MEL dilema
Moderator
Perhaps I can coalesce some of the useful points made previously ?
One needs to be comfortable from where the MEL (via MMEL) is coming...
The aircraft certification is based on everything (non-trivial pax items and the like notwithstanding) working OK.
Now, does this mean that the aircraft somehow becomes dangerous if XYZ is broken ? Not necessarily - of course. However, what it does infer is that the absence of a particular functionality MAY be contraindicated by some regulatory, operational, or commonsense requirement for which the bit of kit provided a particular useful functional capability.
Therefore, if XYZ is broken, it may be necessary to impose one or more restrictions on operation with the defect to maintain the underlying Type standard of airworthiness - whether we are talking about the technical (engineering and maintenance side of things) or the operational (stick and rudder).
As to where the MEL might be used, it is logical to use it when the pilot doesn't have the availability of competent technical support or replacement bits aren't available - to this extent the MEL is a pre-approved list of non-functioning bits of kit which can be tolerated for the operation (albeit with restrictions). As such it makes sense to use the document formally from shortly prior to an operation to the point where the despatch is effective and then repeated on subsequent sectors until maintenance is available down line somewhere.
The essence of the MEL is that it relates to INTENTIONAL despatch with unserviceable bits of kit and, for this, we must maintain the original basis for Type Certification so that the level of risk (think "safety") is consistent with the Type Certification.
At any time it is appropriate for pilots to consult the MEL to get some guidance on what might be useful to know if a bit of kit fails but, in general, for UNINTENTIONAL operation (ie it broke in flight) the QRH, or similar, is the relevant guidance material. It follows that the level of risk may increase in this circumstance - however, the philosophy is that the risk of failure to reach an aerodrome safely has to be maintained at an acceptably low level and the QRH procedures will be designed to achieve this.
Clearly, depending on what breaks, this ideal might be a bit of a pipe dream .. see Sioux City and similar mishaps which go to the point that the crew is the last line of defence ...
Further, it follows that
(a) if something breaks in flight we complete the flight with sensible reference to the QRH - consideration is an unintended operation with a bit broken. We tolerate an increased level of risk.
(b) at that point, if the MEL doesn't give us a get out of jail free card, the aircraft sits where it is until it gets fixed or gets a permit to fly somewhere to achieve that fix - consideration is an intended operation with a bit broken. We are not permitted to tolerate a reduction in notional risk levels.
But MEL limits in flight is a "tabu" and not normally accepted
MEL applies to an intentional operation with a defect - that isn't the case in flight so it doesn't "apply". However, a sensible crew will consult the MEL to get some guidance on what might bite them with the subsequent aircraft recovery.
You have an ETOPS 180 required system that became inop in flight
Depends on the Type and QRH what you might do. My thought would be NOT to continue into an ETOPS situation if I had a sensible alternative - if something untoward occurs, I am short of a convincing argument at the enquiry .. should I live to attend the enquiry .. Similar thing applies with, say, an engine fire system failure shortly after departure - consider the QRH but I would be opting to go get it fixed first before continuing with the flight (considering all the circumstances at the time, of course).
You takeoff in rain, your wiper fails during TO run just above 80kt
The QRH is the relevant guidance. The commander, however, has a responsibility to consider his/her options .. which might include diverting to get the wiper fixed depending on the destination conditions etc.
So you decide to return. Are you getting fired by your company for making a wrong command decision that costed them a canceled flight?
This is a common philosophical dilemma where a prudent airworthiness decision might fly in the face of (technically ignorant) bean counter values. The sensible approach is
(a) have a strong union to provide some Industrial protection, or
(b) do the thing which provides a safe outcome to the flight and, either
(i) fight it in court, or
(ii) look for another job
Sometimes life is very unfair ..
A single pack in high flow is capable of maintaining pressurization and acceptable temperatures throughout the airplane up to the maximum certified ceiling.
So, why fly at the MEL restricted FL250?
Think about the situation at normal cruise level .. if the remaining system elements fail ? The FL250 requirement is an older consideration providing a less urgent need for completing an emergency descent etc. You pays your money and you takes your chances. If fuel doesn't permit, you don't have much option, if it does, you consider your options and pick the best available in the circumstances.
In the end everything will be blamed on the captain
Now, that has the ring of truth ..
Safety of the flight is fully covered by the applicable ECL procedure directives
However, the two levels of acceptable risk are not the same ...
where it says DDG, read MEL. Old term used in our company, since replaced by MEL.
That may be your company's view but it is not general. For DDG think combined MEL/CDL - see http://www.boeing.com/assets/pdf/com...chures/ddg.pdf for some B-speak on the subject.
