DAVE'S OSR AIR COMBAT

Here is a set of air rules I threw together and tested a while back for my Pulp and WWII game. Seems to work pretty well. As always I'm no expert on actual vehicle stats but after checking out a few resources and other systems I've statted several basic planes. I will likely add more and tweak a few things in the future. 

In a side tangent many Fighter planes were BIG. Look at them compared side to side with  tanks. Tanks had the advantage in Heavy Armor of course. 

For use with my Pilot class or whatever you have of your own creations.

Spot Foe
Normal surprise checks with bonus/penalty.

Initiative
Normal + Dex bonus + Miscellaneous (Pilot class bonus, etc.)
+4 if a Maneuver roll was won the previous round.

Maneuvers
Pilot vs Pilot roll (Dex checks)
Success and highest roll wins. Winner gets a +4 to hit and +4 to Initiative bonus the next round.
Tie equals no bonus.

AC
Vehicle AC + Dex bonus + Faster Plane ( +1/25 mph faster)
Flying defensively (no attack attempt) adds +4 

Hit Modifiers
-4 non-Pilot class
+4 maneuver bonus if gained
Speed bonus to AC
+ linked weapon bonus if applicable

Targeting the Engine or Pilot
-6 to attack the engine or cockpit/crew (due to position and better armor at these locations.)
See Engine/Critical System damage below.

Damage to Aircraft
1. IF aircraft is at half Hp's or less, -4 to Piloting rolls.
2. When at half Hp's or less every damaging hit is a critical hit.
3. A natural 20 is a critical hit.
Roll 1d6. On a 1-4  an engine/critical system hit. On a 5-6  1d3 crew are hit.

Aircraft at 0 Hp or less: roll a 1d6. On a 1 it explodes for 6d6 damage to crew. On a 2 it bursts into flame causing 1d6 per round to crew. On a 3-6 it falls from the sky spiraling down in a trail of smoke and flame and impacting in 1d6+2 rounds. Impact damage is 20d6.

Engine/Critical System
x2 damage. 
The damage done  is the percentage chance on a 1d100  that the plane's performance is impacted. IF this roll is successful drop speed by 1/4 of full speed. 

Each additional hit and rolled percent roll drops the speed by another 1/4 of full speed until the plane reaches 0 speed and falls from the sky.

Stalling
IF a natural 1-5 percent is rolled on any of the engine/critical system percentile rolls the engine stalls and the plane begins to fall from the sky.
The Pilot must make an Int check (+ Pilot bonus) - total engine damage to restart it.
The Pilot has 1d4 +2 rounds to get restart or get out. 

Linked Weapons
Multiple machineguns liked to fire at the same time and same target. Each extra weapon gives a bonus to hit or damage as seen on the chart below. If more than one caliber of weapon is linked choose the highest damage for the base damage.

Airplane Bursts
Maximum three attacks per round, 10 bullets per weapon fired per burst ( unlike five per attack in my regular rules air combat requires more to hit). The pilot can choose to use only one or two bursts to conserve ammo. 

AC Bonus and Air Speed
In a plane vs plane combat the speed AC bonus of a slower flying plane subtracted from the bonus of a faster flying plane. The remainder is added as an AC bonus to the faster plane. (The faster plane is better but doesn't completely overwhelm it as it does a ground target.) A P-51 going all-out vs a Messerschmidt 110 going all- out has a +1 AC bonus (7 -6 = 1.)

When speed is reduced either by choice or damage use the lower speeds bonus. 

 Strafing Run
A soldier on the ground is firing at a P-51 mustang. The AC of the plane receives a +7  bonus as it roars by at over 400 mph bumping its AC up to  20 + the Pilot's Dex bonus.

Unfortunately for the pilot it is harder to hit man-sized targets while you're roaring through at 400+ mph. Using all three Machine Gun attacks per each set of available linked weapons allows the Pilot attack an area 30' wide by a number of feet equal to current airspeed. Everyone in this area is rolled against as possible targets but get a bonus to AC equal to the plane's current airspeed bonus plus a cover bonus if they are under partial or soft cover and the War Master rules they can be hit.

Our soldier above who fired at the P-51 gets a +7 to his AC bonus against the plane and since he is standing behind a brick barricade the War Master gives him a +4 cover bonus for a total of +11 to his AC vs the plane.