S8C11 - AIRCRAFT WELDING
Table of Contents
IN-SITU WELDING REPAIRS TO AIRCRAFT
General Requirements and Precautions
1. Aircraft welding and allied processes present a broad range of hazards to personnel and equipment including, fire, electric shock, toxic fumes, and radiation.
2. This chapter prescribes the Approved Maintenance Organisation responsibilities when conducting in situ welding operations to aircraft in support of:
- CAAP 33-1(1) Aircraft Manual Welding - Approvals and Qualifications
- Defence WHS Manual Volume 2 Part 3B Chapter 7—Welding and Allied Processes
- Australian Standard 1674 Set—Safety in Welding and Allied Processes.
IN-SITU WELDING REPAIRS TO AIRCRAFT
3. In-situ welding can only be conducted on aircraft structures/aeronautical product with the direct authority of the SMM or delegate. The welding repair must be conducted by a current qualified aircraft welder, in accordance with the applicable aircraft Structural Repair Manual (SRM), and this chapter.
4. If the repair procedure is not included in the Structural Repair Manual (SRM) and the SMM or delegate considers that an operational requirement exists to justify the increased risks in welding aircraft structures/aeronautical product in-situ, or that it is the only practical method of repair, a Request For Deviation (RFD) in minute or message format, is to be raised and forwarded to the responsible System Program Office (SPO).
5. The responsible SPO will only grant approval where it can be shown that:
- The welding technique to be used for the repair meets design approval by the technical authority for the application intended.
- The operational requirement is such that the delay caused by the removal of the aircraft structures/aeronautical product from the aircraft is unacceptable or removal is impractical.
- A suitable repair cannot be carried out using an alternate approved repair scheme or method.
- It is safe to weld in the area proposed.
General Requirements and Precautions
6. All aircraft welding operations are to comply with the following instructions:
- Only Gas Tungsten Arc Welding (GTAW) is to be performed on aircraft.
- Only aircraft welders qualified in accordance with CAAP 33-1(1) and fully conversant with the AS 1674 Set and authorised by the SMM or delegate, are to be permitted to conduct aircraft welding.
- A Hot Work Permit, referencing the Approved Maintenance Data, is to be obtained from the SMM or delegate for each welding operation conducted on an aircraft. If a hazard is encountered that is not covered on the permit, work is to be stopped until the SMM or delegate provides additional guidance. An example of a Hot Work Permit can be found in AS 1674.1–1997 - Fire Precautions.
- Period of currency of the Hot Work Permit, including starting and finishing time, is not to be more than eight hours. A new permit is required, in the event of the aircraft welding operation ceasing for a period of more than two hours or of extending beyond the currency of the permit.
- No welding is to be conducted, or welding equipment brought into the work area, until a permit has been issued.
- No other work is to be permitted within a 15 metre radius of the location of any GTAW operation.
- If other aircraft are located adjacent to the welding operation, personnel responsible for each aircraft are to be notified in advance that welding is to be conducted.
- A welding blanket or other approved form of protection is to be carefully positioned around the area to be welded to prevent metal splatter or flame from contacting adjacent areas.
- When welding outdoors, the aircraft is to be positioned on a hardstand clear of hangars and other aircraft or equipment. Welding is only to proceed in dry, clear weather with nil or light wind. Changes in wind direction and velocity are to be monitored.
- Signs indicating ‘WARNING – WELDING IN PROGRESS’ are to be displayed in the work area, and adjacent to the main battery switch on the welding equipment.
- Flammable Vapours:
- Welding operations are not to be carried out on aircraft when maintenance is in progress on any system or aeronautical product within the aircraft which contains, or did contain, fuel or other flammable or combustible liquid.
- Welding is not to be carried out on aircraft when maintenance is in progress on the fuel system of another aircraft that is within 15 metres from the point of welding.
- Fuel tank access panels, fuel tank openings and fuel vents are to be closed/capped on all aircraft within 15 metres from the point of welding.
- All fuel lines, valves, manifolds, fuel vents and other fuel aeronautical product on the aircraft on which welding is to be carried out are to be in place, secured, or capped prior to the start of and during the welding operation.
- Prior to the start of welding and at a minimum interval of 15 minutes during the welding operation, a qualified person is to check with a combustible gas analyser to ensure the flammable vapours remain below 5% of the lower explosive limit (LEL) whenever welding is being conducted in the vicinity of flammable vapours. Floor drains in the area of a welding operation are to be checked in the same manner. If the combustible Gas Analyser readings exceed 5% of the LEL, all welding operations are to cease until a reading of less than 5% of the LEL is reached.
