Unexpected ILS frequency change on an automatic-tune ILS aircraft.

Attributes
ACN	287424
Time
Date	199410
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : cvg
State Reference	OH
Altitude	msl bound lower : 2000 msl bound upper : 2000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : cvg
Operator	common carrier : air carrier
Make Model Name	B757 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 18000 flight time type : 2800
ASRS Report	287424
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

VFR approach to runway 18R with ILS backup. (B-757) at about 2000 ft above touchdown I noticed the ILS indications had disappeared. Copilot looked at ILS control panel and noticed the frequency had changed itself from 111.5 (runway 18R) to 108.7 (the frequency for runway 27). He tuned it back to 111.5 and all ILS indications returned. I have no idea how this thing could retune itself, but it would be exiting during a category III approach with autoland. Never seen this before.

Original NASA ASRS Text

Title: UNEXPECTED ILS FREQ CHANGE ON AN AUTO-TUNE ILS ACFT.

Narrative: VFR APCH TO RWY 18R WITH ILS BACKUP. (B-757) AT ABOUT 2000 FT ABOVE TOUCHDOWN I NOTICED THE ILS INDICATIONS HAD DISAPPEARED. COPLT LOOKED AT ILS CTL PANEL AND NOTICED THE FREQ HAD CHANGED ITSELF FROM 111.5 (RWY 18R) TO 108.7 (THE FREQ FOR RWY 27). HE TUNED IT BACK TO 111.5 AND ALL ILS INDICATIONS RETURNED. I HAVE NO IDEA HOW THIS THING COULD RETUNE ITSELF, BUT IT WOULD BE EXITING DURING A CATEGORY III APCH WITH AUTOLAND. NEVER SEEN THIS BEFORE.

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.