<< >> NASA ASRS Report 815882, December 2008

An EMB145 flight crew reports capturing a false glideslope during an ILS 28 approach to ord. Glideslope indications were normal. ATC alerted the crew to an altitude deviation. After stopping the descent the ILS glideslope low indication appeared.

Attributes
ACN	815882
Time
Date	200812
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	msl single value : 4000
Environment
Flight Conditions	IMC
Weather Elements	Ice
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	EMB ERJ 145 ER&LR
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 28
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial
ASRS Report	815882
Person 2
Affiliation	government : faa
Function	controller : approach
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : published procedure other anomaly other
Independent Detector	other controllera
Resolutory Action	flight crew : became reoriented flight crew : returned to assigned altitude flight crew : returned to original clearance
Supplementary
Problem Areas	Navigational Facility Airport
Primary Problem	Navigational Facility

Narrative:

While receiving vectors to runway 28 at ord; we were cleared for the ILS approach. The autopilot was engaged. The localizer captured normally. The glideslope was above us at this point. As the approach continued; the glideslope came alive and appeared to capture normally. At this point; we had positive identification on the localizer frequency and all indications were normal. Approximately 2 miles outside of the adame fix; ATC advised us that our altitude was too low and that we were not to be below 4000 ft until adame. We immediately consulted our approach plate. Then as the pilot flying; I disengaged the autopilot and corrected the altitude. Almost immediately as I did this; the glideslope jumped up to where it should have been the entire approach. I got the plane back on the correct glideslope and flew the rest of the approach without incident.

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Original NASA ASRS Text

Title: An EMB145 flight crew reports capturing a false glideslope during an ILS 28 approach to ORD. Glideslope indications were normal. ATC alerted the crew to an altitude deviation. After stopping the descent the ILS glideslope low indication appeared.

Narrative: While receiving vectors to Runway 28 at ORD; we were cleared for the ILS approach. The autopilot was engaged. The LOC captured normally. The Glideslope was above us at this point. As the approach continued; the Glideslope came alive and appeared to capture normally. At this point; we had positive identification on the LOC frequency and all indications were normal. Approximately 2 miles outside of the ADAME fix; ATC advised us that our altitude was too low and that we were not to be below 4000 ft until ADAME. We immediately consulted our approach plate. Then as the Pilot Flying; I disengaged the autopilot and corrected the altitude. Almost immediately as I did this; the glideslope jumped up to where it should have been the entire approach. I got the plane back on the correct glideslope and flew the rest of the approach without incident.

Data retrieved from NASA's ASRS site as of May 2009 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.