Causes for Replanning
It is usually the case that some constraint or factor changes from when the flight plan was originally developed that causes the pilot or flight crew to replan. There are many such changes common to all operator classes:
.
late departure

.
weather

.
traffic

.
change in destination or alternate status

.
winds

.
aircraft (different performance than predicted, or mechanical problem)

.
medical problem

Replanning tasks
The actual tasks involved in replanning are a subset of those for planning. Major differences are that (1) real time data (e.g., airplane status, performance, fuel burn, weather, etc.) are available rather than predictions and models of those data used in flight planning and (2) from the flight crew’s perspective, there are fewer data and resources to call upon, and pilot workload becomes an issue because replanning must compete with other flight deck tasks and activities that need to be performed.

Inefficiencies
Overall inefficiencies will be summarized at the end of this section, as a lead-in to solutions.

2.2.2.2 Replanning Unique to each Operator Class
General Aviation

Causes for Replanning
Reasons for replanning are not that much different than for other airspace user classes, except pax discomfort (comparable to medical emergency, but much less severe/more common) and “a change of mind” are added.

Replanning / Information Processing Loop
Fundamental Operation for IFR Flights

Planning
Dispatch Dispatch Dispatch Dispatch Dispatch  ATC ATC ATC ATC ATC Considerations of Separation AssuranceTraffic Flow ManagemenOverall System Capact,,  Flight Crew Flight Crew Flight Crew Flight Crew Flight Crew ity Consideration of Individual Flight Safety and the Need for Changes to the Plan and 

Modifying
Figure 7. Information processing loop involved with replanning (General Aviation)
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Replanning in a single-pilot IFR environment is the most basic form of replanning in Instrument Flight Conditions, and for the pilot is very tough in terms of workload. It is easiest to let ATC specify the route modification (ATC will already have a proposal in mind if they are requesting the route modification). Regardless of whether or not the flight plan modification has been supplied by ATC, the pilot is still responsible for determining if the proposed reroute is safe as well as performing the time and fuel burn calculations, see Figure 7 above.

Inefficiencies
The biggest inefficiency facing low-end general aviation pilots is the inability to obtain real-time information for weather that will be encountered along the route of flight. If the pilot cannot see it, then it doesn’t exist. ATC, of course, will advise of severe weather or icing conditions along the route of flight, but not necessarily in a timely manner that will allow the pilot to make decisions when it is optimal or most convenient.
　
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