Saab 340 flight crew has deicing equipment malfunction.

Attributes
ACN	714397
Time
Date	200610
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : saw.airport
State Reference	MI
Altitude	msl single value : 5000
Environment
Flight Conditions	VMC
Weather Elements	Ice
Light	Dusk
Aircraft 1
Controlling Facilities	artcc : zmp.artcc
Operator	common carrier : air carrier
Make Model Name	SF 340B
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	714397
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical inflight encounter : weather
Independent Detector	other flight crewa other flight crewb
Resolutory Action	none taken : unable
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

On descent into saw we began to accrete clear ice. Due to thin cloud deck and ground temperatures; '1 cycle' was selected on the deice boots. I watched the outboard deice boot inflate and noticed that only the inner half of the boot inflated. I pointed this out and we reselected the 1-CYCLE deice again. I again noticed that ice was not being broken off the outer most section of the deice boot. Hp valves were on for all deice attempts. The inner boot on the outer section operated normally. First officer noted that the boots on her side were totally normal. We received no cockpit indication that our boots were not working properly. Several attempts were made once on the ground to see if we still had the same problem. Again only half of the outer boot inflated. Maintenance was contacted once we unloaded all the passenger at the gate. What was most alarming; was that we had an unprotected airfoil surface with no indication to us. We felt lucky that we were able to see the surface visually. Had it been any other surface; we never would have noticed it until we had too much ice and had a controllability issue.

Original NASA ASRS Text

Title: SAAB 340 FLT CREW HAS DEICING EQUIP MALFUNCTION.

Narrative: ON DSCNT INTO SAW WE BEGAN TO ACCRETE CLR ICE. DUE TO THIN CLOUD DECK AND GND TEMPS; '1 CYCLE' WAS SELECTED ON THE DEICE BOOTS. I WATCHED THE OUTBOARD DEICE BOOT INFLATE AND NOTICED THAT ONLY THE INNER HALF OF THE BOOT INFLATED. I POINTED THIS OUT AND WE RESELECTED THE 1-CYCLE DEICE AGAIN. I AGAIN NOTICED THAT ICE WAS NOT BEING BROKEN OFF THE OUTER MOST SECTION OF THE DEICE BOOT. HP VALVES WERE ON FOR ALL DEICE ATTEMPTS. THE INNER BOOT ON THE OUTER SECTION OPERATED NORMALLY. FO NOTED THAT THE BOOTS ON HER SIDE WERE TOTALLY NORMAL. WE RECEIVED NO COCKPIT INDICATION THAT OUR BOOTS WERE NOT WORKING PROPERLY. SEVERAL ATTEMPTS WERE MADE ONCE ON THE GND TO SEE IF WE STILL HAD THE SAME PROB. AGAIN ONLY HALF OF THE OUTER BOOT INFLATED. MAINT WAS CONTACTED ONCE WE UNLOADED ALL THE PAX AT THE GATE. WHAT WAS MOST ALARMING; WAS THAT WE HAD AN UNPROTECTED AIRFOIL SURFACE WITH NO INDICATION TO US. WE FELT LUCKY THAT WE WERE ABLE TO SEE THE SURFACE VISUALLY. HAD IT BEEN ANY OTHER SURFACE; WE NEVER WOULD HAVE NOTICED IT UNTIL WE HAD TOO MUCH ICE AND HAD A CONTROLLABILITY ISSUE.

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.