This is the process whereby pilots may take short periods of sleep (naps), while temporarily relieved of operational duties in accordance with carefully prescribed ‘controlled rest’ procedures, when part of a two-person operating crew of an in-flight aeroplane.
The two main factors affecting the usefulness and operational safety aspects of in-seat rest are the circumstances in which it should be used and the specific issues relating to the transition from a nap to a normal operating role.
These are both addressed by guidance which has been in place for such a long time that effective access to the full scientific justification for it appears to be somewhat limited. Whilst many national and international agencies together with long-haul airlines have published recommendations on how controlled rest should be managed, though without universal agreement. However, a general consensus appears to have developed. For example: The Director General of Civil Aviation, Government of India, recommends 40 minutes controlled rest followed by 20 minute recovery time. EASA recommends 45 minutes rest, plus 20 minutes recovery. Both British Airways and Cathay Pacific, with the cognisance of their respective regulating agencies, have recommended 45 minutes with a 15 minute recovery period. The main research into the subject was carried out in the late 1980’s and early 1990s led by researchers at NASA Ames. Although not the only organization to conduct research (much was also done with British Airways by the RAF Institute of Medicine at Farnborough), the most quoted study (NASA TM 108839) involved a survey of Boeing 747 Classic trans-Pacific flights with the support of United Airlines and Northwest Airlines.
This work concluded, with a high degree of confidence, that a ‘gross’ period of controlled rest lasting just over an hour, incorporating an uninterrupted nap period of 40 minutes, followed by a 20 minute recovery period before receiving a briefing and resuming operational duties, produced measurable benefits and no dis-benefits. Compelling evidence was found that the napping pilots had a higher level of physiological alertness, including during descent and landing, compared to the non napping control group. All rest periods ended not later than one hour before top of descent and no association between which of three rest periods was taken during the cruise and the extent of the subsequent descent and landing alertness margin over control was found. Although no issues in transferring the findings to the two crew case in more automated aeroplanes were foreseen, the findings were qualified by the statement that “the specific application …to the two-person cockpit was not addressed”
These findings do not seem to have been disputed since then and the transition to supporting the option of in-seat rest on two crew operations appears to have been widely accepted. Studies have shown that for two crew operations, an in-seat ‘nap’ of no longer than 30 minutes by one of the pilots was effective provided that cabin staff also checked on the awake pilot while one was napping. The only evidence that in-seat rest is either ineffective, impractical or generates an unaddressed operational safety risk has been found when these originally tested guidance principles have not been broadly followed.
Of course, it must also be recognised that when this process is applied to two man crews, it may on rare occasions be necessary for the resting crew member to be woken earlier than expected. However, it must be understood that in such a situation, safety would not normally allow an instant attempt to return to operational duties.
Sleep, Waking and Sleep Inertia
A period of sleep is characterised as occurring in a sequence of stages which are distinguishable by monitoring brain activity. Stage 1 or 'drowsy' sleep usually occurs during the transition from waking to sleep. This is followed by Stage 2 or ‘shallow’ sleep and then by Stages 3 & 4 or ‘deep’ sleep also described as ‘slow wave sleep’. This deep sleep may begin within half an hour of falling asleep and its duration is influenced by the length of prior wakefulness. Thereafter, an uninterrupted period of sleep will be cyclic with further but shorter periods of deep sleep separated by shallow sleep.
Waking from sleep means that a degree of ‘sleep inertia’ occurs.
Sleep inertia may be defined as a transitory period of impaired performance and alertness which occurs during the period immediately after waking up. The duration of sleep inertia appears to be influenced by the amount of sleep deficit prior to a nap, the time of day that the nap is taken, and the duration of the in-seat nap. It is also likely to be affected by individual susceptibility to its effects.
It may significantly affect the ability of a pilot, who has just woken, to effectively perform their normal duties, and a period of time free of both duties and briefing must follow any period of actual sleep. However, there is not believed to be any conclusive recent research on the duration and extent of any subsequent performance benefits conferred by in-seat napping or on the precise nature of any performance impairments associated with the subsequent sleep inertia. The NASA work quoted above did not investigate sleep inertia or the related issue of the optimum length of nap in terms of subsequent alertness gains beyond observing that the 40 minute nap period had been characterised by only 8% deep sleep, which is the main source of sleep inertia effects upon being woken.
The Benefits of and Issues relating to In-Seat Rest
Whilst it has been widely accepted since the 1990s work that in-seat rest is a means of improving pilot performance during the later stages of long haul flights, it has generally been considered that such naps are most effective if they are taken proactively prior to the onset of fatigue rather than after it has become established. It is also widely recommended that in-seat rest should not be seen as a routine to be anticipated, but as a means to deal with unexpected tiredness in the interests of crew performance towards the end of a long flight where the demands placed upon the crew are likely to rise compared to the cruise. Where the need for significant periods of in flight rest is routinely foreseen, an augmented crew should be rostered. And when referring to ‘in-seat rest’ a distinction must always be drawn between the period actually asleep or ‘napping’ and the longer ‘controlled rest period’ within which that sleep occurs.
It has been stated that in-seat napping of less than half an hour has been shown to increase subsequent levels of alertness, but the usual guidance is that little longer than this is optimum. However, whilst longer naps have demonstrated greater subsequent benefits, the adverse effects of sleep inertia increase as the duration of a nap increases, requiring relatively more recovery time after awakening. Consequently, it is widely recommended that the determination of optimum nap duration should aim to balance the duration and extent of sleep inertia against the duration and extent of the beneficial effects thereafter on pilot alertness and performance.
