Narrative:

On descent from crs to cross the scurry VOR at 6000' the left propeller went into an overspd condition. The crew was unable to feather the propeller, so shut down the left engine. We were unable to stop the rate of descent and an emergency was declared. At 2700' we were finally able to maintain a level flight condition. Communications had been established with company maintenance at dfw and with their help the crew was able to figure out a way to feather the propeller while it was in this high speed condition. (There were no published procedures for this type of emergency). Once the propeller was feathered we were able to climb the aircraft and leveled at 3000' MSL to continue the short distance to the dfw airport where we landed west/O incident. Callback conversation with reporter revealed the following: was able to stop the descent at 2700' and maintain altitude prior to getting the propeller feathered. Full cooperation from center reference the emergency descent. So much drag was caused by the overspding propeller, 163%, they could not stop the descent at a higher altitude. Able to feather the engine when maintenance suggested motoring the engine dry thereby building up oil pressure in the propeller dome resulting in the propeller feathering. Was advised the same thing had happened to another company aircraft, same type, and other companies have had this problem. One losing an aircraft. Unable to identify the cause of the overspd. Company has sent out a procedure for runaway propeller and has changed descent procedure to reduce RPM to 80% and IAS 180. No other action taken to date. Aircraft originally certified west/O an overspd propeller procedure according to the reporter.

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Original NASA ASRS Text

Title: UNABLE TO FEATHER PROPELLER WHEN OVERSPEED DURING DESCENT. OVERSHOT ALT 3300' ACCOUNT EXCESSIVE DRAG.

Narrative: ON DSCNT FROM CRS TO CROSS THE SCURRY VOR AT 6000' THE LEFT PROP WENT INTO AN OVERSPD CONDITION. THE CREW WAS UNABLE TO FEATHER THE PROP, SO SHUT DOWN THE LEFT ENG. WE WERE UNABLE TO STOP THE RATE OF DSCNT AND AN EMER WAS DECLARED. AT 2700' WE WERE FINALLY ABLE TO MAINTAIN A LEVEL FLT CONDITION. COMS HAD BEEN ESTABLISHED WITH COMPANY MAINT AT DFW AND WITH THEIR HELP THE CREW WAS ABLE TO FIGURE OUT A WAY TO FEATHER THE PROP WHILE IT WAS IN THIS HIGH SPD CONDITION. (THERE WERE NO PUBLISHED PROCS FOR THIS TYPE OF EMER). ONCE THE PROP WAS FEATHERED WE WERE ABLE TO CLB THE ACFT AND LEVELED AT 3000' MSL TO CONTINUE THE SHORT DISTANCE TO THE DFW ARPT WHERE WE LANDED W/O INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING: WAS ABLE TO STOP THE DSCNT AT 2700' AND MAINTAIN ALT PRIOR TO GETTING THE PROP FEATHERED. FULL COOPERATION FROM CENTER REF THE EMER DSCNT. SO MUCH DRAG WAS CAUSED BY THE OVERSPDING PROP, 163%, THEY COULD NOT STOP THE DSCNT AT A HIGHER ALT. ABLE TO FEATHER THE ENG WHEN MAINT SUGGESTED MOTORING THE ENG DRY THEREBY BUILDING UP OIL PRESSURE IN THE PROP DOME RESULTING IN THE PROP FEATHERING. WAS ADVISED THE SAME THING HAD HAPPENED TO ANOTHER COMPANY ACFT, SAME TYPE, AND OTHER COMPANIES HAVE HAD THIS PROB. ONE LOSING AN ACFT. UNABLE TO IDENT THE CAUSE OF THE OVERSPD. COMPANY HAS SENT OUT A PROC FOR RUNAWAY PROP AND HAS CHANGED DSCNT PROC TO REDUCE RPM TO 80% AND IAS 180. NO OTHER ACTION TAKEN TO DATE. ACFT ORIGINALLY CERTIFIED W/O AN OVERSPD PROP PROC ACCORDING TO THE RPTR.

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