MEL dilema

[ricfly744]

We learn that MEL is "only" to be referenced to before TO, after airborne, QHR and NNC will do the job. OK, all agree but I want to ask your opinion about some scenarios.

One: You are dispatched by MEL with one Engine driven Generator inop. MEL Operational procedures mandate a test of the Electrical backup system after engine start and confirmation of its operation. So for the condition you need backup system operative. After TO, you loose the backup system, but NNC for that does NOT mention any procedure or concern! no mention to land at nearest airport, but you know you have a MEL condition and that system was required. As NNC does not limit you to continue a long flight and forget about the MEL? would you consider to adopt MEL requirements in flight?

NNC does not always cover for cumulative failures or failures in addition of an already limited MEL dispatched flight. That is my understanding. But MEL limits in flight is a "tabu" and not normally accepted.

Second: You have an ETOPS 180 required system that became inop in flight. MEL would limit your dispatch, but you don't need no refer to it anymore. You continue for 180 ETOPS? You you get fired if you decide to land just before a North Atlantic crossing?

Another one: MEL mentions that L windshield wiper is required for CATlll operations, no NNC or mention of that in any other reference material. You takeoff in rain, your wiper fails during TO run just above 80kt, I believe you will not reject at this point, so it's a GO.........your destination is operating CAT3, and you know that L wiper is required by MEL, but MEL is not required to be referred to in flight so you just disregard this and forget that you know about this requirement?

One more: it has been years since I have flown the B737, but I remember that with one pack inop, you are limited in FL. That info was in the MEL, but not in the NNC. So you happen to know about the MEL limit, and loose a pack while climbing, are you going to climb to a higher level, and CRZ at a higher level than the one in the MEL? you can, as nothing is said in the NNC. So you just disregard the MEL? If you level at the lower FL, you will not reach your destination, as the fuel burn and winds are not as planed. So you decide to return. Are you getting fired by your company for making a wrong command decision that costed them a canceled flight?

Have you ever referred to MEL in flight, used its limitation, and considered the correct thing to do? or you are very straight forward and say MEL is ONLY for dispatch. ...?

[JeroenC]

First question: LEGALLY MEL is not required. However, I consult it inflight to assess the effects. With multiple failures you're earning your money by going beyond SOPs and NNC. Now you have to actually think;)

Q2: our Cat3 checklist (used before ToD) mentions "Aircraft Qualified". This implies to check MEL restrictions. I've compiled an easily accessible list from MEL which I keep handy.

Q3: same as Q1: consult, note the FL250 limitation and make your decision. If you climb to planned cruise level, be VERY cautious with anti ice now...
If the route involves long isolated areas,, think twice.

Consider this: your failure has no NNC implications, only MEL. Destination has no engineering. You can't contact OPS. What would you do?

Whether a company fires you depends more on the company then on your decisions, if you know what I mean.

[cosmo kramer]

After TO, you loose the backup system, but NNC for that does NOT mention any procedure or concern! no mention to land at nearest airport, but you know you have a MEL condition and that system was required.

You don't mention for which type, but given your username I assume you mean Boeing (744).

For Boeing 737 (hence I assume 744 as well, due to commonality), there is a section in the QRH called "checklist instruction", which indirectly covers the question you asked. Under "non-normal checklists", the following is written:

There are some situations where the flight crew must land at the nearest suitable airport. These situations include, but are not limited to, conditions where:
the non–normal checklist includes the item “Plan to land at the nearest suitable airport.”
• fire or smoke continues
• only one AC power source remains (engine or APU generator)
• only one hydraulic system remains (the standby system is considered a
hydraulic system)
• any other situation determined by the flight crew to have a significant
adverse effect on safety if the flight is continued.

So in short, yes, this is covered in the NNC.

[cosmo kramer]

...as for single pack operation, following is written in the systems decription:

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? This requirement is just to satisfy the authorities in some certification requirement, and is not a technical limit on the system.

