deferring defects

[Journey Man]

Hi,

Can I ask what are the general principles and ethics behind deferring defects?

Should defects always be immediately deferred, if that is acceptable for the MEL or should defects at an engineering base be rectified? I am aware that there is some operator leeway, but would appreciate a very general, non-specific general feeling.

If a defect is deferred, is the expiry of the defect extended after investigative action?

Thanks

[samaryaj]

Every mel has an interval during which it has to be repaired. You are right every operator has its own company policy. However if an ac is stationed for a significant amount of time , the defect should be tried to repair it else it is deferred, and then the ac is put under mel. Depending on the type of mel, each mel has an interval like A, B, C, D,
a= as specified in the mel
B= 3 days
C= 10 days
d= 120 days
I hoe this helps...

[Journey Man]

Thanks for the response, samaryaj.

Just trying to clarify how far the boundaries of grey go, how far things can run, etc. RE categories: let's say an item is a Cat C, 10 day item; if there is investigative action (i.e. swapping nav 1 to nav 2, or TXR 1 to TXR 2) does that affect the expiry of the deferred defect, or is that to be carried out within the 10 days allocated as a Cat C item.

Just really struggling to find any guidance on this.

Thanks all

[Gas Bags]

Journey Man,

In its simplest form...An airline buys/leases an airliner to make money. An airliner only makes money when it is flying. When the airliner breaks it stops flying until it is fixed and therefore stops making money for the airline who operates it.

To counter this the manufacturer understands what systems/components etc can break and still allow the operator to fly the airliner safely without fixing them. This is not open ended and therefore time limited. They call them MEL items. As previously stated these MEL items have different catagories that refer to the time limit imposed before the defect must be fixed. i.e. A cat C MEL item can remain broken/inoperable for a maximum period of 10 days before either it is repaired or the aircraft stops operating until it is repaired.

The whole idea of the MEL system is to allow the airliner to keep operating with defects that do not affect safety of flight until such time as they can be repaired without affecting the revenue generating operation of the airliner, within specified time constraints.

So to your original question: It does not matter if the aircraft is in an engineering base when a defect occurs. If the aircraft is in the middle of a days operation and it breaks, if the defect is covered by an MEL and the operator can keep flying the aircraft and thus making money you would always use the MEL and defer the defect. This in turn allows the aircraft to continue flying till the end of the day when it would have otherwise stopped flying anyway, and you then fix the defect.

There are always many variables to this... i.e. if the next sector will take the aircraft away from an engineering base/spares/support for longer than the MEL repair limit will allow then you would fix the defect as opposed to deferring it. This is one of many scenarios affecting the decision to defer or not.

When I was an apprentice in the eighties I attended a company sponsored seminar. One of the questions we were all asked was who paid our wages. We all answered our company did. We were all wrong. The customer pays our wages. So to the other part of your question regarding ethics. Keep the aircraft flying if it is safely allowed to do so under MEL conditions, which in turn keeps the customer happy, and in turn keeps us being paid. Fix the aircraft, wherever possible in a place and at a time that causes the least disruption to the customer.

Troubleshooting does not generally affect the time limit constraints of an MEL. That being said each operator will have laid out in it's MMOE or equivalent the procedure to follow after troubleshooting an MEL and whether or not that troubleshooting cleared the defect or not. The only thing that removes the MEL is fixing the defect. Generally speaking if, for example, the LAE believes that he has fixed a defect that has a 10 day MEL applied to it, on the third day of that time limit, and removes the MEL, but the defect reoccurs on the very first sector following the MEL removal the MEL will be reapplied with the original defect date reinstated and thus seven days will be left. The clock does not get reset. However if the aircraft operates 2 or more sectors and then the same defect reoccurs, most operators procedures will allow the MEL to be reapplied with a fresh 10 day limit.

The last question...No, investigative action only, does not extend the MEL time limit. Refer above.

GB

[Captain Rat]

Also realise that in the real world of aviation, just like many other industries, Airlines don't like spending money on anything such as spares. So you will often have to defer a fault under the MEL because there are no spares. (Even at main base !)

[Epsomdog]

The difference between a good and bad airline, in terms of reliability, is usually the number of deferred defects they carry, across the fleet.

Also beware the cumulative effect of multiple MEL items. For this reason it is always best to fix the problem at the soonest maintenance opportunity.

[Dodo56]

MEL compliance should never be an issue in the world of scheduled airlines, which operate set route networks with contracted line engineering support. However on charters and business ops the aircraft can be operating away from base for some time so cat B items in particular can be problematic. The textbook answer is you fly an engineer out to fix it if you don't have one available down line. Depending on approved MOE procedures the operator may be able to authorise further deferral but you shouldn't count on that. The MEL is what it is for a reason!

