Bright fast moving paralel lights observed

I observed two silver lights flying in formation trailing smaller gold 'sparks'. They flew in a 'W' pattern very fast for a few minutes then changed to a looping flight pattern. At the bottom of some of the 'W' troughs red 'sparks' were emitted. At first I thought they were fireworks however their flight path made this impossible as both lights were in perfect formation on both the up and down strokes of the event.