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Approving variations to existing state FDTL regulations

ICAO SARPs allow for States to offer some limited flexibility to the service providers complying with the prescribed limits by way of variations.  This means that in very limited circumstances and for limited periods of time, a State may allow minor variations to the prescribed limits.  Such approval would permit an operator to schedule outside of the State's flight and duty limitations, without the need for the operator to develop a full FRMS.  It is the State's responsibility to avoid the approval of variations to the FDTLs that meet operational imperatives in the absence of a risk assessment.   The approval process of an operator's risk assessment in support of their request for varying from State FDTLs is discussed in detail in the Manual for the Oversight of Fatigue Management approaches (Doc 9966).

COVID-19 conditions already present additional challenges to crew, even when they are operating within prescribed FDTLs.   Further, an operator may also be using alleviations, such us extensions to medicals, recency or training requirements, to enable operations in COVID-19 conditions, and the possibility of compounded risks with extended FDTLs should also be recognised and addressed.  Therefore, where requests to operate outside of flight and duty limits are sought, the regulator will need to approve their use based on an operator providing a risk assessment that clearly identifies and addresses ALL associated risks, including those related to fatigue.    When evaluating an operator's risk assessment and the proposed mitigations to determine whether approval will be granted, everything is proportionate to the level of safety risk posed by the variation being requested.

Given the extra challenges of operating in COVID-19 conditions, answers to the following questions are of particular relevance when a regulator is evaluating an Operator's risk assessment to support its temporary use of minor variations to national FDTLs:

  • Does the operator identify a method to assess cumulative fatigue on the flights and duties associated with the variation and the full roster pattern?
  • Where bio mathematical models are used by the operator to predict fatigue levels associated with the proposed flight and duty variation, does the operator clearly understand its limitations?  Was operational experience also used to develop the safety case for these flights?
  • Is there evidence of crew support and involvement in the development of the safety case?  For example:
      • Is there evidence that the operator has considered the impact on crew performance of factors such as confinement to room on layover, stress, etc. within the safety case?
      • Has the impact of State restrictions on entry/exit and quarantine of crew members been addressed?
      • Does accommodation and transport during layovers adequately protect crew from infection?
  • Does the operator identify contingency plans for unexpected and changing circumstances?
  • Has the operator identified how it will monitor the effectiveness of the proposed mitigations? 

Some of the types of mitigations that a regulator could expect to see in an operator's risk assessment to address these extra COVID-19 challenges are presented in the table below.


Areas for consideration

Possible mitigations

Route planning


  • The report times and flight departure times should reflect a window(s) for optimal crew alertness.

  • For multiple sector augmented flights, the sector length must allow for adequate inflight sleep.  If the sectors are too short, there might not be adequate opportunity for sleep. If the flight duty period has a long sector followed by short sectors, it can drive greater time awake.

  • Revised dispatch criteria are identified to avoid COVID-related issues that might cause undue workload or fatigue.

  • Suitable and COVID-safe airports for diversions are identified for either operational or fatigue related issues during the operation.  


  • Flight and cabin crews are appropriately augmented as required by the safety risk assessment for each rotation.

  • Pre- and post-flight rest periods enable the crew to be fully rested prior to operation and allow for a full recovery after the operation. Additional pre-trip rest to ensure fitness for duty, and post-flight rest after the specific operation to reduce cumulative fatigue on subsequent duties.

  • Rosters have been adjusted to avoid critical phases of flight during the window of circadian low (WOCL).

  • The use of the same crews for consecutive variation operations is avoided as fatigue can accumulate across a roster pattern, not just in relation to a single trip.

  • Scheduling adjustments are made to accommodate operating the varied FDTLs within the weekly / monthly limits for duty, rest and flight time.

  • On time performance is monitored and changes schedules or pairings are made where there is evidence that the plan is not working as intended.

  • Rest periods and facilities are suitable to enable the crew to be well rested and fit for their rostered duties when operating under the variation.

  • Crew feedback is sought to ensure the mitigations are and remain suitable for the operations using the variation. Where necessary changes to the mitigations or the variation is made as a result of this feedback.

Crew preparation and support


  • Processes are identified for pre-notifying crew for extended duty operations and for ensuring reserve/standby crew are aware of potential for being called in to operate the variation.

  • Fatigue awareness and management briefings, specific to the variation, are developed and provided to crew sufficiently ahead of commencement of operations.

  • Public health corridors from aircraft to airport hotel facilities are provided to limit transit time and challenges generated by the Covid-19 situation.

In-flight fatigue management


  • Methods to maximise in-flight rest time allocation for all crew in support of optimising crew alertness are identified. Emphasis should be placed on having the most rested crew members in control seats (and at crew stations / assigned exits for cabin crew) during the critical phases of flight. 

  • Where crew are expected to obtain in-flight sleep, in-flight facilities must be in line with the fatigue-related science and adequate to facilitate sleep.  Provision of appropriate facilities for on-board sleep and protected cabin spaces (away from passengers, cargo) to support rest.

  • Arrangements have been made to ensure nutritional requirements are suitable and are readily available for the duration of the duty.

  • Crew are provided with the flexibility to allocate rest and operational duties on the day to manage actual sleep / alertness needs of the crew.

  • There is a method to monitor the use of controlled rest and ensure it is used in accordance with Fatigue Management Implementation Guide for Airline Operators (see further guidance below).


The regulator's responsibilities with regards to variations to extend FTDLs should not stop at approving an operator's safety risk assessment.  Rather, the regulator should monitor the effectiveness of the controls and mitigations put in place by an operator to manage the associated risks.  This will assist in evaluating any future applications for minor extensions to FTDLs for limited periods of time.

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