[math]\displaystyle{ \text{Exp}_\text{plane} }[/math] the experience of the plane.
Unlike most other formulas in the game, it is not rounded down.
Recons and land-based planes only have this bonus while on LBAS.
Rank Effects
Fighter Power Bonus
The biggest bonus from plane proficiency is giving a fighter power bonus to help during the Stage 1. The innate bonus is added onto the fighter power bonus of the relevant plane to get the full fighter power bonus.
Carriers get a bonus critical modifier when equipped with high-proficiency planes. This modifier is multiplicative with the normal critical modifier. See here for more details.
Carrier-based planes and seaplanes can be ranked anywhere. The most resource-efficient way is to send them on sorties to surface nodes with little to no air power. It is possible to rank them through LBAS but it gets expensive. The following are recommended spots:
Land-based planes can only be ranked through LBAS. This makes ranking them quite expensive. Outside of events, only 7-4, 6-4, and 6-5 have LBAS available to use for now.
Of these:
7-4 is the best place as it has multiple submarine nodes that are easy to reach, and are on the main resources farming route. This allows any land-based plane to be ranked while doing regular "risk-free" resource farming.
6-5 is also a good place, as it allows the use of two land bases and has a Range 1 submarine node at node B, that can be reached using 1CL and a mix of DD & DE.
Ranks can decrease by 1-2 if a large number of planes are shot down.
Ranks will be reset if the entire squadron is shot down.
Even elite squadrons with default ranks can lose all their ranks.
There is a visual bug where elite squadrons may retain default ranks visually, sortieing them again will update it to their actual value.
Rank loss is calculated before rank gain, therefore it is possible for a squadron that was wiped to retain 1-2 ranks if it did well.
Rank is only calculated once the fleet returns to port.
It is possible to save ranks by quitting the sortie before the results screen is shown. This can be useful during events to save preparation time for boss kills.
Planes must participate in aerial combat or detection to gain/lose ranks.
Planes in 0 slots will not gain or lose ranks.
If planes are not launched due to failing Detection, they will not gain or lose ranks.
In Combined Fleets, when facing a single fleet, no plane in the escort fleet will not gain or lose ranks.
Leveling Speed
Planes gain a certain number of internal proficiency points with some random variance every time they participate in Aerial Combat or Detection. The amount gained depends on the exp-rate group of the plane.
Detection: Seaplanes, SpLB Recons, Large Flying Boats
LBAS Attack, LBAS Defense, Jet Assault, and LBAS Jet Assault also count as Aerial Combat.
Each LBAS Attack wave counts as one round of Aerial Combat, so planes attacking the same node twice gain experience twice. There is no Detection for LBAS, so recons (including Land-based Recons) do not gain experience.
Because Seaplane Bombers participate in both Aerial Combat and Detection, they effectively level twice as fast as other planes of their group in most cases.
Jets receive experience from both Jet Assault and the following Aerial Combat, effectively leveling twice as fast as other planes of their group in most cases. However, Jet Assault does not occur against all-submarine fleets, so they gain experience only once in this case.
Leveling speed is measured in the estimated number of battles it will take to get a plane from no rank to ❱❱.