The mechanical energy of the two engines is the primary source of routine electrical power and hydraulic pressure for the aircraft flight control systems.[28] The aircraft also has an auxiliary power unit (APU), which can provide backup electrical power for the aircraft, including its electrically powered hydraulic pumps; and a ram air turbine (RAT), a type of wind turbine that can be deployed into the airstream to provide backup hydraulic pressure and electrical power at certain speeds.[28] According to the NTSB, both the APU and the RAT were operating as the plane descended into the Hudson, although it was not clear whether the RAT had been deployed manually or automatically.[28]
This is a good RAT:
This is a bad RAT: