Flight crew encounter sjc runway 30L localizer, glide slope fluctuations while on approach.

Attributes
ACN	460528
Time
Date	200001
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : sjc.airport
State Reference	CA
Altitude	msl single value : 4500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : o90.tracon tracon : mdsd.tracon
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 30l other other other vortac
Flight Phase	descent : approach
Route In Use	approach : instrument precision arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial
ASRS Report	460528
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe other anomaly other anomaly other
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : became reoriented flight crew : overrode automation flight crew : regained aircraft control
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Airport ATC Facility
Primary Problem	ATC Facility

Narrative:

During approach to sjc, bay approach cleared flight for ILS approach to sjc at a high altitude. Once on approach, the localizer and glide slope gave indications of almost full scale fly left and right, as well as glide slope, high and low, while on center line of runway 30L sjc, approach. Continued because ground contact and airport in sight. Callback conversation with reporter revealed the following information: flight crew were inbound sjc, turning final in the vicinity of klide intersection (sjc 123016) when the localizer and glide slope deflections occurred. By the time the flight crew reached the outer marker, all localizer, glide slope indications appeared normal. At the equipment's greatest declination point, the localizer deflected 2 dots, the glide slope 3 dots. The aircraft pitched up, then down, then up again as well as directional changes occurred. The PIC disengaged the autoplt, regaining control. The reporter advised that the flight crew has encountered this problem consistently over the last one yr of flying into sjc.

Original NASA ASRS Text

Title: FLC ENCOUNTER SJC RWY 30L LOC, GLIDE SLOPE FLUCTUATIONS WHILE ON APCH.

Narrative: DURING APCH TO SJC, BAY APCH CLRED FLT FOR ILS APCH TO SJC AT A HIGH ALT. ONCE ON APCH, THE LOC AND GLIDE SLOPE GAVE INDICATIONS OF ALMOST FULL SCALE FLY L AND R, AS WELL AS GLIDE SLOPE, HIGH AND LOW, WHILE ON CTR LINE OF RWY 30L SJC, APCH. CONTINUED BECAUSE GND CONTACT AND ARPT IN SIGHT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: FLC WERE INBOUND SJC, TURNING FINAL IN THE VICINITY OF KLIDE INTERSECTION (SJC 123016) WHEN THE LOC AND GLIDE SLOPE DEFLECTIONS OCCURRED. BY THE TIME THE FLC REACHED THE OUTER MARKER, ALL LOC, GLIDE SLOPE INDICATIONS APPEARED NORMAL. AT THE EQUIPMENT'S GREATEST DECLINATION POINT, THE LOC DEFLECTED 2 DOTS, THE GLIDE SLOPE 3 DOTS. THE ACFT PITCHED UP, THEN DOWN, THEN UP AGAIN AS WELL AS DIRECTIONAL CHANGES OCCURRED. THE PIC DISENGAGED THE AUTOPLT, REGAINING CTL. THE RPTR ADVISED THAT THE FLC HAS ENCOUNTERED THIS PROB CONSISTENTLY OVER THE LAST ONE YR OF FLYING INTO SJC.

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.