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HELICOPTER AIR SERVICE PROGRAM 159 use of conventional navigational facilities and flight instruments and consists of the following five phases: 1. Certification of aircraft and qualification of pilots. 2. Climbouts and letdown at Los Angeles Airport and other established FAA facilities, and basic on-top navigation. 3. En route climbout procedures to on-top of stratus conditions. 4. En route IFR navigation. 5. Complete navigational capabilities with letdowns and climbouts at helicopters (1967). PRODUCT INTEGRITY The airframe and major components of Los Angeles Airways S-61 helicopters have been subject to major service rigors due to their extremely high frequency of landing and takeoff in service. Seven areas, defined below, required "full bore" engineering modifications. 1. Electronics. 2. Fuel tank system. 3. Battery installation. 4. Cargo pod installation. 5. Air stair door installation. 6. Main gearbox. 7. Landing gear. As a result of approximately 100 modifications involving airworthiness, flight characteristics, passenger comfort, and maintenance accessibility, overall aircraft availability has increased from approximately 2 hours daily in 1962 to 4.47 hours per day in 1964. These include the following: (a) Power train Thirteen areas were defined as posing serious problems in the power train. It is impossible to draw clear lines of demarcation as to whether they were installation induced, isolated to the engines, or a combination of both. It is now apparent that in mating with turbine engines such highly sophisticated dynamic components as transmissions, rotor heads, and associated systems, much compromise is inevitable. In "campaigning" these to decision, daily utilization has increased from 1.51 hours in March 1962, to 5.30 hours per engine in August 1964. This has the effect of reducing unscheduled removals from 30 per month to 4 at present. It has also reduced maintenance costs per engine-hour due to numerous improvements and modifications. (See "Product Engineering," p. 5, of this appendix.) (b) Power turbine In the early months of 1962, tests revealed a severe vibration problem at cruising speeds at the rear engine support attachment points, the result of which was potentially very dangerous. These severe vibrations resulted in 24 failures of the No. 4 bearing housing at the attachment flange radius with subsequent power turbine wheel rub, and also severe cracking in the power turbine casings was encountered. A three-phase corrective program was instituted, consisting of- 1. Vibratory tests at installation with repeat at periodic intervals. During the corrective program, the repeat tests had to be performed at 100-hour intervals, however, improvement has been such that the checks are now only performed at engine installation. 2. An interim program was established until the apparent resonance of the rear support was corrected. This consisted of a "beef up" of the No. 4 bearing housing attachment flange radius, and "superbalanced" torque shafts. 3. The corrective phase was the design and installation of a rear support damper, which reduced the natural frequency of the rear engine support below the normal operating range of the power turbine. In addition, a forged No. 4 bearing housing was designed to be replaced on a normal attrition basis, which to date has not been required. Since the completion of the program, there has been no failure of the No. 4 bearing housing, and only one case wherein removal was required. This removal was predicated upon exceeding vibratory levels in the "transitory" range, but was within limits in the normal operating ranges. SPECIFIC DESIGN CHANGES The S-61L was the first helicopter designed especially for airline use. In its initial design we incorporated a number of important changes from the basic HSS-2 military configuration. Briefly, these include installation of:
