You need to link a few rules together to get the full effect.
1: Flyers can elect to use the Skyfire special rule (
pg 81)
2: Skyfire allows units to shoot at Flyers, Flying Monstrous creatures and Skimmers with their own
BS. Unless it has Interceptor it can only fire "snap shots" at other targets. (
Pg 42)
3:Blast, ordnance and template weapons may not fire as "Snap Shots" (
pg 33,
pg 52)
So if you wanted to shoot at a flyer with one weapon system (or more up to 4) and use your
BS and then Power of the Machine Spirit a different unit, the weapon firing the different unit would not be able to have the "Ordnance, Blast/Large Blast, or template special rules/weapons type as you would be "Snap shoting" at Non Flyer, Monstrous Flyers, Skimmer targets.
So if you want to blast another Flying unit or a skimmer and DONT want to need 6's to hit switch to "Skyfire" and blast away (minus all the snap fire restrictions)
As far as dropping down to a Skimmer: As long as they are Zooming A flyer only receives a cover save if it "EVADES" . Evade grants it the "Jink" Special rule (
pg 81) thus giving it a 5+ cover save as long as it moves (
pg. 38). which it MUST because it is a Flyer. As a penalty for Evading the Flyer must now fire all weapons as "Snap Shots" (
pg 81) (remmeber the restrictions for snap shooting!).
However, if the Flyer drops down into "Hover Mode" it is now a "FAST SKIMMER" (
pg 81)
A fast Skimmer may only fire 2 weapons if it has moved at Cruising speed (
pg 83) and snap shot the rest. A skimmer may also "Jink" with no penalty of reducing all shots to Snap fire and may get a 4+ save if it moves Flat out. Also if you are a transport, the unit inside may not disembark from a zooming flyer so you MAY (if you are a transport) have to slow down to let folks out.
I THINK that covers just about everything you brought up? I hope its not too confusing for ya