Narrative:

While on an air taxi flight and inside the class D; I was north bound on the east side at 1500 ft MSL when approach notified me that I may have a traffic conflict at 10 o'clock; still a ways out but moving fast and believed to be an A-10 at 1800 MSL on a south east heading; speed was reported as 300K and that they were not in contact with them. Less than a minute later we notified approach that we had visual contact. To us it appeared that the aircraft would pass to our west; then about 20 seconds later we lost visual contact with the A-10 and notified approach. Approach said they were at our 10 o'clock and 8 miles still at 1800 MSL and not talking to any one. I notified approach that I was looking but had negative contact. The next transmission from approach was that the aircraft had turned eastbound; coming straight at us at 1500 MSL and advised an immediate climb. I immediately executed a climbing left turn and saw the airplane as it passed under my nose from left to right. It was so close I could not see the whole plane through my chin bubble and I estimated he passed under us at less than 150 ft. At the time we were 2.6 NM southeast of the airport and in contact with approach control. To my knowledge the military pilot never talked to them.

Google
 

Original NASA ASRS Text

Title: A BK117 suffered an NMAC with a military A10 Warthog within Class D airspace. The A10 pilot was not in contact with ATC.

Narrative: While on an air taxi flight and inside the Class D; I was north bound on the east side at 1500 FT MSL when approach notified me that I may have a traffic conflict at 10 o'clock; still a ways out but moving fast and believed to be an A-10 at 1800 MSL on a south east heading; speed was reported as 300K and that they were not in contact with them. Less than a minute later we notified Approach that we had visual contact. To us it appeared that the aircraft would pass to our west; then about 20 seconds later we lost visual contact with the A-10 and notified Approach. Approach said they were at our 10 o'clock and 8 miles still at 1800 MSL and not talking to any one. I notified Approach that I was looking but had negative contact. The next transmission from approach was that the aircraft had turned eastbound; coming straight at us at 1500 MSL and advised an immediate climb. I immediately executed a climbing left turn and saw the airplane as it passed under my nose from left to right. It was so close I could not see the whole plane through my chin bubble and I estimated he passed under us at less than 150 FT. At the time we were 2.6 NM Southeast of the airport and in contact with Approach Control. To my knowledge the military pilot never talked to them.

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.