United Airlines flight declared an emergency outbound Phoenix-Goodyear Airport.
The flight departed Phoenix for a ferry flight. It climbed to 8,000 ft before the crew declared an emergency (squawk 7700).
The aircraft immediately turned around and requested a priority landing.
The 9-year-old Boeing 737-900ER (registration N62892) was resuming flight operations after maintenance.
The previous flight of this plane was on Aug 13, from Houston.