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HELICOPTER AIR SERVICE PROGRAM     269

speed is approximately 92 gallons per hour. Fuel costs, however, are considerably reduced because of the difference in price of kerosene and aviation gasoline. With fuel cost/gallon for avgas and kerosene at 19 and 11 cents respectively, the PT-6's afford a reduction of $9.45/hour.

3. ENGINE INFORMATION

The current production engine, the PT-6 is approved for an overhaul period of 600 hours and will be approved for 800 hours by April 1965. At time of delivery to CHA in 1967, the TBO will probably exceed 1,200 hours. A 2,000-hour TBO is expected no later than 1969. This engine has a takeoff rating of 550 hp and a maximum continuous rating of 500 hp.

Engine operating costs, including parts and overhaul, are currently estimated at $8 per engine-hour and are forecast to be $5 per engine-hour by 1969. The estimated price of the shaft version (PT-6) is $24,450.

The forecast TBO's and related hourly cost of the PT-6 are as follows:

[[5 columned table]]
|  | TBO (hours) | Hourly cost, 1 engine | Hourly cost, 3-engines | Parts and overhaul, cost per engine |
|---|---|---|---|---|
| 1965|600 1/ | $8.00 2/ | $24.00 | $4,800 |
| 1966 | 800 | 7.00 | 21.00 | 5,600 |
| 1967 | 1,200 | 5.00 | 15.00 | 6,000 |
| 1968 | 1,600 | 4.75 | 14.25 | 7,600 |
| 1969 | 2,000 | 4.50 | 13.50 | 9,000 |
| 1970 | 2,000 | 4.50 | 13.50 | 9,000 |

1/ Manufacture approved.
2/ Manufacturer's forecast of hourly overhaul cost for parts and labor.

4. OPERATIONAL ADVANTAGES

A. Unrestricted performance for VFR, IFR, and vertical operations

With the powerplant composed of three PT-6's, the S-58 could operate under category B, category A, and vertical takeoff operations without off-loading up to any anticipated temperature in the Chicago area. These capabilities would for the first time completely optimize the helicopter for city-center heliports of minimum size, giving CHA complete freedom from the vertical takeoff restrictions which limit payloads of existing twin-turbine helicopters.

B. Elimination of single-engine route circuity

Due to across-the-board category A performance with one engine inoperative, all route circuity can be eliminated with a consequent improvement in block speed.

C. Lower en route minimum altitudes

Reduced altitudes for VFR day and night operatings would be possible, affording improvement to CHA's already enviable scheduled-completion factor.

D. Block speed increase

Since the three PT-6 installation provides full category A performance, en route altitudes can be reduced to the minimum allowed in control area. Also, noise considerations, which in the past have had an effect upon operating altitudes, will be significantly reduced by replacing the piston engine. Finally, the increased power available will allow a greater climb and ground speed during climb, particularly under full payloads. These improvements, combined with the elimination of route circuity, will increase the average block speed by 15 percent or conversely reduce per-mile costs by 15 percent.

5. VIBRATION REDUCTION

The elimination of the piston engine will significantly reduce the vibration levels throughout the aircraft which will have a profound although indeterminate effect upon maintenance costs. There is universal agreement that application of the turbine will accelerate what is even now a very satisfactory rate of TBO advance.