[jester engineer]

Some company mels will have certain specific criteria. For example our company mel states for a tcas fault that the aircraft cannot depart an engineering base with any tcas ADD.

Remember that the MEL can, and often does, have tighter restrictions than the MMEL.

[flame_bringer]

TCAS is an MDD not an ADD.

[turbroprop]

Flame_bringer

Depends on your company procedures and MEL.

My company TCAS is an ADD on depending on the circumstances is even a stopper. .ie we can ADD at certain bases, but our MEL has the not so helpful clause against some items. Aircraft can make a series of flights, but can not be dispatched from a base where repairs can be carried out.

[dervish]

Don't tell the manufacturer you're allowing defects to be deferred!

But faults - ok. :ok:

[Rwy in Sight]

When I board an airliner I have always the question who many items are on this very aircraft MEL. And also how often an Aircraft A320/ 737 type flies with a completely empty MEL?

Rwy in Sight

[transilvana]

Hi guys

A question about deferred items. Who may clear an extension to fly on a deferred item? I just have this problem with one of our company aicrafts, a C item reported a month ago, then we receive a letter from the company staying that CAA has approved an extension of the C item until oct 1st., and that´s almost 2 months sice it was reported

[Exup]

Not sure if I have read this right, but you have a cat c item reported a month ago & you have just got an approved extension. It does not matter who can approve it your aircraft should have been grounded 20 days ago as it has been flying illegally for 20 days.

Your national aviation authority can grant an extension to an mel item, this is usually done before the item runs out and at the discretion of the authority.

Normally your engineering department will request an exstension internally within your company for varies reasons i.e no spares available, this then goes to the flight ops department who agree ( chief captain e.t.c) who will then sign it off & apply to the NAA, if they agree you will receive the required exstension.

So many people do not realise that the MEL is not an engineering document but a flight ops document & as such they are the ones who control it.

[transilvana]

My question is:

The item was reported end of july, then written on the tech log on 08.08. With the extension the deferred item was valid until 29.08.

Following the JAR procedure .81 extension it´s only allowed for 10 more days from the 19.08 until 29.08.

So, how can CAA aprove an extension beyond this limit? Aircraft is already at maintenance facility but company wants it flying all september.

[Terry McCassey]

To digress somewhat, there is a great little Android smartphone Application available free of charge. Just Google ' MEL calculator Android ' or the like and you'll find it. It gives you the MEL expiry dates from the UTC time on your phone, especially useful for calculating the Cat D, 120 day ones ! !

[spannersatcx]

only trouble is our cat D's are 60 days!

[Terry McCassey]

. . . Right !

[spannersatcx]

No, they are, they were originally 120, but in order improve a/c cat D's were changed to 60.

Other operators we handle have 120 day cat D's so the app will come in handy anyway.

[Terry McCassey]

Honest Spanners - I wasn't being sarcastic ! We use the 120 day Cat D's and with the amount of logo lights we defer every day, this phone application for old f*rts like me is invaluable.

[Wirelock]

to correctly defer a defect it should be recorded in the tech log .before further flight that tech log entry is signed off.
what differs one airline from another is how they get this done according the regulations.

[Tech_Log]

Slightly late to the party I know !

As mentioned, defects generally are raised in accordance with the MEL and should be inspected at the nearest opportunity though this depends on the flying schedule and downtime and company rules - some allow non airworthiness defects to be open on short haul until the next Daily check.
But as a general rule any defect raised needs to be closed (fixed) or deferred before flight.

If you're on a sub 40min downtime overseas and it's a broken tray table, chances are you'll defer it.

E.g. A Cat D item I raised on the first of an 8 sector day. It will almost certainly be deferred and rectified at end of the day due to minimum turn around times.
You'd raise an ADD to investigate when there's sufficient time / spares / whatever. However you'll then probably have 6-8hrs downtime overnight where the night shift can investigate. Then obviously they can clear it if spares etc. are available.

With regards an ADD extension (which our company calls a Repeat Interval Extension - RIE - not sure if this is an industry wide thing), this is usually approved by an approved manager.

My question is:

The item was reported end of july, then written on the tech log on 08.08. With the extension the deferred item was valid until 29.08.

Following the JAR procedure .81 extension it´s only allowed for 10 more days from the 19.08 until 29.08.

So, how can CAA aprove an extension beyond this limit? Aircraft is already at maintenance facility but company wants it flying all september.
If it's been raised as an ADD, then extended (RIE'd), I wouldn't have thought it was possible to extended it further.

This is all my understanding at least !
Safe Flying
Tech_Log