Narrative:

My student and I were conducting a training flight at deland airport (fl) to practice patterns and landings. We had an observer on board; another student going on their first airplane ride. The weather was perfect VFR; clear skies and winds out of the west. Three airplanes (including us) were performing left traffic at runway 23 in deland. On our second traffic pattern; my student and I agreed to extend our upwind by a couple miles to allow an incoming C172 to join the downwind; allowing us to stay at a safe distance from them. After the aircraft entered the downwind at the midfield point; my student turned crosswind and made the appropriate radio call on deland's CTAF frequency. At this point; I (the instructor; pilot not flying) heard a fifth aircraft make a radio call; announcing they were southeast of the airfield with the intention of entering the left downing for runway 23. My student turned downwind at the appropriate time and made a second radio call to announce our position and our intention of performing the left downwind to runway 23; behind the other C172 which had joined the downwind 30 seconds earlier. The fifth aircraft made a new radio call; once again announcing they were maneuvering to enter the downwind at the midfield point. At this time; I noticed the target of the unknown aircraft on the mfd; as displayed by the tis-B. I was attempting to find the aircraft visually and gauge how fast they were moving to determine if they would pose a traffic conflict should they continue on their present heading. Using the target on the mfd; I determined that the airplane's trajectory and speed would indeed create a traffic conflict with us. Consequently; I made a 3rd radio call (after my student's first two) to advise the incoming airplane that two aircraft were already on left downwind for runway 23 (us and the other C172); one was on left base and a fourth was on short final. I also suggested over the radio that the incoming aircraft may need to maneuver around to maintain a safe distance from us in the pattern. I did not hear a response from the crew of that aircraft. As my student kept flying the airplane and getting ready to reach the abeam point; I noticed the target on the mfd moving very close to us from behind and to the right; and reaching our altitude (traffic pattern altitude). By turning around in my seat; I was able to locate the aircraft no more than 100 ft behind us; right next to our empennage and at our altitude. It was a white C172 with fixed landing gear. The airplane was flying at a higher airspeed and closing in on us quite rapidly. At this time I decided to take the flight controls and perform an escape maneuver by applying full power and entering a steep climb to gain altitude. Once I determined we were clear and in no further danger; I returned to a normal climb pitch attitude and decide to depart the deland traffic pattern; land and call it a day. It ended up being a good decision to simply depart the pattern and get away from a dangerous situation; return home to let the student; the observer and myself cool down and talk about everything that had happened in the debrief.

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Original NASA ASRS Text

Title: C172 flight instructor reports an NMAC at DED with another C172 entering the traffic pattern midfield. The instructor elects to take evasive action and depart the pattern after being alerted by TIS-B then sighting traffic 100 FT behind and closing.

Narrative: My student and I were conducting a training flight at Deland airport (FL) to practice patterns and landings. We had an observer on board; another student going on their first airplane ride. The weather was perfect VFR; clear skies and winds out of the west. Three airplanes (including us) were performing left traffic at Runway 23 in Deland. On our second traffic pattern; my student and I agreed to extend our upwind by a couple miles to allow an incoming C172 to join the downwind; allowing us to stay at a safe distance from them. After the aircraft entered the downwind at the midfield point; my student turned crosswind and made the appropriate radio call on Deland's CTAF frequency. At this point; I (the instructor; pilot not flying) heard a fifth aircraft make a radio call; announcing they were southeast of the airfield with the intention of entering the left downing for Runway 23. My student turned downwind at the appropriate time and made a second radio call to announce our position and our intention of performing the left downwind to Runway 23; behind the other C172 which had joined the downwind 30 seconds earlier. The fifth aircraft made a new radio call; once again announcing they were maneuvering to enter the downwind at the midfield point. At this time; I noticed the target of the unknown aircraft on the MFD; as displayed by the TIS-B. I was attempting to find the aircraft visually and gauge how fast they were moving to determine if they would pose a traffic conflict should they continue on their present heading. Using the target on the MFD; I determined that the airplane's trajectory and speed would indeed create a traffic conflict with us. Consequently; I made a 3rd radio call (after my student's first two) to advise the incoming airplane that two aircraft were already on left downwind for Runway 23 (us and the other C172); one was on left base and a fourth was on short final. I also suggested over the radio that the incoming aircraft may need to maneuver around to maintain a safe distance from us in the pattern. I did not hear a response from the crew of that aircraft. As my student kept flying the airplane and getting ready to reach the abeam point; I noticed the target on the MFD moving very close to us from behind and to the right; and reaching our altitude (traffic pattern altitude). By turning around in my seat; I was able to locate the aircraft no more than 100 FT behind us; right next to our empennage and at our altitude. It was a white C172 with fixed landing gear. The airplane was flying at a higher airspeed and closing in on us quite rapidly. At this time I decided to take the flight controls and perform an escape maneuver by applying full power and entering a steep climb to gain altitude. Once I determined we were clear and in no further danger; I returned to a normal climb pitch attitude and decide to depart the Deland traffic pattern; land and call it a day. It ended up being a good decision to simply depart the pattern and get away from a dangerous situation; return home to let the student; the observer and myself cool down and talk about everything that had happened in the debrief.

Data retrieved from NASA's ASRS site as of July 2013 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.