Can/do commercial flights change their flight path during flight? Looking at the paths of the same flight on two different days, I noticed they flew very different paths.

Short Path:1

YAY N184B TOPPS ENE PARCH1




Long Path:1

NIBAX G462 TUMAK UL602 ORSOL UL602 DAVUS UL602 TASMI UL602 ITBIT UM860 KABAN UT334
INB UL852 UDROS L621 REVDA UP193 CND UP193 KARIL UL624 LABUK UY444 ELMEK UL726 OKG
UL984 NOSPA TOLVU UN857 GIMER UT300 EVX UT176 LGL UN491 KOKOS UN585 REGHI UN480 
ETIKI NATD DOVEY LACKS BERGH L454 OWENZ CAMRN CAMRN4




I asked a similar question in the past. This is what I want to know:


What are the reasons which can cause a commercial flight to change its path mid-route?
How it is planed and executed?
I am sure the captain is the final authority on this, but who else is informed?




1Route Source: FlightAware.

P.S.: I could not understand the routes at all.
A flight plan is just that, a plan.  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.


  Center, N12345 request 15 right for weather
  N12345 15 right approved for 100 nm, report direct XYZ.


Or they can be initiated by ATC


  N12345, Atlanta, your arrival into EWR is in perpetual holding, I can re-route you over PA or NY or do you need to divert? state intentions.


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 controller has an alternate clearance he can put you on that 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.



In all cases, whether deviation is pilot or controller initiated, both parties are in sync with what the airplane is doing, which will either be a vector or a new clearance.  Your dispatcher will be notified of this change automatically via their dispatch software (which is likely fed data from both ACARS and the FAA).