Late runway change results in descent below cleared altitude at ord for FA50 flight crew.

Attributes
ACN	749371
Time
Date	200708
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	msl single value : 8000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	general aviation : corporate
Make Model Name	Falcon 50
Operating Under FAR Part	Part 91
Navigation In Use	other
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 : 75 flight time total : 5700 flight time type : 1000
ASRS Report	749371
Events
Anomaly	altitude deviation : overshoot non adherence : clearance non adherence : published procedure other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned altitude
Supplementary
Problem Areas	Chart Or Publication Flight Crew Human Performance ATC Human Performance Airport
Primary Problem	ATC Human Performance

Narrative:

On descent into ord the first officer picked up the ATIS which advised of approachs being conducted to the west runways. The FMS was programmed and I briefed the runway 28 ILS. Approximately 25 NM from the airport we were told to turn right to intercept the runway 4R localizer; maintain 8000 ft until degan; cleared ILS runway 4R. We were unprepared for an immediate approach; but did our best getting the approach set up. What we didn't know was the GS is below 8000 ft MSL over degan. So; as we are trained; I armed the approach mode on the fgp as soon as the approach clearance was given and the frequency tuned. Since we were given this runway change on such short notice I let the autopilot fly while the first officer and I reviewed the approach and ran the checklists. I looked up just as the autoplt captured the GS and started a descent from 8000 ft. I noticed that we were about 2 miles short of degan and turned the autoplt off and returned to 8000 ft. Thankfully; we only descended about 150 ft below the assigned altitude before returning. I believe that approach controllers should either warn crews about intercept altitudes verbally or on the approach plate in this type of scenario. I don't believe that we caused any conflict; but we might not be so lucky next time.

Original NASA ASRS Text

Title: LATE RWY CHANGE RESULTS IN DESCENT BELOW CLRED ALT AT ORD FOR FA50 FLT CREW.

Narrative: ON DSCNT INTO ORD THE FO PICKED UP THE ATIS WHICH ADVISED OF APCHS BEING CONDUCTED TO THE WEST RWYS. THE FMS WAS PROGRAMMED AND I BRIEFED THE RWY 28 ILS. APPROX 25 NM FROM THE ARPT WE WERE TOLD TO TURN R TO INTERCEPT THE RWY 4R LOC; MAINTAIN 8000 FT UNTIL DEGAN; CLRED ILS RWY 4R. WE WERE UNPREPARED FOR AN IMMEDIATE APCH; BUT DID OUR BEST GETTING THE APCH SET UP. WHAT WE DIDN'T KNOW WAS THE GS IS BELOW 8000 FT MSL OVER DEGAN. SO; AS WE ARE TRAINED; I ARMED THE APCH MODE ON THE FGP AS SOON AS THE APCH CLRNC WAS GIVEN AND THE FREQUENCY TUNED. SINCE WE WERE GIVEN THIS RWY CHANGE ON SUCH SHORT NOTICE I LET THE AUTOPILOT FLY WHILE THE FO AND I REVIEWED THE APCH AND RAN THE CHKLISTS. I LOOKED UP JUST AS THE AUTOPLT CAPTURED THE GS AND STARTED A DSCNT FROM 8000 FT. I NOTICED THAT WE WERE ABOUT 2 MILES SHORT OF DEGAN AND TURNED THE AUTOPLT OFF AND RETURNED TO 8000 FT. THANKFULLY; WE ONLY DESCENDED ABOUT 150 FT BELOW THE ASSIGNED ALTITUDE BEFORE RETURNING. I BELIEVE THAT APCH CTLRS SHOULD EITHER WARN CREWS ABOUT INTERCEPT ALTITUDES VERBALLY OR ON THE APCH PLATE IN THIS TYPE OF SCENARIO. I DON'T BELIEVE THAT WE CAUSED ANY CONFLICT; BUT WE MIGHT NOT BE SO LUCKY NEXT TIME.

Data retrieved from NASA's ASRS site as of January 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.