When I was younger (early '90) I played a coin-up helicopter game regularly. It's 2D and you look down at the landscape and chopper and the landscape scrolls down so you fly "up" on the monitor. There were four kinds of weapons you could use, red (the default), blue (often most powerful and most used), green or yellow.

You could upgrade them so they got more powerful,and if you switched colors of your weapons by a power-up that appeared at times, you kept the level of upgrades so if you went from blue to red, red was as upgraded as it would have been if you'd used it as long as the blue before you switched.

I can't find it (I suck at using Google), so I hoped anyone here knew of it \o/