For any given rpm, there is a manifold pressure that should  not be exceeded. If manifold pressure is excessive for a given  rpm, the pressure within the cylinders could be exceeded,  placing undue stress on the cylinders. If repeated too  frequently, this stress can weaken the cylinder components  and eventually cause engine failure.  Operating Handbook (POH), but was unable to reach the  airport and was forced to conduct an off-field landing.  It was further explained that a determination was made that the  propeller experienced a failure causing the blade pitch change  mechanism to move to the low pitch stop position. This caused  the propeller to operate as a fixed-pitch propeller such that it  changes rpm with changes in power and airspeed. The low  pitch setting allows for maximum power during takeoff but  can result in a propeller overspeed at a higher airspeed.  A pilot can avoid conditions that overstress the cylinders  by being constantly aware of the rpm, especially when  increasing the manifold pressure. Consult the manufacturer’s  recommendations for power settings of a particular engine to  maintain the proper relationship between manifold pressure  and rpm.  When both manifold pressure and rpm need to be changed,  avoid engine overstress by making power adjustments in  the proper order:  A performance evaluation of the flight condition was  performed for the particular aircraft model involved in this  incident. This evaluation indicated that an airspeed lower  than the best glide speed would have resulted in increased  thrust enabling the pilot to maintain level flight. There are  numerous variables in aircraft, engines, and propellers  that affect aircraft performance. For some aircraft models,  the published best glide speed may not be low enough to  generate adequate thrust for a given propeller installation in  this situation (propeller blades at low pitch stop position).  The operators of aircraft with variable pitch propellers should  be aware that in certain instances of propeller overspeed, the  airspeed necessary to maintain level flight may be different  than the speed associated with engine-out best glide speed.  The appropriate emergency procedures should be followed to  mitigate the emergency situation in the event of a propeller  overspeed; however, pilots should be aware that some  reduction in airspeed may result in the ability for continued  safe flight and landing. The determination of an airspeed that  is more suitable than engine-out best glide speed should only  be conducted at a safe altitude when the pilot has time to  determine an alternative course of action other than landing  immediately.  The engine and/or airframe manufacturer’s recommendations  should be followed to prevent severe wear, fatigue, and  damage to high-performance reciprocating engines.  On March 17, 2010, the Federal Aviation Administration  (FAA) issued Special Airworthiness Information Bulletin  (SAIB) CE-10-21. The subject was Propellers/Propulsers;  Propeller Overspeed in Piston Engine Aircraft to alert  operators, pilots, and aircraft manufacturers of concerns  for an optimum response to a propeller overspeed in piston  engine aircraft with variable pitch propellers. Although a  SAIB is not regulatory in nature, the FAA recommends that  the information be read and taken into consideration for the  safety of flight.  The induction system brings in air from the outside, mixes  it with fuel, and delivers the fuel-air mixture to the cylinder  where combustion occurs. Outside air enters the induction  system through an intake port on the front of the engine  cowling. This port normally contains an air filter that inhibits  the entry of dust and other foreign objects. Since the filter  may occasionally become clogged, an alternate source of  air must be available. Usually, the alternate air comes from  inside the engine cowling, where it bypasses a clogged air  filter. Some alternate air sources function automatically,  while others operate manually.  The document explains that a single-engine aircraft  experienced a propeller overspeed during cruise flight at  7,000 feet. The pilot reported that the application of throttle  resulted in a propeller overspeed with no appreciable thrust.  The pilot attempted to glide to a nearby airport and established  the “best glide” speed of 110 knots, as published in the Pilot’s  7-7  Induction Systems  Propeller Overspeed in Piston Engine Aircraft  • When power settings are being decreased, reduce  manifold pressure before reducing rpm. If rpm is  reduced before manifold pressure, manifold pressure  automatically increases, possibly exceeding the  manufacturer’s tolerances.  • When power settings are being increased, reverse the  order—increase rpm first, then manifold pressure.  • To prevent damage to radial engines, minimize  operating time at maximum rpm and manifold  pressure, and avoid operation at maximum rpm and  low manifold pressure. 