C172 SAFETY PLT ENTERED BOS CLASS B AIRSPACE WITHOUT CLRNC.

Narrative

THIS FLT WAS MY FIRST TIME ACTING AS SAFETY PLT FOR ANOTHER PVT PLT WHO IS WORKING ON HIS INST RATING LIKE ME. AFTER TKOF; HE PUT ON THE HOOD AND I TOLD HIM TO CLB TO 3800 FT ON AN APPROX HDG OF 300 DEGS TO PROCEED TO GDM VOR WHERE WE WOULD PRACTICE SOME APCHS. 3800 FT WAS AN ALT THAT WOULD KEEP US CLR OF BOS CLASS B AIRSPACE. HOWEVER; I LOOKED AT THE SECTIONAL AND SAW WE WERE HEADED TOWARDS B4102 A&B; WHICH WAS ACTIVE TO 3995 FT MSL THAT SATURDAY. I QUICKLY GLANCED OUT THE WINDOW AND SAW A ROAD THAT RESEMBLED RTE 495; WHICH IS SEVERAL MI PAST THE OUTER RING OF THE CLASS B AIRSPACE. I TOLD THE PLT UNDER THE HOOD TO CLB TO 4500 FT AT THAT POINT. SEVERAL MINS LATER; I LOOKED OUT AND SAW THAT WE WERE ACTUALLY JUST PASSING OVER RTE 495. THEREFORE; WHEN WE CLBED TO 4500 FT; WE WERE MOST LIKELY IN THE CLASS B AIRSPACE WITHOUT CLRNC. FURTHERMORE; WHEN ABOVE THE BED CLASS D AIRSPACE ABOVE 2500 FT; ALL ACFT SHOULD CONTACT APCH ACCORDING TO THE BOSTON TCA CHART. WE DID NOT CONTACT BOS APCH AS REQUIRED. BY THE TIME I REALIZED THE PROB; WE WERE ALREADY OUTSIDE OF THE LATERAL LIMITS OF THE CLASS B AIRSPACE. I MENTIONED THIS TO THE OTHER PLT BUT HE DID NOT SEEM CONCERNED. CONTRIBUTING FACTORS: IT WAS MY FIRST TIME FLYING AS SAFETY PLT; BUT THE OTHER PLT EXPECT ME TO HELP WITH NAV IN ADDITION TO WATCHING FOR TFC; WHICH WAS USING THE GPS TO PROCEED TOWARDS AN ARPT. I DECIDED I DID NOT NEED TO USE IT TO HELP DETERMINE WHEN I WAS OUTSIDE OF THE LATERAL LIMITS OF THE CLASS B AIRSPACE. WE HAD NOT ADEQUATELY LOOKED AT CHARTS OR PLANNED THE FLT. I THINK THIS IS IN PART DUE TO THE IDEA THAT THE OTHER PLT WOULD CATCH ANY MISTAKES BEFORE THEY HAPPENED. THE GOOD VFR WX RESULTED IN BUSY SKIES; WITH MANY TFC DISTRS FOR ME TO DEAL WITH. WHILE THIS WAS NOT A MISTAKE THAT APPEARED TO JEOPARDIZE THE SAFETY OF OUR FLT; I STILL FEEL THAT WHEN FLYING WITH ANOTHER PLT; IT MUST BE CLR WHAT EACH PLT IS RESPONSIBLE FOR. I THOUGHT HE WAS FOLLOWING ALONG ON HIS CHARTS WHEN I WAS THE ONLY ONE DOING SO. I CONCLUDED THAT DUE TO LACK OF PREPARATION; FAILURE TO IDENT RESPONSIBILITIES AND THE MANY VFR ACFT THAT DAY; WERE THE MAIN FACTORS IN THIS ERROR.