AD 76-05-11
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Enstrom Helicopter Corporation, The | 280 | Airworthiness Directives; Enstrom Model F-28A and 280 Helicopters |
| aircraft | Enstrom Helicopter Corporation, The | F-28A | Airworthiness Directives; Enstrom Model F-28A and 280 Helicopters |
Unsafe Condition
Fatigue cracks in tail cone attach bolts, particularly in the threaded area and the radius under the base of the bolt head, could result in tail cone detachment.
AI-generated summary from the source AD text. Verify against the official source before acting.
Required Actions
Within 10 hours time in service after the effective date, inspect bolts via dye penetrant or equivalent method. Replace defective bolts before further flight. Within 110 hours, replace AN bolts with specified NAS bolts (NAS146DH-24 for upper, NAS146DH-22 for lower), install MS20002C6 washers, torque to 240 in-lbs, and safety wire. Repeat inspections every 50 hours unless stronger bolts are installed.
AI-generated summary from the source AD text. Verify against the official source before acting.
Compliance Time
Within the next ten (10) hours time in service after the effective date of this AD
AI-generated summary from the source AD text. Verify against the official source before acting.
Affected Aircraft
Enstrom Model F-28A (S/N 03 thru 347) and 280 (S/N 1001 thru 1030) helicopters certified in all categories.
AI-generated summary from the source AD text. Verify against the official source before acting.
Federal Register Abstract
Tail Cone Attach Bolts
Applicability Source Text
Show captured applicability text from the source AD
AD Final Rules - DRS_76-05-11.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 76-05-11 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Enstrom Model F-28A and 280 Helicopters Subject: Tail Cone Attach Bolts Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: 03/18/1976 Make: Enstrom Helicopter Corporation, The Model: 280 | F-28A Product Type: Aircraft Product Subtype: Rotorcraft Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 76-05-11 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: 39-2545 AD NUMBER: 76-05-11 SUBJECT HEADING: Airworthiness Directives; Enstrom Model F-28A and 280 Helicopters ACTION: SUMMARY: DATES: Effective March 18, 1976. ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 76-05-11 ENSTROM: Amendment 39-2545. Applies to Enstrom Model F-28A and 280 helicopters certified in all categories with the following serial numbers: F-28A Models - S/N 03 thru 347 280 Models - S/N 1001 thru 1030 Compliance required as indicated unless already accomplished: (a) Within the next ten (10) hours time in service after the effective date of this AD remove the three (3) tail cone attach bolts and perform a dye penetrant inspection of the bolts for fatigue cracks or an equivalent inspection method approved by the Chief, Engineering and Manufacturing Branch of the Federal Aviation Administration, Great Lakes Region. Note: Particular attention should be given to the threaded area and the radius under the base of the bolt head. (b) Replace any defective bolts with a new bolt of the same part number or a stronger equivalent listed in paragraph (d) prior to further flight. (c) Tail cone bolts of the original design shall be inspected again at 50 hours from the inspection required in paragraph (a) unless replaced with the stronger bolts as listed in paragraph (d). (d) Within 110 hours time in service from the effective date of this AD unless already accomplished replace the three (3) AN bolts attaching the tail cone with the following NAS bolts: Upper attachment point - NAS146DH-24 bolt Lower attachment points - NAS146DH-22 bolt MS20002C6 washers are to be installed under the head. Care should be exercised to insure that the proper bolt grip length is maintained. (e) Torque bolts to 240 in. - lbs. and safety wire. (f) Upon compliance with paragraphs (d) and (e) the inspections listed in paragraph (c) are no longer required. Note: When installing the NAS hardware on some helicopters in the field, it may be necessary to install an additional MS20002C6 or an AN 960-616 washer on the NAS bolts. The additional washers will insure that the bolts will not bottom out on the grip portion of the bolt when torqued to the airframe. Enstrom Service Notes 0029 and 0029A pertain to this same subject. This amendment becomes effective March 18, 1976. FOOTER:
Document Text
