New York (AFP) – After months of back-and-forth, Spirit Airlines announced Wednesday that it was breaking off a merger with Frontier Group, opening the door to a possible takeover by JetBlue. The Spirit-Frontier deal, announced in February, was thrown into doubt in early April when JetBlue Airways unveiled its own takeover bid and subsequently launched a hostile takeover bid as smaller carriers try to gain scale to take on the biggest US airlines. Spirit officials continued to back the Frontier deal, in part due to concerns that the JetBlue offer might face difficulty with antitrust authoritie…