Aviation Accident Report: Standard Airways Flight 388C/Attachment A
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CIVIL AERONAUTICS BOARD
WASHINGTON, D C
Honorable N E Halaby
Administrator
Federal Aviation Agency
Washington 25, D C
Dear Mr Halaby
After investigating the accident involving Seaboard and Western Airlines L-1049D, N6503C, at Idlewild Airport on November 10, 1958, the Board recommended requirement of a mechanical low pitch stop in the Curtiss electric propeller to prevent any inadvertent reversal. Enclosed is a copy of the pertinent letter to the Director of Flight Operations and Airworthiness, dated December 19, 1958. At this time Curtiss-Wright had available a power unit assembly which provided this safety device. Subsequent correspondence from the Bureau of Flight Standards, dated February 20, 1959, indicated that an appropriate proposed airworthiness directive, which pertained to a mechanical low pitch stop, would be submitted to the industry for coordination This action did not result in an official requirement of this feature.
On May 28, 1963, Standard Airways L-1049G, N189S, crashed during approach at Manhattan, Kansas Investigation of the aircraft indicated that the No. 3 Curtiss electric propeller was inadvertently in the reverse range at one degree blade setting, the low pitch setting is 23.8 degrees. Ground inspection of the power unit revealed that the brake cage was not locked to the brake solenoid and had backed off several revolutions. Since this propeller installation did not incorporate a mechanical low pitch stop, the brake was ineffective in fixing the blades at low pitch and preventing blade angles in the reverse range. Although the aircraft burned after crashing, fortunately no fatalities were incurred by the 65 passengers; however, the potential catastrophe is readily apparent.
Several days later on June 3, 1963, Standard Airways L-1049G, N9742Z, feathered the No. 2 propeller after severe surging during cruise over Elkins, West Virginia. After safely landing at Philadelphia subsequent ground operation of the No. 2 powerplant revealed that the propeller would go into the reverse range without throttle selection. Examination of the propeller power unit disclosed that the brake cage 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.
/s/ Alan E. Boyd
Chairman
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FEDERAL AVIATION AGENCY
WASHINGTON 25, D.C.
Dear Mr. Chairman:
This is to acknowledge your letter of June 14, 1963, reference B-1-96, concerning the removal from service of all threaded type brake assemblies and the incorporation of a mechanical low-pitch stop in Curtiss electric propellers.
This matter has been referred to our Flight Standards Service for attention. We will advise you of our final determination in this matter.
Slncerely yours,
/s/ N E. Halaby
N. E. HALABY
Admlnistrator
Honorable Alan S. Boyd
Chairman
Civil Aeronautics Board
Washington 25, D. C.
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FEDERAL AVIATION AGENCY
WASHINGTON 25, D. C.
Dear Mr. Chairman:
This supplements our July 8, 1963, acknowledgment of your letter dated June 14, 1963, reference B-1-96, concerning brake failures of Curtiss propellers on Lockheed 1049G alrcraft.
Based on the recommendations made by the Civil Aeronautics Board and our investigation of the recent accident at Manhattan, Kansas, on May 28, 1963, and incident at Elkins, West Virgina, on June 3, 1963, involving Standard Airways Lockheed 1049G aircraft, made in conjunction with CAB and Curtiss investigators, we have instituted the following corrective measures.
1.Aircraft Maintenance Bulletin FS P 8340 1 CH 38 dated July 9, 1963, was issued on July 24, 1963, to advise our air carrier inspectors that, if the older threaded type brake cage units are not properly tightened and locked, the cage unit can back off, rendering the brake and low pitch stop ineffective. A copy of the bulletin is enclosed.
2.An airworthiness directive is being prepared which will require replacement of older threaded brake cage units with newer bolted configurations.
Regardlng the November 10, 1958, Seaboard and Western accident at New York International Airport, the CAB Aircraft Accident Report, File No. 1-0116, adopted March 22, 1960, indicated the probable cause was an unwanted propeller reversal and a contributing factor was the inadequate overhaul procedure employed by the propeller manufacturer. The CAB analysis noted that the wear of the rotor spline and mating speed reducer sleeve was of sufficient magnitude to cause complete disengagement between the power unit motor assembly and the speed reducer, thus preventing electrical control of the propeller. The analysis also stated these conditions would permit the centrifugal forces on the blades to move them to the flat pitch position and beyond. Action by this Agency resulted in issuance of Airworthiness Directives 58-25-2 and 59-7-1 requiring inspection of the old motor and speed-reducer spline couplings and AD 59-18-3 which required installation of modified oilbath-lubricated spline couplings. Mechanical low pitch stops were not required on the basis of satisfactory service experience of other Curtiss propeller models equipped with the modified spline couplings. This decision has been amply supported by service experience over the last four years, during which no spline coupling failures or malfunctions were reported. There, also, have been no reported failures or malfunctions of the bolted brake cage units for more than ten years. The above maintenance bulletin and installation of new bolted brake cage units should prevent repetition of brake failures as experienced by Standard Airways.
With respect to your recommendation that installation of mechanical low pitch stops be made mandatory, we do not believe there is sufficient justification to require them in view of the corrective action already taken as a result of the Seaboard and Western accident and the corrective action being applied as a result of the Standard Airways accident. Apart from the fact that there is reason to believe the brake failures on the Standard Airways aircraft were due to insufficient tightening of the brake cages to the brake housings, it is noted that the service record on Curtiss propellers has been highly satisfactory over a great number of years and no serious control difficulties have been reported other than the Seaboard and Western and Standard Airways cases. Since the causes of these malfunctions have now been corrected and in view of the fact that the propeller incorporates an electrical low pitch stop actuated by blade angle to prevent unwanted travel below the stop, there ls no evidence to support a mandatory requirement to back up the electrical low pitch stop with a mechanical low pitch stop, which, while contributing little to safety, would impose a considerable financial penalty on the affected operators.
We believe that closer surveillance of the threaded type brake cage units and replacement of the threaded units with bolted configurations will preclude the possibility of further Curtiss propeller brake failures.
Sincerely yours,
/s/ Harold W. Grant
HAROLD W. GRANT
Acting Administrator
Honorable Alan S. Boyd
Chairman
Civil Aeronautics Board
Washington 25, D. C.
Enclosure
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FEDERAL AVIATION AGENCY
Washington, 25, D.C. 20553
In Reply
Refer to: ES-100
Mr. Leon H. Tanguay
Director, Bureau of Safety
Civil Aeronautics Board
Washington, D. C. 20128
Dear Mr. Tanguay:
This supplements our July 30, 1963, reply to Mr. Boyd's letter dated June 14, 1963, reference B-1-96, concerning brake failures of Curtiss propellers on Lockheed 1049G aircraft.
This is to advise that on November 25, 1963, Airworthiness Directive No. 63-24-1 was issued requiring replacement of brake cages within 100 hours' time in service after the effective date of the airworthiness directive. A copy of FAA Airworthiness Directive Issue No. 63-24 is enclosed for your information. Mr. Frank Taylor of your Engineering Division was notified by telephone of this airworthiness directive immediately following its issuance.
As indicated in our July 30, 1963, letter, we believe that closer surveillance of the threaded type brake cage units and replacement of the threaded units with bolted configurations will preclude the possibility of further Curtiss propeller brake failures.
Sincerely yours,
/s/C Schuck
George S. Moore
Director
Flight Standards Service
Enclosure