The E-3 Sentry's airframe is a modified Boeing 707-320B Advanced model. Modifications include a rotating radar dome (rotodome), uprated hydraulics from 241 to 345 bar (3500–5000 PSI) to drive the rotodome,[19] single-point ground refueling, air refueling, and a bail-out tunnel or chute. A second bail-out chute was deleted to cut mounting costs.[20]