The biggest myth in general aviation

image: Civil Aviation Safety Authority

By Nick Stobie

Maintenance releases are a seemingly simple document, but does an endorsed defect automatically ground an aircraft?

The underlying principle behind the maintenance release is communication—they are a tracked and formalised way that pilots, operators and engineers communicate about the airworthiness of an aircraft. Yet despite this straightforward premise, their use can be somewhat mystifying.

I’d like to think most pilots are quite aware of what should be written on the maintenance release, particularly regarding defects. However, too often the implications of writing up defects are murky at best. In private operations where there is no formalised support structure, pilots may be genuinely unaware whether or not an endorsed defect on the maintenance release prevents flight from a legal standpoint. Even with an operations manual or chief pilot to refer to, it’s poorly understood.

The regulations don’t make it all that clear either, with limited guidance on how to defer defects. This lack of clarity leads to a fear of writing up defects, the ultimate outcome of which is that defects just don’t get written up.

Hence forms the biggest myth in general aviation: the clean maintenance release.

Fear and misunderstanding

Aeroplanes break. Often. I’ve had the pleasure of working for several operators that were incredibly proactive and passionate about maintaining their aircraft, and yet even their immaculately maintained and low time aeroplanes developed defects on a regular basis. I’m yet to see an aeroplane genuinely make it through a full maintenance release period without picking up a defect.

One of my biggest personal frustrations is the minor defect that just doesn’t make it onto the maintenance release. A defect that, if everything was correctly understood, wouldn’t stop the aircraft from being flown, but is still operationally relevant to the pilot: the second radio being unserviceable, the ADF not testing correctly, the co-pilot push-to-talk switch not working. In most operations, if managed correctly, these could all be insignificant.
But in the wrong circumstances, the next pilot not knowing about a defect could lead to problems.

For some reason, however, it’s not the fear of disaster that dictates our use of the maintenance release. It’s fear of something else. It’s fear of grounding an aircraft. It’s fear of not being allowed to hire an aircraft again. It’s fear of losing a job. It’s fear of drawing the ire of CASA. Like most fears, this fear is rooted in misunderstanding.

What are defects?

For the most part, pilots know what defects are. Perhaps on an instinctive level, we’re alert for them because of the genuine risk that some defects might pose to our continued existence.

The definition of a defect is broadly segregated into major and minor. AC 20-06 defines a major defect as ‘a defect of such a kind that it may affect the safety of the aircraft or cause the aircraft to become a danger to persons or property’. A minor defect is a defect that is not a major defect. For example: Elevator cable has snapped—major defect; Instrument light has failed—minor defect.

CAR 50 is very clear on what we should do upon finding these defects: ‘a person … who becomes aware of the defect or damage, must endorse the maintenance release of the aircraft … ‘. It’s black and white. If you find a defect, you have a legal obligation to endorse it on the maintenance release.

Unsurprisingly, major defects are very good at making their way onto the maintenance release. Imagine yourself handling both defects—you sure as hell won’t be flying with a disconnected elevator cable. Concern about how dangerous it would be to even attempt flight with a snapped elevator cable would undoubtedly compel even the most hesitant among us to make an entry into Part 2, perhaps with AIRCRAFT UNAIRWORTHY for added emphasis.

However, most of us would argue, given day VMC, that it’s perfectly safe to fly without your instruments being lit. CAO 20.18 doesn’t require it. So why do some among us sweat the small stuff and decide against endorsing minor defects? The answer to this lies in understanding what happens after endorsing the defect.

CAAPs are advisory publications that provide explanation, guidance and context for regulations. CAAP 43-1 discusses maintenance releases and states:

4.2.5 The aircraft may be permitted to fly with an ‘open defect’ if the defect or damage that is endorsed on Part 2 has been assessed by the pilot-in-command or a LAME (licenced on type) and a determination has been made that the defect is not a major defect and that the affected item or system is not required for the intended flight.

