<xs:attribute name="TimeType" use="required">
    <xs:annotation>
        <xs:documentation xml:lang="en"> Describes whether the operational event time is scheduled, estimated or actual.</xs:documentation>
    </xs:annotation>
    <xs:simpleType>
        <xs:restriction base="xs:NMTOKEN">
            <xs:enumeration value="Actual">
                <xs:annotation>
                    <xs:documentation xml:lang="en"> The actual operation time.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
            <xs:enumeration value="Scheduled">
                <xs:annotation>
                    <xs:documentation xml:lang="en"> The scheduled time.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
            <xs:enumeration value="Estimated">
                <xs:annotation>
                    <xs:documentation xml:lang="en"> The estimated time.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
        </xs:restriction>
    </xs:simpleType>
</xs:attribute>