Boeing / MD Helicopters
MD 900 Explorer
Manufactured 1992–2019
Introduction date 1994
First flight 18 December 1992

The MD Helicopters MD Explorer is a light twin-engined utility helicopter designed and initially produced by the American rotorcraft specialist McDonnell Douglas Helicopter Systems. On 18 December 1992, the maiden flight was conducted, initial certification for the type followed roughly two years later. The initial model, the MD 900, was joined by an improved successor, the MD 902, during the late 1990s. The Explorer is currently produced by MD Helicopters. The helicopter is noted for having no tail rotor, using the NOTAR technology instead, giving its tail a unique appearance and quieter sound profile than a more traditional tail rotor.

In January 1989, McDonnell Douglas Helicopters officially announced the launch of the Explorer, which it initially referred to as the MDX. Amongst other things, the Explorer was the first McDonnell Douglas helicopter to incorporate the NOTAR system from its initial design. McDonnell Douglas partnered with Hawker de Havilland of Australia, which handled the manufacturing of the airframes. A total of ten prototypes were constructed, seven of which being used for ground-based tests. McDonnell Douglas Helicopters became a launch customer for Pratt & Whitney Canada's PW200 turboshaft engines, for which it had an exclusive agreement to power the first 128 Explorers with pairs of PW206As. While plans had been mooted to offer the Turbomeca Arrius powerplant as an alternative option, these were subsequently discarded.

On 18 December 1992, the maiden flight of the Explorer took place, performed by ship #2 (N900MD). On 2 December 1994, Federal Aviation Administration (FAA) certification for the Explorer was granted, permitting its use in North America; Joint Aviation Authorities (JAA) certification was received shortly thereafter. However, certification of the Explorer's instrument flight rules (IFR) capability was protracted due to technical difficulties with integration; in February 1997, FAA certification for IFR operations was finally received.