Top 10 Tire Tips per Goodyear
- CHECK TIRE PRESSURES DAILY. Daily pressure checks are critical because aircraft tire assemblies can lose as much as 5% of inflation pressure in 24 hours.
Aircraft tire pressure must be checked when the tires are cool (at ambient temperature) because heat generated during taxis, takeoffs, and landings can result in elevated pressure readings. - REMOVE TIRES THAT ARE MORE THAN 10% UNDERINFLATED, if they have been taxied. Under-inflation greatly increases tire stress in service, wearing the tire shoulder area faster and damaging the tire’s inner liner – potentially making the tire unserviceable.
- AVOID OVERINFLATION AS IT OFTEN LEADS TO UNEVEN TREADWEAR and reduced traction, making the tread area more susceptible to cuts and placing greater stress on aircraft wheels and landing gear.
- WAIT 12 HOURS BEFORE PUTTING NEW TIRES IN SERVICE AFTER INITIAL INFLATION. All tires will stretch after the initial inflation, causing a volume increase and thus a drop in pressure. Tires should not be placed in service until they’ve been inflated for a minimum of 12 hours. The pressure should then be checked and inflation added, if necessary.
- RE-CHECK INFLATION 24 HOURS after the 12-hour stretch period to make sure the assembly is still holding inflation properly. This is especially important for tubeless assemblies, because they can lose pressure from multiple locations, such as the wheel valve, o-ring, fuse plug, overpressure plug, wheel cracks and similar areas.
- MINIMIZE VIBRATION WITH PROPER TIRE AND WHEEL ASSEMBLY. All tires are balanced at the factory. The red balance dot on the sidewall is to be aligned with the inflation valve for optimum tire and wheel assembly balance with less vibration. Gear misalignment, worn or loose gear components, improperly torque axle or wheel nuts, flat-spotted tires, and similar problems can cause vibration on an aircraft.
- AVOID THE #1 CAUSE FOR EARLY TIRE REMOVAL – FOREIGN OBJECT DAMAGE. By diligently clearing all foreign objects from hangar floors and ramps, foreign object damage can be reduced. Even something as innocuous as a washer can cut a tire that is under heavy load.
- REMOVE DAMAGED TIRES IF FABRIC PLY CORDS ARE VISIBLE, and cord exposure exceeds acceptable limits. Cuts, cracks, and other conditions may require removing the tire from service. For specific information, see the Goodyear Aviation Tire Care & Maintenance manual.
- EXAMINE TIRES FOR UNEVEN WEAR, AND CORRECT THE CAUSE such as gear misalignment or improper tire inflation. Tires with camber-induced asymmetric wear can be demounted and mounted in the reverse direction to extend the tires life.
- REMOVE TIRES WHEN THREAD IS WORN TO THE BASE of any groove at any spot, or to the depth stated by the aircraft manufacturer.
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.