4.2.6 In order to avoid doubt, it is recommended that when a pilot, LAME or appropriate authorisation/authority holder assesses a defect as not being a major defect, an entry should be made in the Clearing endorsements column to the effect that the defect is not a major defect.

Can I fly with a defect?

In Australia particularly, flying with defects is an almost essential part of operating aircraft. Finding engineers to fix your aircraft at short notice is hard enough when you’re at a major airport, let alone the remote confines of central Australia.

In flight school, we’re generally taught that defects go on the maintenance release. However, what isn’t well taught is what happens next. In training and theory, our responsibility as pilots ends once pen goes to paper. You might swap into another aircraft or just cancel the flight. Anecdotally I’ve heard of many flight schools where students don’t even get this far—writing in Part 2 of the maintenance release is a joy reserved only for instructors. In reality you don’t always have the easy exit of having somebody else sort out the problem.

The specific answer to ‘Can I fly with an open or uncleared defect’ varies depending on your type of operation and its category. CAO 20.18 10.1A states that, for private and aerial work operations, the equipment required for the flight must be serviceable. Flight manual equipment and requirements are also mandatory per CAR 138. So long as the defect isn’t required equipment, you’re able to fly, and the defect can be deferred for later rectification.

Exactly how to defer a defect on a maintenance release is not specifically laid out in the regulations. CASA does offer some guidance on flight with defects in the form of a CAAP.

In short: write the defect up in Part 2, then defer it by declaring it to not be a major defect in the clearing endorsements column. You might also set out any operational restrictions on use that may be relevant (i.e. don’t use the passenger seat if the seatbelt is broken).

The game changes subtly when we move to charter and RPT operations, where CAO 20.18 requires that ‘all instruments and equipment that it carries, or is fitted with, under sub-regulation 207 (2) of CAR 1988 must be serviceable before take-off’. This line has been one of contention and is somewhat ambiguous, however, the current CASA interpretation seems to be that instruments and equipment carried under CAR 207 are those required by the relevant appendix of 20.18. Any items surplus to this are hence not required to be serviceable. This interpretation is not stated in any available literature or regulation at the time of writing; however, CASA’s Maintenance guide for pilots is the official policy document for these matters. Arguably this interpretation is unclear among the community and formal clarification would be beneficial—there was a time when this line was taken to mean all fitted equipment, even items over and above those required by 20.18.

Like other operations, defects occur away from base. In spite of the overarching requirement for all mandatory equipment to be serviceable, CAO 20.18 10.1 goes on to allow some degree of pragmatism for dealing with minor defects in charter and RPT operations, with four avenues to allowing flight: a) get approval from CASA in the form of a permissible unserviceability (PU), b) the defect is a permissible unserviceability as set out in the aircraft’s approved operators minimum equipment list (MEL), c) get approval from CASA in the form of a special flight permit (SFP) or d) the defect is a passenger convenience item only.

The specifics of how defects are dealt with varies between operators, as unfortunately there are several methods of deferring defects. Your company operations manual should have a specified procedure for deferring defects. Ultimately this manual has been approved by CASA and should therefore be your first point of reference. LAMEs, Chief Pilots and HAAMCs may be able to direct you to make deferring or clearing entries for certain defects.

In all cases, an endorsement in Part 2 is still required, with the subsequent action (be it rectification, deferral under a PU/MEL/SFP or otherwise) detailed in the clearing endorsements column.

Permissible unserviceabilities and minimum equipment lists

One of the risks of flying with a defect is that you as a mere pilot may not be able to fully appreciate the implications of that defect. Even in simple aircraft, systems integrate with one another and the unforeseen consequences of a defect may present a threat to safety. Additionally, complex operations may have an extensive list of required equipment for various circumstances (day/night/VFR/IFR etc.), keeping track of which may be difficult.

