An air carrier pilot complains of GS signal on runway 12R at msp.

Attributes
ACN	522154
Time
Date	200108
Day	Mon
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : msp.airport
State Reference	MN
Altitude	agl bound lower : 1000 agl bound upper : 2000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw.artcc
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 12r
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 160 flight time total : 20000 flight time type : 2000
ASRS Report	522154
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Supplementary
Problem Areas	Airport Navigational Facility ATC Facility
Primary Problem	Airport

Narrative:

The GS signal for the runway 12R approach into msp is subject to adverse interference from ground traffic. The cockpit indication, when the interference was present, showed us consistently over 1 1/2 dots high (at the published altitudes/fixes down the localizer). The WX NOTAMS, and a message on the msp ATIS, made mention of possible GS interference on runway 12R. However, to this flight crew, ground interference was expected as an interrupted or fluctuating indication. Quite the contrary, the GS indication was a steady, bent signal which could have left the aircraft unacceptably low. The msp TRACON supervisor acknowledged the 'continuing problem' with the runway 12R GS interference which, he said, could result in altitude errors of 500-1000 ft.

Original NASA ASRS Text

Title: AN ACR PLT COMPLAINS OF GS SIGNAL ON RWY 12R AT MSP.

Narrative: THE GS SIGNAL FOR THE RWY 12R APCH INTO MSP IS SUBJECT TO ADVERSE INTERFERENCE FROM GND TFC. THE COCKPIT INDICATION, WHEN THE INTERFERENCE WAS PRESENT, SHOWED US CONSISTENTLY OVER 1 1/2 DOTS HIGH (AT THE PUBLISHED ALTS/FIXES DOWN THE LOC). THE WX NOTAMS, AND A MESSAGE ON THE MSP ATIS, MADE MENTION OF POSSIBLE GS INTERFERENCE ON RWY 12R. HOWEVER, TO THIS FLC, GND INTERFERENCE WAS EXPECTED AS AN INTERRUPTED OR FLUCTUATING INDICATION. QUITE THE CONTRARY, THE GS INDICATION WAS A STEADY, BENT SIGNAL WHICH COULD HAVE LEFT THE ACFT UNACCEPTABLY LOW. THE MSP TRACON SUPVR ACKNOWLEDGED THE 'CONTINUING PROB' WITH THE RWY 12R GS INTERFERENCE WHICH, HE SAID, COULD RESULT IN ALT ERRORS OF 500-1000 FT.

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.