The northmost and southmost pig can be tricky if you didn't detonate the northmost TNT.
For level 1-27 aim the first Blue Bird barely above the smaller planet, splitting late to cause the TNT-tower to topple rightward. The two explosions should clear all pigs from the top half of the planet. Use another Blue Bird to pop the final pig.
This level features a new concept. The flashing red lights atop the two TNT crates are actually connected. Detonating one will also detonate the other one.
This level's chain reaction for TNT is the template for most levels in Cosmic Crystals. (Two TNT are connected)