(1) Subject to section 78A, if the annual rate of salary of an eligible employee who has not attained his or her maximum retiring age and is not entitled to partial invalidity pension in accordance with section 77 decreases under such circumstances that CSC is satisfied that the decrease can properly be regarded as attributable to physical or mental incapacity and:
(a) the number of complete years included in the period that would have been his or her period of contributory service if he or she had ceased to be an eligible employee on the day immediately preceding the day on which that rate decreases is not less than 8 years; or
(b) where the number of complete years included in that period is less than 8 years:
(i) a benefit classification certificate is not in force in respect of him or her immediately before that last - mentioned day; or
(ii) a benefit classification certificate is so in force in respect of him or her but CSC is of the opinion that the physical or mental incapacity was not caused, or substantially contributed to, by a physical or mental condition or conditions specified in the certificate or a physical or mental condition or conditions connected with such a condition or such conditions;
he or she is entitled to a partial invalidity pension in accordance with this section.
(2) The annual rate of partial invalidity pension to which a person is, at any time, entitled by virtue of subsection (1) is:
(a) except where paragraph (b) applies:
(i) if the annual rate of his or her salary is, at that time, not less than one - half of his or her previous annual rate of salary--an amount per annum ascertained in accordance with the formula:
where:
"A" is an amount per annum equal to the annual rate at which invalidity pension would have been payable to him or her in accordance with section 68 if he or she had become entitled to invalidity benefit on the day on which he or she became entitled to partial invalidity pension and had made an election under subsection 68(1) and if subsection 68(4A) did not apply to him or her.
"B" is an amount per annum equal to the annual rate that would have been his or her final annual rate of salary if he or she ceased to be an eligible employee on the day immediately preceding the day on which he or she became entitled to partial invalidity pension.
"C" is an amount per annum equal to his or her previous annual rate of salary; and
"D" is an amount per annum equal to his or her annual rate of salary; or
(ii) if the annual rate of his or her salary is, at that time, less than one - half of his or her previous annual rate of salary--such annual rate as CSC, in its discretion, determines, being an annual rate not less than the rate that would be payable to the person if subparagraph (i) applied to him or her; or
(b) where:
(i) there was in force in respect of the person, immediately before he or she became entitled to partial invalidity pension in accordance with this section, a benefit classification certificate; and
(ii) CSC is of the opinion that the physical or mental incapacity referred to in subsection (1) was caused, or substantially contributed to, by a physical or mental condition or conditions specified in the certificate or a physical or mental condition or conditions connected with such a condition or such conditions;
then:
(iii) if the annual rate of his or her salary, at that time, is not less than one - half of his or her previous annual rate of salary--an amount per annum ascertained in accordance with the formula:
where:
"A" is an amount per annum equal to the annual rate at which invalidity pension would have been payable to him or her in accordance with section 71 if he or she had become entitled to invalidity benefit on the day on which he or she became entitled to partial invalidity pension and had made an election under subsection 71(1) and if subsection 71(4A) did not apply to him or her.
"B" is an amount per annum equal to the annual rate that would have been his or her final annual rate of salary if he or she ceased to be an eligible employee on the day immediately preceding the day on which he or she became entitled to partial invalidity pension.
"C" is an amount per annum equal to his or her previous annual rate of salary; and
"D" is an amount per annum equal to his or her annual rate of salary; or
(iv) if the annual rate of his or her salary is, at that time, less than one - half of his or her previous rate of salary--such annual rate as CSC, in its discretion, determines, being an annual rate not less than the rate that would be payable to the person if subparagraph (iii) applied to him or her.
(3) Upon the annual rate of salary of a person to whom partial invalidity pension is payable in accordance with this section becoming equal to or greater than his or her previous annual rate of salary, his or her entitlement to that pension is, by force of this subsection, cancelled.
(4) Upon a person to whom partial invalidity pension is payable in accordance with this section ceasing to be an eligible employee, his or her entitlement to that pension is, by force of this subsection, cancelled.
(5) Subject to subsection (6), a reference in this section to the previous annual rate of salary of a person to whom subsection (1) applies shall be read as a reference to the rate that was his or her annual rate of salary immediately before he or she became entitled to partial invalidity pension under this section.
(6) Where at any time CSC, having regard to any changes in rates of remuneration which have occurred since a person referred to in subsection (5) became entitled to partial invalidity pension and which CSC considers to be relevant, is of the opinion that the previous annual rate of salary of the person should, for the purposes of this section, be a rate other than the rate referred to in subsection (5) or a rate specified by CSC in a previous determination made under this subsection, CSC may determine that, for the purposes of this section, the previous annual rate of salary of the person shall, from the date of the determination or such other date as is specified in the determination, be deemed to be such rate as is specified in the determination.
(7) Subject to subsection (8), a reference in the preceding provisions of this section to the annual rate of the salary of a person to whom subsection (1) applies shall, notwithstanding any change in that rate of salary, be read as a reference to the rate that was his or her annual rate of salary on the day on which he or she became entitled to partial invalidity pension under this section.
(8) Where at any time CSC, having regard to any changes in the annual rate of salary of a person referred to in subsection (7) which have occurred since he or she became entitled to partial invalidity pension and which CSC considers to be relevant, is of the opinion that the annual rate of salary of the person should, for the purposes of this section, be a rate other than the rate referred to in subsection (7) or a rate specified by CSC in a previous determination made under this subsection, CSC may determine that, for the purposes of this section, the annual rate of the salary of the person shall, from the date of the determination or such other date as is specified in the determination, be deemed to be such rate as is specified in the determination.