A spate of sleeping air traffic controller incidents in the USA, which has seen one Federal Aviation Administration executive resign, has triggered scrutiny of scheduling practices, but controller fatigue has long been under the microscope of industry and government.
The well-documented events of sleeping or otherwise unreachable controllers span from the smallest of airports in Lubbock, Texas, and Reno-Tahoe International airport to Miami and Seattle.
A dozing controller on the night shift at Washington National spurred a heightened study by the FAA of controller habits that revealed the subsequent sleeping events.
Although the events have only recently come to the forefront of the national news media, controller fatigue and scheduling have been under study for decades.
A comprehensive study of controller fatigue published by Mitre in September 2010 details numerous studies of shift work effects in general, and specifically on controllers.
One conclusion Mitre cites, from a study conducted as far back as 1995, summarised the response of 921 controllers asked to estimate the effects of overtime and shift work on performance.
An obvious finding showed significant degradation of performance in 12h versus 8h shifts. The midnight shift for an 8h duration, the study says, had as much degradation as a 12h shift.
The dozing controllers in both Miami and Washington National were working overnight shifts.
Shaken into action by the mounting disclosures of dozing controllers, the FAA and US Department of Transportation have swiftly issued new scheduling guidelines, while the head of FAA's Air Traffic Organisation, Hank Krakowski, resigned.
US controllers now must have a minimum of 9h off in between shifts and cannot swap shifts unless that minimum has been achieved. Controllers are also prohibited from switching to an unscheduled midnight shift following a day off. It is not clear how compliance with the new procedures is being enforced.
The experience level of the controllers involved in the recent incidents is unknown, but the FAA hired a raft of controllers during the latter half of the last decade, including 5,000 from 2005 to 2009 to replace retiring controllers, according to National Air Traffic Controllers Association head Paul Rinaldi in testimony before the US Congress in February.
In April 2010, the inspector general of the US DoT raised a concern that FAA's screening does not sufficiently evaluate aptitude in screening tests of newly hired trainees.
Rinaldi said NATCA was working with FAA to improve the placement process for new hire controllers.