ALTDEV. ALSO POSSIBLE ERRONEOUS PENETRATION OF CLASS D AIRSPACE.

Narrative

APCH CLRED US TO DSND TO 4000 FT AND GAVE US A HDG. WE DSNDED OUT OF BASES AT APPROX 6000 FT MSL AND SHORTLY THEREAFTER WE RPTED TO APCH THAT WE HAD THE ARPT IN SIGHT. APCH RESPONDED BY TURNING US 30 DEGS R AND SAYING THAT THE NEXT CTLR WOULD HAVE OUR VISUAL APCH CLRNC. APCH THEN SWITCHED US TO THE FINAL APCH CTLR. AFTER CHKING ON; CTLR TURNED US BACK 30 DEGS L TO OUR ORIGINAL HDG AND CLRED US DIRECT TO THE ARPT. THE CTLR ALSO GAVE US A TFC CALLOUT THAT WAS AT OUR 3 O'CLOCK POS 1000 FT ABOVE US MOVING THE OPPOSITE DIRECTION. I MISUNDERSTOOD OUR CLRNC TO BE CLRED FOR A VISUAL APCH AND BEGAN A VERY GRADUAL DSCNT. AT THE TIME WE WERE ONLY AROUND 10 MI OUT FROM THE ARPT OF INTENDED LNDG. THE COLUMBUS APCH CTLR RPTED TO US THAT WE WERE 400 FT LOW AND THAT WE HAD ALSO VIOLATED OHIO STATE ARPT'S CLASS D AIRSPACE. HE THEN CLRED US FOR THE VISUAL APCH. AN UNEVENTFUL LNDG FOLLOWED AND NO ONE INSTRUCTED US TO CONTACT ANY ONE AT THE TIME REGARDING THE ALTDEV. OHIO STATE ARPT IS A CLASS D AND THEREFORE WOULD ONLY EXTEND 2500 FT AGL -- WELL BELOW THE 3700 FT MSL ALT THAT WE HAD ACCIDENTALLY DSNDED TO. WE AS A CREW ALLOWED OURSELVES TO BECOME DISTRACTED BY THE FREQ AND HDG CHANGES AS WELL AS THE TFC CALLOUT. I NOW DO NOT TURN ON THE ACFT'S LNDG LIGHTS UNTIL I HAVE BEEN CLRED FOR THE APCH (VISUAL OR INST). I ALSO DO NOT TURN ON THE TAXI LIGHT UNTIL I HAVE BEEN CLRED TO LAND. I FEEL THAT IF IN APCH'S CLRNC OF 'PROCEED DIRECT THE ARPT' THEY HAD ALSO INCLUDED 'MAINTAIN 4000 FT' OUR ALTDEV WOULD NOT HAVE OCCURRED. SUPPLEMENTAL INFO FROM ACN 294928: THE ALT ALERT WENT OFF IN THE COCKPIT AND HE STATED WE ARE CLRED THE VISUAL AND I SAID OK AND THEN REALIZED I DID NOT REMEMBER HEARING THAT CLRNC; BUT SINCE I WAS LOOKING FOR THE TFC I MIGHT HAVE MISSED THE CALL. JUST AS THE THOUGHT CAME TO MIND TO ASK THE CTLR; THE APCH CTLR ASKED OUR ALT AND STATED WE HAD VIOLATED OHIO UNIVERSITY AIRSPACE.