On July 24, 2006, at 1300 eastern daylight time, an Embraer EMB-135LR, N703MR, operated by American Eagle Airlines Inc. as flight 4514, was substantially damaged during pushback at Newark Liberty International Airport (EWR), Newark, New Jersey. There were no injuries to the 2 flightcrew, 1 flight attendant, or 13 passengers. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the planned flight to General Edward Lawrence Logan International Airport (BOS), Boston, Massachusetts. The scheduled passenger flight was conducted under 14 CFR Part 121. According to the Manager of Flight Safety at American Eagle Airlines, a tug operator was attempting to push the airplane back from a gate. As the tug began to move, the landing gear tires skidded against the tarmac, and the pushback was aborted. Approximately 14 inches of skid marks were observed near the main landing gear tires. The airplane sustained damage to the forward pressure bulkhead, forward longerons, and nose landing gear. The captain reported that all preflight checklists were completed, and the flightcrew waited about 8 to 10 minutes for weight and balance data. During that time, the air conditioner was off, as the pneumatic air supply was needed for an air start of the engines. The captain completed the Before Start Checklist and started both engines to try and cool the cabin. The captain further stated that after the ground equipment was clear of the airplane, he released the parking brake when the pushback clearance was received. The captain then informed the tug operator that he was cleared to push. After about 3 to 5 feet of movement, there was a sudden jolt and the airplane came to a stop. The captain added that after the impact, the tug operator asked him to set the parking brake, which he did. The first officer stated that the parking brake was released after the pushback clearance was received. Review of the cockpit voice recorder (CVR) revealed at: 12:43:54, the first officer read the before starting engines checklist, including the challenge and response of "parking brake set." 12:48:23, the captain discussed departure issues with a ground crewman, and the ground crewman subsequently advised that he was changing the pneumatic air supply from conditioning air to ground start. 12:55:08, the flightcrew received aircraft departure information, and the captain reviewed the takeoff weights and data. 12:55:53, the captain read the before starting engines checklist items, advised the ground crewman he was ready to start engines, and started both engines. 12:58:10, the captain then advised the ground crewman that both engines were started and "it is okay to disconnect." 12:59:13, the first officer read the after start checklist, and the ground crewman advised he was ready for pushback. 12:59:39, the first officer received pushback clearance from ramp control. 12:59:57, the captain advised the ground crewman that the flight was cleared for pushback; the ground crewman replied, "here we go," followed by the sound of impact. After the impact, the ground crewman asked the captain to set the parking brake and the captain responded, "parking brake set." Except for the first officer referring to the parking brake set during the before starting engines checklist, no other reference to the parking brake was heard on the CVR prior to the accident. In addition, the captain and ground crewman used non-standard phraseology when discussing the pushback. Review of the American Eagle Embraer Aircraft Operating Manual Revealed: "...Starting at the Gate, then Push-out This procedure will be used primarily when an external air start is required. Normally, only the #2 Engine will be started at the gate. The #1 Engine will be started after the tow bar is removed and the ram area is clear. Guideperson will advise Captain: "Ramp to cockpit, parking brake set, all secure below, cleared to start." This indicates that the doors and windows are closed, chocks are removed, loading bridge is retracted and the ramp area is clear. When ready to start engines (and having obtained engine start clearance, where required), Captain will verify closed - windows and MFD and EICAS door messages are displayed: "Cockpit to ramp, parking brake set, starting #___." If external power and/or external air supply is used for start, Captain will advise the Guideperson when to disconnect the external power an/or external air supply. Guideperson will advise Captain: "All secure below, standing by for steering disengaged and parking brake released... When ready to push-out after obtaining push-out clearance, where required, the Captain will advise Guideperson: "Parking brake released, steering disengaged, ready to push." At the end of push-out, Guideperson will advise: "Parking brake set." The tug used for pushback was a Stewart and Stevenson GT-50. Review of American Eagle Guidelines (published December 2005) revealed that the tug was larger and more powerful than the preferred tugs used to pushback regional jet aircraft; however; the Stewart and Stevenson GT-50 was approved, with caution, to be used at stations were a preferred tug was not available. On the day of the accident, a preferred tug was not available at the Newark, New Jersey station.