How to deal with several MEL items?

[cauc0001]

Dear Everyone,

I was confused that if we encountered two or three faults items, number one fault require reduce RTOW 1300KG, number two fault require reduce RTOW 2500kg, number three fault require to reduce 2300kg.
How can I do the calculation? Because in the MEL, which said each MEL is only apply to one fault can not consider combined fault.
Thank you for your help.

[FlightDetent]

cauc0001: this is somewhat uncharted territory.

There are two things you need to keep in mind.

1) Some guidance is provided by the manufacturer in the MASTER-MEL (MMEL). As a pilot for an airline, you are not allowed to operate based on that guidance alone. MMEL is only a document from the factory, not for operational use.

2) Any airline must create its own AIRLINE-MEL, which is subject to approval by the local CAA. Usually, they take the MMEL from factory and fill small but necessary key information and guidance according to the airline's procedures and local CAA regulation.

If your AIRLINE-MEL says that dispatch with multiple defects is not allowed, you are not allowed to fly. Not only that, also the Maintenance Department is not allowed to release the aircraft to you!

--- some additional information, only as an example-------

Originally Posted by Airbus M-MEL year 2012

CRITERIA FOR DISPATCH

The decision of the Commander of the flight to have inoperative items corrected before the flight Will take precedence over the provisions contained in the MEL. The Commander may request requirements above the minimum listed, whenever in his judgment such added equipment is essential to the safety of a particular flight under the special condition prevailing at the time.

The MEL cannot take into account all multiple unserviceabilities. Therefore, before dispatching an aircraft with multiple MEL items inoperative, it must be assured that any interface or inter-relationship between inoperative items Will not result in a degradation in the level of safety and/or an undue increase in crew workload. It is particularly in this area of multiple discrepancies and especially discrepancies in related systems, that good judgment, based on the circumstances of the case, including climatic and en-route conditions, must be used.

Originally Posted by Some European Airline MEL

Before dispatching an aeroplane with multiple MEL/NEF items inoperative, it must be checked that any interface of inter-relationship between inoperative items will not result in degradation in the level of safety and/or an undue increase in crew workload. It is particularly in this area of multiple discrepancies and especially discrepancies hi related systems, that good judgment, based on the circumstances of the case including climatic and en-route conditions must be used.

In the event pilot in command and/or the respective maintenance staff have any doubt concerning the application of the MEL/NEF, contact XXX Airlines (XXX) MCC personnel via mobile phone or using any other communication. Taking into account all relevant factors XXX MCC personnel with co-ordination with Engineering Department will then release a recommendation to the pilot in command.

---------------------

What 3 problems with weight penalty did you have?

[Eric Janson]

Originally Posted by cauc0001

Dear Everyone,

I was confused that if we encountered two or three faults items, number one fault require reduce RTOW 1300KG, number two fault require reduce RTOW 2500kg, number three fault require to reduce 2300kg.
How can I do the calculation? Because in the MEL, which said each MEL is only apply to one fault can not consider combined fault.
Thank you for your help.

If you took the 2500kg penalty that would already account for the other 2 penalties imho. That assumes these penalties all apply to the take-off phase.

You would still need to do the operational procedures (if any) for each fault.

[wiedehopf]

If one failure would be reduced braking and the other no reversers for example, you couldn't even be sure adding the reductions to each other is enough.
The percentage reduction in for example braking deceleration might even multiply with each other resulting in a reduction greater than the sum.

You would really have to talk about the specific MEL item to even make an educated guess how the RTOW reductions interact with each other.

Edit: Bad example, reversers aren't used for RTOW calculations (i think) but i hope it's clear what i mean.

[Skyjob]

Without more details as to what the penalties are for the answer cannot be given

[Mad (Flt) Scientist]

Originally Posted by Eric Janson

If you took the 2500kg penalty that would already account for the other 2 penalties imho. That assumes these penalties all apply to the take-off phase..

There's absolutely no guarantee of that, without knowing precisely what the RTOW penalty is intended to achieve for each case. If all three defects have an impact on climb capability, then they may well be additive and you'd need to combine the penalties.

But in the case of the original question, it's easy. The MEL says no multiple defects are allowed. End of.

[Nomad2]

Ask yourself.
1. Is it safe?
2. Ok, it's safe, but is it legal?
3. Ok, it's safe and it's legal, but will I be able to defend my decision to go, at a subsequent board of enquiry?

PiC, kinda means what the initials stand for, ya know!

[FullWings]

Originally Posted by Mad (Flt) Scientist

There's absolutely no guarantee of that, without knowing precisely what the RTOW penalty is intended to achieve for each case. If all three defects have an impact on climb capability, then they may well be additive and you'd need to combine the penalties.

But in the case of the original question, it's easy. The MEL says no multiple defects are allowed. End of.

What he said.

It does seem somewhat unusual for only one defect per airframe to be allowable, as this would increase the likelihood of an AOG situation considerably. It could be that the requirements are worded/translated(?) in a strange manner as a conventional MEL/DDG will normally have conditions against some defects which require normal operation of other systems but allow multiple defects. I agree that with lack of relevant guidance, performance defects should be considered additive.

As an aside, it’s always a good idea to stop for a think when carrying multiple defects: given the vast array of combinations, it’s quite possible that you might be the first person to have encountered/considered such a mix...

[Mad (Flt) Scientist]

Originally Posted by FullWings

It does seem somewhat unusual for only one defect per airframe to be allowable, as this would increase the likelihood of an AOG situation considerably. .....

Could the original question actually perhaps relate to CDL not MEL? While MEL does indeed typically put specific "interoperability" crietria against each item, showing which may be combined specifically, CDL may well have a more simple "no more than one large or three minor allowed" overall statement? Just a guess.

[Skyjob]

Originally Posted by Mad (Flt) Scientist

But in the case of the original question, it's easy. The MEL says no multiple defects are allowed. End of.

That's not quite what the OP wrote, nor what appears to be the text in MEL.
The MEL is a document created to enable a crew to deal with a single identified problem.
As the combination of items is endless, there cannot be a MEL in existence covering every combination of MEL items in existence.

... each MEL is only apply to one fault can not consider combined fault

The OP advised us that his MEL conform to this, as it cannot advise on combined faults.

It does seem somewhat unusual for only one defect per airframe to be allowable, as this would increase the likelihood of an AOG situation considerably.

Resultant of the MEL introduction being read properly, this is thus not the case, and the unusual is in fact usual.

There's absolutely no guarantee of that, without knowing precisely what the RTOW penalty is intended to achieve for each case.

100% agreed!
Unless we get shared the MEL items and aircraft type, we cannot make this assessment.