# STC SH657NW - Type: Supplemental type certificate - Status: Current, Reissued - Holder: Siam Hiller Holdings Inc, United States - Description: Installation of Allison 250-C18A, -C18C, -C20, -C20B engine and related changes. - Applied: November 11, 1974 - Status date: May 15, 2009 - Product: Aircraft, Rotorcraft - Certification basis: Part 21, Part 27, Part 133 - Data sheets: [TCDS 2H3](https://openairdocs.org/tcds/2H3) - Certificate PDF: https://openairdocs.org/files/sha256/68/ed/68ed1ec03897ad9bdb773389f107f4b81a3b5a9a20eae32c8f3a3536965e2912 - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/B3BA8071D52422C6862575C80076847A.0001 - DRS record last changed: December 6, 2025 - Page: https://openairdocs.org/stc/SH657NW ## ADs that name it (3) - [AD 2005-10-13](https://openairdocs.org/ad/2005-10-13): Turbine energy absorbing ring · Rolls-Royce 250-B17B, 250-B17C, 250-B17D and 7 more. Effective Jun 22, 2005. Named in the applicability - [AD 80-23-02](https://openairdocs.org/ad/80-23-02): Turbine Power Conversions · Allison 250-C20/250-C20B engine (Siam Hiller Holdings STC SH177WE or 2 others). Effective Nov 20, 1980. Named in the applicability - [AD 79-23-07](https://openairdocs.org/ad/79-23-07): Soloy Conversion per STC SH657NW · Allison 250-C18A, -C18C, -C20, -C20B engine (Siam Hiller Holdings STC SH657NW). Effective Nov 26, 1979. Named in the applicability ## Approved models (10) - Bell Helicopter Textron 47G-2A ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-2A-1 ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-3B ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-3B-1 ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-3B-2 ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-3B-2A ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-4 ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-4A ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-5 ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) - Bell Helicopter Textron 47G-5A ([TCDS 2H3](https://openairdocs.org/tcds/2H3)) ## What the certificate says This is OCR from the scanned FAA certificate. OCR can misread letters and numbers. United States of America Department of Transportation Federal Aviation Administration Supplemental Type Certificate Number: SH657NW This certificate issued to: Siam Hiller Holdings, Inc. 925 M Street Firebaugh, California 93622 Certifies that the change in the type design for the following product with the limitations and conditions therefor as specified hereen meet's the airworthiness requirement's of Part * of the Civil Sir Poegulations and Feveral Aviation Regulations. * See page 6 of this STC for certification basis. Original Product Type Cerlificate Number: 2H3 Make: Bell Model: 47G-2A, 47G-2A-1, 47G-3B, 47G-3B-1, 47G-3B-2, 47G-3B-2A, 47G-4, 47G-4A, 47G-5, 47G-5A Description of Type Design Change: Installation of an Allison 250-C1OD (T63-A-700), 250-C18A, 250-C18C, 250-C20, or 250-C20B engine and related changes in accordance with Hiller Aircraft Corporation Master Drawing List 660-100 reissued on March 22, 1991, November 30, 1995, and January 1, 1999, or later FAA approved revisions; or Soloy Corporation Master Drawing List 660-100 dated August 1, 1979, or later FAA approved revisions. (See Note 9 of STC Addendum SH657NW). Limitations and Conditions: Approval of this change in type design applies basically to the above model rotorcraft only. This approval should not be extended to other rotorcraft of this model on which other previously approved modifications are incorporated unless it is determined that the interrelationship between this change and any of those other previously approved modifications will introduce no adverse effect upon the airworthiness of these rotorcraft. A copy of the STC and Addendum No. SH657NW must be included in the permanent records for the modified rotorcraft. If the holder agrees to permit another person to use this certificate