Narrative:

While conducting an IFR flight in IMC conditions from otis AFB to moore aaf in a mlt turbo propeller aircraft we descended 1400' below a published route segment of an instrument approach. I realized the error upon leveling off at the wrong altitude and immediately climbed back up and continued the approach to near weather minimums at moore aaf (aye). I feel the following sequence of events lead to this inadvertent action. On a direct leg from putnam VOR to gardner VOR we were handed off to boston approach approximately 3 minutes out of the IAF gardner VOR. Boston acknowledged us at 4000' but did not issued any further clearance. We asked for an approach clearance and waited for a reply as we were getting ready to hold over gdm as published on the enroute chart. Approach asked if we had the current weather at moore aaf and we replied negative while approaching the IAF. Immediately after the weather and while passing over gdm VOR turning to enter holding an approach clearance was issued. Inside the cockpit I was studying the holding pattern depiction as well as flying the aircraft. The copilot was copying weather and talking with approach control. We hadn't discussed the approach as we normally do partially due to all the ATC communication that was on going for this short IFR flight. In looking at the overview for the VOR approach to moore aaf I turned the aircraft right to intercept the 009 degree gdm radial and looked down to the profile view and mentally read 2100' as the MDA for the segment from gdm to berlo int and descended to that altitude. The copilot did not recognize this error either. Upon leveling off at 2100' and taking a moment to review the approach I realized the error and climbed back up to 3500'. We were switched over to moore tower at gdm VOR so we could not hear if boston center was monitoring our approach. Contributing factors to this action I feel were inadequate crew approach briefing. Confusion upon arrival at the IAF as to further clearance from ATC. ATC handoffs so close to the IAF. VOR approach profile view should have a dark line extending horizontally left of berlo int 11.6 DME to help indicate the IAF is prior to this point. At a glance comparing the overview with the profile view indicates a descent upon passing gdm VOR. I've flown this approach before, a long time ago, and knew about this segment. In the confusion I overlooked a 'small' detail (3500 to berlo int 099 degree (11.6) that was almost fatal.

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Original NASA ASRS Text

Title: MLT DESCENT BELOW MINIMUM ENROUTE ALT STARTING VOR TACAN APCH INTO AYE.

Narrative: WHILE CONDUCTING AN IFR FLT IN IMC CONDITIONS FROM OTIS AFB TO MOORE AAF IN A MLT TURBO PROP ACFT WE DESCENDED 1400' BELOW A PUBLISHED ROUTE SEGMENT OF AN INSTRUMENT APCH. I REALIZED THE ERROR UPON LEVELING OFF AT THE WRONG ALT AND IMMEDIATELY CLIMBED BACK UP AND CONTINUED THE APCH TO NEAR WEATHER MINIMUMS AT MOORE AAF (AYE). I FEEL THE FOLLOWING SEQUENCE OF EVENTS LEAD TO THIS INADVERTENT ACTION. ON A DIRECT LEG FROM PUTNAM VOR TO GARDNER VOR WE WERE HANDED OFF TO BOSTON APCH APPROX 3 MINUTES OUT OF THE IAF GARDNER VOR. BOSTON ACKNOWLEDGED US AT 4000' BUT DID NOT ISSUED ANY FURTHER CLRNC. WE ASKED FOR AN APCH CLRNC AND WAITED FOR A REPLY AS WE WERE GETTING READY TO HOLD OVER GDM AS PUBLISHED ON THE ENROUTE CHART. APCH ASKED IF WE HAD THE CURRENT WEATHER AT MOORE AAF AND WE REPLIED NEGATIVE WHILE APCHING THE IAF. IMMEDIATELY AFTER THE WEATHER AND WHILE PASSING OVER GDM VOR TURNING TO ENTER HOLDING AN APCH CLRNC WAS ISSUED. INSIDE THE COCKPIT I WAS STUDYING THE HOLDING PATTERN DEPICTION AS WELL AS FLYING THE ACFT. THE COPLT WAS COPYING WEATHER AND TALKING WITH APCH CTL. WE HADN'T DISCUSSED THE APCH AS WE NORMALLY DO PARTIALLY DUE TO ALL THE ATC COMMUNICATION THAT WAS ON GOING FOR THIS SHORT IFR FLT. IN LOOKING AT THE OVERVIEW FOR THE VOR APCH TO MOORE AAF I TURNED THE ACFT RIGHT TO INTERCEPT THE 009 DEG GDM RADIAL AND LOOKED DOWN TO THE PROFILE VIEW AND MENTALLY READ 2100' AS THE MDA FOR THE SEGMENT FROM GDM TO BERLO INT AND DESCENDED TO THAT ALT. THE COPLT DID NOT RECOGNIZE THIS ERROR EITHER. UPON LEVELING OFF AT 2100' AND TAKING A MOMENT TO REVIEW THE APCH I REALIZED THE ERROR AND CLIMBED BACK UP TO 3500'. WE WERE SWITCHED OVER TO MOORE TWR AT GDM VOR SO WE COULD NOT HEAR IF BOSTON CENTER WAS MONITORING OUR APCH. CONTRIBUTING FACTORS TO THIS ACTION I FEEL WERE INADEQUATE CREW APCH BRIEFING. CONFUSION UPON ARRIVAL AT THE IAF AS TO FURTHER CLRNC FROM ATC. ATC HANDOFFS SO CLOSE TO THE IAF. VOR APCH PROFILE VIEW SHOULD HAVE A DARK LINE EXTENDING HORIZONTALLY LEFT OF BERLO INT 11.6 DME TO HELP INDICATE THE IAF IS PRIOR TO THIS POINT. AT A GLANCE COMPARING THE OVERVIEW WITH THE PROFILE VIEW INDICATES A DESCENT UPON PASSING GDM VOR. I'VE FLOWN THIS APCH BEFORE, A LONG TIME AGO, AND KNEW ABOUT THIS SEGMENT. IN THE CONFUSION I OVERLOOKED A 'SMALL' DETAIL (3500 TO BERLO INT 099 DEG (11.6) THAT WAS ALMOST FATAL.

Data retrieved from NASA's ASRS site as of August 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.