ILS system was turned off while air carrier was on approach during IMC WX on coupled approach.

Attributes
ACN	142371
Time
Date	199004
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : den
State Reference	CO
Altitude	msl bound lower : 600 msl bound upper : 700
Environment
Flight Conditions	IMC
Light	Dusk
Aircraft 1
Controlling Facilities	tower : den
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 3 Turbojet Eng
Flight Phase	descent : approach
Route In Use	arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 240 flight time total : 15670
ASRS Report	142371
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	other anomaly other
Independent Detector	other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	Other
Supplementary
Primary Problem	ATC Human Performance
Air Traffic Incident	other

Narrative:

While on an ILS/coupled approach to runway 35R at den the tower controller requested us to report the runway in sight. At 700' AGL we reported the runway in sight and the controller announced that he was 'switching' the ILS. We had no idea what he was talking about and queried him as to what he meant. He announced that the ILS was being turned off for our landing runway and turned on for runway 8R. We requested him to 'stand by 1.' this was done in order that we disconnect the autoplt from the ILS to prevent a possible confusion action by the autoplt. We did so and landed normally. This could have possible been a disastrous situation and we feel that during IMC conditions when autoplt couplers are being used, the controllers should be aware that the sudden removal of the ILS NAVAID could cause a serious problem in the cockpit with possible disastrous consequences. No other G/south guidance was available to this runway.

Original NASA ASRS Text

Title: ILS SYSTEM WAS TURNED OFF WHILE ACR WAS ON APCH DURING IMC WX ON COUPLED APCH.

Narrative: WHILE ON AN ILS/COUPLED APCH TO RWY 35R AT DEN THE TWR CTLR REQUESTED US TO RPT THE RWY IN SIGHT. AT 700' AGL WE RPTED THE RWY IN SIGHT AND THE CTLR ANNOUNCED THAT HE WAS 'SWITCHING' THE ILS. WE HAD NO IDEA WHAT HE WAS TALKING ABOUT AND QUERIED HIM AS TO WHAT HE MEANT. HE ANNOUNCED THAT THE ILS WAS BEING TURNED OFF FOR OUR LNDG RWY AND TURNED ON FOR RWY 8R. WE REQUESTED HIM TO 'STAND BY 1.' THIS WAS DONE IN ORDER THAT WE DISCONNECT THE AUTOPLT FROM THE ILS TO PREVENT A POSSIBLE CONFUSION ACTION BY THE AUTOPLT. WE DID SO AND LANDED NORMALLY. THIS COULD HAVE POSSIBLE BEEN A DISASTROUS SITUATION AND WE FEEL THAT DURING IMC CONDITIONS WHEN AUTOPLT COUPLERS ARE BEING USED, THE CTLRS SHOULD BE AWARE THAT THE SUDDEN REMOVAL OF THE ILS NAVAID COULD CAUSE A SERIOUS PROB IN THE COCKPIT WITH POSSIBLE DISASTROUS CONSEQUENCES. NO OTHER G/S GUIDANCE WAS AVAILABLE TO THIS RWY.

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.