One needs to be comfortable from where the MEL (via MMEL) is coming...
The aircraft certification is based on everything (non-trivial pax items and the like notwithstanding) working OK.
Now, does this mean that the aircraft somehow becomes dangerous if XYZ is broken ? Not necessarily - of course. However, what it does infer is that the absence of a particular functionality MAY be contraindicated by some regulatory, operational, or commonsense requirement for which the bit of kit provided a particular useful functional capability.
Therefore, if XYZ is broken, it may be necessary to impose one or more restrictions on operation with the defect to maintain the underlying Type standard of airworthiness - whether we are talking about the technical (engineering and maintenance side of things) or the operational (stick and rudder).
As to where the MEL might be used, it is logical to use it when the pilot doesn't have the availability of competent technical support or replacement bits aren't available - to this extent the MEL is a pre-approved list of non-functioning bits of kit which can be tolerated for the operation (albeit with restrictions). As such it makes sense to use the document formally from shortly prior to an operation to the point where the despatch is effective and then repeated on subsequent sectors until maintenance is available down line somewhere.
The essence of the MEL is that it relates to INTENTIONAL despatch with unserviceable bits of kit and, for this, we must maintain the original basis for Type Certification so that the level of risk (think "safety") is consistent with the Type Certification.
At any time it is appropriate for pilots to consult the MEL to get some guidance on what might be useful to know if a bit of kit fails but, in general, for UNINTENTIONAL operation (ie it broke in flight) the QRH, or similar, is the relevant guidance material. It follows that the level of risk may increase in this circumstance - however, the philosophy is that the risk of failure to reach an aerodrome safely has to be maintained at an acceptably low level and the QRH procedures will be designed to achieve this.
Clearly, depending on what breaks, this ideal might be a bit of a pipe dream .. see Sioux City and similar mishaps which go to the point that the crew is the last line of defence ...
Further, it follows that
(a) if something breaks in flight we complete the flight with sensible reference to the QRH - consideration is an unintended operation with a bit broken. We tolerate an increased level of risk.
(b) at that point, if the MEL doesn't give us a get out of jail free card, the aircraft sits where it is until it gets fixed or gets a permit to fly somewhere to achieve that fix - consideration is an intended operation with a bit broken. We are not permitted to tolerate a reduction in notional risk levels.
But MEL limits in flight is a "tabu" and not normally accepted
MEL applies to an intentional operation with a defect - that isn't the case in flight so it doesn't "apply". However, a sensible crew will consult the MEL to get some guidance on what might bite them with the subsequent aircraft recovery.
You have an ETOPS 180 required system that became inop in flight
Depends on the Type and QRH what you might do. My thought would be NOT to continue into an ETOPS situation if I had a sensible alternative - if something untoward occurs, I am short of a convincing argument at the enquiry .. should I live to attend the enquiry .. Similar thing applies with, say, an engine fire system failure shortly after departure - consider the QRH but I would be opting to go get it fixed first before continuing with the flight (considering all the circumstances at the time, of course).
You takeoff in rain, your wiper fails during TO run just above 80kt
The QRH is the relevant guidance. The commander, however, has a responsibility to consider his/her options .. which might include diverting to get the wiper fixed depending on the destination conditions etc.
So you decide to return. Are you getting fired by your company for making a wrong command decision that costed them a canceled flight?
This is a common philosophical dilemma where a prudent airworthiness decision might fly in the face of (technically ignorant) bean counter values. The sensible approach is
(a) have a strong union to provide some Industrial protection, or
(b) do the thing which provides a safe outcome to the flight and, either
(i) fight it in court, or
(ii) look for another job
Sometimes life is very unfair ..
A single pack in high flow is capable of maintaining pressurization and acceptable temperatures throughout the airplane up to the maximum certified ceiling.
So, why fly at the MEL restricted FL250?
Think about the situation at normal cruise level .. if the remaining system elements fail ? The FL250 requirement is an older consideration providing a less urgent need for completing an emergency descent etc. You pays your money and you takes your chances. If fuel doesn't permit, you don't have much option, if it does, you consider your options and pick the best available in the circumstances.
In the end everything will be blamed on the captain
Now, that has the ring of truth ..
Safety of the flight is fully covered by the applicable ECL procedure directives
However, the two levels of acceptable risk are not the same ...
where it says DDG, read MEL. Old term used in our company, since replaced by MEL.
That may be your company's view but it is not general. For DDG think combined MEL/CDL - see http://www.boeing.com/assets/pdf/com...chures/ddg.pdf for some B-speak on the subject.
