A PILOT CONDUCTING FORMATION FLT TRAINING IN THE LEAD ACFT; WAS GIVEN TFC INFO AFTER DEPARTING BUT FAILED TO PASS THAT TFC INFO ON TO THE FOLLOWING ACFT CAUSING A NEAR MISS FOR THE SECOND ACFT.

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I WAS ACTING AS AN INSTRUCTOR AND CONDUCTING FORMATION FLT LEAD TRAINING FOR THE PIC IN THAT ACFT. WE WERE DASH #1 IN A FLT OF TWO DEPARTING ZZZ FOR FORMATION FLT TRAINING. PRIOR TO DEP; WE INFORMED TWR THAT WE WOULD BE A NON-STANDARD FORMATION AND TWR ACKNOWLEDGED. WE PLANNED FOR DASH #2 TO MAINTAIN 1.5 NM IN TRAIL OF DASH #1. DASH #1 DEPARTED WITH ITS XPONDER ON AND DASH #2 DEPARTED WITH ITS XPONDER IN STANDBY. ATIS RPTED THAT PRIMARY RADAR WAS OTS AT THE TIME OF DEP. DASH #1 RECEIVED TKOF CLRNC FOR THE FLT FROM RWY 21 AND REQUESTED TO FLY 270 DEGS FOR 2 MINS PRIOR TO TURNING R TO 360 DEGS. AS WE TURNED FROM 270 TO 360 DEGS; ATC CALLED TFC (DASH 8; Q400) AT 9 O'CLOCK POS; NBOUND THAT WAS ENTERING R TFC FOR RWY 21. WE MADE VISUAL CONTACT WITH THE TFC AND RADIOED ATC. ATC TOLD US TO MAINTAIN VISUAL SEPARATION FROM THE TFC AND WE ACKNOWLEDGED. WE (DASH #1) DID NOT VERIFY THAT DASH #2 ALSO HAD THE TFC IN SIGHT. THE FLT CONTINUED NORMALLY AND FREQ CHANGED WITH ATC AS WE TRANSITIONED OUT OF THE ZZZ TRSA FOR OUR TRAINING. DURING OUR FLT DEBRIEF AT THE CONCLUSION OF THE FLT; I WAS TOLD BY THE CREW OF DASH #2 THAT THE Q400 HAD PASSED DIRECTLY OVER THEM AT 400-500 FT SEPARATION DURING OUR DEP. DASH #2 DID NOT HAVE VISUAL WITH THE Q400 PRIOR TO THE Q400 PASSING OVER THEM. I BELIEVE THAT CONTRIBUTING FACTORS WERE: FAILURE OF DASH #1 TO CONFIRM THAT DASH #2 HAD VISUAL WITH THE TFC BEFORE ACKNOWLEDGING THE TFC; PRIMARY RADAR BEING INOP; AND DASH #2 SQUAWKING STANDBY.