N.Y.C. Charter § 276: Section 276. Annual appropriations to the sinking funds.

For the redemption of the corporate stock redeemable from the several sinking funds of the city established prior to July first, nineteen hundred eighty-one there shall be included annually in the budget and paid into each of such sinking funds an amount to be estimated and certified by the comptroller, which amount shall be not less than the aggregate of such annual contributions, as calculated at the time each issue of corporate stock redeemable from such sinking fund was made, would be sufficient if thereafter annually contributed to such fund together with the accumulations of interest thereon computed at the rate of four per centum per annum to meet and discharge such outstanding corporate stock when the same shall be payable; provided, however, that if at the close of a fiscal year there is in any sinking fund a surplus over and above the reserve required by such sinking fund computed as hereinabove provided, the comptroller, in estimating the amount to be included for such sinking fund in the budget, shall reduce the amount of the annual contributions by the amount of such surplus. Amounts received annually from the operation of any rapid transit railroad for the construction, equipment or acquisition of which corporate stock redeemable from any such fund shall have been issued, shall not be considered or treated as surplus, but such amounts shall be deducted from the amount certified by the comptroller for the budget for the ensuing year.