obtain a good rest. it must not be combined with any cockpit-naps. the drug also has no side effects, improving sleep quality without causing insomnia or any detrimental effects on next-day alertness. as pilots know, they must not have any amount of a drug present in their systems at the time they begin duty. however, sleep expert matthew walker has questioned the use of such hypnotic sleep drugs as they may not induce real sleep. implementation of a personal checklist to rate fatigue before a flight can aid the decision of whether a pilot feels he is fit to fly. the samn-perelli checklist is a good measure with a scale of 1 to 7, with 1 meaning "fully alert" and 7 meaning "completely exhausted and unable to function." implementation of fatigue prediction models, such as the sleep, activity, fatigue, and task effectiveness model, optimize scheduling by being able to predict pilot fatigue at any point in time. although the mathematical model is limited by individual pilot differences it is the most accurate existing prediction because it takes into account time-zone changes, time awake, and length of previous rest. sleep and fatigue monitoring: using wrist-worn sleep monitors to track sleep accurately. traditionally, sleep is tracked through personal estimation which is inaccurate. with this technology, regulators could implement operating restrictions or cautions for pilots with less than eight hours of sleep in the previous 24 hours. in early 2007, the 201 airlift squadron of the district of columbia air national guard (ang), successfully integrated the fatigue avoidance scheduling tool fast into its daily scheduling operations. this integration required the full-time attention of two pilot schedulers, but yielded valuable risk mitigation data that could be used by planners and leaders to predict and adjust critical times of fatigue in the flight schedule. in august 2007, the air national guard aviation safety division, under the direction of lt col edward vaughan, funded a project to improve the user interface of fast, permitting daily use by pilot schedulers and integration with automated flight scheduling software. this improved, user-responsive interface, known as flyawake, was conceived and managed by captain lynn lee and developed by macrosystems. the project cited empirical data collected in combat and non-combat aviation operations, and challenged the u.s. government's established policies regarding fatigue as a factor in degrading human performance. cockpit design head-up display (huds) reduce the necessity of the pilot having to focus on the far runway and near instruments. the accommodation process is no longer needed, optimal in diminishing the onset of fatigue. blinking lights on aircraft avionics are extremely effective at capturing a pilot's attention, however, they contribute to fatigue. the maximum benefit is achieved by initially using blinking lights to capture the pilot's attention, but then displaying the message on a steadily lit background. further considerations aircraft are becoming increasingly automated, often resulting in the flight crew becoming complacent because of less direct involvement especially during the cruise phases of a long haul flight. long legs in cruise may cause pilots to become bored, thus incrementing the prevalence of risk because it will take a pilot a longer time to resume full alertness in case of emergency. airlines schedule two crews or a junior first officer as a strategy to combat boredom during the cruise phases of flight. "keep awake" routines are another countermeasure. they consist of small events in flight designed to start a false problem that has previously been inputted by a flight engineer. "keep awake" routines do not affect flight safety and their purpose reattain the pilot's full alertness and undivided attention. regulations national aviation regulators typically use the hours-of-service approach to prevent fatigue. the hours-of-service is usually measured by flight duty period which is defined as "a period which commences when a flight crew member is required to report for duty... and which finishes when the aircraft is parked with no intention of ". limits are generally set on flight duty time across daily, weekly, and monthly time periods. these limits differ based on: what type of operation is being conducted, the time of day, and whether the flight is single-pilot or multi-pilot. there are also requirements for time free from duty after consecutive days on duty. all icao member states place some kind of operational limit, but there are differences in how this is done across nations. a survey of ten nations found that a total of twelve different operational factors were regulated, with each country regulating six factors on average. however, these factors are often measured in different ways and vary significantly in limit. many experts in aviation safety find that the current regulations are inadequate in combating fatigue. they point to high prevalence rates and laboratory studies as evidence for the current systems failure. while the current system helps prevent extended sleep deprivation, it does not take into account circadian rhythm disruptions, time of day, or accumulated sleep debt. one study found that the findings show "a need to raise the level of knowledge within the industry regarding the causes and consequences of fatigue and of processes for its management". accidents and incidents related to pilot fatigue american airlines flight 1420 crash in little rock, arkansas american international airways flight 808 was a mcdonnell douglas dc-8 that crashed short of the runway at nas guantanamo bay, cuba on august 18, 1993. this is the first accident in history for which pilot fatigue was cited as the primary cause. korean airlines flight 801 was a boeing 747 en route to antonio won pat airport which crashed into a hill three miles away from the runway. the accident killed 228 out of the 254 people on board, including the flight crew. the captain failed to brief the first officer on the approach procedure and descended below the minimum safe altitude. the captain's fatigue "...degraded his performance and contributed to his failure to properly execute the approach." in 1985, aeroflot flight 7425, a tupolev tu-154, stalled and crashed in uzbekistan (then part of the soviet union) due to pilot error. severe crew fatigue was found to have contributed to the accident, which killed all 200 people aboard the aircraft. on american airlines flight 1420 fatigue was found to be a contributing factor. eleven people were killed when the mcdonnell douglas md-82 crashed in little rock, arkansas in 1999. corporate airlines flight 5966 crashed short of the runway on approach to kirksville regional airport in 2004 after its fatigued pilots had been on their sixth consecutive day of flight and on duty for 14 hours that day. the ntsb found the accident was caused by the pilots' failure to follow established safety procedures, while conducting a non-precision approach in imc and that "...their fatigue likely contributed to their degraded performance." pilots operating go! airlines flight 1002 in october 2008, a thirty-six-minute leg from honolulu to hilo, fell asleep and overshot their destination by 30 nautical miles. subsequently, they woke up and landed the airplane safely. the day the incident occurred was the third consecutive day pilots started duty at 5:40 am. colgan air flight 3407 crashed in the us in 2009, killing 50 people (all 49 on board and one person on the ground). the ntsb concluded that the flight crew were experiencing fatigue, but was unable to determine how much it degraded their performance. on january 25, 2010, ethiopian airlines flight 409 crashed into the mediterranean sea shortly after takeoff from beirut, lebanon, killing all 90 occupants on board. it is widely believed that fatigue among the crew was a contributing factor in the accident. on may 22, 2010, air india express flight 812 crashed on landing at mangalore international airport, india, killing 158 occupants on board. the captain had fallen asleep during the flight, but woke up before the landing. pilot fatigue was identified as a probable contributor to the 2010 afriqiyah airways flight 771 crash in an official report, published on 1 march 2013. the plane with 93 passengers and 11 crew members on board crashed during a go-around at tripoli airport, killing everyone but one person on board. asiana airlines flight 214 crashed at san francisco international airport while conducting a visual approach, killing three of the 307 people on board the boeing 777-200er. the ntsb determined that the flight crew had mismanaged the approach due to both boeing and asiana airlines inadequate documentation the 777's systems, asiana airline's insufficient training, and "flight crew fatigue, which likely degraded their performance". on august 14 the same year, ups airlines flight 1354 crashed on approach to birmingham–shuttlesworth international airport on august 14, 2013. both pilots, the only people on board the aircraft, were killed. the approach was unstabilized due to the flight crew's failure to monitor their altitude and their mismanagement of the flight management computer, both of which were a result of fatigue.