New Tricks. Understanding Approved Data for NDT. Steve Swift Pty Ltd 2012

Transcription

1 New Tricks Understanding Approved Data for NDT Presented by Steve Swift at the Quality and Testing in Aircraft Maintenance seminar at the Novotel Brighton Beach, Sydney, 15th November Steve is an aeronautical engineer. For seven years, he designed aircraft structure for Hawker de Havilland, Douglas, Boeing and others. Then, for 26 years, he regulated structural inspection programs for the Civil Aviation Safety Authority (CASA), often with help from NDT inspectors. Steve has presented papers internationally on the technical and human factors of inspection. His work has been recognised by an Australia Public Service Medal, and by the Whittle Safety Award from the International Federation of Airworthiness. He now runs his own training and consulting company.

2 Caveats Civil only CARs only Structure only I no longer work for CASA 2

3 This Lycoming Service Instruction is for NDT of piston engine parts during overhaul. It is causing problems for inspectors. 3

4 The main problem is Lycoming requiring NDT able to find the smallest indication, without saying how small that is. What should the inspector do? Let s first review our understanding of approved data for NDT. 4

5 Outline Who can approve NDT data? What is the standard? New tricks for inspectors Lycoming Service Instruction 5

6 Who can approve NDT data? Level 1? Level 2? Level 3? All of the above? None of the above? Under CASA s rules, who can approve NDT data? Let s look at CASA s rules... 6

7 Is NDT maintenance? endorsement on a licence. maintenance means any task required to ensure, or that could affect, the continuing airworthiness of an aircraft or aeronautical product, including any one or combination of overhaul, repair, inspection, replacement of an aeronautical product, modification or defect rectification. means that part of an aerodrome to be used for Civil Aviation Act 1988 First, is NDT maintenance? 7 Here s the definition of maintenance from the Civil Aviation Act. Clearly, NDT is maintenance.

8 Approved data? 42V Maintenance: approved maintenance data (1) A person carrying out maintenance on an Australian aircraft must ensure that the maintenance is carried out in accordance with the applicable provisions of the aircraft s approved maintenance data. Penalty: 50 penalty units. Note Regulation 2A sets out what is approved maintenance data for an aircraft. Civil Aviation Regs 1988 Does maintenance need approved data? 8 Here s CAR 42V. Clearly, maintenance needs approved data. The Note refers us to Regulation 2A for more about approved data.

9 Sources and approvers 2A Approved maintenance data (1) Subject to subregulation (3), the approved maintenance data for an aircraft, aircraft component or aircraft material consists of the requirements, specifications and instructions that are: (a) contained in the maintenance data set out in subregulation (2); and (b) applicable to the maintenance of the aircraft, aircraft component or aircraft material, as the case requires. (2) For the purposes of paragraph (1) (a), the maintenance data are: (a) requirements in: (i) regulations 42U, 42W, 42X, 42Y, 42Z and 42ZA or in instruments made under those regulations; and (ii) directions (however described) made under an airworthiness directive or under regulation 25, 38 or Here s the start of CAR 2A. The rest lists the sources and approvers of approved data. 9 Are any or all of the NDT levels on the list? No, an inspector cannot approve NDT data. It is only approved if it comes from, or is approved by, someone on CAR 2A s list, such as the manufacturer of the aircraft or engine, or CASA.

10 Airworthiness Bulletin 02-5 Administration and Control of Aircraft Welding and NDT Approved Maintenance Data Welding and NDT must be carried out in accordance with approved maintenance data as defined in CAR2A. Where new welding or NDT procedures are produced, or equipment that is different from that recommended by the aircraft or component manufacturer is to be used, written approval from CASA or an Authorised Person is required. Airworthiness Bulletin 02-5, Administration and Control of Aircraft Welding and NDT, confirms that NDT needs approved data, which must come from the manufacturer or be approved by CASA. 10

11 Who can approve NDT data? Level 1? Level 2? Level 3? All of the above? None of the above? So, the answer to the question of who can approve NDT data is None of the above. 11

12 What is the standard for approval of NDT data? AS 3669? NAS 410? The ASTM for the method? MSG-3? The certification basis for the aircraft? The next question is, if NDT data must be approved, what is the standard for its approval? 12 In this slide, the first two standards are for personnel not process. The next two could be helpful but are not essential. The only essential standard is the certification basis for the aircraft. When the CARs for maintenance require continued airworthiness, that is the airworthiness standard they want continued. All maintenance, including NDT, must meet and assure that standard. Everything else is negotiable.

