HS125 flight crew is questioned by ATC regarding intercept altitude on ILS for mdw.

Attributes
ACN	590420
Time
Date	200308
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : mdw.airport
State Reference	IL
Altitude	msl single value : 4000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	general aviation : corporate
Make Model Name	BAe 125 Series 800
Operating Under FAR Part	Part 91
Navigation In Use	ils localizer & glide slope : 4r other
Flight Phase	descent : approach
Route In Use	arrival : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : corporate
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 150 flight time total : 5300 flight time type : 800
ASRS Report	590420
Person 2
Affiliation	company : corporate
Function	flight crew : first officer
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to original clearance
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During vectors to ILS runway 4R approach at mdw, I received a clearance which contained, 'descend and maintain 2000 ft till established, maintain 180 KTS or greater to the marker. Contact tower 118.7. Cleared ILS runway 4R.' mins later tower asked us to return to approach. The controller asked, 'what are you doing at 2000 ft?' I responded, 'that was the altitude we were assigned and read back.' the controller responded, 'the intercept altitude is 2600 ft.' I reported level at 2600 ft moments later and changed to tower 118.7 at the marker. No TCASII or GPWS alerts were generated. In my judgment, this miscom occurred due to multiple factors. The speed or rapidity of the approach clearance and the large number of elements made it difficult to receive. Also, I did not clarify each element of the clearance, as the frequency was congested and the pace rapid. My copilot and I still believe we were cleared to 2000 ft, but the complexity of the clearance may also have contributed to our aircraft being 600 ft low on the localizer to runway 4R before correcting to 2600 ft for GS intercept.

Original NASA ASRS Text

Title: HS125 FLT CREW IS QUESTIONED BY ATC REGARDING INTERCEPT ALT ON ILS FOR MDW.

Narrative: DURING VECTORS TO ILS RWY 4R APCH AT MDW, I RECEIVED A CLRNC WHICH CONTAINED, 'DSND AND MAINTAIN 2000 FT TILL ESTABLISHED, MAINTAIN 180 KTS OR GREATER TO THE MARKER. CONTACT TWR 118.7. CLRED ILS RWY 4R.' MINS LATER TWR ASKED US TO RETURN TO APCH. THE CTLR ASKED, 'WHAT ARE YOU DOING AT 2000 FT?' I RESPONDED, 'THAT WAS THE ALT WE WERE ASSIGNED AND READ BACK.' THE CTLR RESPONDED, 'THE INTERCEPT ALT IS 2600 FT.' I RPTED LEVEL AT 2600 FT MOMENTS LATER AND CHANGED TO TWR 118.7 AT THE MARKER. NO TCASII OR GPWS ALERTS WERE GENERATED. IN MY JUDGMENT, THIS MISCOM OCCURRED DUE TO MULTIPLE FACTORS. THE SPD OR RAPIDITY OF THE APCH CLRNC AND THE LARGE NUMBER OF ELEMENTS MADE IT DIFFICULT TO RECEIVE. ALSO, I DID NOT CLARIFY EACH ELEMENT OF THE CLRNC, AS THE FREQ WAS CONGESTED AND THE PACE RAPID. MY COPLT AND I STILL BELIEVE WE WERE CLRED TO 2000 FT, BUT THE COMPLEXITY OF THE CLRNC MAY ALSO HAVE CONTRIBUTED TO OUR ACFT BEING 600 FT LOW ON THE LOC TO RWY 4R BEFORE CORRECTING TO 2600 FT FOR GS INTERCEPT.

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.