60-01-05 LOCKHEED: Amdt. 74 Part 507 Federal Register January 6, 1960. Applies to all 188A and 188C Aircraft.
Compliance required as indicated.
Continuing investigation of the propeller deicing power transfer relay has shown the design of the relay is such that properly tightened terminals cannot be assured for a practical interval of time due to cold flowing of plastic relay body. Upon arrival at the next station where maintenance personnel are available, deactivate the propeller deicing system by pulling the control circuit breaker on the main and essential direct current bus at the forward load center. Placard the propeller deicing system inoperative.
On arrival at main base disconnect 8-gage power wires from the priority A and B bus to the propeller deicing power relay. Type and stow at priority bus end.
With the propeller deicing system deactivated, aircraft may be dispatched into known icing conditions if Icex compound (B. F. Goodrich Company Adhesive Depressant No. 6) is applied to all propeller blade fairing heater boots and spinners under the following conditions: After initial application, Icex compound shall be reapplied after cumulative exposure to not more than six hours precipitation during flight or after 50 hours elapsed time, whichever occurs first.
(Lockheed Alert Bulletin No. 403 wired to all operators on November 27, 1959, covers this same subject.)
The propeller electrical deicing system may be returned to operative status when the original propeller ice control relay (Lockheed P/N 613649-1, Leach P/N 9202-4516) has been removed and a new relay (Lockheed P/N 613422-17, Hartman B124-GL) has been installed in the circuit and physically located in the main transfer relay box in a manner approved by an authorized representative of the Administrator. When the propeller electrical deicing system has been reactivated in this manner, Icex compound will no longer be required for aircraft dispatching into known icing conditions.
(Lockheed Alert Bulletin No. 403 wired to all operators on November 27 covers the deactivation of the original Leach relay and the use of Icex compound. Lockheed 188 Service Bulletin No. 403, effective December 15, 1959, describes a satisfactory and approved means of installing the replacement Hartman relay.)
This airworthiness directive sent by telegram to all operators of Lockheed 188A and 188C aircraft on December 8, 1959.