Permissible unserviceabilities can be approved by CASA for a specific flight or period on a defect-by-defect basis. To negate seeking approval for every unserviceability, MELs detail certain permissible unserviceabilities—for each, it lists if and how it might be acceptable to fly with that defect. A PU or MEL item might specify that other equipment needs to be serviceable to permit flight or that a maintenance action (e.g. pulling and tagging a circuit breaker) needs to be completed. It might also require the unserviceable equipment to be placarded and will specify for what duration of time that defect is acceptable to fly with. Some items may require rectification within 24 hours or at the completion of the next flight, whereas other may be acceptable for even several months.

Some operators may have unique requirements, making them less able to tolerate certain defects. An unserviceable cabin intercom might be acceptable for a charter operator carrying passengers, but unacceptable for an air ambulance operation which requires continuous communication between pilot and medical crew. These requirements will be considered when designing a MEL, which itself is derived from a manufacturer’s master minimum equipment list.

Special flight permits

Invariably defects arise in aircraft from time to time that the regulations and/or safety considerations dictate would normally be unacceptable and make an aircraft unairworthy. Circumstances may preclude rectification of that defect at the aircraft’s location.

Take for example a privately-owned Cessna 182 located on a private property. It’s been a particularly wet winter and the strip has been waterlogged for a good two months. By the time the strip is usable again, the maintenance release has passed its calendar expiry. So how can the aircraft be flown to a maintenance provider without a valid maintenance release?

This is where special flight permits come in. An application can be made to CASA or a delegate to permit a flight that would otherwise not be possible. CASA will consider the specific circumstances and may issue a Special Flight Permit if safe to do so.

Back to first principles

Regardless of your obligations and the legality of flight, the underlying premise of communication should dictate whether pen goes to paper on the maintenance release. Put yourself in the shoes of the next pilot and ask, ‘Is this something I would like to be made aware of before I fly the aircraft?’ If you’re unsure about writing a defect up and you answer ‘yes’ to this question, it’s probably a sign that an entry into Part 2 is needed.

*Background for this article was provided by Peter Ball, CASA Aviation Safety Advisor for the Northern Territory.

CASA’s Maintenance guide for pilots is available from the CASA Online Store:

Further information on Advisory Circulars is available at


  1. The word that stands out like dogs balls here is FEAR!!! There’s the answer to 99% of all MR issues!

  2. “In short: write the defect up in Part 2, then defer it by declaring it to not be a major defect in the clearing endorsements column. You might also set out any operational restrictions on use that may be relevant (i.e. don’t use the passenger seat if the seatbelt is broken)”. In my experience if it is cleared then it is history unless there is a reference and record of the deferred defects and time limit.

  3. Excellent article, further to this is also the need for the maintenance provider to review, capture and rectify all these defects, major or minor. Even though they may be endorsed to clear for further flight, the defect is still present until rectified.

  4. Problem is, pilots don’t have access to the aircraft log book & the red maintenance release has only a tiny area to write up a defect.

  5. MR system would have a chance of working if pilots could nominate, in their opinion, whether a defect was major (grounding) or minor (advisory) without the threat of legal sanctions if their judgement was called into question.
    There is a noble and practical intent behind the MR system which is screwed by the dire legal implications if CASA get involved in a punitive way, therefore the common attitude is put nothing in writing which is likely to bite you in a future legal action.
    The legal situation is exacerbated by the situation that CASA treats offenses as a “strict liability offences” which have consequences under criminal law.
    CASA threatened a friend with criminal action because he failed to endorse his maintenance release after he had smoke in the cockpit because of a pinched wire. His defense was he was the aircraft owner, was the only pilot flying the aircraft and had every intention of rectifying the problem prior to flight. He was seriously concerned about gaining a criminal record as a result of CASA’s threats.

    • Well said, I said pretty much the same as you in one word, fear! Fear from the regulator, fear from the hire Co and fear from the boss, (apply whatever is applicable!) As soon as you write something on that legal document you are wide open to a minefield!

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