Show stored source text (verify against official source)
AD Final Rules - DRS_76-05-11.html Copy URL Print/Save as PDF Document Versions Feedback Details AD Number: 76-05-11 Document Type: AD Final Rules Docket Number: Unknown Subject Heading: Airworthiness Directives; Enstrom Model F-28A and 280 Helicopters Subject: Tail Cone Attach Bolts Status: Current Citation: This information is not available. Citation Publish Date: Effective Date: 03/18/1976 Make: Enstrom Helicopter Corporation, The Model: 280 | F-28A Product Type: Aircraft Product Subtype: Rotorcraft Affected AD: Superseded AD: Affected By: Superseded By: Service/Office: Office of Primary Responsibility: CFR Part Reference: Part 39 Comments: AIRWORTHINESS DIRECTIVES FINAL RULES: 76-05-11 CITATION: This information is not available. PAGE NUMBER: DOCKET NUMBER: Unknown AMENDMENT: 39-2545 AD NUMBER: 76-05-11 SUBJECT HEADING: Airworthiness Directives; Enstrom Model F-28A and 280 Helicopters ACTION: SUMMARY: DATES: Effective March 18, 1976. ADDRESSES: FOR FURTHER INFORMATION CONTACT: SUPPLEMENTARY INFORMATION: REGULATORY TEXT: 76-05-11 ENSTROM: Amendment 39-2545. Applies to Enstrom Model F-28A and 280 helicopters certified in all categories with the following serial numbers: F-28A Models - S/N 03 thru 347 280 Models - S/N 1001 thru 1030 Compliance required as indicated unless already accomplished: (a) Within the next ten (10) hours time in service after the effective date of this AD remove the three (3) tail cone attach bolts and perform a dye penetrant inspection of the bolts for fatigue cracks or an equivalent inspection method approved by the Chief, Engineering and Manufacturing Branch of the Federal Aviation Administration, Great Lakes Region. Note: Particular attention should be given to the threaded area and the radius under the base of the bolt head. (b) Replace any defective bolts with a new bolt of the same part number or a stronger equivalent listed in paragraph (d) prior to further flight. (c) Tail cone bolts of the original design shall be inspected again at 50 hours from the inspection required in paragraph (a) unless replaced with the stronger bolts as listed in paragraph (d). (d) Within 110 hours time in service from the effective date of this AD unless already accomplished replace the three (3) AN bolts attaching the tail cone with the following NAS bolts: Upper attachment point - NAS146DH-24 bolt Lower attachment points - NAS146DH-22 bolt MS20002C6 washers are to be installed under the head. Care should be exercised to insure that the proper bolt grip length is maintained. (e) Torque bolts to 240 in. - lbs. and safety wire. (f) Upon compliance with paragraphs (d) and (e) the inspections listed in paragraph (c) are no longer required. Note: When installing the NAS hardware on some helicopters in the field, it may be necessary to install an additional MS20002C6 or an AN 960-616 washer on the NAS bolts. The additional washers will insure that the bolts will not bottom out on the grip portion of the bolt when torqued to the airframe. Enstrom Service Notes 0029 and 0029A pertain to this same subject. This amendment becomes effective March 18, 1976. FOOTER:
Source: Official FAA Source ↗
Retrieved: Apr 8, 2026
Rights: U.S. Government Public Domain
This site is not affiliated with or endorsed by the FAA. Always verify with official sources.
Related Airworthiness Directives
2018-02-01 Recurring
final ruleAirworthiness Directives; The Enstrom Helicopter Corporation Helicopters
Unsafe Condition: Cracks in the main rotor spindle, which could result in loss of a main rotor blade and subsequent loss of control of the helicopter.
2017-26-03
final ruleAirworthiness Directives; The Enstrom Helicopter Corporation Helicopters
Unsafe Condition: Failure of a rod end bearing assembly may result in the loss of a main rotor blade.
2012-11-05
final ruleAirworthiness Directives; Enstrom Helicopter Corporation Helicopters
Unsafe Condition: Failure of the cyclic trim system, which may lead to reduced controllability and subsequent loss of control of the helicopter.
2007-11-02
final ruleAirworthiness Directives; Enstrom Helicopter Corporation Model F-28A, F-28C, F-28F, TH-28, 280, 280C, 280F, 280FX, 480, and 480B Helicopters
Unsafe Condition: Corrosion in the main rotor push-pull control rods (push-pull rods) can lead to pitting, internal moisture, or failure, potentially causing severe in-flight vibration and loss of control.