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Tuesday, December 30, 2014

Probing ‘unusual route request’ by missing AirAsia plane

Large scale re-routing for weather will occur when an organized line of convection impacts a major route.
airasia mapKUALA LUMPUR: Indonesian Transport Ministry official, Hadi Mustofa, said missing AirAsia Indonesia QZ8501 asked for an unusual route before it lost contact.
What are the reasons which can cause a commercial flight to change its path mid-route?
How is it planned and executed?
If the pilot is the final authority on this, who else is informed?
Aviation Beta (AB) has some answers.
Aviation Beta runs Aviation Stack Exchange, a question and answer site for aircraft pilots, mechanics, and enthusiasts.
A flight plan is just that, a plan, according to AB. A flight can deviate from its cleared route for many reasons, the most common of which are:
  • Weather
  • Traffic
  • Shortcuts
Weather reroutes are often initiated by the crew.
Large scale re-routing for weather will occur when an organized line of convection impacts a major route. Even a short deviation for weather may result in an amended route if the Air Traffic Control (ATC) has an alternate clearance he can put you (the pilot) on i.e. it works for you (being on a clearance and on-route is slightly less work for a controller than being on a carte-blanche deviation).
Traffic conflicts are usually short term vectors, but if you have an aircraft slowly overtaking you, you may be moved to a parallel route or have you altitude changed.
These, like the weather example above, would result in amended clearances.
Shortcuts are often requested to cut corners or try to make up some time lost in a long taxi on the ground. These are usually crew initiated, but sometimes ATC will solicit them. Regardless of what route is submitted in a flight plan, ATC will generally clear you via a preferred routing.
These routes aren’t always the shortest distance between a departure and arrival and this is where shortcuts can be requested. Usually this just means skipping a fix or getting direct routing to a later fix in your clearance. The availability of shortcuts is a function of traffic, time of day, agreements between ATC sectors, what region you are in and what altitude you are at.
When you are on international flights, another issue you may run into is political and could result in some or all aircraft being routed to avoid certain airspace.
Lastly, your dispatcher may re-route you and ATC will clear you along a new route.

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