WASHINGTON, Sept 27 (Reuters) - New orders for key U.S.-made capital goods increased solidly in August, keeping business spending on equipment on track for another quarter of strong growth. The Commerce Department said on Monday orders for non-defense capital goods excluding aircraft, a closely watched proxy for business spending plans, rose 0.5% last month. These so-called core capital goods orders gained 0.3% in July. Economists polled by Reuters had forecast core capital goods orders increasing 0.4%. (Reporting by Lucia Mutikani, Editing by Raissa Kasolowsky)