew rest period, as previously discussed.
Completed surveys can be faxed, scanned and emailed, or emailed from an integrated link within the .pdf document to a specific research project email address. Alternatively, if offline surveys can be successfully implemented, direct submission can be undertaken.
During the project paper documents will be stored in a secure filing cabinet at the researchers home address. Electronic files will be stored on a desktop and portable computer, that both have password security only accessible to the researcher. At the completion of the project, paper documents will be destroyed after the data is aggregated.
Data Analysis Plan
Surveys will be analysed to determine crew rest periods that had significant extraneous impacts not associated with body z-axis motion on crew rest quality; due to such aspects as lighting, noise, and others. Reports containing these extraneous aspects will, in the first case, be disregarded from further analysis.
Remaining reports will be analysed to determine the presence or absence of body z-axis motion. These reports will be analysed to determine the differential in fatigue and sleepiness levels between commencement and conclusion of the crew rest period.
A comparison will then be made between those reports with an absence of body z-axis motion and those with, and the subsequent differential, if any, between these determined.
Is the subsequent differential statistically significant?
If the result is positive, significant further opportunities for research become available. The implications for other transport modes is readily apparent, and this research may act as a pilot study, with the benefit of being able to refine techniques and methods before committing to the larger project.
- Carpenter,H and Prichard,M, The Oxford Companion to Children’s Literature (Oxford University Press, 1984), pp. 326.)
- Rosekind, M.R. et al., 2000. Crew factors in flight operations XII: a survey of sleep quantity and quality in on-board crew rest facilities. Available at: http://ntrs.nasa.gov/search.jsp?R=20010038243.
- Caldwell, J.A., 2004. Fatigue in Aviation. Travel Medicine and Infectious Disease, 2005(3), pp.85–96. Available at: message:%3C2935600.3684.1432030411823.JavaMail.prodapps@nschwweba03-app%3E.
- Roach, G.D., Darwent, D. & Dawson, D., 2010. How well do pilots sleep during long-haul flights? Ergonomics, 53(9), pp.1072–1075. Available at: http://www.tandfonline.com/doi/abs/10.1080/00140139.2010.506246.
- Signal, T.L. et al., 2012. In-Flight Sleep of Flight Crew During a 7-hour Rest Break: Implications for Research and Flight Safety. SLEEP, pp.1–7. Available at: http://www.journalsleep.org/ViewAbstract.aspx?pid=28739.