MEP

MEP stands for Mobile Electric Power unit, though in some contexts the M can mean Motor or the unit may be called a Ground Power Unit (GPU). In aviation maintenance, an MEP is a standalone generator mounted on wheels or a trailer that supplies electrical power and compressed air to an aircraft when its engines are shut down. It plugs into receptacles on the fuselage, typically near the nose gear, and serves as a temporary replacement for the power that the aircraft's own engine-driven generators and air compressors would normally produce.

MEPs come in various sizes matched to aircraft electrical demand. A small twin-engine regional aircraft might use a 30 to 60 kVA unit, while a wide-body jet could require 90 kVA or more. Most MEPs deliver three-phase AC power at 115/200 volts and 400 Hz (standard aircraft frequency), though some also provide DC power through a conversion system. The compressed air output is typically regulated to 40 to 50 psi and connects via a single umbilical hose to the aircraft's pneumatic inlet.

The MEP must be positioned carefully and connected through proper bonding and grounding cables to prevent static discharge damage to avionics. Maintenance crews use MEPs during line checks, troubleshooting, component replacement, and overnight parking when the aircraft must remain powered for cabin lighting, galley systems, or avionics cooling. A common failure mode is inadequate frequency stability: if the MEP's engine speed drifts, 400 Hz-sensitive equipment like flight management systems can malfunction or refuse to initialize.

Quality of power matters in ways that differ sharply from ground infrastructure. Aircraft systems are sensitive to harmonic distortion and voltage transients. A poorly maintained MEP with worn alternator brushes or a failing voltage regulator can introduce noise that trips avionics circuit breakers or corrupts data buses. Maintenance crews must verify frequency and voltage before connecting to any aircraft, and many operators now require periodic load testing and frequency calibration of their MEP fleet.

MEPs are essential infrastructure at every maintenance hangar and line station, yet they are often overlooked in favor of more visible equipment. Downtime caused by a failed MEP can ground multiple aircraft because work cannot proceed without external power. Operators typically maintain one MEP in reserve and rotate units through scheduled servicing to catch failures before they cascade into schedule disruptions.