[172_driver]

The restriction is FL250 for the 737. During recurrent training we had just that scenario, one pack inop, and it was stressed to us that FL250 is just a MEL requirement not something you have to obey once in flight. About the same time the Swedish accident investigation board released a report of a 737 that had a decompression. They had initially a bleed trip off but continued climb to FL410. Then a second bleed trip off as a result of one air cond pack not being able to pressurize. Due to the fact that these things continue to happen led them to recommend EASA and FAA to change the QRH to reflect the same limitation as the MMEL does (FL250).



Conclusions
The assessment made by the crew when the climb had to be aborted was in line with the company's procedures. The flight altitude could be reduced without disruptions or delays and stabilised at Flight Level 100. The oxygen masks in the cabin were activated manually. The commander carried out a debriefing with the crew and passengers after landing. The persons that had experienced discomfort in connection with the flight received help in dealing with their impressions and experiences.
Since the introduction of this aircraft model in the late nineties, the Type Certificate Holder, Boeing, has carried out a number of controlled introductions of improved components, but the result of this work has not extended the operating time before a failure has occurred.
The operator's maintenance measures have changed following similar incidents in the past; a checking procedure has been introduced. In the event that one of the Bleed Air Systems is non-operational, checks are made to ensure that the remaining system has the capacity to maintain the cabin pressure during flight up to Flight Level 250. The occurrence discussed in this investigation has re- sulted in implementation of functional tests on mentioned components on B- Check.
The FAA's airworthiness directive to modify the detection and presentation (ATA 31) of malfunctions in the pressurisation system is a sign that the design still has a high fault incidence and requires improvement.
SHK believes that the limitation introduced for application when flying with one Air Conditioning System inoperative, in accordance with MMEL 21-01, in which the operating altitude is limited to Flight Level 250, also should be taken into consideration when one system becomes non-operational during a flight in progress.
The incident was caused by the remaining cabin pressurisation system not be- ing able to pressurise the cabin at the altitude where the airplane operated.

Recommendations
EASA and the FAA are recommended to:
Act to change the Boeing B737 QRH – NNC “Bleed Trip Off” so that a limita- tion of the flight altitude should be taken into consideration in the event of fail- ure of one pressurisation system during flight in the same way as when this is identified before dispatch (Cf. MMEL point 21-01).
RL 2013:03 R1

Full report: http://www.havkom.se/virtupload/reports/RL%202013_03e.pdf

[latetonite]

AFAIK, if one pack fails in flight, you are still allowed to continue as planned.
Now it is a captain's decision, all based on circumstances.

[cosmo kramer]

Interesting post 172_driver, and somewhat contradicts what I wrote in the previous post. But then not quite anyway...

As such the entire "checklist instruction" section is well worth a careful read. In the end everything will be blamed on the captain:
In all situations, the captain must assess the situation and use good judgment to determine the safest course of action.

A good systems knowledge is hence required. For the case of single pack, my opinion is that the captain didn't use good judgement climbing to FL410:

Above FL370 the pressure controller changes schedule from max differential pressure of 7.8 to 8.35 psi. Hence, above FL370 the demand of bleed-air becomes higher. The bleed air demand is satisfied by taking bleed-air from stage 5 and 9 of the compressor. With their low weight, and after leveling off, the cruise thrust would have been low as well, causing an increased demand of (hot) stage 9 bleed-air. So the bleed trip off would be due to a bleed air overheat:
Soon after the aircraft levelled out at the predetermined altitude, the right-side system activated a “Bleed Trip Off” warning.

A level off at FL370 would have made more sense as the last 4000 feet brings little to nothing in operational value (at most a few kg fuel saved on the short flight they were doing), and hence flying at this lower level would not have caused any disruption in the schedule. Also an increase in speed to increase the thrust output, and lower the demand for (hot) stage 9 bleed-air. Since the report mentions the stage 9 valve for the operating side was regulating out of limits (the other side outright broken, causing the first bleed trip off), maybe the bleed would have tripped anyway, but it would probably have reduced the risk staying in FL370.

