The sleep quality and (dis)comfort sitting upright was studied among 40 participants who took a nap at home. They were asked to take a nap at 17:00h on three consecutive days. The backrest had to be at a different angle every day: upright, reclined and more reclined. They were asked to record the backrest angle of the three positions and report the length of the sleep, the sleep quality, comfort and discomfort and influence of other factors each during each nap. From the 120 cases (3 conditions, 40 participants), the cases where participants were not able to sleep had an average backrest angle of 110˚, which was significantly different from the cases where participants were able to sleep, who had an average backrest angle of 118˚. The scores in the more upright position (<110˚) resulted in significantly more discomfort and a lower sleep quality than in the reclined positions (>123˚). As the conditions were arranged by the participants, there was much variation in outcomes. Therefore, future research under more standardised conditions is recommended.@en

This master graduation thesis explores the possibilities for improving the comfort experience for watching in flight entertainment (IFE) and sleeping in a business class (BC) and premium economy class (PEC) aircraft seat trough (mainly) headrest design.
Experimental and extensive literature research on sleeping and watching IFE in transit results in design requirements and recommendations for the (aircraft) seating industry. The study on head support for watching IFE in a slouched posture resulted in a scientific publication in Applied Ergonomics. Further research and development is proposed of a premium economy headrest supporting for sleeping with a limited recline and head-neck support for watching IFE in premium cabins. In addition, the exploration of a highly personalised BC bed-seat is advised.

Sleeping full-flat in BC
The earlier mentioned focus on headrest design is less applicable on BC sleep. Here the focus should be on overall bed design and control features. Nevertheless, as new generation BC seats provide full flat sleeping capabilities, it is advised to level the headrest with the backrest when in full-flat mode (becoming a part of the mattress surface area) and provide a separate pillow based on the passengers choice. This gives passengers more freedom of posture and approximates the conditions passengers are used to at home, which is important to sleep quality. Also disturbing factors should be minimised as much as possible. This includes cabin services and belt checks.
One of the challenges BC passengers face is the lack of control over their own activities and environment within the cabin. A BC bed-seating concept is proposed which includes personal flight scheduling features, which gives BC passengers the option to opt in or out of services and schedule their own activities. Their choices will be communicated by displays outside the seat (e.g. non-disturb and seatbelt on sign) and in the galley. In addition, automated seatbelt checks prevent flight attendants (FA's) to wake BC passengers. This can improve passenger's sense of control and prevent unwanted disturbance by cabin crew.
In search of improving the bed-seat experience, it was found that the firmness per area of the seat should be adjusted according to the taken posture for proper support. When seated, firm support is needed at the pelvis region, as most of the body weight can be carried here. When sleeping lateral, that same area should soft, to allow the pelvis to sink for a straight alignment of the spine. In addition, anthropometric differences and preferences (e.g. firmness) require personal optimised support. Exploration of a bed-seat that can actively adapt to the taken posture by and anthropometrics of the passenger is advised.

Sleeping with limited recline in PEC
Sleeping with limited recline in PEC is challenging. Muscles relax when entering deep sleep, which causes the head slide, nod and fall. This triggers the sleep-wake system, waking up the passenger. Without adequate support of the head passengers will not be able to have a qualitative sleep, as they will not go trough deep sleep and REM cycles (which account for physical and mental recovery respectively). Two headrest designs are proposed which support the head by a jaw line on the side ‘wings’, as the load of the head can be carried here and prevent the head to fall and nod. One design iterates on existing headrests, requiring the addition of two rotational hinges and jaw-line support on the ‘wings’, allowing it to create a ‘bowl shape’ the head can rest in. Implementation might be relative simple, but further prototyping is advised. The other design is more radical, as it articulates sideways following natural movement of the head during sleep. When going sideways (over the Z-axis), the headrest turns (over the Y-axis) ’catching’ the head, preventing it of falling down. The mechanics to articulate this headrest are more challenging and require further research and development.

Watching IFE in premium cabins
People prefer to watch IFE and TV in a slouched posture (reclined backrest and leg support), as is possible in premium cabins like BC and PEC. In current aircraft seats passengers lack head/neck support, as they flex their head forward to have a perpendicular view on the IFE screen. Prolonged contraction of the neck and eye muscles to sustain view on the IFE screen (e.g. during multiple movies) may fatigue the muscles, lead to pains and discomfort. Pillows offered in premium cabins may offer some support, but – depending on the thickness and material – may be insufficient. The scientific study in this thesis shows that head support improves the ‘expected comfort’ and may lower muscle tension in the neck as shown in an AnyBody™ simulation. This was however not validated by an EMG study, which showed no difference in major flexion and extension neck muscles. The discovery was that humans search for a neutral posture, with minimal strain on the musculoskeletal system. This could explain the lack of a significant difference. However, further research on the long-term (dis)comfort is advised. Nevertheless, a proposed design of a forward tilting headrest based on a simple friction hinge may be an interesting solution to improve passenger comfort when watching IFE.

This master thesis thus shows that through headrest design comfort of premium aircraft passengers can be improved for watching IFE and sleeping with limited recline. Aircraft seat manufacturers are therefore advised to further research and develop proposed headrest designs, as current headrest are insufficient and/or underexposed in seat design.