Air carrier on NDB approach has erratic signal. Breaking out of clouds corrects to align with course...

Attributes
ACN	161582
Time
Date	199011
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : ama
State Reference	TX
Altitude	msl bound lower : 200 msl bound upper : 2000
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ama tower : ama
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach descent other
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : commercial pilot : flight engineer pilot : instrument pilot : atp
Experience	flight time last 90 days : 200 flight time total : 11000 flight time type : 5000
ASRS Report	161582
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Experience	flight time last 90 days : 250 flight time total : 5100 flight time type : 650
ASRS Report	161689
Events
Anomaly	aircraft equipment problem : less severe non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course other
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other
Situations
Navigational Aid	Unspecified

Narrative:

Approaching ama to shoot the NDB 4 approach, receiving normal identify on NDB. Turned onto final about 1-2 mi outside the station and signal became weak, erratic but still gave a identify. Needle gave indication of station passage and started descent to MDA. After station passage needle was highly erratic; while giving the needle a few moments to settle down, we broke out at 800' AGL, and stopped the descent there. VOR back-up orientation and a call from ATC revealed us to be right of course. Corrected to left and visually acquired airport. We were VFR just beneath the overcast during this phase of flight about 200' above MDA. In the future: should initiate missed approach at first sign of bad signal and being overloaded. Ask for lower final to get established in strong x-wind. Supplemental information from acn 161698. After landing tower told us that the NDB had a history of not being reliable during rain. During the approach I had indented and monitored NDB as the strength of the identify weakened. I asked approach about the status of NDB. They said it monitored good.

Original NASA ASRS Text

Title: ACR ON NDB APCH HAS ERRATIC SIGNAL. BREAKING OUT OF CLOUDS CORRECTS TO ALIGN WITH COURSE.

Narrative: APCHING AMA TO SHOOT THE NDB 4 APCH, RECEIVING NORMAL IDENT ON NDB. TURNED ONTO FINAL ABOUT 1-2 MI OUTSIDE THE STATION AND SIGNAL BECAME WEAK, ERRATIC BUT STILL GAVE A IDENT. NEEDLE GAVE INDICATION OF STATION PASSAGE AND STARTED DSNT TO MDA. AFTER STATION PASSAGE NEEDLE WAS HIGHLY ERRATIC; WHILE GIVING THE NEEDLE A FEW MOMENTS TO SETTLE DOWN, WE BROKE OUT AT 800' AGL, AND STOPPED THE DSNT THERE. VOR BACK-UP ORIENTATION AND A CALL FROM ATC REVEALED US TO BE R OF COURSE. CORRECTED TO L AND VISUALLY ACQUIRED ARPT. WE WERE VFR JUST BENEATH THE OVCST DURING THIS PHASE OF FLT ABOUT 200' ABOVE MDA. IN THE FUTURE: SHOULD INITIATE MISSED APCH AT FIRST SIGN OF BAD SIGNAL AND BEING OVERLOADED. ASK FOR LOWER FINAL TO GET ESTABLISHED IN STRONG X-WIND. SUPPLEMENTAL INFO FROM ACN 161698. AFTER LNDG TWR TOLD US THAT THE NDB HAD A HISTORY OF NOT BEING RELIABLE DURING RAIN. DURING THE APCH I HAD INDENTED AND MONITORED NDB AS THE STRENGTH OF THE IDENT WEAKENED. I ASKED APCH ABOUT THE STATUS OF NDB. THEY SAID IT MONITORED GOOD.

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.