to alter the product, the holder shall give the other person written evidence of that permission. The FAA will reissue the certificate in the name of the transferee and forward it to him. TRANSFER ENDORSEMENT Transfer the ownership of the Supplemental Type Certificate Number to (Name of transferee) (Address of transfer) (Number and street) (City, State, and Zip code) from (Name of grantor) (Print or type). (Address of grantor) (Number and street) (City, State, and Zip code) Extent of Authority (if licensing agreement): Signature of grantor (In ink): United States of America Department of Transportation Federal Aviation Administration Supplemental Type Certificate (Continuation Sheet) Number: SH657NW ADDENDUM Limitations and Conditions: of Type Certificate Data Sheet 2H3 apply except as follows: This STC Addendum, which is part of Supplemental Type Certificate No. SH657NW, prescribes Limitations and Conditions: under which the product for which the STC was issued meets the airworthiness requirements of the certification basis stated herein. A copy of this STC Addendum is required to be maintained as part of this modified rotorcraft permanent records. Supplemental Type Certificate HOLDER: Siam Hiller Holdings, Inc. Bell 47G Series as modified by this STC (normal category) Engine Allison 250-C10D (T63-A-700), 250-C18A, 250-C18C, 250-C20, 250- C20B Fuel MIL-T-5624 grade JP-4 or JP-5, aviation turbine fuels ASTM D1655 Jet A or A-1 (or Allison spec. EMS) or Jet B. See FAA approved Rotorcraft Flight Manual for alternate cold weather and emergency fuels. Oil Engine MIL-L-7808G or MIL-L-23699B and subsequent revisions thereto. Transmission MIL-L-6082 grade 100, 80, 60, or 40 (See RFM). Engine Rating With 600 series With 900 series (5 minutes) Transmission Transmission 260.6 H.P. 270.0 H. P. See Note 3 for applicable conditions. Engine Limits Gas producer (N1) 250-C10D (T63-A-700) 250-C20/C20B 250-C18A/C18C Max. continuous 104% (53,165 RPM) 105% (53,518 RPM) Transient overspeed (15 seconds) 105% (53,676 RPM) 106% (54,028 RPM) United States of America Department of Transportation Federal Aviation Administration Supplemental Type Certificate (Continuation Sheet) Number: SH657NW Engine Limits Output shaft (N2) For all steady state conditions 100% 6000 RPM for 250-C10D (T63-A-700), C250-C18A/C18C 6016 RPM for 250-C20/C20B) Transient overspeed (15 seconds) 250-C20D (T63-A-700), 250-C18A/C18C: Varies from 110% (6600 RPM) at idle to 105% (6300 RPM) at takeoff. 250-C20/C20B: Varies from 113% (6900 RPM) at idle to 105% (6411 RPM) at takeoff. Torque With 600 Series With 900 Series (5 minutes) Transmission Transmission Sea level to 250-C10D (T63-A-700) 250-C10D (T63-A-700) 250-C18A/C18C 250-C20/C20B 250-C18A/C18C 250-C20/C20B 14,000 feet 78 psi 63.0 psi 81 psi 65.0 psi 16,000 feet 73 psi 59.0 psi 75 psi 60.0 psi Straight-line variation between points given. (Max. Cont.) Sea level to 16,000 66 psi 50.5 psi 66 psi 50.5 psi feet Turbine Outlet 250-C10D (T63-A-700) T'emperature 250-C18A/C18C 250-C20 250-C20B Max. cont. 693°C (1280°F) 737°C (1359°F) 738°C (1360°F) Takeoff (5 min.) 749°C (1380°F) 793°C (1460°F) 810°C (1490°F) Transient (6 sec.) 843°C (1550°F) 843°C (1550°F) 843°C (1550°F) Oil Inlet Temperature Engine: Maximum 225°F Minimum -65°F Transmission: Maximum 130°C (266°F) United States of America Department of Transportation Federal Aviation Administration Supplemental Type Certificate (Continuation Sheet) Number: SH657NW Rotor Limits Power on - N2 Tach Maximum 355.5 rpm (100%) Minimum 348 rpm (98%) Power off - Rotor Tach Maximum 370 rpm (104 %) Minimum 322 rpm (90.6%) Airspeed Limits Skid Gear - CAS Sea level to 4,000 ft. 105 mph 4,000 ft. to 16,000 ft. decrease VNE 5mph per 1,000 ft. Altitude Limit 16,000 feet C. G. Range Gross Weight Longitudinal 2950 Ibs. (-2.0) to (+2.5) 2300 Ibs. (-2.0) to (+4.0) 2100 Ibs. (-2.0) to (+4.0) Maximum Weight 2950 Ibs. Number of Seats 3 (pilot and 2 