13 1+1 Transport Canada Transports Canada q'ype Certificate (})ata Sheet Number: A-177 Issue No.: 15 Approval Date: Refer Below Issue Date: December 12, 2011 This Type Certificate Data Sheet (TCDS), which is part of Type Certificate No. A-177, prescribes the conditions and limitations under which the product(s) for which the type certificate was granted meet(s) the standards of airworthiness required by the Canadian Aviation Regulations. Type Certificate Holder: Models Bombardier Inc. P.O. Box 6087, Station "Centre-Ville" BD-700-1AI0 BD-700-1A11 Montreal, Quebec H3C3G9 1. BD-700-1AI0 (Transport Category) Global Express Approved July 31,1998 Global Vision Flight Deck* Approved June 3,2011 Global 6000* Approved December 12, 2011 * See NOTES 6, 7 and 8 for Global Vision Flight Deck (GVFD) and Global 6000 definitions. Certification 1. Maximum Canadian Airworthiness Manual Chapter k& 525, Airworthiness lb. Standards: Basis Transport Category Aeroplanes, at Change 6 dated December 30, 1993 which is equivalent to FAR 25 including amendments 25-1 through and Canadian Additional Airworthiness Requirements. The Certification Basis - the airworthiness standard for maintenance as well as design - is on the Type Certificate Data Sheet. In this example, for a Canadian aircraft, it is the Canadian equivalent to FAR 25. That s in Canada. What about Australia? 13

14 Here s the Australian Type Acceptance Certificate. It says the Australian certification basis is the same as Canada s. 14

15 New tricks What do FAR 25 and other airworthiness standards require for NDT? Few inspectors know. It s not their fault. It s just that NDT courses don t teach it. And, engineers keep it as their mysterious secret. 15

16 Three stages missable detectable critical Here s a fatigue crack growing from a rivet. The airworthiness standards require dividing its growth into three stages: - First, it is missable, which depends on the NDT method and other factors; - Second, it is detectable ; and - Finally, it is critical, which is when the structure is weak and could break. 16

17 Inspection interval < detectable time missable detectable critical Then the inspection interval must be less than the detectable time so that a crack missed by one inspection won t be critical before the next. Simple? Yes. Universal? All civil and military airworthiness standards require it, whether they call it damage tolerance, safety-by-inspection or reliability-centred maintenance. Essential? It is so fundamental there is no other way. Which is why I hope CASA s Ageing Aircraft Management Program (AAMP) eventually includes it.* 17 * I would prefer guesses of the right variables to a matrix tool of others. For example, CASA's current matrix tool could not tell where cracks could still be missable when critical, which is common for old aircraft designs. Nor could it help an inspector know which NDT might help.

18 Graphically critical crack size detectable detectable time missable time Here s the same, graphically. It s how aeronautical engineers normally do it. Where do they get their info to draw graphs like this? They get the growth curve and the critical size from clever engineering called fracture mechanics. Or, if they re lucky, they ll have test results or service experience. But how do they choose an inspection method and estimate missable? They need advice from an experienced inspector. The airworthiness standards are flexible. The inspector can propose any technique, for any method, to any standard, as long as they conservatively estimate what is missable. 18

19 Why engineers should ask inspectors Missable has most effect on interval - More than growth and critical NDT is tricky - It needs an expert Engineers are optimists - They think NDT can find more than it can Should coordination be mandatory? - As CASR 21.M requires coordination across disciplines for design approval 19

20 Don t be pressured! critical crack size detectable detectable time missable time If you re an inspector, and an aeronautical engineer does ask for your advice, here s a warning: don t let them pass their pressures onto you. Their bosses or clients are pressuring them for long detectable times, for less maintenance. Instead of this graph, they d prefer this... 20

21 Graphically critical crack size detecable detectable time missable time Reducing the maximum missable crack size by a little increases the detectable time by a lot. It is why engineers pressure inspectors to find smaller and smaller cracks. 21

22 me, many years ago 22 As an aeronautical engineer I know the pressures, and I have tried to pass them to inspectors.

23 Resist the pressure Avoid pride Change the question - What is the smallest crack you could find? - What is the largest crack others could miss? How could you resist the pressure? Here s two more tricks. 23 Avoid pride. If you are an inspector, don t try to impress the engineer with how small a crack you can find. One way is to change the question. If the engineer asks you about the smallest crack you can find - as they often do - ask them to ask you, instead, about the largest crack others could miss. It is no longer about you, so you can be impartial. And it is no longer about the best result, but the worst.

24 The Lycoming SI? Ask Lycoming - Just about crack size - Or for whole technique Or ask CASA So, back to Lycoming s Service Instruction. What should an inspector do about it not specifying crack size. They could ask Lycoming. Just about crack size. Or, for the whole technique. Lycoming s technique would automatically be approved data. Any other would need CASA s approval. I hope CASA know the crack size. 24

25 New maintenance rules? Approved maintenance data - CASR Dictionary 15 Sources - Manufacturer, 145 org, CAMO - Not CASA Allow industry standards So far, I ve only talked about NDT for maintenance under the 1988 Civil Aviation Regulations. How will it change under the new maintenance rules, like Parts 42, 145 and the rest, in the CASRs? The slide is a summary. For more information, ask CASA. 25

26 Summary NDT is maintenance Maintenance needs approved data CAR 2A lists approvers - Manufacturer, CASA...not NDT Level 3 Top standard is aircraft cert basis Resist pressure from aeronautical engineers - Resist pride - Change the question 26

27 Teamwork Approved 8 October 2010 DATE John!Cormick DIRECTOR OF AVIATION SAFETY 27 As I have said, approved data for NDT needs teamwork between inspectors and engineers. I would like to thank all the NDT inspectors who have helped me throughout my career.

28 Questions? If you have any questions or comments, or would like to discuss airworthiness training or consulting, please contact me. 28