- Electrical and Oxygen Systems:
- The battery on the aircraft being welded is to be disconnected and the battery bus bar, power and engine circuit breakers pulled. Ground power is to be disconnected and removed from the area. To prevent inadvertent connection of external power, a ‘DO NOT CONNECT POWER’ sign is to be placed on the external power receptacle.
- Batteries are to be removed from the immediate vicinity of any welding operation and stored in a safe location.
- All liquid oxygen is to be removed/depleted from the oxygen system.
- No outside welding operations are to be carried out whilst a liquid oxygen dumping operation is being carried out within an oxygen designated area (due to large amounts of liquid oxygen being dumped during this process). No aircraft welding operation is to commence until the liquid oxygen has totally dispersed.
- All welding operations are to be prohibited within 50 metres of oxygen replenishing operations and liquid oxygen Ground Support Equipment (GSE).
- Welding Equipment:
- The welding equipment is to be mounted and securely fastened to a wheeled trolley to prevent tipping and the regulator and gauge is to be serviceable and in calibration. Welding equipment is to be attended by a person deemed competent to be able to deactivate the equipment.
- The aircraft and welding equipment are to be bonded together with appropriate and correctly earthed to an approved serviceable earthing point. The welding equipment earthing clamp must be positioned on the aircraft or aeronautical product being welded as close as possible to the repair area.
- The use of non-flameproof lighting, switches, plugs and sockets may be authorised in hazardous areas by the issue of a Hot Work Permit by the Responsible Fire Officer. Welding equipment electrical leads are to be heavy-duty sheathed flexible, not less than 1.5 mm2 or 30/0.25 mm strands.
- Mains power electrical leads used in all in-situ aircraft welding operations are to be protected by Earth-Leakage Core Balance (ELCB) devices.
- A warning sign is to be placed on welding generating equipment stating, ‘WARNING – Keep two metres horizontally clear of aircraft engines, fuel tank areas, and vents’.
- Flammable vapours accumulate at ground level; therefore, all electrical equipment including welding equipment and associated leads/cables are to be more than 0.5 metres above the hangar floor, with the exception of the grounding lead/cable whilst working in hazardous zones 1 and 2 in accordance with AS/NZS 60079.10.1:2009—Explosives Atmospheres – Classification of Areas – Explosive Gas Atmospheres. Ground leads are to be as close to the area to be welded as possible, and clamps used on such ground leads are be of the ‘G’ clamp type, and not the clip type. Components that could produce arcs, sparks, or hot metal under any condition of operation are to be of the totally enclosed type.
- Explosive Ordnance. All explosive ordnance is to be removed from the aircraft prior to commencing welding operations.
- Fire Protection:
- At least one Aqueous Film Forming Foam (AFFF) hand portable fire extinguisher (9 L) and one AFFF wheeled fire extinguisher (50 L) is to be positioned in the immediate area of the welding operation and available for immediate use.
- A qualified fire monitor is to be assigned to operate the fire equipment in the event of a fire emergency and also act as the safety officer. The assigned person is to monitor the entire welding operation and is not to leave the task unless properly relieved by another authorised person. In the event of a hazardous situation developing, the fire monitor as the designated safety officer has the authority to halt the welding operation and render assistance as required.
- As a minimum, when welding operations are performed in an aircraft hangar, the hangar is to be protected with an automatic foam sprinkler system that meets the requirements of MFPE 2011 - Manual of Fire Protection Engineering Chapter 8—Aircraft Hangars—Fire Safety paragraphs 20 to 29.
- When welding operations are to be performed, and to avoid false alarms or accidental actuation of the fire protection equipment provided, there is a requirement to consider the type of automatic fire detection equipment installed in the hangar, eg flame detectors. The welding operation Hot Work Permit is to reflect all fire protection isolations and subsequent re-activation.
- The specific location where the welding is being carried out is to be roped off or otherwise segregated by physical barrier to prevent unintended entry into the welding area. A sign reading ‘Welding Operations in Progress’ must be prominently displayed.
- Good housekeeping is to prevail in the welding area.
- Combustible material that cannot be removed is to be covered with a safely secured non-flammable cover.
- Oily surfaces and oil spills are to be hosed down, then covered with an appropriate substance, eg sand. Rubbish, oily rags and combustible materials are to be removed from the welding area.
7. On completion of in-situ welding, a thorough inspection of the aircraft surrounding structure or aeronautical product is to be carried out. Removal of fuel vent covers/plugs and, if necessary, functional testing of associated/nearby systems should be carried out to ascertain that no secondary damage has occurred.