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AOC informs the crew of developing weather situation
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Overheard from other aircraft on Center frequency (the “partyline”)
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Weather radar, if the aircraft is close enough to the weather cells
How does replanning occur?
It is usually the case that the AOC will anticipate the need for rerouting before the aircraft is in the vicinity of the weather. This means the AOC is developing a replanning solution prior to ATC considering a reroute for the aircraft in question. The dispatcher at the AOC will, usually, develop a new route that skirts the inclement weather in order to minimize the added flight time, which they equate with schedule disruption.
The dispatcher will make some preliminary estimates of fuel required for the new route to determine if the aircraft has sufficient fuel onboard to make fly the new route. If there is not enough fuel to fly the new route with the original alternate (and the required reserves), the dispatcher may examine the option of declaring a new alternate. This will require a quick check of the new alternate’s weather situation. When the new route is deemed to be “reasonable” from the dispatcher’s perspective, they will contact the crew using a direct VHF link, such as SELective CALling (SELCAL), inform the flight crew of the developing weather situation and suggest the reroute. The flight crew will then perform their own calculations of fuel required for the new route. If the flight crew deems the replan a reasonable strategy, they will contact ATC and request an amended flight plan.
Conclusions and Commentary
While the AOC is working to replan the aircraft’s route around weather, ATC may be making plans for rerouting entire jetways around severe weather situations. ATC’s enact Severe Weather Avoidance Plans (SWAP) that move entire jetways to the North/South or East/West around regions of severe weather. The effect of a SWAP is similar to throwing a boulder into a stream. The water flowing down the middle of the stream is moved to the edge of the rock, the water flowing near the edge of the stream flows an even further, more extreme route along the edge of the stream. This metaphor is appropriate for jetways in a SWAP situation. The jetways that were headed directly for the severe weather are moved so they barely skirt the weather (similar to the AOC strategy for rerouting). The jetways that were barely skirting the weather are moved further away from the weather in order to “make room” for the traffic that has been moved to barely skirt the weather.
The upshot of this is that the anticipatory move on the part of the AOC can actually work against them. If they re-file the flight plan to barely skirt the weather, prior to the SWAP being enacted, then the aircraft will be pushed further away from the weather when the SWAP is put into place. Unfortunately the ability to append intent to a flight plan is not currently supported, otherwise the airline (AOC and flight crew) engaging in this anticipatory behavior could “save” their place in line by declaring they spotted the developing weather situation first - and “First Come, First Served” is an operating philosophy of the US Air Traffic Control system. The philosophy is simply not supported at the current time, because the intent of flight plan changes is information that is not entertained in the current system. The air traffic service provider only has tools to deal with WHAT, not WHY.
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