In a bowl, combine chicken, calamansi juice, soy sauce, garlic, 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper. Marinate in the refrigerator for about 2 hours to a maximum 4 hours.
Drain chicken from marinade and pat dry.
In a shallow dish, combine flour, corn starch, baking powder, and the remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. Whisk well.
Dredge chicken in flour mixture to fully coat.
In a wide, thick-bottomed pan over medium heat, heat about 2 inches deep of oil to 350 F.
Add chicken in batches and cook, turning on sides, until golden brown, crisp, and cooked through.
Remove from pan and drain on a wire rack. Serve hot.