Narrative:

I was diverting to groton, ct (gon), because of low ceilings and visibility at my intended destination airport, and I made the decision to divert as I was passing the field at 8000 ft. I was being controled by providence approach control, and requested the diversion from them. They accepted my request, and gave me vectors to final for the VOR 23 approach to groton. Surface winds at groton were from 150 degrees at 6 KTS. Ceiling was described as 1100 ft broken at the field, and the altimeter was 29.91. At a heading of 210 degrees, pvd approach told me to maintain 2000 ft until established on final and cleared me for the approach. I intercepted the final approach course and descended to 1700 ft outside the FAF (babet intersection). I noticed that the crosswind was substantially greater on final than I had anticipated, and that I needed more correction to maintain proper final approach course. I was released by approach to change to the tower frequency after being established on final. I began a descent from 1700 ft to 650 ft at what I thought was babet, which is defined by the final approach radial from tmu and R183 from orw. I believe I may have entered the radial for orw incorrectly, closer to 177 degrees or 180 degrees, and consequently, my distance from tmu was greater than it should have been. I had a GPS unit in the airplane, and it was reporting my distance from gon, but in correcting for the crosswind, I took longer to double-check my distance than I should have, and began my descent before making this double-check. As I was noticing the GPS distance and realizing that I might have been descending early, the tower called to say that pvd approach had reported that I was below the proper altitude for the segment and should check my altimeter setting immediately. At the time of this call, I was at approximately 1450 ft MSL. I climbed to 1700 ft until I was sure I was past the FAF, and then continued to approach, descending to 650 ft and flying at that altitude until I could see the airport and complete a landing. I believe there were 2 human performance factors that may have been contributory to this problem. First, as a relatively inexperienced instrument pilot, I found myself pressed to quickly brief the approach, descend the airplane smoothly, and maintain heading properly while being vectored. In the future, I will ask for more time to prepare more thoroughly. Second, I had spent about 40 mins at 10000 ft before asking for lower about 30 mins before passing groton and deciding to divert there, and on reflection, I may have been suffering some residual effects of mild hypoxia. In the future, I won't ask for altitudes above 8000 ft without using oxygen if there is any chance of flying in IMC afterwards.

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Original NASA ASRS Text

Title: PLT OF C172 DSNDED PREMATURELY ON VOR RWY 23 APCH TO GON. PVD APCH CTLR RECEIVED MSAW ALERT, ADVISED GON LCL CTLR WHO ALERTED PLT. PREMATURE DSCNT WAS CAUSED BY INCORRECT VOR RADIAL BEING SET TO IDENTIFY FAF.

Narrative: I WAS DIVERTING TO GROTON, CT (GON), BECAUSE OF LOW CEILINGS AND VISIBILITY AT MY INTENDED DEST ARPT, AND I MADE THE DECISION TO DIVERT AS I WAS PASSING THE FIELD AT 8000 FT. I WAS BEING CTLED BY PROVIDENCE APCH CTL, AND REQUESTED THE DIVERSION FROM THEM. THEY ACCEPTED MY REQUEST, AND GAVE ME VECTORS TO FINAL FOR THE VOR 23 APCH TO GROTON. SURFACE WINDS AT GROTON WERE FROM 150 DEGS AT 6 KTS. CEILING WAS DESCRIBED AS 1100 FT BROKEN AT THE FIELD, AND THE ALTIMETER WAS 29.91. AT A HDG OF 210 DEGS, PVD APCH TOLD ME TO MAINTAIN 2000 FT UNTIL ESTABLISHED ON FINAL AND CLRED ME FOR THE APCH. I INTERCEPTED THE FINAL APCH COURSE AND DSNDED TO 1700 FT OUTSIDE THE FAF (BABET INTXN). I NOTICED THAT THE XWIND WAS SUBSTANTIALLY GREATER ON FINAL THAN I HAD ANTICIPATED, AND THAT I NEEDED MORE CORRECTION TO MAINTAIN PROPER FINAL APCH COURSE. I WAS RELEASED BY APCH TO CHANGE TO THE TWR FREQ AFTER BEING ESTABLISHED ON FINAL. I BEGAN A DSCNT FROM 1700 FT TO 650 FT AT WHAT I THOUGHT WAS BABET, WHICH IS DEFINED BY THE FINAL APCH RADIAL FROM TMU AND R183 FROM ORW. I BELIEVE I MAY HAVE ENTERED THE RADIAL FOR ORW INCORRECTLY, CLOSER TO 177 DEGS OR 180 DEGS, AND CONSEQUENTLY, MY DISTANCE FROM TMU WAS GREATER THAN IT SHOULD HAVE BEEN. I HAD A GPS UNIT IN THE AIRPLANE, AND IT WAS RPTING MY DISTANCE FROM GON, BUT IN CORRECTING FOR THE XWIND, I TOOK LONGER TO DOUBLE-CHK MY DISTANCE THAN I SHOULD HAVE, AND BEGAN MY DSCNT BEFORE MAKING THIS DOUBLE-CHK. AS I WAS NOTICING THE GPS DISTANCE AND REALIZING THAT I MIGHT HAVE BEEN DSNDING EARLY, THE TWR CALLED TO SAY THAT PVD APCH HAD RPTED THAT I WAS BELOW THE PROPER ALT FOR THE SEGMENT AND SHOULD CHK MY ALTIMETER SETTING IMMEDIATELY. AT THE TIME OF THIS CALL, I WAS AT APPROX 1450 FT MSL. I CLBED TO 1700 FT UNTIL I WAS SURE I WAS PAST THE FAF, AND THEN CONTINUED TO APCH, DSNDING TO 650 FT AND FLYING AT THAT ALT UNTIL I COULD SEE THE ARPT AND COMPLETE A LNDG. I BELIEVE THERE WERE 2 HUMAN PERFORMANCE FACTORS THAT MAY HAVE BEEN CONTRIBUTORY TO THIS PROB. FIRST, AS A RELATIVELY INEXPERIENCED INST PLT, I FOUND MYSELF PRESSED TO QUICKLY BRIEF THE APCH, DSND THE AIRPLANE SMOOTHLY, AND MAINTAIN HDG PROPERLY WHILE BEING VECTORED. IN THE FUTURE, I WILL ASK FOR MORE TIME TO PREPARE MORE THOROUGHLY. SECOND, I HAD SPENT ABOUT 40 MINS AT 10000 FT BEFORE ASKING FOR LOWER ABOUT 30 MINS BEFORE PASSING GROTON AND DECIDING TO DIVERT THERE, AND ON REFLECTION, I MAY HAVE BEEN SUFFERING SOME RESIDUAL EFFECTS OF MILD HYPOXIA. IN THE FUTURE, I WON'T ASK FOR ALTS ABOVE 8000 FT WITHOUT USING OXYGEN IF THERE IS ANY CHANCE OF FLYING IN IMC AFTERWARDS.

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.