Not to go into a discussion about that particular flight in general, but a couple of other points speaking in favor of FL370. It is not mentioned that the crew tried to restore the bleed to the remaining pack, which I find strange. This is a slow decompression scenario. As did the commander manually and unnecessarily deploy the cabin oxygen masks (cabin altitude never exceeded 14.000 feet). Also, the crew to donned oxygenmasks despite the cabin altitude was below FL100 (no cabin altitude warning yet).

It seems to me it got hectic, and being at FL410 probably didn't contribute to reduce the stress level (time of useful continuousness at that level probably being on their minds too). Had they been at FL370 they would have bought themselves valuable time (1-2 minutes), enabling the whole process to go slower and less stressed. E.g. to start a descent and reset the trip off, before going into a full blown emergency descent.

While every attempt is made to supply needed non–normal checklists, it is not possible to develop checklists for all conceivable situations.

It's always easy to look in hindsight, and it may have been a top crew that in this one occasion put themselves in a bad position. But with pressurization problems I wouldn't go above FL370. Maybe it due to experience, I had fluctuating climb rate in FL390 some years ago. The same considerations (higher differential pressure) led to the decision to descent to FL370, which caused the fluctuations to stabilize. Afterwards we learned that there had been some sort of problem with the regulating of the outflow valve. Less stress on a system = less likelihood that it will fail.

The whole topic here could be reduced to "airmanship", which includes knowing the equipment you operate thoroughly... It's not addressed in the report, instead the Swedes put all the blame on Boeing, and none pilots operating "by the book". And surprisingly none either on their state owned airline (despite both both stage 9 valves were found to be broken and outside regulating limits respectively). I sincerely hope that Boeing will not impose further limits based on this, I think it's enough that we have to brief cabin altitude warning before each flight of the day because of Helios.

Thanks for an interesting link, which gives cause for consideration on how to handle such a malfunction.

[Skyjob]

ricfly744 - the answers given mostly relate to 737 type, as already stated by some contributors.

Back to your original non-type specific question:

MEL applies before dispatch, once dispatched it becomes reference material. For instance if a failure occurs, nothing stops you and thus you may want to check your MEL after having actioned QRH and NNC to ensure that operationally you can continue having arrived at your (nearest suitable) destination or if an en-route technical stop may be more prudent to avoid a lengthy delay due e.g. no engineering cover. Any restrictions in MEL apply before despatch.

Cumulative failures are not accounted for in neither MEL nor QRH, this is where you need to start thinking of how the systems have an effect on each other. It may well be that two independent small failures could have huge consequences but individually treated as non-important.

Q1 can only be answered knowing what type you refer to, as losing a system may downgrade you to a single source of either electric/hydraulic/air is a backup system is no longer working in a twin aircraft, but may not have a huge impact on a quad. In the case of a twin with single course of X you may now have to declare a Mayday, whereas had a backup system still been in place, a PanPan may have sufficed.

Q2 ETOPS (180 or other) has selected entry requirements, thus once in flight prior to entering ETOPS sector you must have e.g. 3 sources of electric, thus on e.g. a 737 which does not have the benefit of a RAT, the APU must be running. This in turn requires a high altitude APU start, or leaving the APU running after engine start until after your ETOPS sector has been completed. Should the APU fail once inside the ETOPS sector, you still have two sources remanning, thus continue not declare negative ETOPS which has further implication such as leaving the ETOPS track if flying in NAT. This APU issue is not the case for e.g. a 767 which has a RAT which when deployed can provide electrical power as a second system.

Q3 The CAT3 briefing requires you to know that all required items for an approach are working, thus are independent of MEL. However, if failure had happened prior dispatch you would've been downgraded to CAT2 or 1 as appropriate.

Q4 FL limitation on 737 is version dependent, NG is better equipped then Classics or older versions, so before an answer can be given to your question here, as some have done, the type reference is required.

