EMB ERJ 190/195 ER/LR
Flight Crew Air Transport Pilot (ATP)
Flight Deck / Cabin / Aircraft Event Illness / Injury; Ground Event / Encounter Other / Unknown
Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Company Policy; Aircraft; Equipment / Tooling; Human Factors
During pushback the tow bar became disconnected. Captain stopped the aircraft using the emergency/parking brake. The sudden stop resulted in both flight attendants sustaining injuries requiring evaluation at the hospital. Captain requested FAA jumpseater to check on the flight attendants and solicit medical help from the passengers as needed. He reported both flight attendants had lost consciousness and one was bleeding; and that on board medical professionals were tending to them. Captain instructed me to coordinate getting medics while he called Dispatch. I requested EMT/ambulance through Ops and also requested airstairs be brought to the aircraft so the EMTs would have swift access to the aircraft. With passengers (those tending to the flight attendants) up; unknown status of tow bar assembly; and not wanting to  further jar the flight attendants if further difficulties should arise on tow-in; we were hesitant to move the aircraft. It became apparent that Ops was unable to timely provide airstairs.  We were informed a new tow bar had been attached and inspected; and then were towed back to the gate. The Captain and I disarmed the boarding door and the flight attendants were then taken to the hospital. The parking brake is rarely used to stop the aircraft; thus the finesse required to do it without lurch would be very difficult to achieve.  If the Number 1 Hyd Pump was on during pushback; partial normal brakes would be retained and the nose wheel steering would still be de-energized.   Some carriers have procedures requiring the flight attendants to be seated until the pushback is complete. Unfortunately these events are not that uncommon; this is the second time in less than a year I've seen a tow bar fail on push back.
Cleared to push from Ramp Control and communicated with pushback crew to begin pushback via interphone. Shortly after pushback began; before any engines were started; I noticed the aircraft accelerating unusually fast rearward and at the same time noticing the tug moving away from the aircraft. It was obvious the tug had disconnected from the aircraft. There were no communications or visual signals from pushback crew of a problem. With engines off; the only available braking is from the parking/emergency brake. I slowly began applying the parking/emergency brake being aware from recent 190 simulator training of its sensitivity; but it still led to a fast stop which resulted in both cabin attendants receiving injuries. An FAA Aviation Safety Inspector was in the cockpit jumpseat at the time. He immediately volunteered to help the flight attendants. Both he and the First Officer did a wonderful job assisting me in getting medical attention to the flight attendants!The tow bar disconnected from the nose gear during pushback. While very rare; I have had tow bars disconnect in the past; but it was usually preceded by a rough start or stop by a tug. In this case; it seemed like the tug just pushed us backwards and the aircraft sped away from the tug as if we were never connected. The FAA Aviation Safety Inspector went to talk to the pushback crew and to inspect the tug and tow bar. He told me that he believes the tow bar was defective.During pushback with engines off we should be able to power the electric hydraulic pump for system 1 and/or system 2 to provide either inner or outer brakes so that braking is available through the toe brakes; providing superior control versus the parking brake handle. I believe other Airlines power the electric hydraulic pumps for system 1 or system 2 prior to pushback on their 170's and 175's. Maybe we should keep our flight attendants seated during all pushbacks and maybe all taxi. Every pilot in the airline business has seen rough pushbacks/tows and of course airport vehicles cutting off taxing airplanes requiring sudden stops.
EMB190 flight crew experiences a break away during pushback requiring the use of the parking brake to stop the aircraft. The sudden stop causes both flight attendants to fall and be seriously injured.