New flight rostering rules have been imposed on all Singapore carriers, in line with a global push to ensure accidents do not happen because of crew fatigue.
The Civil Aviation Authority of Singapore (CAAS) introduced the changes in June, following a major review which included discussions with Singapore Airlines (SIA) and other local carriers, The Straits Times has discovered.
The move comes at a time when Asia is experiencing a growing number of flights, which experts believe could put a strain on manpower resources. Among the revisions is one which demands that pilots do not handle more than two night flights a week.
When determining rest periods in between flights, airlines must also consider whether the flights before and after are operated in the day or night.
The rule takes into account the fact that the body does not react and adjust to situations in the same way throughout the day.
Airlines are now also required to monitor their crew closely to ensure that they are performing at the highest level of alertness during duty hours, and submit regular reports to the CAAS.
Before the changes, airlines' typical approach to managing crew fatigue had been to set limits on maximum daily, monthly and yearly flight and duty hours, and mandate minimum breaks within and between duty periods.
The general rule of thumb was a minimum 10 hours' rest after being on duty for under 10 hours. For longer flights, the rest period had to be at least as long as the duty time.
Setting such arbitrary limits that are not founded on research and science is an ineffective way to manage crew, according to the United Nations' International Civil Aviation Organisation and the International Air Transport Association which are leading the global move for airlines to review their policies.
A CAAS spokesman said this is an important area of focus "as fatigue is recognised as a major human factor element that affects crew members' (flight and cabin crew) ability to do their job".
So far this has not been the main cause in any incidents at Changi Airport but it has been a "contributory factor in some", though the spokesman would not elaborate further.
SIA spokesman Nicholas Ionides said the airline supports the changes, calling them a step forward in ongoing initiatives to enhance operations and ensure an "appropriate level of alertness for crew". He added that rosters have already been adjusted to reflect the changes.
The Tokyo-Los Angeles flight, for example, used to be operated by one captain and two first officers, with all three crew required to be in the cockpit throughout the flight. Now, it is two captains and a first officer, with two of them on the flight deck at any one point while the third rests.
The changes do not impact the overall number of pilots needed, Mr Ionides said.
Captain William Teng, chairman of the SIA branch of the Air Line Pilots Association (Alpa-S), said: "The changes are timely, given that we now operate more longer sectors with planes that can fly farther than when the rules were first drawn up several decades ago."