On September 10, 2010, at about 1315 eastern daylight time, a Cessna 150, N7922E, owned and operated by a private individual, incurred substantial damaged during a forced landing following a partial loss of engine power shortly after takeoff from the Fayette Airport (WV59), Fayetteville, West Virginia. The airline transport rated pilot and the private pilot passenger received serious injuries. Visual meteorological conditions prevailed for the Title 14 Code of Federal Regulations Part 91, personal flight. The pilot stated that the preflight and ground run prior to flight were unremarkable. During the initial climb the airplane engine's rpm gage indicated 1900 and the airplane would not gain altitude. He elected to land in a field and the airplane collided with trees before impacting the ground. The pilot was able to call for assistance and both pilots were taken to the hospital due to their injuries. The responding Federal Aviation Administration inspector stated that post recovery examination of the airplane revealed fuel in the fuel tanks and observed up to the carburetor system. All cylinders had compression when checked. The right magneto developed sparks to all corresponding plugs. The left magneto produced spark to one plug only. The magnetos, carburetor, and spark plugs were retained for further testing. A review of the airplane maintenance records revealed that the last annual inspection was on April 27, 2010 ,at 2,512 total hours. The magnetos were inspected on August 11, 1994 at 2418 total hours, March 6, 1996 at total 2422, and October 14, 2002 at 2,459 total hours. Examination of the left magneto with National Transportation Safety Board oversight revealed that the exterior appearance of the magneto was consistent with the unit having been in service for a length of time. No exterior damage was observed and the magneto rotated when done so by hand with internal discrepancies noted. When it was disassembled the distributor gear was observed with 12 each gear teeth sheared from the disk, which the sheared gears were recovered within the magneto assembly. The separation was noted starting/ending at the magneto timing block location marker. The distributor cap was observed with indications of arching in-between the housing area. The coil and condenser were tested and found unremarkable. It was noted that the magnetos were required to have the riveted style impulse coupling checked every 100 hours in service as per Airworthiness Directive (AD) 78-09-07, AD 96-12-07, and AD 2005-12-06 and it's identifiable by the missing mark "A" in the lower right corner of the magneto's data plate. Any time after the year 1978, when the magneto was opened, in the case of a riveted impulse coupling examination, the distributor gear was required to be replaced with the updated distributor gear, if not done so as per Teledyne Continental Ignition Systems, Service Bulletin 658. Both magnetos had the old style distributor gear, dating prior to 1978. Teledyne Continental Ignition Systems, Service Bulletin 658 makes warning reference not to use any gear holding tool for this may cause hidden damage to the distributor gear and subsequent engine failure.