A general review of the issues surrounding all forms of in-flight rest by operating flight crew published by the UK CAA concluded that “large variations in experimental design and measurement have made the provision of guidance on the recovery from napping very difficult. However, based on current knowledge, at least 20 minutes should be allowed to elapse between awakening and the resumption of duties.” The same review also noted that at the time of publication, there was a lack of information on:
- the influence of the circadian rhythm on the sequence of sleep stages
- the impact of the sleep stage sequence on sleep inertia effects afterwards
- the efficacy of taking more than one nap as an alternative to a longer one
The detail in guidance given by both Regulators and Operators on in-seat rest varies but the maximum period asleep is generally recommended as between 30 and 40 minutes. Many operators suggest that when planning in seat rest, the total ‘no duties’ period within which an in-seat nap should occur should be up to twice the time actually asleep. This allows for an initial 5 to 10 minutes for ‘sleep preparation and a period of at least 20/25minutes for recovery. This generalisation errs on the conservative and since the effects of sleep inertia are known to vary from person to person, many will feel fully recovered in less time.
Getting the most out of in seat rest
Where in-seat rest is approved as ‘controlled rest’, Operations Manuals should contain procedures for its use and these should take precedence over anything in this article. If there is no such guidance and no explicit prohibition of the practice, then the following practical considerations when planning and undertaking such rest may be useful in helping to maximise the benefit whilst minimising the risks. They are based on the procedures developed by ICAO / IFALP / IATA which are published as Appendix B of the First Edition of ICAO Doc 9966 ‘Fatigue Risk Management Systems for Regulators’.
- Rest should be planned and undertaken only in the cruise and a serviceable AP and A/T should be available and engaged.
- The aircraft commander must ensure that the crew member(s) remaining awake are adequately briefed and that if the commander is napping and there is more than one pilot awake, a senior pilot is designated.
- The senior member of the cabin crew should be advised of the intention and instructed to ensure that contact is made with the flight deck by interphone at one or more pre-arranged times to verify that the awake pilot remains so and is prompted to wake the napping pilot at the time when the agreed period asleep will have been achieved.
- the napping pilot should set their seat back from the controls to preclude inadvertent interference.
- any aircraft management activity which requires cross checking by another pilot shall not take place unless a second pilot is available to do this, which means that a decision to permit on seat rest to commence must have been preceded by a realistic assessment of any such activity is likely to arise.
In the case of two pilot crews, the awake pilot must not leave their seat for any purpose at any time during the whole controlled rest period.
- where actual sleep has taken place, a recovery period in proportional to the time asleep must be allowed before any operational duties, including the receipt of an updating brief, occur so that the effects of sleep inertia are recognised.
- Controlled rest periods should terminate a least 30 minutes before the top of descent
- Helpful accessories such as ear plugs, eye shades and neck supports should be permitted if they help individual pilots to maximise the benefit from napping.
Appendix C of IFALPA/ICAO/IATA ‘FRMS Implementation Guide for Operators’ reiterates the main points for crews to keep in mind.
NOTE: Particular attention must be paid to controlling the length of any ‘nap’ to within the maximum permitted and, especially when there are only two pilots on the flight deck, to ensuring the cabin staff are aware of their responsibility to check on the flight deck at regular intervals.
In-Seat Rest on the Ground
It may seem to be a rather different situation from the in flight case, but if in-seat napping takes place whilst the aircraft is on the ground with engines off between sectors, then exactly the same considerations in relation to the maximum time asleep and the need to have a non-operational recovery period to counter the effects of sleep inertia apply. One of the examples quoted below concerns just such a situation. Few Operations Manuals explicitly cover this scenario in their content on fatigue risk management.
Current State Regulatory Requirements and Guidance Material
Examples of State Regulatory Requirements / Guidance Material include those issued by EASA under GM1 CAT.OP.MPA.210 - MITIGATING MEASURES – CONTROLLED REST, and Transport Canada as Part VII - Commercial Air Services, Standard 720.23 "Controlled Rest on the Flight Deck".
Related Accident and Incidents
The following events all illustrate the need for flight crew to recognise the importance of a recovery period proportional to the sleep inertia generated by a nap - and thereby be able to appreciate the reasoning which underlies the procedures applied by those operators who sanction the controlled rest option.
- Boeing 767-300 2011 On 14 January 2011 an Air Canada Boeing 767-300 was midway across the Atlantic Ocean eastbound at night when the First Officer, who had just woken from an exceptionally long period in-seat rest, suddenly but erroneously perceived a collision risk from oncoming traffic and without warning intervened to dive the aircraft before the Captain could stop him causing 16 occupant injuries. His behaviour was attributed to the effect of ‘sleep inertia’ following a much longer period of sleep than permitted by Air Canada procedures. It was concluded that many Air Canada pilots did not understand the reasoning behind these procedures.
- Boeing 737-800 2010 On 22 May 2010, an Air India Express Boeing 737-800 overran the landing runway at Mangalore when attempting a go around after thrust reverser deployment following a fast and late touchdown off an unstable approach. Almost all of the 166 occupants were killed when control was lost and the aircraft crashed into a ravine off the end of the runway. It was noted a relevant factor in respect of the approach, landing and failed go around attempt was probably the effect of ‘sleep inertia’ on the Captain’s performance and judgement after a prolonged sleep en-route.
- Boeing 777-300 2010 On 11 Jan 2010, an Air France Boeing 777-300ER successfully rejected a night take off from Lagos from significantly above V1 when control column pressure at rotation was perceived as abnormal. The root and secondary causes of the incident were found to be the failure of the Captain to arm the A/T during flight deck preparation and his inappropriate response to this on the take off roll. It was considered that his performance may have being an indirect consequence of his decision to take a 40 minute period of in-seat rest during the 90 minute transit stop at Lagos.