Extracted From:    AC No. 43-16A
    ALERT NO. 307
    February 2004

Cessna; Model 421C; Golden Eagle III; Damaged Engine Exhaust Pipe Riser; ATA 7810

While in IFR flight, the pilot reported the loss of manifold pressure and exhaust gas temperature instrumentation readings. However, manifold pressure stabilized at lower than normal readings. He made a precautionary landing at the closest airport.

The technician pressure checked the exhaust system and found a 2-½ inch hole at the exhaust data plate on the left inside exhaust riser (P/N 8294-3). The damage was not visible without a mirror.

The submitter believed the cause of this incident was due to uneven heating and cooling of the pipe under the data plate, which is welded to the pipe.

The submitter suggested welding the data plate on the outside of the exhaust pipe to allow easier inspections. He also suggested eliminating the data plate and electronically etch information on the riser.

Part total time-unknown.