passengers) (-30) Maximum Baggage See loading instructions in FAA approved Rotorcraft Flight Manual. Fuel Capacity 61.6 Gal. (+5) (usable 57.5 Gal.) See Note 1. Oil Capacity Engine 5.5 quarts Transmission 5 quarts Rotor Blade and Control Movements (Rigging): For rigging information, refer to Bell Model 47G -3B-1 maintenance manual for the turbine converted model rotorcraft listed on this certificate except where superseded by Hiller Aircraft Corporation Service Bulletin 01-660 dated November 14, 1978, or later FAA approved revision, or Soloy Conversions, Ltd Service Bulletin 01-660 dated November 14, 1978, or later FAA approved revision. Serial Numbers Eligible same as shown on Type Certificate Data Sheet 2H3. Data Pertinent to All Models Datum Same as shown on Type Certificate Data Sheet 2H3. United States of America Department of Transportation Federal Aviation Administration Supplemental Type Certificate (Continuation Sheet) Number: SH657NW Certification Basis 1. Civil Air Regulation (CAR) 6 effective December 20, 1956, including amendment 6-1, 6-3, 6-4 (Exemption No. 70 for Model 47G-3 and Exemption No. 2950 for all those turbine powered models listed in this STC with the extended skid gear modification installed). 2. The following paragraphs of Federal Aviation Regulations part 27: 27.33(b)(3) (Amdt. 27-2), 27.45 thru 27.79 (Amdt. 27-1), 27.143 (Amdt. 27-1), 27.361(a) (Amdt. 27-1), 27.901 thru 27.991 (Amdt. 27-1), 27.993 (Amdt. 27-2), 27.995 thru 27.1091 (Amdt. 27-1), 1093(b)(1) (Amdt.27-9), 27.1121 thru 27.1145 (Amdt. 27-1), 27.1163 (Amdt. 27-2), 27.1183 thru 27.1193 (Amdt. 27-1), 27.1194 (Amdt. 27-2), 27.1195 (Amdt. 27-5), 27.1301 thru 27.1309 (Amdt. 27-1), 27.1337 (Amdt. 27-1), 27.1351 (Amdt. 27-1), 27.1353 (Amdt. 27-1), 27.1521 (Amdt. 27-1), 27.1549 thru 27.1559 (Amdt. 27- 1), 27.1583(b) and (f) (Amdt 27-1), 27.1587 (Amdt. 27-1), 27.1589 (Amdt. 27-1). Equipment The following must be installed in the rotorcraft for airworthiness certification subsequent to the incorporation of this STC. 1. The basic required equipment as prescribed in the applicable airworthiness regulations (see certification basis outlined above). 2. FAA approved Hiller Aircraft Corporation Rotorcraft Flight Manual dated November 4, 1998, or later FAA approved revision, or Soloy Corporation Rotorcraft Flight Manual dated September 6, 1978, which is required in lieu of that specified for the basic unmodified Bell 47G series. NOTE: Equipment items approved for the basic Bell 47G series are not eligible with this STC unless such items are also shown in the above noted flight manual. 3. Ballast must be installed in accordance with Hiller Aircraft Corporation Drawing List 660-100 dated January 1, 1999, or Soloy Corporation Drawing 660-100 dated August 1, 1979, or later FAA approved drawings. United States of America Department of Transportation Federal Aviation Administration Supplemental Type Certificate (Continuation Sheet) Number: SH657NW NOTE 1. Current weight and balance data, including a list of equipment included in the certificated empty weight and loading instructions when necessary, must be provided at the time of airworthiness certification for return to service. The certificated empty weight and corresponding center of gravity location must include unusable fuel and undrainable oil as follows: Fuel: 13.9 Ibs. (+5) Oil: Negligible NOTE 2. Refer to the applicable FAA approved Rotorcraft Flight Manual for required placards and instrument markings. NOTE 3. The rating shown for the Allison 250-C20 and 250-C20B engines is based on zero ram, dry inlet air, no accessory loads, and no bleed air; and is available at sea level to approximately ISA +40°F. See Powercheck Charts for power available from C10/C18 series engines in RFM Supplement No. 10. NOTE 4. Except where superseded or supplemented by the items listed below, the retirement times for the modified Bell 47G series rotorcraft are unchanged from that