Narrative:

Departed ellington field on a us customs mission. Opened our VFR flight plan with montgomery county FSS after departure. Climbed to 2500' and overflew galveston. Contacted schole field on unicom and obtained a local altimeter setting. Proceeded off shore toward the southwest corner of grid 6. Descended to our search altitude. Entered grid track and sighted a few more vessels. En route to identing vessels a coast guard helicopter appeared on our port side. The helicopter was about 200-250' away. Proceeded toward vessels with coast guard on part side. Helicopter moved to within 100' of our port side. The helicopter moved toward a after position of our aircraft. I was afraid to change my flight path or alter my altitude because of the close proximity of the helicopter. The helicopter maneuvered to different positions around us. It was noticed on my starboard side, at the 6 O'clock position, and also at a lower altitude on our port side. Attempted to contact the coast guard helicopter on my aircraft radio and on a portable civil air patrol radio. After no successful results contacted montgomery county radio FSS to get a message via landline to inform coast guard we were on an approved flight plan and were legally out in the gulf. The coast guard departed soon after that. Proceeded with the grid search west/O further contact with another aircraft. Idented a total of 33 different vessels. Maintained an altitude of 250' on aircraft altimeter. Maintained 500' clearance of all obstructions. Observed called out descending altitude below 500'. Attempted to not cross the heading of any vessel which was underway.

Related reports:

Google
 

Original NASA ASRS Text

Title: PLT OF SMA ON CAP CUSTOMS MISSION IDENTIFYING SURFACE VESSELS WITHIN A PRESCRIBED GRID WAS APCHED BY A COAST GUARD HELICOPTER THAT CAME WITHIN CLOSE PROX.

Narrative: DEPARTED ELLINGTON FIELD ON A U.S. CUSTOMS MISSION. OPENED OUR VFR FLT PLAN WITH MONTGOMERY COUNTY FSS AFTER DEP. CLBED TO 2500' AND OVERFLEW GALVESTON. CONTACTED SCHOLE FIELD ON UNICOM AND OBTAINED A LCL ALTIMETER SETTING. PROCEEDED OFF SHORE TOWARD THE SW CORNER OF GRID 6. DSNDED TO OUR SEARCH ALT. ENTERED GRID TRACK AND SIGHTED A FEW MORE VESSELS. ENRTE TO IDENTING VESSELS A COAST GUARD HELI APPEARED ON OUR PORT SIDE. THE HELI WAS ABOUT 200-250' AWAY. PROCEEDED TOWARD VESSELS WITH COAST GUARD ON PART SIDE. HELI MOVED TO WITHIN 100' OF OUR PORT SIDE. THE HELI MOVED TOWARD A AFTER POS OF OUR ACFT. I WAS AFRAID TO CHANGE MY FLT PATH OR ALTER MY ALT BECAUSE OF THE CLOSE PROX OF THE HELI. THE HELI MANEUVERED TO DIFFERENT POSITIONS AROUND US. IT WAS NOTICED ON MY STARBOARD SIDE, AT THE 6 O'CLOCK POS, AND ALSO AT A LOWER ALT ON OUR PORT SIDE. ATTEMPTED TO CONTACT THE COAST GUARD HELI ON MY ACFT RADIO AND ON A PORTABLE CIVIL AIR PATROL RADIO. AFTER NO SUCCESSFUL RESULTS CONTACTED MONTGOMERY COUNTY RADIO FSS TO GET A MESSAGE VIA LANDLINE TO INFORM COAST GUARD WE WERE ON AN APPROVED FLT PLAN AND WERE LEGALLY OUT IN THE GULF. THE COAST GUARD DEPARTED SOON AFTER THAT. PROCEEDED WITH THE GRID SEARCH W/O FURTHER CONTACT WITH ANOTHER ACFT. IDENTED A TOTAL OF 33 DIFFERENT VESSELS. MAINTAINED AN ALT OF 250' ON ACFT ALTIMETER. MAINTAINED 500' CLRNC OF ALL OBSTRUCTIONS. OBSERVED CALLED OUT DSNDING ALT BELOW 500'. ATTEMPTED TO NOT CROSS THE HDG OF ANY VESSEL WHICH WAS UNDERWAY.

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.