Narrative:

On final approach the flaps did not activate. The flaps on the mdt are electrically controled and hydraulically activated. As sufficient runway was available, I continued the approach to a normal landing. All other systems using the same hydraulic system operated normally. Flap activation failures on this aircraft are not uncommon. As with many other system's on this aircraft, the system may be returned to normal by deactivating all electrics and then cycling the system. This procedure did not reactivate the flaps. A call to maintenance was initiated. During the call my first officer noticed the flaps were now working. On previous occasions this had occurred after long flts where the aircraft was subject to low temperatures. Since I had been flying for over 2 hours at FL250 with an OAT at -55 degrees C and not in visible moisture, and since the system now worked fine, I assumed the cold soak to be the cause. Maintenance was not available on site, so I elected not to write the discrepancy up as I considered it an intermittent problem that warmer temperatures had solved. Upon returning to base, I wrote the problem up as an information only entry. FAA is considering certificate action based on their position that I accepted for flight an unairworthy aircraft. In addition, they consider the write up unacceptable. My remarks concerning the FAA are hearsay as I have not been approached by the FAA. Maintenance confirmed to me subsequently that my assessment was correct in that apparently an o-ring in the flap hydraulic distribution valve has a tendency to constrict allowing hydraulic fluid to circulate through the valve west/O actuating the flaps. The mfr is apparently aware of the problem. The constrictions are as a result of cold soak.

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Original NASA ASRS Text

Title: FLAPS ON AN ACR MDT WOULD NOT EXTEND FOLLOWING A 2+ HOUR FLT WITH OAT -55 DEGREES C. AFTER WARM UP ON THE GND THE FLAPS OPERATED NORMALLY.

Narrative: ON FINAL APCH THE FLAPS DID NOT ACTIVATE. THE FLAPS ON THE MDT ARE ELECTRICALLY CTLED AND HYDRAULICALLY ACTIVATED. AS SUFFICIENT RWY WAS AVAILABLE, I CONTINUED THE APCH TO A NORMAL LNDG. ALL OTHER SYSTEMS USING THE SAME HYD SYS OPERATED NORMALLY. FLAP ACTIVATION FAILURES ON THIS ACFT ARE NOT UNCOMMON. AS WITH MANY OTHER SYS'S ON THIS ACFT, THE SYS MAY BE RETURNED TO NORMAL BY DEACTIVATING ALL ELECTRICS AND THEN CYCLING THE SYS. THIS PROC DID NOT REACTIVATE THE FLAPS. A CALL TO MAINT WAS INITIATED. DURING THE CALL MY F/O NOTICED THE FLAPS WERE NOW WORKING. ON PREVIOUS OCCASIONS THIS HAD OCCURRED AFTER LONG FLTS WHERE THE ACFT WAS SUBJECT TO LOW TEMPS. SINCE I HAD BEEN FLYING FOR OVER 2 HRS AT FL250 WITH AN OAT AT -55 DEGS C AND NOT IN VISIBLE MOISTURE, AND SINCE THE SYS NOW WORKED FINE, I ASSUMED THE COLD SOAK TO BE THE CAUSE. MAINT WAS NOT AVAILABLE ON SITE, SO I ELECTED NOT TO WRITE THE DISCREPANCY UP AS I CONSIDERED IT AN INTERMITTENT PROB THAT WARMER TEMPS HAD SOLVED. UPON RETURNING TO BASE, I WROTE THE PROB UP AS AN INFO ONLY ENTRY. FAA IS CONSIDERING CERTIFICATE ACTION BASED ON THEIR POS THAT I ACCEPTED FOR FLT AN UNAIRWORTHY ACFT. IN ADDITION, THEY CONSIDER THE WRITE UP UNACCEPTABLE. MY REMARKS CONCERNING THE FAA ARE HEARSAY AS I HAVE NOT BEEN APPROACHED BY THE FAA. MAINT CONFIRMED TO ME SUBSEQUENTLY THAT MY ASSESSMENT WAS CORRECT IN THAT APPARENTLY AN O-RING IN THE FLAP HYD DISTRIBUTION VALVE HAS A TENDENCY TO CONSTRICT ALLOWING HYD FLUID TO CIRCULATE THROUGH THE VALVE W/O ACTUATING THE FLAPS. THE MFR IS APPARENTLY AWARE OF THE PROB. THE CONSTRICTIONS ARE AS A RESULT OF COLD SOAK.

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.