Air traffic control (ATC) is a service provided by ground-based controllers who direct aircraft on the ground and through controlled airspace, and can provide advisory services to aircraft in non-controlled airspace. The primary purpose of ATC worldwide is to prevent collisions, organize and expedite the flow of traffic, and provide information and other support for pilots. In some countries, ATC plays a security or defensive role, or is operated by the military.
To prevent collisions, ATC enforces traffic separation rules, which ensure each aircraft maintains a minimum amount of empty space around it at all times. Many aircraft also have collision avoidance systems, which provide additional safety by warning pilots when other aircraft get too close.
In many countries, ATC provides services to all private, military, and commercial aircraft operating within its airspace. Depending on the type of flight and the class of airspace, ATC may issue instructions that pilots are required to obey, or advisories (known as flight information in some countries) that pilots may, at their discretion, disregard. Generally the pilot in command is the final authority for the safe operation of the aircraft and may, in an emergency, deviate from ATC instructions to the extent required to maintain safe operation of their aircraft.
Air traffic flow management (usually seen abbreviated as ATFM) is the regulation of air traffic in order to avoid exceeding airport or air traffic control capacity in handling traffic, and to ensure that available capacity is used efficiently.
Reason for use
Because only one aircraft can land or depart from a runway at the same time, and because aircraft must be separated by a certain time to avoid collisions, every airport has a finite capacity; it can safely handle only so many aircraft per hour. This capacity depends on many factors, such as the number of runways available, layout of taxi tracks, availability of air traffic control, and current or anticipated weather. Especially the weather can cause large variations in capacity because strong winds may limit the number of runways available, and poor visibility may necessitate increases in separation between aircraft. Air traffic control can also be limiting, there are only so many aircraft an air traffic control unit can safely handle. Staff shortages, radar maintenance or equipment faults can lower the capacity of a unit. This can affect both airport air traffic control as well as en-route air traffic control centers.
When an air traffic control unit that will control a flight reaches capacity, arriving aircraft are directed towards holding patterns where they circle until it is their turn to land. Because aircraft flying in circles is an inefficient and costly way of delaying aircraft, it is preferable to keep them on the ground at their place of departure, called a ground delay program. This way, the delay can be waited out on the ground with engines off, saving considerable amounts of fuel. Obviously, careful calculation of en route time for each flight (and the effect of current wind upon it) and traffic flow as a whole is needed, which is highly dependent on computers.
Operation in Europe
All IFRflight plans are tracked by a CFMU (central flow management unit). Each airport and air traffic control sector has a published maximum capacity. When capacity is exceeded, measures are taken to reduce the traffic. This is termed regulation. The aim is to use capacity effectively, keeping the average delay as low as possible, while ensuring capacity is not exceeded.
As a (highly simplified) example, if two flights are scheduled to arrive at an airport at exactly the same time, and the airport can handle one aircraft every 5 minutes, the aircraft may be assigned delays to ensure that the second aircraft arrives 5 minutes after the first. Similarly, the first aircraft will be required to depart on schedule and not allowed to depart late. This way, the second aircraft will not need to wait in the air.
In practice, the process is much more complex and highly computerized. One aircraft may be subject to several regulations at the same time. For example, a flight from Amsterdam to Paris may be regulated both by limited capacity at Paris as well as by limited capacity in Belgian airspace.
In some cases, it may be possible to avoid delay by taking a different route. For instance, if Belgian airspace was the only regulation for the flight in the previous example, changing the route to avoid Belgium and going via Germany instead might allow a flight to depart without delay, although the route might be a bit longer. In many cases, airlines authorize the CFMU to make changes in a flight’s route to avoid delay.
Certain flights are exempted from regulation. For instance time-critical flights carrying human organs for organ transplantation. If such flights are scheduled, regular traffic will be delayed instead.
If an airport is completely closed unexpectedly (for instance, because the only runway is blocked), a zero rate may be set for a certain time period (e.g. until the runway is expected to be reopened), which will cause all inbound flights to be issued a delay that will cause them to arrive after the reopening time. Flights already en route would either enter the holding or divert to an alternate airport.
