An air carrier large transport had a false GS allowing the aircraft to be low over the ground.

Attributes
ACN	253054
Time
Date	199309
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : bna
State Reference	TN
Altitude	msl bound lower : 2000 msl bound upper : 2000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	tower : bna tower : msp
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Aircraft
Flight Phase	descent : approach
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp pilot : cfi pilot : instrument
Experience	flight time last 90 days : 210 flight time total : 15000 flight time type : 10800
ASRS Report	253054
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other controllera other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Navigational Facility
Air Traffic Incident	other
Situations
Navigational Aid	Unspecified

Narrative:

Rain had moved through during the previous hour. Prior to the final approach fix, runway 20R, we got a GS below the normal GS. No flags. Identify normal. An small aircraft on approach before us received 'climb immediately, show you at 900 ft' instructions from the controller on multiple approachs. Callback conversation with reporter revealed the following information: the reporter has talked to several people about this but has heard nothing official about it. The WX was basically VFR with low scuddy clouds crossing the airport. The rainstorm that had just gone through had put out a lot of water which may have caused the problem. The reporter believes that the old problem of false GS high is now past by the advent of better equipment.

Original NASA ASRS Text

Title: AN ACR LGT HAD A FALSE GS ALLOWING THE ACFT TO BE LOW OVER THE GND.

Narrative: RAIN HAD MOVED THROUGH DURING THE PREVIOUS HR. PRIOR TO THE FINAL APCH FIX, RWY 20R, WE GOT A GS BELOW THE NORMAL GS. NO FLAGS. IDENT NORMAL. AN SMA ON APCH BEFORE US RECEIVED 'CLB IMMEDIATELY, SHOW YOU AT 900 FT' INSTRUCTIONS FROM THE CTLR ON MULTIPLE APCHS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR HAS TALKED TO SEVERAL PEOPLE ABOUT THIS BUT HAS HEARD NOTHING OFFICIAL ABOUT IT. THE WX WAS BASICALLY VFR WITH LOW SCUDDY CLOUDS XING THE ARPT. THE RAINSTORM THAT HAD JUST GONE THROUGH HAD PUT OUT A LOT OF WATER WHICH MAY HAVE CAUSED THE PROB. THE RPTR BELIEVES THAT THE OLD PROB OF FALSE GS HIGH IS NOW PAST BY THE ADVENT OF BETTER EQUIP.

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.