[5LY]

I know of a guy who ignored the FL250 restriction in the 737-400 MEL with a pack off line and climbed to a higher altitude. After a couple of hours on a long flight the flight attendants started collapsing. There was enough air coming in to pressurize but no air exchange. It was a full, charter configured a/c. Eventually oxygen levels had depleted to the point that the ones running about went down.

[LindbergB767]

Sky job

Sorry but B767 need APU for Etops since the RAT do NOT produce electricity. only Hydraulic
But there is and Hydraulic generator who start automatically when you loose both AC busses
Which is powered from centre hydraulic system

[ricfly744]

Good and quick feedback from many of you, just a few hours after my post. Great!

I am now flying the B777, and new in this company. Was told by some colleagues that here, where we fly, if I land somewhere other than destination, causing disruption, based on MEL in flight reference, I would be fired. - MEL is only for dispatch. I don't agree and hope management thinks differently.

About the CAT3/L wiper scenario, I created (used) it to generate a discussion with fellow Captains here, and compare my interpretation to other's. The only place where this requirement is mentioned is the MEL, and all here said they would never refer to it in flight. So they would not know it is a requirement. In fact very few people know it.

Some system requirements are obvious for ETOPS and we all would consider them, one is the lower cargo fire indication and extinguishing sys., in fact, a very good example of referring to MEL inflight. The NNC for Cargo Comp. bottle low press or Fire Detection sys fail, does not mention any ETOPS limitation, and in case you get one of these fails before entering ETOPS, are you referring to MEL in flight or not? I certainly would. Now, lets take a look at B777 MEL 32-21-01-01, on this one, you will need at least 75% of Cabin Lights to operate beyond 60 minutes (ETOPS) for night operations. Not obvious.

I do understand that Boeing does not cover all situations and in the end, you are in a "grey area's" Captains discretion situation where even managers, TRIs and TREs will not be unanimous about the best decision. If you are too conservative and divert or return you may be terminated, if you continue, and something goes wrong, the same! That is your job and for what you get paid for.

[flyboyike]

If a safety-related diversion is ground for termination at your outfit, I'd say look for a different job.

[cosmo kramer]

About the CAT3/L wiper scenario, I created (used) it to generate a discussion with fellow Captains here, and compare my interpretation to other's. The only place where this requirement is mentioned is the MEL, and all here said they would never refer to it in flight.
So are you saying, that if your destination airport is CAT3 weather and your left viper becomes inop, you would divert because it's a MEL item??

Would you do the same, even if the airport is covered in fog (no rain) and circumstances does not require it's use?

Remember, our job here is not only to perform safe flight, but (cost) efficient too! A diversion in the above circumstances is not efficient... hence, the one doing so is not meeting his job description.

What does your "List of Required Airborne Equipment" for CATI/II/III ops say about windshield vipers? That is a lot more relevant than the MEL (I'll bet it says both vipers must be operative "If required").

[ricfly744]

No Cosmo, not at all, I agree with you on being a productive employee for my company, and would likely GO on this one.

My opinion is not important, In fact, I prefer to omit it. I want to know your's, I want to learn with you, this is my motivation in this post.

My company's issued LOW VIS OPS CHECKLIST does not mention wipers, nor the AUTOBRAKE sys, also required by MEL for CAT3. This item, may make an operational difference for safety, however, for the wipers, I really don't see a good reason not to land.

[Skyjob]

LindbergB767 - Apologies for quoting 767 incorrectly, I have yet to fly it...

Back to the thread:

My company's issued LOW VIS OPS CHECKLIST does not mention wipers, nor the AUTOBRAKE sys, also required by MEL for CAT3. This item, may make an operational difference for safety, however, for the wipers, I really don't see a good reason not to land.

The LOW VIS OPS CHECKLIST assumes you have dispatched with a CAT3 aircraft and prior to making a CAT3 approach requires you to check your minimum equipment is still there. Dispatch requirements for CAT3 are more strict, hence items appear in the MEL to downgrade the aircraft which do not appear in the LOW VIS OPS CHECKLIST.

