Narrative:

Cruise at FL330; day; clear; smooth. Aircraft experienced a violent and severe event that felt like an impact; like a car accident; with a pitch down and airframe shudder that extended throughout the aircraft. It was one; instant impact that was so severe that I could hear galley items impacting and felt a deceleration. If we had not had our seat belts on it would have tossed us from our seats. I immediately clicked off the autopilot thinking that an engine had exploded. The engine instruments all were normal and steady. I checked the cabin pressure and noted steady and appropriate cabin altitude and differential. I checked the door lights and saw no open door indications. There were no warning lights or caution lights. Since we still had pressurization we concluded it was probably not a bomb; although a bomb would have felt and sounded the same. As we had eliminated all normal system failures we discussed the possibility of a control or airframe malfunction or damage. Captain declared an emergency and selected a nearby airport for landing. Flight attendants called reported no injuries. Captain gave the flight attendants a briefing and a PA to passengers. I began a shallow descent and slowed to 250 KTS in consideration of the possibility of an airframe or control problem and spiraled down to the airport. There was no QRH checklist for these circumstances; so we completed the descent checklist and before landing checklist. The captain took the aircraft on final and made an overweight landing at 135;000 pounds. Rate of descent was 200 FPM and touchdown was smooth. After landing; arff inspected the aircraft and found no obvious damage. Taxied to the gate. As we see in the case of a lightning strike; each passenger said it felt like the impact was directly under their seats; no matter where they were sitting. As passengers deplaned they were clearly shaken; but they all had positive attitudes and patience. This must be directly credited to the excellent cabin crew. They had very little to go on but were able to reassure the passengers while going from doing a cabin service to an emergency landing. I concur with all of captain's decisions and compliment his handling of this event and the care he demonstrated for his crew throughout our time on the ground.

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Original NASA ASRS Text

Title: A MD80 crew experienced a violent and severe flight disruption at FL330 caused by a compressor stall. An emergency was declared with a diversion to a nearby airport.

Narrative: Cruise at FL330; day; clear; smooth. Aircraft experienced a violent and severe event that felt like an impact; like a car accident; with a pitch down and airframe shudder that extended throughout the aircraft. It was one; instant impact that was so severe that I could hear galley items impacting and felt a deceleration. If we had not had our seat belts on it would have tossed us from our seats. I immediately clicked off the autopilot thinking that an engine had exploded. The engine instruments all were normal and steady. I checked the cabin pressure and noted steady and appropriate cabin altitude and differential. I checked the door lights and saw no open door indications. There were no warning lights or caution lights. Since we still had pressurization we concluded it was probably not a bomb; although a bomb would have felt and sounded the same. As we had eliminated all normal system failures we discussed the possibility of a control or airframe malfunction or damage. Captain declared an emergency and selected a nearby airport for landing. Flight attendants called reported no injuries. Captain gave the flight attendants a briefing and a PA to passengers. I began a shallow descent and slowed to 250 KTS in consideration of the possibility of an airframe or control problem and spiraled down to the airport. There was no QRH checklist for these circumstances; so we completed the Descent Checklist and Before Landing Checklist. The Captain took the aircraft on final and made an overweight landing at 135;000 LBS. Rate of descent was 200 FPM and touchdown was smooth. After landing; ARFF inspected the aircraft and found no obvious damage. Taxied to the gate. As we see in the case of a lightning strike; each passenger said it felt like the impact was directly under their seats; no matter where they were sitting. As passengers deplaned they were clearly shaken; but they all had positive attitudes and patience. This must be directly credited to the excellent cabin crew. They had very little to go on but were able to reassure the passengers while going from doing a cabin service to an emergency landing. I concur with all of Captain's decisions and compliment his handling of this event and the care he demonstrated for his crew throughout our time on the ground.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.