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TECH TIPS

Emergency Engine Shut Downs

The Fuel Shut-off Valve P/N 394230-X on the TPE331 engines has two methods of cutting fuel to the engine, electrical and mechanical.  Electrically the valve is closed by placing the Run/Crank/Stop (RCS) switch in the “STOP” position. To close the valve mechanically the Condition lever is placed in the “Emergency Stop” position.

In the Mitsubishi Flight Manual under Normal Procedures, Starting Engines there is a CAUTION statement which reads “IF ANY MALFUNCTION OCCURS, ENGINE STOPS, OR RPM STAGNATES PRIOR TO 40% RPM DURING STARTING PROCEDURES, SHUT DOWN ENGINE IMMEDIATELY BY PLACING CONDITION LEVER IN EMERGENCY STOP POSITION.”

In addition to placing the Condition Lever in the “Emergency Stop” position the RCS switch should be placed in the “STOP” position with power on the aircraft to electrically close the solenoid portion of the Fuel Shut-off Valve.

If the valve is not closed electrically, when the condition lever is moved to the “TAXI” position the valve will be in the “Open” position.  When electrical power is applied the aircraft boost pumps will supply low pressure fuel into a possibly hot engine turbine section.  This condition may allow the fuel to ignite causing an “After Fire”.  The “After Fire” has the potential to cause aircraft damage, or an excitable line person with quick access to a fire extinguisher could turn something minor into a very expensive event.

Veritherm Valves

Each engine installed on a MU2 is equipped with a unit, mounted above the nose case, commonly referred to as a veritherm valve.  The basic function of this valve is to route scavenge oil from the engine to the airframe mounted oil cooler.  From time to time the veritherm valve installed on your aircraft may require maintenance due to leaks or excessive oil temperature indications.

    In the event repair or replacement of this unit is required, extra caution should be exercised while installing the AN unions into the valve body.  The 90 and 45 degree unions in particular can be installed too far into the valve body.  When this occurs these unions can make contact with the internal valve assembly.

    As the oil temperature reaches approximately 100 degrees centigrade the internal valve will close routing oil through the cooler.  In the event one or both of these unions are improperly installed the flow of oil through the cooler will be partially or completely blocked.
   Depending upon current conditions and actual valve operation this condition may not be immediately apparent until temperatures increase due to a rise in OAT or increased ground operations.  If this condition exists when oil temperature increases and the valve closes, engine oil will start to vent from the oil tank vent drain due to the blockage in the veritherm valve. In the event there is only a partial blockage or there is some wear at the internal valve seat this condition may only result in elevated oil temperatures.

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