Safety topic from Episode 5

Ageing aircraft and SIDs

How’s your favourite old aircraft going? Over the years, you’ve religiously handed it over to your local LAME for its 100 hourly inspection and you keep a keen eye on the exterior structure, checking rivets, pivot points and control surfaces. You’re always checking the information available to you on the panel, making sure Ts and Ps are in the green, and you’ll notice when she starts running rough. Actually, she’s up for her 40th birthday soon, so you’ve even given her a nice new paint job and she’s come up a treat. But do you really know what’s going on deep inside the bowels of the old girl? Ladies are notoriously good at hiding their age. 

The Australian newspaper recently reported that “CASA is concerned that planes in Australia are operating well beyond their original design assumptions. The air safety watchdog is moving to head off potential safety problems with older aircraft as the average age of the nation’s general aviation fleet hits 40 years.”

CASA seeks to address the issue of ageing piston engine aircraft in Australia and offer registered operators and owners guidelines on better managing their ageing aircraft into the future.

For Pieter van Dijk, Principal Engineer Maintenance and Mechanical Systems at CASA, it is a subject he has spent considerable time exploring in an effort to help owners understand how it may potentially impact them personally. He believes the key is in educating owners as to the likelihood of their aircraft suffering the detrimental effects of ageing. Fundamental to the concept are the issues of how and why all aircraft will age at a varying rate, depending upon its circumstances during three main phases of its life:

  • Pre-manufacture (what were the original design assumptions?)
  • Manufacture (techniques used at the time)
  • Post-manufacture (operational environment, maintenance, storage)

On the maintenance issue, Pieter encourages owners to lift their head out of the sand for a moment and do some personal research on the real health of their aircraft, suggesting they ask their LAME what parts of the aircraft are NOT being inspected during the normal 100 hourly inspection. It’s an interesting question.

We cannot escape the fact that the current average age of single and multi-engine fixed wing aircraft in Australia is 40 years, and 97 per cent of multi-engine piston aircraft are older than the typical 20 year design life. There is also an increasing use of older jet aircraft in regional areas. Whichever source you consult, the facts are the same. “All aircraft could be considered to be ageing aircraft from the day of manufacture. However, the rate at which an individual aircraft ages is dependent on a range of factors that are unique to that particular aircraft. The extent of ageing is dependent on how that aircraft has been individually operated, maintained and stored during its life.” 

Transfer that to people, and you get the idea. From the maternity ward to the Jason recliner, it’s fair to say we’re in control of our own ageing process. It’s all about looking after our body and giving it what it needs for maximum longevity and flawless function. OK, so ‘flawless’ might be a stretch, but most of us are aiming for achievable outcomes, like:

  • Keeping ourselves safe: 
    • Guarding against a fall which may be brought on by a weak or fatigued joint. Aircraft cabling, operational surfaces and hinges need the same attention. There is obvious benefit in uncovering signs of early corrosion in wing structures and undercarriage brackets.  
  • Maintaining healthy arteries and blood pressure 
    • These are vital components that keep our body functioning properly. Similarly, aircraft wiring and the oil, fuel & hydraulic systems must be checked for integrity.
  • Staying disease-free 
    • Recognising an innocuous spot before it turns into a cancerous lump if left untreated. Corrosion in an aircraft starts small. The only indicator might be one missing rivet. Out of sight, out of mind is a risky approach. 

One direct result of the push to control the detrimental effects of ageing aircraft is the Supplemental Inspection Documents (SIDs) initiative. It’s fair to say, the mandatory introduction of SIDs has prompted some robust dialogue within the General Aviation industry in Australia. A necessary evil? The jury is still out on that one. 

It may seem trite to discuss the expense of a safety initiative before the obvious accident-saving benefits, but it is a poignant element of the dialogue. In many cases, the SIDs are inspecting vital structural elements in the aircraft that have never been looked at since the aircraft was first manufactured, possibly half a century ago. The type of damage the SIDs uncovers is not normally discovered during typical 100 hourly/12 month inspections.

The cost of the basic SIDs inspections can be relatively minor if the aircraft has been well maintained and looked after over its life. To the owner, this amount assures peace of mind of the structural integrity of the aircraft.

However, rectifying any damage found as a result of undertaking the SIDs inspections can cost many tens of thousands of dollars, depending on the severity of the damage. It is those aircraft where extensive damage has been detected that have relatively high repair bills that are typically attributed to the SIDs inspections. This otherwise undiscovered damage represents a significant threat to the safety of flight of the aircraft.

Our Out-n-Back crew spent many hours talking to pilots and aircraft owners in the bush who spoke of their concerns about priorities. On their property, their aircraft is an essential working tool which they are currently operating in adherence with CASA’s maintenance regulations. Despite there being no argument that SIDs is in place to enhance safety, the reality is that many owners will not be able to continue operating their aircraft due to the cost of the SIDs inspections.   

SIDs – what’s that about? 

CASA has handed down a ruling that all operators of Australian-registered Cessnas are required to comply with Cessna’s SIDs. These SIDs apply to all aircraft whether they are in commercial service or private use and they set forth an extensive program of structural inspections designed to assure the continued safe operation of single engine aircraft. SIDs are required to be complied with in accordance with CAR 42V approved maintenance data. 

Visual inspection techniques are utilised to detect corrosion and cracks caused by metal fatigue. Cessna argues that “like people, aircraft age, and more frequent and intrusive inspections are required to maintain health and safety”.

Some of these inspections are relatively easy, but some are invasive, labour-intensive and costly. (Hence the robust debate amongst aircraft owners.) The SIDs specify a complex matrix of initial and repetitive compliance times for these various inspections. Aviation Ruling 1/2014 details more information on compliance dates. 

The most labour-intensive inspections are to be done initially when the aircraft reaches 20 years old, and then repetitively every three, five or ten years thereafter. Of course, since all Cessna 300/400-series piston twins and all 200-series singles and the vast majority of 100-series singles are 30-60 years old, all of them are now past due for these inspections. 

To refer back to the previous medical analogy, the argument for not conducting SIDs inspections on your aircraft is similar to that of a person not partaking in medical screening for cancer as they get older. Furthermore, the cost of any MRI, CAT Scan, X-Ray or blood test is relatively minor compared to the full costs associated with addressing any cancer that may be found as a result. In both cases, the likelihood of you living longer is increased.

Of course, all aircraft are subject to the ageing process, not just Cessnas. Whilst you listen to hangar talk, make sure you are well informed on the SIDs program. Follow the links below to important resources that explain what is involved and why the program is necessary to prevent potential accidents caused by metal fatigue and corrosion within an aircraft’s frame. SIDs have already uncovered alarming evidence of such damage in older aircraft. It goes without saying that, left undetected and untreated, disease leading to structural failure is only a case of ‘when’ not ‘if’.