Page:CAB Accident Report, Standard Airways Flight 388C.pdf/16

Honorable N. E. Halaby (2) had completely backed off the brake solenoid, rendering the brake ineffective. This Curtiss electric propeller installation also did not feature a mechanical low pitch stop.

Both of these propeller malfunctions involved the brake assembly with the threaded type cage, in which the brake cage is screwed to the brake solenoid. The safety margin of the locking device in this design has proven inadequate in both of these malfunctions. Since this threaded type brake assembly has displayed susceptibility to either improper assembly or maintenance malpractice which might result in a serious accident, the Board recommends that all threaded type brake assemblies be removed from service and replaced by the later bolted design.

Both of these propeller malfunctions have also demonstrated the basic need for a mechanical device to prevent inadvertent operation of the propeller in the reverse range. Accordingly the Board resubmits the recommendation that a mechanical low pitch stop assembly be incorporated in Curtiss electric propellers as expeditiously as possible.

Various particulars of this matter have been discussed with Mr. John Morris of your FS-140 section, Mr D. Ballard of Air Carrier Office, Kansas City, and Mr Henry Weiss of Engineering and Manufacturing Branch, New York.

Sincerely yours,

/s/ Alan E. Boyd

Chairman

Attachment A (page 2 of 6)