COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Robinson R22 Series Helicopters
AD/R22/35
Amdt 1
Rotor Mast Shaft Nuts 12/92
Applicability: All R22 series helicopters in service as at 30 June 1992 with the exception of the following:
- Helicopters S/No 2178 and on; and
b. Helicopters with main rotor gearboxes manufactured or overhauled by the Robinson Helicopter Company after 15 June 1992.
Requirement: 1. Unless already internally inspected for mast shaft nut looseness since 30 March 1992, remove main rotor gearbox from aircraft using procedures specified in the R22 maintenance manual.
Note: Any gearbox previously inspected for nut looseness since 30 March 92 may remain in service subject to a log book certification declaring that compliance with the AD is not applicable and referring to a statement of actual work carried out during such inspection.
2. Remove sump of gearbox noting number and position of shims between case and sump and inspect both shaft nuts, P/N A153-1 and lock washers, P/N A269-1 for looseness or damage.
3. Using special tool MT 124-1 remove both nuts, clean shaft and nut threads using MEK.
4. Inspect gear teeth for signs of damage and also, inspect dowels on gear carrier for damage. Report any damage or looseness of nuts to the CAA immediately.
5. If undamaged and no wear is apparent, fit a new lock washer on shaft ensuring the lock washer dowel pin locating holes are correctly mated with the dowel pins on the gear carrier. Coat threads of the lock nut with Loctite 620 and, while still wet, assemble nut on rotor shaft.
6. Using special tool MT 124-1, or suitable equivalent, torque nut from 135 to 140 ft-lbs. Ensure 2 tabs of the lock washers align with nut. Do not untorque nut to align lock washer tabs with nut.
7. Install second tab washer and align 2 tabs with first nut. Apply Loctite 620 to threads of lock nut and, while still wet, install. Torque nut from 75 to 90 ft-lbs using special tool MT 124-1 or a suitable alternative.
8. Ensure lock washer tabs are correctly bent and not cracked, four tabs to upper lock nut and two to lower locknut. Repeat requirements 5, 6 and 7 if tabs found cracked.
9. Install new o-Ring P/N A215-271 on sump. Lubricate with A257-2 oil and install sump.
COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
CAUTION
Be sure all sump bolts have the same shim stack-up as measured in Requirement 2.
10. Torque the sump bolts and drain plug as follows:
Eight locknuts on the AN4 bolts, 70-80 in-lbs plus nut drag. Two MS20074 bolts (cap screws), 60 in-lbs and safety wire. Drain plug A7620, 150 in-lbs and safety wire.
Note: Be sure that the A059-62 ground wire is re-attached under the nut located aft of the fwd RH mount.
11. Using procedures specified in the R 22 maintenance manual re-install gearbox in helicopter and carry out associated maintenance manual requirements.
Compliance: At the next inspection for issue of a maintenance release after 1 August 1992 or by 31 March 1993, whichever occurs first. Requirements 2 to 10 are to be carried out by organisations specifically approved by the CAA to carry out this directive.
Note: Arrangements have been made for certain acceptable organizations to obtain the necessary spares and tooling to carry out this work. A listing of those organizations can be obtained by contacting a CAA District Airworthiness Office.
Should an operator be unable to achieve compliance through this source, consideration will be given to extending the approval to other organizations highly experienced with helicopter gearbox heavy maintenance, upon request, provided they can obtain the necessary spares and tooling support.
Background: Amendment 1 to this AD is raised to exempt specific helicopters and main rotor gearboxes from teardown, inspection and reassembly because the Robinson Helicopter Company has introduced new inspection, torqueing and assembly procedures that make it unnecessary for the nominated helicopters and main rotor gearboxes to comply with this Directive.
The Directive was raised initially because there have been 2 reported cases of failure of the mast support structure due to the rotor shaft nuts becoming loose and allowing the rotor shaft to pull through the retention bearing in the gearbox. Both incidents occurred as collective was being pulled on the ground and were characterised by the shearing of the rivets attaching the mast bearing outer housing to the main rotor shaft as the vertical loads transferred from the main gearbox bearing to the top of the mast.
The failure was accompanied by a loud cracking sound and in one case an increase in manifold pressure as the effective length of the pitch change links altered the rotor pitch setting as the mast shaft moved vertically. Several more instances of loose nuts have been confirmed by inspection; one with fretting of tab washer and nuts, another with gear wear/spalling and others with no other apparent damage.
