An ATR42 in cruise at 14000 feet declared an emergency and diverted due to loss of the green hydraulic system pressure and quantity caused by a failed fitting or line.

Narrative

Rewritten in plain English from NASA’s original all-caps telegraphic report — facts, figures, and terminology preserved.

While at altitude enroute from ORD to La Crosse, WI, a cockpit panel light illuminated indicating hydraulic fluid 'low level.' The Pilot Not Flying (the Captain) ran through the appropriate abnormal checklist which, among other things, required the shutoff of one of our hydraulic pumps. The checklist stated that as a new result we would lose the ability to normally extend the landing gear and that we would lose all normal braking.

The Pilot Not Flying informed company of our problem while Pilot Flying (myself) turned the aircraft around back to ORD and informed ATC of our problem. We were cleared by radar vectors to ORD, had to execute an emergency gear extension procedure (gravity gear extension), landed on runway 27L, slowed using reverse thrust only, and finally came to a stop with the emergency/parking brake on one of the 'high speed' taxiways. Since we could not taxi without brakes, passengers and bags were unloaded by our company out on the taxiway. There were no passengers or crew injuries and no damage to aircraft except leaking hydraulic fluid from the belly of the aircraft.

Callback conversation with reporter revealed the following info: The reporter stated the exact cause of the hydraulic fluid loss is unknown as maintenance only advised the crew a line or a fitting on the line failed. The reporter said the segment of line and fitting leaking were in the green system located in the wheel well.