Slot and calculated take-off time
The CFMU issues delays by means of a CTOT (calculated take-off time), also known as slot time or simply slot. The slot is actually a period of time within which take-off has to take place; in Europe (Eurocontrol) it is defined between −5 and + 10 minutes from CTOT. The aircraft is required to be at the runway, ready for departure at its CTOT, the leeway is for air traffic control to integrate the aircraft into the other traffic.
If a slot is missed (or if it is already certain in advance that it will be missed), CFMU assigns a new one. A different aircraft which has a slot because of the same regulation may be issued an improvement on its slot to make use of the newly available capacity. The slot and any revisions are communicated to the aircraft operator as well as the air traffic control unit at the departure airport via a special network called AFTN.
It is perhaps surprising to some, that, for example, a delay in Istanbul may be incurred because inclement weather is expected at the destination in London, 3 hours later, even though the weather in Istanbul is good and there is no congestion. Blaming a delay on the departure airport or the airline is often not correct. Capacity limitations of the airspace between the two aerodromes, in the en-route segment, can also be a reason for delays.
So I will make kwento na ha? Ge. Kasi late na ako nagising, as a daily routine nagbubukas ako ng tumblr, napapasarap ayun nalelate. Dapat di talaga ako malelate sa Trigo Class ko kaso wala na e. Sinabayan pa ng traffic ayun 1 hour late na sa class so nagCUT na ako. After nun nag iChill ako at nagtext si Renz na papunta na sila at ako naman ay pumunta na sa LRT statino Central to be exact. Then nakita ko na sila nag LRt at nagshuttle nakarating sa MOA at pagkapasok namin ay nagbihis si Rence at nakita ko sila Carlo,Nica at Ate Ara tapos ayun nagpunta na sa Cinema One. Teng ene demeng bleggers! hahaha. Dami kong di kilala pero may nakakakilala sakin at nagpapicture *tuwang tuwa ako* then ayun nakipagharutan sa mga kakilala kong bloggers.
Eto na yung kilig moment e. Niyakap ako ni Mika!! Si Mikanggutom mga frends!! KILIGNESS OVERLOAD! Di ako nakapagsalita (Oxygen Please). Kinausap nya ako di ako makasagot kasi nga ano. OO Crush ko sya nung PJMU pa hahaha. Kala ko di sya pupunta pero hayyyyy. Tapos ayun start na ng movie at ako naman sumama sa mga hindi nanuod nanlibre si SHUPAW ng pagkain YUM YUM YUM! At ayun nabusog ako. Salamat.
NagPadis kami. Nagyosi ako hayyys, tas uminom ng ¼ na baso ng san mig light. Shet lashing na ako hahaha. De jk. Tapos ayun na nga nagkaroon ng HAPPY MOMENTS ang Kuya nyo then tambay onti tas umuwi na.
Wala talaga akong maisip na isama kundi ang ka movie bonding ko palagi si mama. yes. hanggang hunger games po eh nasasama ko si mama para manuod.. haha! :) we’re more of a movie fan kaya siguro, isang tanong ko lang kay mama eh umoo na kagad sya kahit wala pang final date noon. haha! (dapat nga siya ang kasama ko sa percy kaso she is sick during that time). At dahil kay mama, naging “behave” ako towards meeting others. napakaformal with halong awkwardness ang pag-introduce ko sa mga kakilala ko kay mama. though she is already oriented with tumblr/blogging/etc. hehe.. pasensya na sa iba na first time ko lang nakita doon. mahiyain at awkward lang. >.<
anyway.. let’s go to the actual meet-up itself. Pre-show. ramdam mo naman na meet-up talaga, may pictures dito, pictures dyan. medyo nag-solo kami ni mama at kaming dalawa lang ang nagpicture.. haha! though i think everyone is already excited to see the movie. :)
Show time. lights-off! everyone is silent! i really appreciate yung mga tumblrista na nakasama sa meet-up. behaved audience sila. and very responsive. ganun yung mga gusto kong kasama sa loob ng movie house. nakakadala. hehe. and i think there were 2 applause for the film first eh dun sa sinira ni ….. yung … kaya natapos yung … (hindi ako spoiler.. haha) and syempre, yung end ng movie, kung saan ipinakita ang transition ng CATCHING FIRE to MOCKINGJAY.. gawd.. there were moments na naiiyak na talaga ako sa mga scenes. O.O from the rebellion, to previously fallen tributes, to passionate kissing scenes (oo, nakakaiyak yun para sakin). hehe. and yung pagka-intense ng movie, nung umikot nga yung ano eh … (no spoiler) eh naramdaman ko na umikot din ako kasama nila.. haha.. or ako lang talaga nakaramdam nun? hehe.. marami ring nakakakilabot scenes, isa na dun yung concluding part ng movie, ang transition ng MOCKING JAY. pero sabi nga ni mama, “Tignan mo tayong lahat, nung natapos ang movie, NGA-NGA”. literal naman talaga na nakaNGA-NGA.. yun na yun? ang bigat ng ending ng 2nd installment. wishing for the BOOK 3 na..!!!! please?! hehe..
Post Show. kabaligtaran ng “ang bigat ng ending” thing, pagkalabas na pagkalabas ng mga tumblrista, ramdam mo “spirit” ng tumblr. ang saya ng lahat. :) indicating na successful ang meet-up. kaya congrats kay pat, beben, miss maica, kay jai and sa lahat ng organizers.. wag magsasawang mag-organize ah.. hee. :p
and i enjoyed my time sa meet-up, di nga lang with other tumblristas (cos walang chance. haha) but i enjoyed the thought na we all love the movie that we are watching. :) plus, WE LOVE THE BUTTON PINS!!!! <3 hmm.. can i consider my mom as the oldest tumblr meet-up attendee? hehe. :p
until next time! SEE YOU ALL IN DISTRICT 13.. (i sound so geekish na. :p)
Gaya nga ng sabi ko sa previous posts, di kami nakanood ng movie (except kay Jastin). 2nd Catching fire nya yan pero dahil first time nya dumalo sa isang meetup (diba 2nd na? first yung sa UPLBMU? haha), kelangan ko syang suportahan. Tawang tawa lang ako kasi para siyang bata non, hinayaan ko na lang dahil first time nya raw. HAHAHA.
Ito na rin ang pagkakataon para mag-catch up with masters, at sa wakas, may complete picture na ulit kami. hehehehe
Glad to see old faces. nakakatuwa rin na nginitian pa rin ako ng mga tumblrista kahit di ako ka-close. Pasensya na, mahiyain talaga ako at yung mga kakilala ko lang ang nilapitan ko. opposites talaga kami ni J. hehe.
Pero sobrang nabwiset lang ako dun sa mga maiingay at todo kung makapagkwentuhan sa loob ng sinehan HABANG NANONOOD. Pucha lang? Bawat moment ng movie, kung makareact, utas na utas lang? Tapos yung iba naman chika to the max talaga na ang ingay ingay tapos grupo grupo pa ang mga putragis. Haynako. Okay sana kung bulungan lang diba pero yung iba, HINDI TALAGA. Haynako. Hindi ko tuloy masyadong na-enjoy yung feels ng movie kahit napakarami naman talagang feels na dumapo sa aking buong pagkatao. Mga nabawasan lang ng 10-15% feels.
Meron pa. Sa mga eksena naman. Yung kay Mags. Huhu. Bwiset na bwiset ako dun sa mga tumatawa sa kanya. Huhu. Pero sa akin lang naman to. Wala akong pakialam kung ano sasabihin niyo pero may soft spot talaga sa puso ko si Mags (old people in general) kaya affected ako masyado. Huhu. Ah basta. Ingayan lang. BWISET.