COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Wheels and Tyres
AD/WHE/4
Amdt 4
Inflation of Tyres with an Inert Gas 9/98
Applicability: All aircraft over 5700 kg MTOW and all those below 5700 kg MTOW fitted with tyres with a rating in excess of 266 km per hour (160 mph), except those tyres installed on aircraft with fixed non-retracting undercarriages.
Requirement: To ensure that all tyres fitted to braked wheels do not contain more than 5% of oxygen by volume, accomplish paragraph 1 or 2 below. Either of these procedures is acceptable, or they may be used together:
- Install a placard, either in each wheel well or on or near each landing gear strut incorporating braked wheels, and in a location so as to be easily seen by a person performing routine tyre servicing. The placard shall state
“ INFLATE TYRES WITH NITROGEN ONLY”; or,
2. Incorporate into the aircraft maintenance program, procedures that include the following items:
- On braked wheels, install only tyres that have been inflated with dry nitrogen or other gases shown to be inert such that the gas mixture does not exceed 5% oxygen by volume.
b. Tyres on braked wheels may be serviced with air at remote locations where dry nitrogen is not available, provided that:
- the oxygen content does not exceed 5% by volume; or,
ii. within the next 15 hours time in service, the tyre must be purged of air and inflated with dry nitrogen so that the oxygen does not exceed 5% by volume.
Note: FAA AD 87-08-09 Amdt 39-5613 refers.
Compliance: This amendment becomes effective on 13 August 1998.
COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 107 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Background: This Directive was issued in response to the catastrophic loss of an airliner and reports of severe damage to others as a result of wheel well tyre explosions. The explosion of the tyres has been attributed to the spontaneous combustion of gases generated within the tyres at elevated tyre temperatures. Inflation of tyres with an inert gas reduces the oxygen content to a level below that at which ignition is sustainable.
Amendment 2 reflected the fact that 120+ mph tyres, though “high speed” may be fitted to some aircraft not intended to be affected by this directive.
Amendment 3 excluded those fixed undercarriage aircraft that have over time been re- certificated at higher weights and now exceed the 5700 kg crossover point.
Amendment 4 is issued to align this directive more closely with the FAA AD that prompted the initial issue of this directive.
Amendment 3 of this airworthiness directive became effective on 6 November 1997. Amendment 2 of this airworthiness directive became effective on 25 February 1988. The original issue of this airworthiness directive became effective on 31 August 1987.
Overview
The Civil Aviation Regulations 1998, as amended by the Commonwealth of Australia, address a significant safety concern within the aviation industry, particularly regarding tyre explosions in wheel wells, which can lead to catastrophic outcomes. This was enacted to mitigate the risk of spontaneous combustion in tyres at elevated temperatures by mandating the use of inert gases for tyre inflation. The Civil Aviation Safety Authority (CASA), under the authority of the Australian Parliament, issued this directive to ensure that all tyres fitted to braked wheels of aircraft with a maximum takeoff weight (MTOW) over 5700 kg and those under 5700 kg fitted with high-speed tyres, do not contain more than 5% oxygen by volume. The policy objective is to enhance aviation safety by reducing the likelihood of tyre explosions, thereby protecting both aircraft and passengers. The directive mandates either the installation of placards indicating the requirement to inflate tyres with nitrogen only or the incorporation of specific procedures in the aircraft maintenance program to ensure compliance with these safety standards.
Scope and Application
The Civil Aviation Regulations 1998, specifically Part 39 - 107, issued by the Civil Aviation Safety Authority, applies to all aircraft with a maximum takeoff weight (MTOW) over 5700 kg and those under 5700 kg equipped with tyres rated above 266 km per hour (160 mph), excluding those with fixed non-retracting undercarriages. The directive mandates that tyres on braked wheels must not contain more than 5% oxygen by volume, achieved either by installing a placard indicating that tyres should be inflated with nitrogen only, or by incorporating procedures in the aircraft maintenance program that ensure tyres are inflated with dry nitrogen or other inert gases with similar oxygen content restrictions. This directive became effective on 13 August 1998 and aligns with the Federal Aviation Administration's AD 87-08-09 Amdt 39-5613. The directive was issued in response to incidents of tyre explosions due to spontaneous combustion at elevated temperatures, and subsequent amendments have refined its scope to exclude certain aircraft configurations over time.
Key Provisions
The Civil Aviation Regulations 1998, as amended, contain provisions regarding the inflation of tyres with an inert gas, specifically for aircraft over 5700 kg MTOW and those with tyres rated above 266 km per hour (160 mph) (PART 39 - 107). This directive, AD/WHE/4, mandates that the oxygen content in tyres on braked wheels should not exceed 5% by volume to prevent tyre explosions caused by spontaneous combustion. Two primary methods of compliance are outlined: either installing a placard stating "INFLATE TYRES WITH NITROGEN ONLY" in a visible location (paragraph 1) or integrating specific procedures into the aircraft maintenance program (paragraph 2). In the latter, tyres must be inflated with dry nitrogen or an equivalent inert gas, with provisions for temporary use of air if nitrogen is unavailable, requiring subsequent nitrogen inflation within 15 hours of service.
Compliance with these directives is mandatory for all relevant aircraft. Owners and operators must ensure that tyres on braked wheels are properly inflated with nitrogen or another inert gas, adhering to the outlined procedures. If a placard is used, it must be prominently displayed in the wheel well or near the landing gear strut. Maintenance programs must include detailed instructions for the use of nitrogen and the procedure to follow if air is used temporarily. The amendment history reflects efforts to refine the applicability and improve safety standards, with the latest amendment, Amendment 4, aligning more closely with the FAA AD that prompted the directive's original issue.
Failure to comply with the airworthiness directive can lead to significant safety risks, including the potential for tyre explosions during flight. The regulations do not explicitly state civil or criminal penalties for non-compliance but imply severe consequences due to the safety-critical nature of the directive. Given the catastrophic potential of tyre explosions, any non-compliance could result in severe regulatory action, including fines or operational restrictions for the aircraft until compliance is achieved.