Date: 201603
Local time of day: 1201-1800
Location: ZDC.ARTCC, VA
Flight conditions: IMC
Weather elements / visibility: Turbulence
Light: Daylight
Aircraft: Piper Twin Piston Undifferentiated or Other Model
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Cruise
Airspace: Class E ZDC
ATC / advisory: Center ZDC
Aircraft component: Standby Magnetic Compass
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Single Pilot
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Commercial
Human factors: Communication Breakdown; Situational Awareness
Anomaly: ATC Issue All Types; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Took Evasive Action; Flight Crew Regained Aircraft Control
Contributing factors: Airspace Structure; Human Factors; Weather
Primary problem: Weather

Narrative: The pre-flight briefing from FSS indicated that for the IFR flight a cold front would pass through the Maryland area. Due to strong tailwinds at 9;000; the aircraft arrived in the Delaware/Maryland vicinity (35nm northeast PXT on V16); on an IFR flight plan prior to the trailing edge of frontal passage. No convective activity was forecast; reported; or experienced in flight. There was no precipitation encountered. There were no altitude; routing or course assignment deviations. All ATC clearances were complied with; including a descent from 9;000 msl to 7;000 which then put the aircraft in IMC with moderate turbulence. The aircraft did not have 'real time' weather radar but did provide two sources of nexrad weather depicting light precipitation.Although I requested to remain at 9;000; to remain above the weather; ATC was unable to approve the request 'due to the Philadelphia area arrivals'. Accepting and complying with the ATC assigned altitude descent to 7;000 was in retrospect; a mistake. I should have negotiated a more easterly course to avoid the weather; but what happened instead is that the aircraft experienced moderate and intermittent severe turbulence. When reporting this to ATC; they questioned the intensity of the turbulence; and I confirmed 'severe' turbulence with intermittent loss of control of the aircraft.There were several frequency changes as the flight transitioned ZDC center; and several Potomac approach sectors. In order to get ATC's attention and clearance for a deviation east of the weather; I had to advise [ATC of] the flight condition; and that a turn east was now required immediately for an urgent situation. The subsequent sectors (Dover RAPCON Approach and Atlantic City TRACON) responded with the turn east of the area of turbulence; vectors around the weather; and the flight proceeded as normal. During the period of moderate turbulence; while on an assigned heading; ATC called with an amended route clearance. Due to aircraft handling in turbulent IMC conditions; I had to advise 'Unable to copy' an amended clearance.There was no injury and no aircraft damage; although during the turbulence; a portable remote GPS antenna moved across the glare shield to a position just under the compass. Later in the flight when on vectors for the approach; it became necessary to report an inop gauge (the compass); although it did not impact navigation or the visual approach segment of flight. The problem was corrected in-flight when I noticed that the earlier turbulence moved the remote GPS antenna to close proximity to and affecting the compass. Moving the antenna device (the size of a book of matches) to its original position on the side of the glare shield immediately corrected the compass issues.This experience reminded me that as the PIC; I should not have accepted the descent to 7000 issued by Washington Center; because it caused unnecessary challenging flight operations in turbulent IMC conditions. I should have negotiated a different routing while at 9;000; in VMC; without turbulence; instead of subjecting the flight to an urgent condition (turbulence) by complying with ATC. Next time; if I can see that a descent along the filed routing could subject the flight to moderate (and momentary severe) turbulence; I will advise ATC that I am unable to accept the descent on the current routing; and negotiate a routing around turbulent IMC; for safety.




Synopsis: The pilot of a twin engine Piper reported accepting an ATC descent clearance in IMC conditions with significant turbulence resulting in a momentary loss of control.