A DC9-30 captured a false GS approaching buf runway 23 from right of course.

Attributes
ACN	639934
Time
Date	200412
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : buf.airport
State Reference	NY
Altitude	msl single value : 2300
Environment
Weather Elements	Snow
Light	Night
Aircraft 1
Controlling Facilities	tracon : buf.tracon
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 190 flight time total : 16000 flight time type : 6000
ASRS Report	639934
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical non adherence : far non adherence : published procedure non adherence : clearance other anomaly other other spatial deviation other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : returned to intended or assigned course flight crew : overcame equipment problem flight crew : regained aircraft control
Consequence	Other
Supplementary
Problem Areas	Flight Crew Human Performance Navigational Facility Aircraft
Primary Problem	Flight Crew Human Performance

Narrative:

ILS runway 23 approach vectored at 2300 ft. Approximately 800 ft overcast, 2 mi visibility. Note briefed on approach that the 'GS unusable from right.' vectored from right on intercept heading. No DME on localizer. Both captain and first officer on ILS frequency due to procedures to ensure good signal. Turned on localizer and cleared for approach from a point I guessed would be very close to ADF OM at an altitude that should intercept GS prior to ADF. Localizer started coming across and localizer capture light illuminated and I called it. The autoplt intercepted the GS at a point that I thought was acceptable as we were near the localizer. The descent rate of the autoplt increased at an unusual rate and what I thought was the needle swing of ADF marker passage was actually the needle moving with the card as we intercepted the localizer. About that time I sensed something was not right. A false GS capture was not suspected at that moment but I knew something was wrong, as we had not passed the marker yet. I turned autoplt off and leveled about 500 ft below assigned altitude just as the formerly captured localizer went full left on the HSI. At that moment, approach questioned our altitude and mentioned false GS problems from right side. Climbed back to 2300 ft and re-intercepted localizer and GS for a successful landing. This approach is a big trap and the first officer and I both interpreted the approach note that if we did have a problem it would just be 'no' GS not a false one. Our non-glass aircraft with no DME on approach and a false localizer (also with no flags showing) are big factors. From now on, I will have the PNF tune any DME that can help with position and realize that a note on 'GS unusable' could mean a false GS. Also, our trained procedure to always select automatic approach on autoplt when cleared for approach may not always be appropriate. This buf approach needs to be fixed. One other factor might be that I have been off the DC9 for approximately 14 months and just re-qualified on DC9 and have flown only 3 trips when this happened. During the 14 months I flew first officer on a B757.

Original NASA ASRS Text

Title: A DC9-30 CAPTURED A FALSE GS APCHING BUF RWY 23 FROM R OF COURSE.

Narrative: ILS RWY 23 APCH VECTORED AT 2300 FT. APPROX 800 FT OVCST, 2 MI VISIBILITY. NOTE BRIEFED ON APCH THAT THE 'GS UNUSABLE FROM R.' VECTORED FROM R ON INTERCEPT HDG. NO DME ON LOC. BOTH CAPT AND FO ON ILS FREQ DUE TO PROCS TO ENSURE GOOD SIGNAL. TURNED ON LOC AND CLRED FOR APCH FROM A POINT I GUESSED WOULD BE VERY CLOSE TO ADF OM AT AN ALT THAT SHOULD INTERCEPT GS PRIOR TO ADF. LOC STARTED COMING ACROSS AND LOC CAPTURE LIGHT ILLUMINATED AND I CALLED IT. THE AUTOPLT INTERCEPTED THE GS AT A POINT THAT I THOUGHT WAS ACCEPTABLE AS WE WERE NEAR THE LOC. THE DSCNT RATE OF THE AUTOPLT INCREASED AT AN UNUSUAL RATE AND WHAT I THOUGHT WAS THE NEEDLE SWING OF ADF MARKER PASSAGE WAS ACTUALLY THE NEEDLE MOVING WITH THE CARD AS WE INTERCEPTED THE LOC. ABOUT THAT TIME I SENSED SOMETHING WAS NOT RIGHT. A FALSE GS CAPTURE WAS NOT SUSPECTED AT THAT MOMENT BUT I KNEW SOMETHING WAS WRONG, AS WE HAD NOT PASSED THE MARKER YET. I TURNED AUTOPLT OFF AND LEVELED ABOUT 500 FT BELOW ASSIGNED ALT JUST AS THE FORMERLY CAPTURED LOC WENT FULL L ON THE HSI. AT THAT MOMENT, APCH QUESTIONED OUR ALT AND MENTIONED FALSE GS PROBS FROM R SIDE. CLBED BACK TO 2300 FT AND RE-INTERCEPTED LOC AND GS FOR A SUCCESSFUL LNDG. THIS APCH IS A BIG TRAP AND THE FO AND I BOTH INTERPED THE APCH NOTE THAT IF WE DID HAVE A PROB IT WOULD JUST BE 'NO' GS NOT A FALSE ONE. OUR NON-GLASS ACFT WITH NO DME ON APCH AND A FALSE LOC (ALSO WITH NO FLAGS SHOWING) ARE BIG FACTORS. FROM NOW ON, I WILL HAVE THE PNF TUNE ANY DME THAT CAN HELP WITH POS AND REALIZE THAT A NOTE ON 'GS UNUSABLE' COULD MEAN A FALSE GS. ALSO, OUR TRAINED PROC TO ALWAYS SELECT AUTO APCH ON AUTOPLT WHEN CLRED FOR APCH MAY NOT ALWAYS BE APPROPRIATE. THIS BUF APCH NEEDS TO BE FIXED. ONE OTHER FACTOR MIGHT BE THAT I HAVE BEEN OFF THE DC9 FOR APPROX 14 MONTHS AND JUST RE-QUALIFIED ON DC9 AND HAVE FLOWN ONLY 3 TRIPS WHEN THIS HAPPENED. DURING THE 14 MONTHS I FLEW FO ON A B757.

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.