SF340 crew descends below charted altitude on approach in czyz airspace.

Attributes
ACN	415915
Time
Date	199809
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : ciu
State Reference	MI
Altitude	msl bound lower : 2400 msl bound upper : 4000
Environment
Flight Conditions	Mixed
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : czyz
Operator	common carrier : air carrier
Make Model Name	SF 340A
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	descent : approach descent other
Route In Use	approach : straight in arrival other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 250 flight time total : 4850 flight time type : 1130
ASRS Report	415915
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 2100 flight time type : 450
ASRS Report	415284
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : clearance non adherence : published procedure other spatial deviation
Independent Detector	other controllera other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were descending from cruise altitude to land at the ciu airport, approaching the airport from the southeast. We were expecting to get a visual approach to runway 33, and were anticipating the controller to give us a lower altitude than the assigned 4000 ft MSL (which we were flying at). At 4000 ft we were just in the bases of the overcast layer and had intermittent ground contact below. This is the first time both myself or the copilot had been to the ciu airport. We asked the controller for lower, as we wanted to break out and go visually. When he advised us that this altitude was as low as he could give us, we were about 15 mi from the airport. I realized we wouldn't get in visually so I asked for a vector to the NDB approach to the landing runway. We were practically on the inbound course anyway. We were rushed and didn't look at the approach plate close enough. There is a stepdown fix on the approach at around 30 DME fix from another VOR's crossing radial. At this point we could descend to 2400 ft to VFR conditions, which is what we wanted to do. (Just use the approach to get below the bases and go visually.) when we tuned in the crossing VOR's radial and DME to determine our stepdown fix, it read 28.5 DME. We proceeded down to 2400 ft, as we were on the inbound course established and believed we had crossed the stepdown fix. We broke out visually and had the field in sight. The controller told us to climb back to 4000 ft as we had descended too early. We climbed back into the clouds and figured out that instead of the DME normally counting down as we expected, it should have gone up based on the angle of the crossing radial. At 28.5 DME, we were actually 1.5 mi away from the stepdown. Instead we thought we were 1.5 mi inside (past) the fix. Some factors that led us into this situation were that we were expecting a visual approach initially and hadn't expected to use the approach until we were very close to the airport. This led us to rush the approach brief and not carefully review the approach plate as we would normally do. This could have been a deadly mistake in mountainous terrain. Next time I will try to establish from the controller what approach to expect further out from airports. If the WX is marginal, I will ask for the approach further out and have more time to set up and brief the approach.

Original NASA ASRS Text

Title: SF340 CREW DSNDS BELOW CHARTED ALT ON APCH IN CZYZ AIRSPACE.

Narrative: WE WERE DSNDING FROM CRUISE ALT TO LAND AT THE CIU ARPT, APCHING THE ARPT FROM THE SE. WE WERE EXPECTING TO GET A VISUAL APCH TO RWY 33, AND WERE ANTICIPATING THE CTLR TO GIVE US A LOWER ALT THAN THE ASSIGNED 4000 FT MSL (WHICH WE WERE FLYING AT). AT 4000 FT WE WERE JUST IN THE BASES OF THE OVCST LAYER AND HAD INTERMITTENT GND CONTACT BELOW. THIS IS THE FIRST TIME BOTH MYSELF OR THE COPLT HAD BEEN TO THE CIU ARPT. WE ASKED THE CTLR FOR LOWER, AS WE WANTED TO BREAK OUT AND GO VISUALLY. WHEN HE ADVISED US THAT THIS ALT WAS AS LOW AS HE COULD GIVE US, WE WERE ABOUT 15 MI FROM THE ARPT. I REALIZED WE WOULDN'T GET IN VISUALLY SO I ASKED FOR A VECTOR TO THE NDB APCH TO THE LNDG RWY. WE WERE PRACTICALLY ON THE INBOUND COURSE ANYWAY. WE WERE RUSHED AND DIDN'T LOOK AT THE APCH PLATE CLOSE ENOUGH. THERE IS A STEPDOWN FIX ON THE APCH AT AROUND 30 DME FIX FROM ANOTHER VOR'S XING RADIAL. AT THIS POINT WE COULD DSND TO 2400 FT TO VFR CONDITIONS, WHICH IS WHAT WE WANTED TO DO. (JUST USE THE APCH TO GET BELOW THE BASES AND GO VISUALLY.) WHEN WE TUNED IN THE XING VOR'S RADIAL AND DME TO DETERMINE OUR STEPDOWN FIX, IT READ 28.5 DME. WE PROCEEDED DOWN TO 2400 FT, AS WE WERE ON THE INBOUND COURSE ESTABLISHED AND BELIEVED WE HAD CROSSED THE STEPDOWN FIX. WE BROKE OUT VISUALLY AND HAD THE FIELD IN SIGHT. THE CTLR TOLD US TO CLB BACK TO 4000 FT AS WE HAD DSNDED TOO EARLY. WE CLBED BACK INTO THE CLOUDS AND FIGURED OUT THAT INSTEAD OF THE DME NORMALLY COUNTING DOWN AS WE EXPECTED, IT SHOULD HAVE GONE UP BASED ON THE ANGLE OF THE XING RADIAL. AT 28.5 DME, WE WERE ACTUALLY 1.5 MI AWAY FROM THE STEPDOWN. INSTEAD WE THOUGHT WE WERE 1.5 MI INSIDE (PAST) THE FIX. SOME FACTORS THAT LED US INTO THIS SIT WERE THAT WE WERE EXPECTING A VISUAL APCH INITIALLY AND HADN'T EXPECTED TO USE THE APCH UNTIL WE WERE VERY CLOSE TO THE ARPT. THIS LED US TO RUSH THE APCH BRIEF AND NOT CAREFULLY REVIEW THE APCH PLATE AS WE WOULD NORMALLY DO. THIS COULD HAVE BEEN A DEADLY MISTAKE IN MOUNTAINOUS TERRAIN. NEXT TIME I WILL TRY TO ESTABLISH FROM THE CTLR WHAT APCH TO EXPECT FURTHER OUT FROM ARPTS. IF THE WX IS MARGINAL, I WILL ASK FOR THE APCH FURTHER OUT AND HAVE MORE TIME TO SET UP AND BRIEF THE APCH.

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.