power-egg
A complete unitized modular engine installation, consisting of engine and all ancillary equipment, which can be swapped between suitably designed equipment.
power-egg: drop-in engine module ready to bolt on
A power-egg is a fully assembled engine unit that arrives at the maintenance bay as a single replaceable component. It bundles the engine core with its integral accessories, fuel control unit, engine-mounted pump, starter generator, gearbox section, and all plumbing and wiring harnesses, into one sealed package. Maintenance technicians remove the failed unit and install the replacement without needing to rebuild or reconfigure individual subsystems on the airframe.
This modular approach emerged in military aviation during the 1960s and 1970s, where rapid turnaround and field reliability mattered more than detailed troubleshooting. Modern commercial turbofan engines, particularly those on business jets and some regional airliners, are increasingly designed around power-egg architecture. The Rolls-Royce Allison 250, common in helicopters, exemplifies the concept: engine, transmission, and accessory gearbox arrive as one unit, mounted on the airframe via four standard hard points.
Swapping protocol and constraints
Power-egg replacement requires careful handling of residual fuel and hydraulic fluid, precise alignment of mounting flanges, and re-certification of engine parameters before flight. The aircraft design must accommodate the power-egg's envelope and vibration signature; you cannot simply graft a power-egg meant for one airframe type onto another. Maintenance records must track serialized engines separately from airframes, since these modules are often overhauled off-aircraft and rotated through fleet pools or returned to manufacturer repair shops.
Cost trade-offs are significant. A power-egg reduces labor hours at the operator's base and minimizes hangar time, because troubleshooting is done by the overhaul facility, not the flight line. However, the design eliminates some field repair options; certain faults that might be corrected by component swap on a traditional engine may require entire power-egg replacement. Resale value of used power-eggs remains stronger than assembled engines because they arrive in known configuration and with defined service history.