20080611843569I

(-23) During the descent to the destination airport at approximately FL200 in the vicinity of everett, WA, the flight crew and other aircraft occupants heard and felt a distinct thump. The captain checked all engine instruments and noted no change or abnormal indications. A flight attendant called the flight deck due to passenger inquiries, but the flight crew could not provide an answer as to the cause. Another flight attendant call was made later in the descent to inform the captain that a passenger reported having seen something that looked like a panel. After an uneventful landing in bellingham, WA (bli), an inspection revealed a large dent on the inboard leading edge of the right wing (on the slat). The dent was approximately 8 inches across, 6 inches vertically, and 2 inches deep. There was no blood or feathers to indicate a bird might have been the cause. There was also a small dent on the leading edge of the right engine nose cowl. This dent could be readily seen from the front of the aircraft looking rearward and was at the 10 o'clock position. The airline flew a new slat section to bli and repaired the right wing dent that night. Airline maintenance personnel at bli inspected the airplane and verified there were no missing parts or doors that could have caused the damage. They also inspected the right engine to verify that no FOD damage was present. Maintenance personnel also replaced the right engine nose cowl after flying revenue flights for one day. The airline received permission from Boeing engineering to fly with the minor dent for one day to provide time to transport the replacement part. An FAA operations inspector assigned to the allegiant air cmt was onboard in the cockpit during this incident and was assigned as the FAA iic for this investigation. The possiblility that the object was a weather balloon has been considered. However, weather balloons are launched on a standard schedule that does not correlate with the time of this flight. Therefore, it is very unlikely this was a balloon launched by the national weather service. Radar data from the seattle air route traffic control center indicates there were no other aircraft at a higher altitude and in a position from which a part may have fallen. We are skeptical about the possiblility of a bird strike, since there were no visible signs of blood or feathers on the aircraft. The airline has forwarded the damaged wing slat to Boeing for testing in order to possibly identify the object that was hit. We are sitll awaiting the results of these tests. If additioanl information is learned from the Boeing tests, we will send an amendment to FAA form 8020-23.