MAINTENANCE TIPSPTUPTU inhibition is achieved by closing the solenoid valves (they arefail safe open) at the PTU manifolds, and for maintenance actions byalso disconnecting the coupling on the yellow (right) side of the unit.The PTU operation is inhibited at first engine start and during cargodoor operation.NOTE: At the second engine start, the inhibition is removed whenthe second engine master switch is set to ON then the PTUwill operate momentarily for self test purpose.RATA RAT retraction module controls the RAT stowage procedure. Thismodule is installed on the blue servicing panel.NOTE: To prevent a possible extension during maintenance work,a RAT safety tool must be installed.SAFETY PRECAUTIONSTo prevent an unwanted operation of the PTU, the isolation couplingmust be disconnected.Keep the RAT extension area clear of ground equipment andpersonnel. Install the RAT safety device before working in the RATarea.