listed in Type Certificate Data Sheet 2H3. These additional/superseded times are as follows: Component Part Number Replacement Period Hours Adapter plate Soloy 660-2101 3750 Drive shaft Soloy 660-2408 4000 Engine mount (basket) Bell 47-612-171-123 2500 Bell P/N 47-130-110-1 main rotor thrust bearing is not eligible for use on Bell 47 rotorcraft incorporating this turbine conversion. NOTE 5. Information essential to the maintenance and servicing of rotorcraft modified in accordance with this STC is contained in the pertinent model Bell Helicopter Company maintenance and overhaul instructions and in the Soloy Corporation supplements to these documents. NOTE 6. External load operations under part 133 must be conducted within the limitations and in accordance with the requirements of the FAA Approved Rotorcraft Flight Manual Supplement for the Hiller or Soloy cargo hook support system. Models equipped with United States of America Department of Transportation Federal Aviation Administration Supplemental Type Certificate (Continuation Sheet) Number: SH657NW the 900 series transmission meet the structural requirements of the certification basis for external load operations at 3200 pounds maximum gross weight provided the weight in excess of 2950 pounds is not imposed on the landing gear. NOTE 7. For Allison 250-C10D (T63-A-700), 250-C18A/C18C, and 250-C20/C20B engine installations, a hydraulic pump drive gearbox and pump is eligible to be installed in accordance with appropriate data contained in Soloy Drawing List 660-100 dated August 1, 1979, or later, for use with various hydraulic powered equipment installations. This gearbox and pump may be installed on rotorcraft to be operated in normal category provided deactivation procedures contained in Hiller or Soloy Service Instruction 66002 have been complied with. Limitations and conditions to be subsequently evaluated as part of the installation and operation of these various items of hydraulically powered equipment (spray systems, etc.) are also contained in this abovementioned Service Instruction. An Allison 250-C18A/C18C, 250-C20/C20B fuel line modification must be accomplished in accordance with Hiller or Soloy STC SH769NW prior to installation of the above discussed Hydraulic Pump Drive Gearbox and Pump, Hiller or Soloy Service Instruction 66002. NOTE 8. The Soloy Turbine Converted Bell 47G series rotorcraft with the 900 series transmission has demonstrated satisfactory operation in the restricted category agriculture special purpose at 3200 Ibs. gross weight with the limitations specified in the FAA approved Flight Manual Supplement for the Cargo Hook/Load Support Kit. If operations are conducted which involve imposing 3,200 Ibs. on the landing gear, the rotorcraft must be inspected in accordance with Hiller or Soloy Service Bulletin No. 16-660 and found satisfactory before it is returned to the standard category. Agriculture systems approved for installation must provide a dump capability to be eligible for gross weight operation in excess of 2,950 Ibs. NOTE 9. Installation of an Allison 250-C10D (T63-A-700), 250-C18A, or 250-C18C engine must be in accordance with Hiller Aircraft Master Drawing List 660-100 revised January 1, 1999, or later FAA approved revisions; or Soloy Master Drawing List 660-100 revision dated March 27, 1989, or later FAA approved revisions. - END - ## Every issue (3) - May 15, 2009: Reissued, Current. [certificate](https://openairdocs.org/files/sha256/68/ed/68ed1ec03897ad9bdb773389f107f4b81a3b5a9a20eae32c8f3a3536965e2912) - April 15, 2009: Reissued, Historical. [certificate](https://openairdocs.org/files/sha256/15/be/15be8f18c6b765ebacb277f4e37b9f46b8e86c43368075a0e277a09c9cc9e815) - August 19, 2005: Reissued, Historical. [certificate](https://openairdocs.org/files/sha256/10/f0/10f004132b32eb72cacdbb7fc862bd4b5c8ac2f9e9de0063c852b9ed666d7ec2) --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.