Narrative:

A fellow pilot and I went up to fly approachs today for currency. I'm the PF. We flew the ILS runway 35 at mht to a missed twice. On the second missed; approach tells us they're changing runways and they'll set us up for the ILS runway 17 instead. We're vectored around a bit. We get a close and relatively sharp turn to final approach course and it's then that I notice the CDI needle is deflected the wrong way. I hadn't really been paying attention to it; focusing on assigned heading and my handheld GPS instead. I was confused; and kept chasing the needle; only to have it do exactly the opposite of what I expected based on the corrections I was making. I checked the chart 109.1; checked navigation 2 109.1. I got fixated on thinking I somehow pulled out the wrong chart; or tuned the wrong frequency. I turned on the autoplt in approach mode thinking maybe I was just disoriented. The autoplt did a worse job than I was doing. I started to think the CDI was reverse sensing. I switched the autoplt to reverse mode and it started flying the correct course; even though the CDI was reversed. That confirmed that the CDI was reverse sensing. I kept looking at the chart thinking I missed something. I asked my safety pilot to verify the chart and the frequency. Meanwhile; I got low -- a couple hundred ft low. I'm so fixated on thinking I've screwed something up -- radio not set right; didn't read the chart; I had to have missed something -- that I'm not paying enough attention. Luckily it's VMC and I've got a safety pilot. I'm still outside the outer marker; so I climb back up to GS intercept altitude. The GS doesn't seem right. It's not way off; but not really moving as I'd expect it. There's no flag; so I'm receiving a signal. After GS intercept (needle's basically centered at the marker) I start descending. Again; the needle's moving a bit; but doesn't really seem to be moving according to my descent rate. A couple of mi out; safety pilot says; 'I see 4 red lights on the PAPI.' the GS needle is maybe 1 DOT low. I executed a missed approach; informing mht tower of the missed. After discussing the situation with several pilots; I've come to realize that mht tower never switched the localizer from runway 35 to runway 17 when they changed runways. I idented the localizer frequency via morse code identify when I flew the approach into runway 35; but didn't identify the localizer again when I commenced the approach into runway 17. Had I idented the localizer a second time; I would have realized I was receiving the localizer signal from the runway 35 approach end; effectively flying an unpublished back course approach with a false GS.

Google
 

Original NASA ASRS Text

Title: PA28 PLT IS CONFUSED ABOUT LOC AND GS RESPONSES WHILE SHOOTING PRACTICE ILS APCHS. LATER DISCOVERS TOWER HADN'T CHANGED ILS TRANSMITTERS WHEN SWITCHING RWYS.

Narrative: A FELLOW PLT AND I WENT UP TO FLY APCHS TODAY FOR CURRENCY. I'M THE PF. WE FLEW THE ILS RWY 35 AT MHT TO A MISSED TWICE. ON THE SECOND MISSED; APCH TELLS US THEY'RE CHANGING RWYS AND THEY'LL SET US UP FOR THE ILS RWY 17 INSTEAD. WE'RE VECTORED AROUND A BIT. WE GET A CLOSE AND RELATIVELY SHARP TURN TO FINAL APCH COURSE AND IT'S THEN THAT I NOTICE THE CDI NEEDLE IS DEFLECTED THE WRONG WAY. I HADN'T REALLY BEEN PAYING ATTN TO IT; FOCUSING ON ASSIGNED HDG AND MY HANDHELD GPS INSTEAD. I WAS CONFUSED; AND KEPT CHASING THE NEEDLE; ONLY TO HAVE IT DO EXACTLY THE OPPOSITE OF WHAT I EXPECTED BASED ON THE CORRECTIONS I WAS MAKING. I CHKED THE CHART 109.1; CHKED NAV 2 109.1. I GOT FIXATED ON THINKING I SOMEHOW PULLED OUT THE WRONG CHART; OR TUNED THE WRONG FREQ. I TURNED ON THE AUTOPLT IN APCH MODE THINKING MAYBE I WAS JUST DISORIENTED. THE AUTOPLT DID A WORSE JOB THAN I WAS DOING. I STARTED TO THINK THE CDI WAS REVERSE SENSING. I SWITCHED THE AUTOPLT TO REVERSE MODE AND IT STARTED FLYING THE CORRECT COURSE; EVEN THOUGH THE CDI WAS REVERSED. THAT CONFIRMED THAT THE CDI WAS REVERSE SENSING. I KEPT LOOKING AT THE CHART THINKING I MISSED SOMETHING. I ASKED MY SAFETY PLT TO VERIFY THE CHART AND THE FREQ. MEANWHILE; I GOT LOW -- A COUPLE HUNDRED FT LOW. I'M SO FIXATED ON THINKING I'VE SCREWED SOMETHING UP -- RADIO NOT SET RIGHT; DIDN'T READ THE CHART; I HAD TO HAVE MISSED SOMETHING -- THAT I'M NOT PAYING ENOUGH ATTN. LUCKILY IT'S VMC AND I'VE GOT A SAFETY PLT. I'M STILL OUTSIDE THE OUTER MARKER; SO I CLB BACK UP TO GS INTERCEPT ALT. THE GS DOESN'T SEEM RIGHT. IT'S NOT WAY OFF; BUT NOT REALLY MOVING AS I'D EXPECT IT. THERE'S NO FLAG; SO I'M RECEIVING A SIGNAL. AFTER GS INTERCEPT (NEEDLE'S BASICALLY CTRED AT THE MARKER) I START DSNDING. AGAIN; THE NEEDLE'S MOVING A BIT; BUT DOESN'T REALLY SEEM TO BE MOVING ACCORDING TO MY DSCNT RATE. A COUPLE OF MI OUT; SAFETY PLT SAYS; 'I SEE 4 RED LIGHTS ON THE PAPI.' THE GS NEEDLE IS MAYBE 1 DOT LOW. I EXECUTED A MISSED APCH; INFORMING MHT TWR OF THE MISSED. AFTER DISCUSSING THE SITUATION WITH SEVERAL PLTS; I'VE COME TO REALIZE THAT MHT TWR NEVER SWITCHED THE LOC FROM RWY 35 TO RWY 17 WHEN THEY CHANGED RWYS. I IDENTED THE LOC FREQ VIA MORSE CODE IDENT WHEN I FLEW THE APCH INTO RWY 35; BUT DIDN'T IDENT THE LOC AGAIN WHEN I COMMENCED THE APCH INTO RWY 17. HAD I IDENTED THE LOC A SECOND TIME; I WOULD HAVE REALIZED I WAS RECEIVING THE LOC SIGNAL FROM THE RWY 35 APCH END; EFFECTIVELY FLYING AN UNPUBLISHED BACK COURSE APCH WITH A FALSE GS.

Data retrieved from NASA's ASRS site as of May 2009 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.