Think about it, would you test IF the L WIPER is working prior to commencing an approach? Nor can you test the AUTOBRAKE if warning comes no selecting it inflight for landing preparation. But if before dispatch you have such items inoperative, they WILL affect you. Certain inflight failures do not have such implication, others do...

[flyburg]

Below is an explanation given in one of our reference guides.

7. MEL PENALTIES VERSUS ECL RESTRICTIONS

The difference between DDG penalties and ECL restrictions for the same failure, can be clarified as follows:

DDG: The requirements in the DDG are, amongst others, based on a (next critical) en-route failure, after dispatching the aircraft with the respective component unserviceable.

ECL: In flight, procedures are based on the assumption that the next critical failure, during that particular flight, will not occur. The manufacturer,s Operations Manual, AOM and ECL procedures are therefore based on different criteria than the DDG.

When consulting the DDG in flight, it should be realized that restrictions in the DDG are only applicable for (the next) departure. Safety of the flight is fully covered by the applicable ECL procedure directives.

Further information can be found in the limitation section and checklist section. I.E. What is the minimum equipment required for cat 2 or 3 or how to deal with multiple failures.

In your example, the wiper failure during take off does not affect cat 3 ops at destination.

Also, one pack failure during flight does not require you to descend to FL 250! Another pack failure would be covered by the NNC, namely an emergency descent.

One gen failure requires the APU(on some AC) failure of the other gen requires a diversion as per checklist instruction section.

Hope this helps

Ps where it says DDG, read MEL. Old term used in our company, since replaced by MEL.

[Kefuddle]

EASA and the FAA are recommended to:
Act to change the Boeing B737 QRH – NNC “Bleed Trip Off” so that a limita- tion of the flight altitude should be taken into consideration in the event of fail- ure of one pressurisation system during flight in the same way as when this is identified before dispatch (Cf. MMEL point 21-01).
RL 2013:03 R1
Really? That strikes me a pretty dumb suggestion. The whole point of restricting cruise alt before takeoff with one pack is to limit risk. Whilst on the ground it is easy and risk free to replan the flight at FL240/250, defer the defect, refuel and depart. The point of being allowed to continue at the planned level in flight is that forcing the crew to descend, reevaluate range, endurance, weather and options in general is far and way more risky than simply continuing, diverting or returning as per the planned profile and conditions.

[cosmo kramer]

My company's issued LOW VIS OPS CHECKLIST does not mention wipers
If you say it's a checklist, I assume this is a list of items you have to run through, during normal ops, before each CAT3 approach, to ensure nothing has been forgotten?

You must have a "List of Required Airborne Equipment" as well, buried in your OM-A somewhere. This is the list you should refer to if something is broken inflight.

[733driver]

Gentlemen (and Gentlewomen)

Without getting all technical and type specific, I think it is fair to say that legally the MEL only applies before departure (definitions may vary).

However, it is our job to make use of all available resources, of which the MEL is one, including in flight.

We then need to make an informed decision as to the safest course of action.

I will also say (although it should be obvious), that just because the MEL allows us to depart with a certain item inop, it is still the commander's responsibility to accept (or not) the aircraft. This becomes especially applicable in a multiple failures scenario.

Bottom line: I would always try to look at the MEL for further guidance when deciding on the safest course of action, on the ground, or airborne. However, the need for this will greatly depend on the quality of the abnormal and emergency checklists provided. On some aircraft they really don't go into a lot of detail so any additional info is most welcome.

[Ollie Onion]

As stated above, once dispatched the MEL is for reference only. I will always refer to it though with ANY airborne fault. Most importantly it will allow you to assess the serviceability of the aircraft once you have landed. If the fault has a maintenance procedure associated with it you may not want to land at your destination if you don't have engineering coverage.

As for ETOP's we have an ETOP's checklist that we refer to for inflight failures, this takes precedence over the MEL. There are failures that the ETOPS checklist allows for continuation whereas the MEL may stop dispatch on an ER flight.

[john_tullamarine]

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/commercial/aviationservices/brochures/ddg.pdf for some B-speak on the subject.