Overview
The Civil Aviation Regulations 1998, established by the Australian Parliament, are designed to regulate civil aviation and ensure safety. Among the various parts and amendments to these regulations, Part 39 - 105 focuses on the Civil Aviation Safety Authority's (CASA) Schedule of Airworthiness Directives, which are mandatory instructions aimed at maintaining airworthiness standards. One such directive, AD/R22/35 Amendment 1, specifically addresses issues with the rotor mast shaft nuts in Robinson R22 Series Helicopters. This directive was introduced to address safety concerns arising from the failure of mast support structures due to loose rotor shaft nuts, which led to critical incidents and potential hazards. The policy objective behind this directive is to prevent similar occurrences by enforcing rigorous inspection, maintenance, and repair procedures on the specified helicopters, thereby enhancing aviation safety.
The directive outlines a series of requirements for the inspection and, if necessary, the replacement of the rotor mast shaft nuts in Robinson R22 Series Helicopters, with certain exceptions for helicopters with newer gearboxes. The directive mandates that all applicable helicopters undergo a thorough inspection and, if required, the reassembly of the main rotor gearbox using specified procedures. Compliance with these directives is essential for airworthiness certification and is to be achieved by approved maintenance organisations. The intent is to ensure that all helicopters meet the stringent safety standards set forth by CASA, thereby mitigating the risk of future failures and ensuring the continued safety of civil aviation operations.
Scope and Application
The Civil Aviation Safety Authority's Airworthiness Directive AD/R22/35 Amendment 1 applies to all Robinson R22 series helicopters in service as of 30 June 1992, with specified exceptions. Notably, helicopters with serial numbers 2178 and above, as well as those with main rotor gearboxes manufactured or overhauled by the Robinson Helicopter Company after 15 June 1992, are exempt from the directive. This regulation mandates specific actions to address the safety concern of loose rotor mast shaft nuts, which have been implicated in multiple incidents of structural failure. Operators must adhere to detailed procedures for inspecting, replacing, and reassembling the main rotor gearbox, ensuring compliance with these stringent safety measures. The directive stipulates that compliance must be achieved by the next inspection for a maintenance release after 1 August 1992 or by 31 March 1993, whichever comes first. The inspection and repair work must be carried out by organizations specifically approved by the Civil Aviation Safety Authority, although arrangements are in place for highly experienced organisations to obtain necessary approval upon request, provided they can secure the required spares and tooling support.
Key Provisions
The Civil Aviation Regulations 1998, Part 39 - 105 Civil Aviation Safety Authority Schedule of Airworthiness Directives, specifically addresses the Robinson R22 Series Helicopters through AD/R22/35 Amendment 1. This directive concerns the inspection, replacement, and reassembly of the rotor mast shaft nuts (section 1). The primary requirement is that all R22 series helicopters in service as of 30 June 1992, excluding certain specified models, must have their main rotor gearbox removed and inspected for the looseness or damage of the shaft nuts and lock washers (section 1). If the gearbox has not been inspected since 30 March 1992, it must be removed following the procedures specified in the R22 maintenance manual (section 1.2). If the gearbox has been inspected, a log book certification can declare compliance with the AD not applicable, referencing the inspection details (section 1.3).
The obligations imposed by this directive are stringent and detailed, requiring operators to remove the gearbox, inspect and potentially replace the shaft nuts and lock washers, and reassemble the gearbox in accordance with the maintenance manual procedures (sections 1.2-1.11). Operators must ensure that all sump bolts have the same shim stack-up and are torqued correctly, and they must reattach the A059-62 ground wire under the nut aft of the forward right mount (sections 1.9-1.10). The directive mandates that the inspection and reassembly work be performed by organizations specifically approved by the Civil Aviation Safety Authority (CASA), with arrangements in place for certain approved organizations to obtain necessary spares and tooling (section Compliance).
The directive outlines clear consequences for non-compliance, though specific penalties are not mentioned in the text. However, given the nature of aviation safety directives, non-compliance could result in significant civil or criminal penalties. The directive stipulates that compliance must be achieved by the next inspection for a maintenance release after 1 August 1992 or by 31 March 1993, whichever is earlier (section Compliance). Failure to adhere to these requirements could potentially lead to grounding of the aircraft until compliance is achieved, resulting in financial and operational repercussions for the operator. CASA may also extend approval to other experienced organizations if necessary, provided they can obtain the required support (section Compliance Note). The directive was initially raised due to two reported cases of mast support structure failure caused by loose rotor shaft nuts, highlighting the critical importance of compliance with these safety directives (section Background).