Major alliance carriers servicing Philadelphia to Sydney routes in April typically include combinations of American Airlines, United Airlines, Delta Air Lines (partnering with international carriers), and Qantas through code-share partners. Consider alliance benefits like lounge access, baggage allowances, and points accrual when choosing carriers. For convenience and frequent-flyer perks, compare layover hubs: American (via LAX/DFW), United (via SFO/ORD), and Delta (via LAX/MSP/ATL) — each offers different schedules and equipment. Use secondary keywords like 'best airline PHLA to SYD' and LSI phrases such as 'PHLA to SYD carrier review' to refine your search.