Narrative:

I departed small aircraft X IFR off runway 11 with a 220 degree heading assigned. Approximately 3 mins later, small aircraft Y called ready heading basically the same general direction (swbound). Scanning the BRITE, I noticed small aircraft X 2 NM south of bed on what appeared to be a 220 degree heading. Considering that X type is faster than Y type I, who was now training a developmental, instructed my student to depart aircraft Y and assign a 220 degree heading also. (220 degree is the maximum southwest heading I can assign aircraft off runway 11 by letter of agreement). What happened next, I am unsure of because of 2 reasons: I was talking in depth to the trainee explaining instrument approach procedures. I allowed my attention to be diverted for too long of a period of time. Radar coverage south and southwest of hanscom field is nonexistent after 2 NM (due to high buildings blocking radar pulses). Apparently Y overtook X and departure control was forced to turn 1 of the aircraft to avert a conflict. In the future, not assuming that an aircraft (of same category) will be faster and not getting distraction could alleviate a situation like this of happening again.

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Original NASA ASRS Text

Title: LTSS BTWN 2 SMA ACFT DEPARTING SAME ARPT IN IMC WX. OPERATIONAL ERROR.

Narrative: I DEPARTED SMA X IFR OFF RWY 11 WITH A 220 DEG HDG ASSIGNED. APPROX 3 MINS LATER, SMA Y CALLED READY HDG BASICALLY THE SAME GENERAL DIRECTION (SWBOUND). SCANNING THE BRITE, I NOTICED SMA X 2 NM S OF BED ON WHAT APPEARED TO BE A 220 DEG HDG. CONSIDERING THAT X TYPE IS FASTER THAN Y TYPE I, WHO WAS NOW TRAINING A DEVELOPMENTAL, INSTRUCTED MY STUDENT TO DEPART ACFT Y AND ASSIGN A 220 DEG HDG ALSO. (220 DEG IS THE MAX SW HDG I CAN ASSIGN ACFT OFF RWY 11 BY LETTER OF AGREEMENT). WHAT HAPPENED NEXT, I AM UNSURE OF BECAUSE OF 2 REASONS: I WAS TALKING IN DEPTH TO THE TRAINEE EXPLAINING INST APCH PROCS. I ALLOWED MY ATTN TO BE DIVERTED FOR TOO LONG OF A PERIOD OF TIME. RADAR COVERAGE S AND SW OF HANSCOM FIELD IS NONEXISTENT AFTER 2 NM (DUE TO HIGH BUILDINGS BLOCKING RADAR PULSES). APPARENTLY Y OVERTOOK X AND DEP CTL WAS FORCED TO TURN 1 OF THE ACFT TO AVERT A CONFLICT. IN THE FUTURE, NOT ASSUMING THAT AN ACFT (OF SAME CATEGORY) WILL BE FASTER AND NOT GETTING DISTR COULD ALLEVIATE A SITUATION LIKE THIS OF HAPPENING AGAIN.

Data retrieved from NASA's ASRS site as of July 2007 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.